# 1/4 Scale Benz Engine (Inch) Model



## Ken Brunskill (Jun 10, 2020)

Attached is the 1st three (3) part designed for an 1/4 Scale Benz Engine Model. I am choosing this scale because I have a nice 6 1/2 Diameter Flywheel already, also because my wife & I are planning to move to a Sr Living Apartment in another few years, making size a factor. 

Looking for some comments and insights on the fabrication, being a fair welder in possession of a Miller Econo Arc/Tig welder, I am considering replicating what would normally be castings with weldments, I don't see that as a particularly difficult hurdle, yet the choice of materials, and of course cost needs consideration. So look for the collective wisdom of you my peers.

The  3D model and drawings are being created in Solidworks 2020-2021 Student Version (Being a veteran allows one to get that super powerful program for $20/year!)


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## Ken Brunskill (Jun 21, 2020)

Update on material & fabrication process criteria:

Have decided on using schedule 80 pipe for the Head, Cylinder & Bearing Base. Cost and process is far better with steel than aluminum @2X the cost, or stainless @4X the cost. Simple enough fabrication with TIG welding, plus any consideration of wear makes steel superior to aluminum.


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## Ken Brunskill (Jul 23, 2020)

Now one month and a few hrs. of designing and learning has gone by, the 1st pass design is complete. The bore is 7/8" and the stroke is 1 3/8" the flywheel is the only thing purchased so far, it will end up being 6 1/2" O.D. X 5/8" thick. 

Now to get some Solidworks help, so I can get everything to rotate as expected, however being inexperienced as I am, need to get the gears to mesh and the Exhaust Valve Spring to actuate that mechanism, yet more learning to be had .

Still would appreciate any and all comments/suggestions regarding the fabrication methodology. As mentioned earlier expect to fabricate out of Sched. 80 Steel Pipe and most likely braze. However as with all of you, willing to consider other methods and or materials.


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## deverett (Jul 24, 2020)

Ken
If you have access to Model Engine Builder magazine issue 25, have a look at the description and picture of Iqbal Ahmed's fully functional 1/4 scale 1886 Benz Motorwagen.
All made on a Sherline lathe.

Dave
The Emerald Isle


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## awake (Jul 24, 2020)

Ken,

I am sorry that I missed your original post, so just now responding to your question about this fabrication approach.

Can you do weldments instead of castings? Yes, absolutely, with one caveat: just like a fresh casting, you need to allow extra material so that you can machine to size _after_ welding. Even with the most careful use of TIG welding, you will lose any precision machining done up to that point.

Now, take my comments with a grain of salt - I boast the tremendous amount of experience of one - count 'em, one! - completed build, with a second about half-way complete. But my strategy on both builds has been to use TIG welding where it makes sense, whether to save on material or make it easier to fabricate.


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## Ken Brunskill (Jul 24, 2020)

awake said:


> Ken,
> 
> I am sorry that I missed your original post, so just now responding to your question about this fabrication approach.
> 
> ...


Good point and that is already in mind, as the plan is to make the weldments to what would normaly be castings. What I am working through in my mind is how to document these, in the pencil/velum days, we exhibited that with. 'phantom' lines showing the casting, now with Solidworks & 3D modeling . . . . yet something new to learn.


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## mrehmus (Jul 25, 2020)

deverett said:


> Ken
> If you have access to Model Engine Builder magazine issue 25, have a look at the description and picture of Iqbal Ahmed's fully functional 1/4 scale 1886 Benz Motorwagen.
> All made on a Sherline lathe.
> 
> ...


Dave,
Actually, Iqbal had only a Sherline mill at the time which I found amazing but a mill can be used as a lathe.


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## Jasonb (Jul 26, 2020)

I'd say welding may not be suitable for all those items, the smaller stuff would be better silver soldered (silver brazed) it is what I would mostly use on an engine of that size with maybe the occasional weld as the first stage of a fabrication then adding smaller parts by soldering that way things don't fall apart when heated.

It is also possible to solder small items to larger ones first as it is easier to get upto soldering temperature, then weld these together particularly with your TIG as the heat is localized and won't melt the solder.

As mentioned above treat it like a casting that you are fabricating then do final machining after soldering though you don't need to worry about draft angles or shrinkage just machining allowances.

This shows how I would do a cylinder in the first post Recreating a Stuart Lightweight, head with bolt bosses similar to yours in this post Recreating a Stuart Lightweight and a forked bearing yoke Woody - but not quite a Forest


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## Ken Brunskill (Jul 26, 2020)

Jasonb said:


> I'd say welding may not be suitable for all those items, the smaller stuff would be better silver soldered (silver brazed) it is what I would mostly use on an engine of that size with maybe the occasional weld as the first stage of a fabrication then adding smaller parts by soldering that way things don't fall apart when heated.
> 
> It is also possible to solder small items to larger ones first as it is easier to get upto soldering temperature, then weld these together particularly with your TIG as the heat is localized and won't melt the solder.
> 
> ...


Jason,
We are of the same mind on the fabrication technique, my plan was/is to tack weld with TIG, then braze to acheive the fillet apearance. it has been many years since I did any brazing, (Silver Soldering yes, but not brazong with brass rod) so am interested in the latest materials.


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## awake (Jul 26, 2020)

Have you tried TIG brazing? I've only experimented a bit, and got it too hot, but seems like a promising technique ...


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## Ken Brunskill (Jul 26, 2020)

awake said:


> Have you tried TIG brazing? I've only experimented a bit, and got it too hot, but seems like a promising technique ...


Hmmm, never heard of it, can you eloborate? I'll do some searching on the Web as well as check in with my Airgas supplier.


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## awake (Jul 26, 2020)

My experience is limited, as I noted, but I'll share what little I know, and hopefully others will correct me where I get it wrong!

TIG brazing uses DC current and argon just the same as for TIG welding steel, but instead of a steel filler, it uses a silicone bronze filler rod - not the same as a gas brazing rod, and no flux needed, though clean metal is (as usual) required. You keep the heat down so that the base material does not melt, but only gets hot enough to melt on the bronze filler. It does not "wick" into the joint the way silver solder does - just lays down on the joint - but apparently creates a very strong joint. As I understand it, you can TIG braze a wide variety of metals, including not only steel and cast iron, but I think I recall reading you can even TIG braze copper alloys - not sure about that.

I seem to remember reading something about an aluminum-bronze filler rod which requires the use of AC rather than DC - I'm not sure when you would use this rather than the silicon bronze - but I am rapidly reaching the outer limits of what little I know or have read!


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## Doug Cygan (Jul 27, 2020)

Hi Ken,
Nice work! You're doing a great job! I've been interested in building one of these too. I have a small hobby foundry setup and a couple of 3D printers to make patterns. If you'd like to share your OBJ or STL files, I can see if I'd be able to make cast aluminum parts.
Doug


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## Ken Brunskill (Jul 27, 2020)

Doug Cygan said:


> Hi Ken,
> Nice work! You're doing a great job! I've been interested in building one of these too. I have a small hobby foundry setup and a couple of 3D printers to make patterns. If you'd like to share your OBJ or STL files, I can see if I'd be able to make cast aluminum parts.
> Doug


Doug, now that would be interesting! Let's correspond off this forum so as not to get off topic, email me at [email protected]. BTW what software are you using?


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## Ken Brunskill (Aug 17, 2020)

Feeling quite good about having progressed to this point with Solidworks, I appreciate all the comments and suggestions thus far. Too that point I have the assembly of the parts to the point that the timing can be established as well as the lengths can be established and studied. 

This U Tube video show the 3D model operating from TDC (Start of explosion) through one all 4 cycles and back to the start of the explosion. Note the Exhaust Valve opening and closing, and the Intake Valve's slot passing past the corresponding slot in the cylinder.

I certainly feel that having acquired this skill will allow me to analyze models and lessen the frustrations in future builds.

On the fabrication aspect, I am fairly certain I will proceed with the Sched. 80 Steel pipe and Braze the bits to replicate the castings.


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## Ken Brunskill (Aug 29, 2020)

Jasonb said:


> I'd say welding may not be suitable for all those items, the smaller stuff would be better silver soldered (silver brazed) it is what I would mostly use on an engine of that size with maybe the occasional weld as the first stage of a fabrication then adding smaller parts by soldering that way things don't fall apart when heated.
> 
> It is also possible to solder small items to larger ones first as it is easier to get upto soldering temperature, then weld these together particularly with your TIG as the heat is localized and won't melt the solder.
> 
> ...


Jason, appologies for this late response.
Must say that your photos are thorough and speak volumes for the nice work you have accomplished. Trust that they provide insight on techniques and setup to those interested in your approach. Does inspire me to be vigiliant regarding when it comes to fabricating the parts that would otherwise be castings for the 1/4 scale Benz, probably ought to do that for the entire project.


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## Cddeshon (May 1, 2021)

Hi Ken.  I haven’t seen any activity on this thread for a while; I don’t know if this project is proceeding or not.  I’m also looking at the  Benz motorwagen (the entire vehicle including the engine) as a possible project.  I purchased the Model Engine Builder article but am disappointed in that no detail information was provided.  I was hoping for at least elevation drawings, or even drawings with basic measurements so I could ascertain some type of scale.

what are you working from?  Do you have a set of drawings, or at least some accurate photos?

I can’t seem to find Anything except for the profusion of videos on the internet.  Before I just go out on my own and design something that ‘sort of’ resembles the motorwagen, I’d like to have something concrete to work from.

thanks for any information, avenues to research, or anything else you can and are willing to suggest.

craig


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## Jasonb (May 2, 2021)

Should be easy for you Craig, just an Otto on it's side 

I'd also be interested in any progress on this one.

I think I may have seen some drawings, will try and find them again, Also on ME there is a guy building a Ford Quadricycle if the Benz is not your only option, few photos may inspire you either way





						Model Engineer
					






					www.model-engineer.co.uk


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## Ken Brunskill (May 2, 2021)

Cddeshon said:


> Hi Ken.  I haven’t seen any activity on this thread for a while; I don’t know if this project is proceeding or not.  I’m also looking at the  Benz motorwagen (the entire vehicle including the engine) as a possible project.  I purchased the Model Engine Builder article but am disappointed in that no detail information was provided.  I was hoping for at least elevation drawings, or even drawings with basic measurements so I could ascertain some type of scale.
> 
> what are you working from?  Do you have a set of drawings, or at least some accurate photos?
> 
> ...


Craig, obviously I have not been actively pursuing the Benz project, partly because I'd not seen much interest, partly because I've been involved with two other projects, finally, and not the least of, my tendency is to have too many irons in the fire. Now in reply to your query:
Being in the USA, having Inch vs. Metric  equipment & measuring tools, I wanted to model in about 1/4 scale in inches. I found and was supplied some Metric 1/3 scale drawings, then being the maverick I wanted to avoid castings. Seeing this as an opportunity to do some designing (furthering my SolidWorks skills), I began designing with weldments vs. castings. With a little encouragement I'd continue on. If you or anyone else is truly interested and would be willing to participate in some positive dialog on this design, let me know


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## Cddeshon (May 2, 2021)

Hello Ken

Thanks for your timely reply.  I can sympathize with having too many “irons in the fire”.  I too am in the USA (Raleigh, NC) so my tooling is imperial.  I spend most of my social networking time on MEM where I’ve authored several build threads, not so much time here in HMEM.

I would be happy to participate in a dialogue regarding this project; my problems would be that I know nothing about weldments and my design software is Alibre.  Not much intersection there.  I have no welding skills, and at my advanced age, I don’t see the need to acquire them.  I can’t see well enough to weld anymore anyway.   I manage to machine from the solid, reasonable representations for most of my “castings”.  From the limited views of the Benz engine I’ve seen to date I don’t see an immediate problem with machining a reasonable resemblance of any of the castings I’ve seen on the engine.  You do have better documentation than I so I can see where you’re ahead of me in that regard and possibly I might see where machining was not a recommended way. 

Also I believe you are making the engine alone; I was thinking of the entire vehicle; though that would require an expansion of my experiences and modeling skills to date as I have no prior experience in making spoked wheels or bending tubing.

Still, I’d be happy to be a sounding board for your thoughts and possibly were you to go your way and I mine, the trading and comparing of information in progress might be interesting.

I haven’t decided upon this project for a certainty; obtaining some level of drawings of the vehicle and engine where I could at least measure relative distances would help me in my decision.  I want to get a feel for the relative sizes of the different parts of the vehicle, then choose a scale, and then determine if this is something I really want to pursue or not.   I build many of my models from photos of the original… example: the Otto Langen engine I’m currently building.  But it would be nice to get some level of documentation before I start seriously thinking of this as a project.


I’ll ask if you would share the source of your metric drawings.  I assume these are for the engine alone though if they were for the vehicle that would be phenomenal.

Craig


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## Jasonb (May 3, 2021)

I'd also be interested in seeing this one develop. It's an engine that I have liked the look of for a while but buying from Torsen at TS is a bit of a pain as he only accepts bank transfer and you have to also pay his bank costs for non Euro payments as well as my bank's which makes it expensive.

Craig, you should be able to open Solidworks part files with Alibre depending on what version you have though they will just open as a single part not all the sketches etc that were used to create each part but can be modified from that or a drawing produced.

I take it you have seen Tom's 1:1 scale build of the engine and wagon that he did on here  a number of years ago


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## Ken Brunskill (May 4, 2021)

Craig & Jasonb,

Appreciate the encouragement, it is enough to boost my enthusiasm for getting back to this project. Attached is just the head as completely done. Naturally since I have not fabricated one yet, I am guessing at what the fillet radius would be, I'm thinking of brazing as it tends to leave a larger fillet, Silver Solder would be stronger and I'll do that for the inner part like the 'D' shape in the head (Will be out of sight and with the higher temp. required won't be affected by the subsequent brazing of the Mtg, & Exhaust Bosses.

I had a good friend who came to my shop 1/week to work on his engine, he passed last Sunday  , and I am trying to sort out how to rearrange my thought, time and projects, this project may well be just what I need to handle the sense of grief.

Also I've attached a couple of doc's from the source I used to get the proportions right, one is from the set of drawings that were or are still sold in Europe, the other is from an HMEM post. That and some deductive measuring, calculator work and head scratching brought me to where I am.

Craig, nice looking work on the stuff in your ID photo, looks as if we are about the same vintage, I was born in 1939, you?


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## Cddeshon (May 5, 2021)

Hi Ken and Jason…(Jason’s is a former acquaintance from MEM)

Looks like Jason and I have your interest back.  Sorry to hear about your friend; I lost one of my mentor’s last year.  I have a few of his tools to remember him by so he’s still with me when I’m in the shop.  Regarding age; I don’t like to publish it… to many crazies out there trying to steal your identity.  I’ll just say that you have me beat by a decade, give or take.



Thanks for the information you've provided.  I’m assuming the one photo showing the cylinder castings isn’t yours since you’ve stated you’re going with weldments.  The head you have designed looks pretty good; probably a bit more detail than I’d contemplate.

I poked around here on HMEM and found the thread to which you refer… (another Karl Benz 1886 Engine and Motor Wagon) that appears to have a lot of the detail for which I was searching.  Don’t know why my initial search didn’t find it.  I have lots of reading and planning to do before I might contemplate a design and build.



I did find a 5 curved spoke flywheel that could be cut down to possibly resemble the flywheel on the motor wagon engine from Martin Models in Oregon  (5½" Flywheel 5-Spoke Curved)  I haven’t looked into seeing what scale that might work out to.

I’m still heavily involved with my current build and don’t want to distract my thinking on another project just quite yet… probably around mid summer I can start thinking seriously about a possible motor wagon build.  Meanwhile, if you continue with your build I’ll be watching, commenting, and maybe participating if you ask.  Craig


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## Jasonb (May 6, 2021)

I could not open the head notes yesterday but can now. That is going to be quite a small item to weld and grind down all the fillets after and even if brazed quite a bit of grinding but you are probably a better welder than me!

 My thoughts on a part like that would be to turn the head including the flange, counter bore for some rods here each of the head studs go and then make a block for the exhaust with a concave cut and silver solder it all together. I can get a reasonable fillet with silver solder and something like JB Weld can be used to add a bigger one if needed.

Similar head construction











The Cylinder and "Fork" both look like a similar turning first would be the way to go then solder on the bits to the cylinder. Fork again turned and cut away teh end to form the two prongs and add location slots down the sides. Solder on the two webs down the sides and two blocks for the bearings at the end.

A cylinder that was turned and had the bosses soldered on


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## Cddeshon (May 6, 2021)

Jasonb said:


> I could not open the head notes yesterday but can now. That is going to be quite a small item to weld and grind down all the fillets after and even if brazed quite a bit of grinding but you are probably a better welder than me!
> 
> My thoughts on a part like that would be to turn the head including the flange, counter bore for some rods here each of the head studs go and then make a block for the exhaust with a concave cut and silver solder it all together. I can get a reasonable fillet with silver solder and something like JB Weld can be used to add a bigger one if needed.
> 
> ...


Great ideas and nice job Jason.  I did simular to what you did on the Witte model I built a while back, except that I attached the cylinder boss (an igniter boss in my case)  with small screws and sealed it with JB weld.  Made the fillets with JB weld too.


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## Ken Brunskill (May 7, 2021)

Craig & Jason,

OK did not take a lot of urging to reignite my interest, here is this morning's Solidworks effort, the attached is what I see as the logical approach to making the head from solid material, it would all be steel the colors are merely for component identification. I'll of course create drawings for each part, then for the machining of the weldment. The tapered pins are just that, standard taper pins available in most good hardware stores. 

You had guessed correctly on the source of the metric drawings, that post was what interested me in the 1st place.

Thanks for the pointer for Martin Flywheel castings, now to decide size.


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## Ken Brunskill (May 7, 2021)

Jasonb said:


> I could not open the head notes yesterday but can now. That is going to be quite a small item to weld and grind down all the fillets after and even if brazed quite a bit of grinding but you are probably a better welder than me!
> 
> My thoughts on a part like that would be to turn the head including the flange, counter bore for some rods here each of the head studs go and then make a block for the exhaust with a concave cut and silver solder it all together. I can get a reasonable fillet with silver solder and something like JB Weld can be used to add a bigger one if needed.
> 
> ...


Definitely nice looking job, as mentioned a little JB Weld, sanding & painting it will look great. Is that silver solder or braze. my silver soldering does not leave that much of a fillet.


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## Ken Brunskill (May 7, 2021)

Cddeshon said:


> Hi Ken and Jason…(Jason’s is a former acquaintance from MEM)
> 
> Looks like Jason and I have your interest back.  Sorry to hear about your friend; I lost one of my mentor’s last year.  I have a few of his tools to remember him by so he’s still with me when I’m in the shop.  Regarding age; I don’t like to publish it… to many crazies out there trying to steal your identity.  I’ll just say that you have me beat by a decade, give or take.
> 
> ...


Craig, looked at the Martin Casting site, and the 7" curved spoke flywheel would (IMHO) the best choice for this 1/4 scale, that is what I,m going to go with.


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## Jasonb (May 8, 2021)

It's silver solder about 620deg C melting point. I don't have oxy so can't really get the heat for brazing though I do have an old carbon arc "torch" it seldom gets used.


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## Ken Brunskill (Jun 2, 2021)

Spent some time noodling out how to approach this engine as a weldment vs. a casting. 

I have the head machined and ready for brazing, just need to replenish my acetylene first. (Concept attached.)

Today completed designing Rev 1a of the cylinder and components, starting to be convinced it is quite doable as a non casting.
Outside components are Mild Steel, inside is Cast Iron. Might change the Intake boss to Bronze.
Rough dimensions for those wondering the OD is 2" stock cleaned up to 1.94" OD at the flange overall length of this component Assy is 3".

The bore will be 1.125 ID.


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## Cddeshon (Jun 3, 2021)

Looks really good Ken.  I’m thinking you could achieve the same result using something like J B weld.  It’s good to around 500 degrees F and might be easier to manage making fillets?


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## Ken Brunskill (Jun 4, 2021)

Cddeshon said:


> Looks really good Ken.  I’m thinking you could achieve the same result using something like J B weld.  It’s good to around 500 degrees F and might be easier to manage making fillets?


Thanks Craig, for strength, my thought is to tack with TIG (I have an Miller Econo TIG) and fill with the 620 deg.  Silver solder mentioned by jasonb, the JB Weld I'll use to obtain consistent fillets. It will all be painted Red any way. 
Later this week end I'll post something where I have changed the component colors only to illustrate them in an assembly. 
If there is interest I'd consider making detail drawings available at a modest price, but that will be after I've made an engine that runs (maybe by some time in 2022).


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## Ken Brunskill (Jun 6, 2021)

As promised here is how  I plan to fabricate the three main parts that would most often be castings. Also is a photo of the head components which is ready for welding. On the welding, since I was out of acetylene I stopped in a my local Airgas supplier and ended up with Radnor 95/5 that has a 460 deg. melting point and purportedly will leave a controllable fillet (we shall see ).
The colors are only for illustration and communication purposes.
Cheers all, Ken


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## Jasonb (Jun 6, 2021)

Is there some form of porting within the head that means you have to use a separate "purple" part rather than just mill the "D" shaped recess into the "grey" outer head?

I'll be interested to see how the welding comes out, as I said it would be all silver soldering if I were doing it as I only have stick welding and am not that good.


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## Cddeshon (Jun 8, 2021)

I was wondering that also Jason?


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## TonyM (Jun 9, 2021)

Hi Ken. 
I was wondering what compression ratio you were expecting. The 1/3 model from Tolsten Shure has a very low 2:1 compression and runs badly usually firing every other ignition stroke.  To get it to run reasonably well I increased it nearer to 4:1.  I filled in the D comletely and then some. 

Tony


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## Ken Brunskill (Jun 11, 2021)

Jasonb said:


> Is there some form of porting within the head that means you have to use a separate "purple" part rather than just mill the "D" shaped recess into the "grey" outer head?
> 
> I'll be interested to see how the welding comes out, as I said it would be all silver soldering if I were doing it as I only have stick welding and am not that good.


Jason,
No there is no porting in the head, the valve at the top opens the passage to the exhaust, there is a slide valve that opens the fuel inlet. I felt it easier to make the 'D' shaped area a separate piece as that allowed me to clamp the 'housing' and turn the inside & outside (Photo attached.)

I have a Miller Econo TIG and am considering using it to 'Tack Weld' the components as that would allow me to clamp the components in the desired position, then I thinking a combination of silver solder and or the 95/5 that has a low melt temp, I want to be able to control the fillet. Of course I can accomplish that with JB weld. Now saying this, it strikes me  as a good idea to use some scrap to see how the various processes work out - will do that tomorrow and post the results, along with a description of the process details. (Had not thought about that until doing this reply, Duh .)

Tony, I have not worked out what the compression ratio is just yet as this is still the the design stage, will definitely think about how to reduce the volume in the 'D' area. If the 'D' area is completely filled how did you resolve the exhausting?


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## TonyM (Jun 12, 2021)

Ken Brunskill said:


> Tony, I have not worked out what the compression ratio is just yet as this is still the the design stage, will definitely think about how to reduce the volume in the 'D' area. If the 'D' area is completely filled how did you resolve the exhausting?



I bored out the head casting to remove the D shape, most of the flange, and flatten the inner face, I then made an insert with a flange to fill that space. The piston side of the insert is also spiggoted to reduce the space in the bore. There is a central exhaust port 6mm drill to just past the full depth of the valve. After loctiting the spigot in the head I bored the exhaust valve port 3mm past the 6mm hole. 

In your case, and it's something I intend to do for the future, you could make the two piece head to include a water jacket.


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## Ken Brunskill (Jun 12, 2021)

TonyM said:


> I bored out the head casting to remove the D shape, most of the flange, and flatten the inner face, I then made an insert with a flange to fill that space. The piston side of the insert is also spiggoted to reduce the space in the bore. There is a central exhaust port 6mm drill to just past the full depth of the valve. After loctiting the spigot in the head I bored the exhaust valve port 3mm past the 6mm hole.
> 
> In your case, and it's something I intend to do for the future, you could make the two piece head to include a water jacket.


Tony,

Great idea, I checked my original idea (Glad I have not welded anything yet! !), that cavity was .05 cu in, this redesign reduces that 20% to .04 cu in. Does not seem like a lot but in a model might make a huge difference. Now to the shop to re-remake that combustion chamber.


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## Jasonb (Jun 13, 2021)

That looks more like an 80% reduction as the cavity is a whole lot smaller now


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## Ken Brunskill (Jun 13, 2021)

Jason,

Bingo! You are absolutely correct I'd mis-read the volume numbers initially the smaller version is 88% smaller. Original is .33 cu in, smaller is .04 cu in.

About the welding, did a small welding experiment today, finding plain silver soldering is perfect see photo.  Left side is Safety Silv, Middle is plain silver solder I think provides the best fillet, and is what I'll go with & Right side is Tack welded with TIG which leaves too large a fillet (hidden by pin) with my welder (low end controls are not so good). If I want a larger fillet that will be done with JB weld. 
I have a small furnace and believe that will be my best bet for doing the silver soldering, as I can flux the parts, place a small piece of silver solder in the crevasse and heat to a known temperature, these were done with a torch.


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## Jasonb (Jun 15, 2021)

Another reason the TS engine may be low on compression is that their website says 44mm stroke but the original engine was 150mm stroke so at 1/3rd scale that would give an extra 6mm of piston travel which would make a fair bit of difference. Bore is OK at 30mm as that is 1/3rd of the 90mm original.


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## Ken Brunskill (Jun 16, 2021)

Interrupted a cabinet project to noodle out the compression ratio on the inch 1/4 scale benz at top dead center the volume of the combustion chamber with the reduced cavity is .57 cu inch and the volume of the chamber at bottom dead center is 2.945 cu in, that comes out to be north of 5:1, if I am doing this right (my first time). Thought is to have a 1" bore and a 2 3/8" stroke. Maybe bring the top of the piston up some by making a chamfer cut to allow the spark to ignite the gas, any comments?


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## Cddeshon (Jun 16, 2021)

I don't have a lot of experience in compression ratios and designing engines.  I did design and build a Witte hit and miss a while back and I set the compression ration at around four to one by design.  The engine fired every other available available power cycle and I couldn't seem to 'fix' this without changing the compression ratio. Seeing I couldn't really get the governor to control the engine either this was probably a good thing as hitting every time it would have just run away.


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## Jasonb (Jun 17, 2021)

Some of these early engines did have quite low compression ratios, my I F Allman for example is about 2:1 (1.75cu.in at TDC, 3.5cu.in at BDC) and it even runs better bleeding out some of the compression. So if you allowed for that extra bit of stroke I expect the TS kit would come out similar rather than the 1.5:1 mentioned earlier. We need to remember that these things ran at 2-300 rpm so need to think along the lines of hit and miss engines not higher reving tether or RC engines with their built for speed ethos.

2 3/8" stroke would be very long for the 1/4 scale engine scaling upto 240mm rather than the original 150mm so unless the engine frame is stretched you may get into problems with the angle of the conrod being too large and hitting the sides. 1" bore is 1/3.5 scale so 43mm stroke would be the same scale so maybe 1 3/4" to 1 7/8" would keep proportions and still up compression slightly. A "packer" could always be added to the underside of the head or the top of the piston both with suitable clearances to bring the CR up if it was found to be needed.


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## Badhippie (Jun 17, 2021)

Hello 
Don’t forget it is possible to change C/R by the placement of the top compression ring. Also you can change the top of the piston to change the C/R 
Thanks 
Tom


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## Ken Brunskill (Jun 17, 2021)

Great comments! Thanks


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## Ken Brunskill (Jun 17, 2021)

Jasonb said:


> Some of these early engines did have quite low compression ratios, my I F Allman for example is about 2:1 (1.75cu.in at TDC, 3.5cu.in at BDC) and it even runs better bleeding out some of the compression. So if you allowed for that extra bit of stroke I expect the TS kit would come out similar rather than the 1.5:1 mentioned earlier. We need to remember that these things ran at 2-300 rpm so need to think along the lines of hit and miss engines not higher reving tether or RC engines with their built for speed ethos.
> 
> 2 3/8" stroke would be very long for the 1/4 scale engine scaling upto 240mm rather than the original 150mm so unless the engine frame is stretched you may get into problems with the angle of the conrod being too large and hitting the sides. 1" bore is 1/3.5 scale so 43mm stroke would be the same scale so maybe 1 3/4" to 1 7/8" would keep proportions and still up compression slightly. A "packer" could always be added to the underside of the head or the top of the piston both with suitable clearances to bring the CR up if it was found to be needed.


This design has been accomplished more from visual observation of photo's and bit's & pieces of the metric plans posted way back . . . my thoughts are shortening the Cylinder Base, would not look right, of course I could make the piston taller (move the wrist pin down) to accomplish that, however think the wrist pin needs to be as near the top of the piston as feasible.


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## Jasonb (Jun 18, 2021)

A longer conrod would have the same effect as it will move the piston closer to the head and have the added bonus of reducing any risk of the rod hitting the sides with any increase in stroke. I would aim to have the top face of the piston come right to the edge of the spark plug hole at TDC, from what I can see the TS design has it stop quite a bit short of that.  I also think the TS version has the spark plug a bit too far down the cylinder when compared to full size photos (mostly replicas), so a bit more compression ratio can be gained if that is nearer the head by 1/8" on the 1/3rd model so maybe 3/32" on a 1/4 scale. Combined with a true scaling of the 150mm stroke and reducing the head void should put it at about 4:1 CR.

I did find a German hobbiests site yesterday who had made a 1/3rd scale one, this was before TS brought their kit out. He mentions that the original engine had a compression ratio of 2.5:1 but he did increase it on his model


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