Tiny I.C. Engine

[AussieJimG]

Thank you Stefan, I had seen most of Jan's site before but not that section.

Jim

 

[MrTin]

I have just been put onto this little engine, by a guy on the English Model Engineer forum.
I have only a Peatol lathe (Taig) with a vertical slide, I have no milling machine, but want to build an IC engine. If the base of this engine can be done using my limited gear, I could do it.
Can somebody explain if I can do the milling for this engine on my Peatol/Taig.
If so, I can crack on.

Cheers,
Martin

 

[GailInNM]

Martin,
The frame is the only thing that is likely to give you any problems. It is 2.6 inches long and you only have travels of one and a half vertical and one and three-quarter inches horizontal. I think you could do it but you might have to re-clamp a couple of times to cover the areas required. The sides of the frame could be cleaned up okay if you use a fly cutter, very gently, so you could cover the entire area.

Another alternative, would be to build an air cooled version. I have built a number of the air cooled versions and the frame on them is only 1.687 long. It does complicate the cylinder a little bit as it then has fins to cut instead of being a simple sleeve, but this is offset by not having to machine the water hopper on the frame. Although I made a number of other changes in my engines, all the other "TINY" parts are interchangeable with the different frame and cylinder. I think I moved the fuel tank mounting holes a little bit to accommodate a slightly different fuel tank that is trivial. If you wanted to go with an air cooled version I can send you my frame and cylinder drawings.

Gail in NM

 

[MrTin]

Gail, that's very generous of you and I would appreciate them.
I wondered if I could make the frame in brass, with silver soldered joints.
Could the engine still be completed as a water cooled one if I did that? Kind of half and half?
But I think, as you said, the frame could be done carefully, by reclamping for the milling. I was even thinking that the cavity could be drilled out and filed. Most of my brass modelmaking/patternmaking work has been filed to shape. I'm used to it!
I do like this Tiny engine, but have also come up with a typically crazy idea of 4-stroking an existing 2-stroke. I have a pair of Merco 61s that I got for a tenner at a dog show!. One is fine. The other, well, I reckon a new head with valve gear belt driven from behind could be an interesting design challenge with everything doable on the small machine. I will go and dig one out tomorrow.

But I do think the Tiny could be a first attempt, so I would indeed like your plans, Gail.

I will PM you my address.
Cheers,
Martin

 

[GailInNM]

Martin,
I emailed you the appropriate drawings earlier this evening.

I can see no problems in fabricating the frame out of brass and silver soldering it together. Actually, I think that if you used a few small brass screws to hold the parts together that it would be perfectly solid enough even if it were soft soldered. If 3/16 or 5 mm brass were used for the load bearing components the additional weight would help dampen out vibrations at higher speeds. They are not bad as it is, but the engine does try to walk around a little bit if you open it up to where it is running above 5000 RPM. I certainly would not be apprehensive about a build up frame and tank/base.

Keep us posted about your build. I am always interested in "Tiny's".
Gail in NM

 

[MrTin]

Gail, that is very encouraging.
And very kind of you to send me the air-cooled mods drawings, which have arrived this morning.

I'd be likely to have more luck silver soldering the brass frame together, than setting it up for drilling and tapping for screws. I have never had any luck getting drills to go where I want them! I even had an optical centre punch, but lost the acrylic optic bit. Whereas, I spent many years making brass patterns, all silver soldered.

Many thanks for the Tiny drawing mods and the encouragement.
Cheers,
Martin

 

[Jonathan_M]

Dear All,

I'm planning to build a Tiny over the next few months with the aim of using it to drive an electric generator that will be fitted to a 16mm scale garden railway loco. It will be air cooled, and built with the piston vertical in order to have a smaller footprint in the loco. I have made a start by drawing the engine in Onshape, using metric units. This has meant converting and then rounding where possible in order to give easy to use dimensions. Below is a screen shot of the finished engine in OnShape.

I haven't included every component, but all of the key parts for checking the alignment and dimensions are there. I have made the model a public document, so if you are registered with Onshape you should be able to open it. The camshaft, pushrod and rocker arrangement doesn't work when you turn the crankshaft, as Onshape doesn't have a cam or tangent mate at the moment. However, just drawing and assembling in 3D was a really good learning experience, enabling me to get the rocker arm length right, the crankcase design resolved and the pushrod and inlet valve lengths finalised.

https://cad.onshape.com/documents/56bc5928e4b0c3373eb7a6c6/w/867b8d8dd751a285e55290ba

One thing I have noticed is that with the piston design as published by PutPutMan, the skirt projects below the bottom of the cylinder at bottom dead centre. Something tells me that this isn't right.

GailinNM has already been of great help to me with lots of advice and provision of his air cooled sketches and I'd like to publicly thank him for sparing his time to help me.

 

[10K Pete]

The piston skirt extending at BDC is quite typical of H&M engines and is
correct for the Tiny.

I love the concept of your project; a Tiny Generator for a rail road! Why not
extend the idea and use it, or a larger version, for the prime mover??
Cool!!!

Pete

 

[GailInNM]

Jonathan,
Sorry to be slow in responding but my Internet has been acting up for a few days so I haven't been doing any posting. But better late than never welcome to HMEMand please join in the fun with your continued posting.

Your drawing looks great. I went to the Onshape site and played around with it for about half an hour. It was lots of fun. Thanks for posting it and making it public. It looks like you're off to a very good start.

Yes, the piston does stick out a little bit from the cylinder at bottom dead center. This worked out to my advantage on the first lapped piston versions that I built as I could dribble oil on the piston to lubricate it. Later I added an oil cup to the cylinder and the oil distribution groove on the piston though that was not necessary. The piston length could be reduced a little bit but like Pete says it was a common practice on full-scale hit and miss engines for the piston to protrude a little bit so I just left it that way. With my cast-iron piston and cylinder I only need about one drop of oil in the oil cup an hour for lubrication and I use no oil in my fuel.

I am currently running in two more of the hit and miss Tiny's that I recently completed. In the hit and miss mode governed at 3000 RPM they both get a little over three hours of run time on 9 mL of gasoline. With the hit and miss govenor disabled they peak out at a little over 6000 RPM. With the fuel mixture richen up a little bit to reduce the RPM to about 5000 they get about 35 minutes on 9 mL of fuel.

Gail in NM

 

[steve-de24]

Gail, I have a question about the design of the Tiny that I think your extended running can answer. Have you had any problems with the unusual big end bearing split line design? I'm thinking of having this little engine (an air cooled version I think) as my next project, I've never done a 4-stroke sparkie before so a lot to learn if I take it on. Regards, Steve.

 

[GailInNM]

Steve,
I have had no problems with the big end on any of my Tiny hit and miss engines, even on the ones that have a lot of hours on them.

The big end does open up a little bit but not enough to cause an audible knock or any problems in running. About the same amount as a 2.5 cc commercial glow engine gets after 50 or 100 hours of operation. I think most of it is just flattening out the machining marks left by the reamer when I ream the big end.

My construction is the crankshaft is made of 1144 stress proof steel with the crank pin well polished. The crankshaft runs in ball bearings for support. The connecting rod is made of 2024 aluminum which has similar wear characteristics to Dural which was used on many commercial two-stroke model airplane engines.

For lubrication I use a full synthetic SAE 0-20 motor oil. I put a drop on when assembling and then put a drop on whenever I think about it, probably every 20 or 30 hours of runtime.

I use that oil because it has been the only thing that I have found that will not gum up the valve stems because of the high head temperature. I tried a variety of regular motor oils and instrument oils and they all would cause the intake valve to stick after 10 or 20 hours of operation. with the full synthetic oil I have never had a valve stick.

Keep us posted on your build. Always interested.
Gail in NM

 

[grapegro]

Hello Gail,
I use fully synthetic oil on all machinery I have, I find it very good on my lathe,drills and mill in stopping rust in the cooler months. It sticks well, spreads well and lasts well.
Norm

 

[steve-de24]

Gail,
Thanks for taking the time to reply and the reassurance with the big end design. Your tip regarding the oil you use is filed away for later. I will need to source some higher strength steel and aluminium for the crankshaft and con-rod but that will give me a good excuse to attend one or two of the model engineering shows we have in the UK. Again thanks for your interest.
Regards, Steve

 

[GailInNM]

Norm,
Thanks for chiming in on the synthetic oil. It really solved a problem for me with the Tiny valves. Rust is not a real problem for me here in the high desert Southwest US. Typical humidity here is in the 10 to 20% range. You probably get more precipitation on a wet weekend than I do in a year.

Steve,
The crankshaft does not need to be a high strength steel, but rather one that works easily. I use 1144 because it is easy to turn and get a good finish on and the fact it has no tendency to warp when cutting the off-center crank pin. I have made a lot of similar cranks out of 12L14 leaded steel which is roughly the equivalent to your EN1A. They often times worked a little bit when the crank pin was turned but they were easy to straighten with hand pressure in the lathe using a dial indicator. 12 L 14 also tends to rust more than the 1144, but if you read my note to Norm you know that that is not a problem for me.

Any fairly hard aluminum should work well for the connecting rod. I think the 2024 that I used is probably one of the best but it was also used because it is very easy source in the US. I don't remember the UK equivalent for it but as long as it is not a real soft grade I wouldn't worry too much about using anything that is available unless you plan to run your engine for long periods of time as I do.

Gail in NM

 

[steve-de24]

Gail, thanks for the info. I have some leaded EN1a so that's my crankshaft material sorted (although I'm a bit reluctant to eliminate reasons why I 'must' attend model engineering shows this year.....).
The UK grade of aluminium equivalent to 2024 is HE15 which is approx. 50% stronger than HE30 which is equivalent to your 60xx grades.
Regards,
Steve

 

[gbritnell]

While I had some spare time I thought I would build an air cooled Tiny. I will be incorporating some of the modifications that others have made along the way like using ball bearings for the crankshaft. I have trouble fueling my Tiny so I lengthened the base by .100 and moved the filler back the same amount. I pondered how to mount the cylinder without just pressing it into the base so I came up with threads. The thread diameter splits the existing metal wall on the drawing so it comes out darn close to .50 inches. The thread count is 40. I machined the base to the overall dimensions then chucked it in the 4 jaw chuck and picked up the center of the cylinder. I drilled and bored the hole then threaded it. The cylinder is made from Durabar iron and the threads cut very nicely. I will snug it in place and then lay out the centers for the head mounting screws. This way everything will be lined up. The plan for this one is to mount a hit and miss mechanism either like Gail's or some concoction of his and mine.
gbritnell

 

[steve-de24]

George,
Thanks for sharing the modifications you are making to the basic design and your build photos.
You've grabbed our attention.
Steve

 

[gbritnell]

The engine is coming along nicely. Since last posting I have the crank, rod, piston and complete head finished which will be shown in the posted pictures.
The rod is made from 6061 aluminum for lightness. I deviated from the drawings by making the throw bore bigger to accept split bearings. I found that on my other Tiny the rod journal wears quite a bit with the high rpm.
The piston is made from aluminum also. I eliminated the O ring and lapped the piston to the bore.
The head is made from iron and the valves are W-1 drill rod. I used the same procedure for the head as I did on the first engine. I left extra stock on the top surface and then using a plug type cutter made from drill rod I cut bosses around the valve guide holes giving a little more support to the valve stems.
I had modified the spark plug entry angle on the first engine and did so on this one.
Now comes the 'Tiny' work!
I mentioned in my last posting that I was going to use a combination of Gail's mechanism and some of my own design for this engine.
Gail was gracious enough to supply me with some extra parts that he had made for his governor so I started there. I slid the spool and flywheel onto the crankshaft then held the centrifugal arm and weight in place so I could get a measurement. Rather than use the bracket I had I decided to use a circular type bracket with extended arms to hold the arms. I then made a sketch and proceeded to machine what I had drawn.

 

[gbritnell]

I initially made the crankshaft longer on one side to accommodate a governor mechanism of some sort. With the bracket machined I installed the arms and slid the assembly onto the crankshaft. I found out that even by making the crankshaft longer I didn't have enough space to install the necessary links to make everything work properly. Knowing that the gear width from the drawing is wider than it needs to be I fixtured the cam gear and removed .030 from the face of the gear. The crank gear was slid onto a mandrel and locked in place with the set screw and .030 was removed from it also. The flywheel was again slid on the crank to check for spacing and at the point I had enough room the flywheel was still about .04 beyond the end of the crankshaft so I started looking for another way to get more room.
The cam follower is .140 wide at the circular mounting end and narrowed down to .125 where the pushrod locates. The pushrod is only .094 diameter so if I made a new follower and reduced the base width to .120 and the upper part to .105 I would still have room to spotface with a .094 ball mill, so that was the next step.
With the follower narrowed I could then take an additional .02 from the cam gear on the cam side. I set the gear back up in my split bushing and removed .020. I then remounted the crank gear and took an equal amount off of it.
I now needed to make new pivot bolts for both the cam follower and the cam gear. That follower was easy but the cam gear bolt would now need to be redesigned to accept a lock-out arm.
I turned up a shoulder bushing leaving and extra .125 on the outboard side. I tightened it into the threaded hole and marked a reference line onto it so that the flats and slot would be properly oriented after machining.
With the bushing still on the rod I mounted it into my dividing head, milled the flats, cut the slot and drilled for the pivot bolt.
Another trial assembly and everything looked good.

 

[gbritnell]

Now for the lockout arm. Being as the pushrod floats in the small pocket in the cam follower and really has no way of being attached with a clevis I had to come up with a way of supporting the pushrod while it was being held in the open position. I decided that if I extended the lockout arm and machined it so it would straddle the pushrod it would serve two purposes, one to support the pushrod when it might fall out of the conical pocket and two to lockout the pushrod for the coasting cycles.
With all the bits and pieces assembled I took some more dimensions and made up another sketch. The rear of the lockout arm would fit into the spool with a round tip, no problem but it took a little figuring to get the other end.
I put a piece of steel in the mill vise and cut it to the overall dimensions. I then put the pivot hole in. Using a .125 end mill I profiled all of the shape from my sketch. I then mounted a slitting saw and cut the pushrod slot into the end. The lockout arm is .062 thick but .145 thick where the support area is so I milled the top surface in this setup.
Once the arm was removed from the parent stock it would be virtually impossible to hold so with the slitting saw I cut the part off in two levels, one to give me the .062 width and one for the widened end. The extra stock would have to be removed by hand filing and burring.
I lightly cleaned up all the surfaces and slid the lockout arm into it's bracket and the crankshaft spool. I moved the governor weights to the outside position, moving the lockout arm into the 'lock' position. I then realized that as the arm angles inward it starts to touch the cam gear so I took it out and filed a clearance angle on the inside surface. Reassemble and recheck. I left extra stock on the arm so that there would only be a tiny boss which would catch a stop on the pushrod. I filed more stock away, checking and rechecking as I went. I finally got the arm to work as intended by moving the governor weights in and out. The support area for the pushrod is always engaged over the rod. I turned up a small bushing and threaded it for a 1-72 set screw. This would be the stop for the lockout arm.
You can see in the two pictures the lockout arm in both postiions.