# My Two Cylinder Design - Feedback welcome



## smpstech (Jun 20, 2013)

I had been working on these plans on and off for quite a long time, and now that I will have access to a very well equipped shop in the near future, I actually want to build it. I have read through many a threads here on the website and then realized I had a lot of problems with my design. 

But here it is now, it's a 2 cylinder flathead engine using a 3/4" bore by 3/4" stroke. I designed it so that it would be quick and easy to machine, being that I will have limited time to use the shop. I will have access to very fast 4 axis CNC mills as well as CNC lathes, so I'm not too worried with some of the more complex shapes. 







Engine Block. The valve chest is directly connected to the crankcase, and the camshaft will be lubricated by oil splashed from dippers on the bottom of the connecting rods. The intake/exhaust runners are 1/4". 






Top of the cylinder head. The blue area represents area that will have coolant flowing through it. I am relying heavily on the cooling in the head to also cool the block. To aid in this, I am planning on making the headgasket out of copper. 






This is the bottom of the head, the white areas are the combustion chambers. Compression is near as makes no difference 7:1. 






This is the rotating assembly. I am planning on using three piston rings, all made of PTFE (Teflon) which is good for 500F. The top two will be compression rings and the bottom will be the oil control ring. The wrist pin will be full floating, and will be retained by the piston rings. All the bearings are using standard Oilite bearings from McMaster Carr as well as the piston rings are standard PTFE Orings from McMaster. 






This is the profile of the cam. The intake/exhaust cam lobes have identical specs. There is a 112 degree lobe separation angle. The duration is 208 degrees, and the lift is .05625". 

There is of course more to do. I am not sure if I want to integrate the other half of the main bearings into the oil pan or not yet. The water pump still needs to be designed. Many things need to be fine tuned yet, as well as the ignition system worked out, though that will be a fully electronic setup.


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## Goldflash (Jun 20, 2013)

Like what you are doing, some suggestions. It appears that your crank throws are at 180 Degrees apart. To simplify the engine crankshaft manufacture  and  it may be easier to have a 360 Degree Crank as per the old British parallel twin motorcycles such as triumph Norton BSA etc . IE both pistons rise and fall together but fire 360 degrees apart . 
I am not sure about PTFE for piston Rings. I have used it on gas compressors operating at 3600 psig ( 750hp ) but discharge gas temperature is limited to a Max of 150 Degree C and under API rules piston speed can not exceed 1000 Feet per minute.
PTFE has a very high co efficient of expansion and you will need a lot of end clearance and also allow for side clearance or those rings will jam in the ring groove of the piston and can do a lot of damage.  
I would stick to good old cast iron for the piston ring and you may find that 1 ring per piston will more than likely be OK.


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## stevehuckss396 (Jun 20, 2013)

208 degrees seems awefully low. Might want to bump that up to at least 240. She's going to struggle when trying to take a breath.


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## johnny1320 (Jun 20, 2013)

parallel twins usually have both cylinders at TDC at the same time, then there is always one cylinder firing on the down stroke, looks good, I am designing a parallet twin myself but it will be over head enclosed valve train.


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## jwcnc1911 (Jun 20, 2013)

This is looking to be a nice project.  I'll follow this closely.  Good luck with your project!


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## Art K (Jun 20, 2013)

Hi,
I agree that you should go with the 360 degree crank, otherwise it will have a rather unusual lope. Is there a particular reason for not having a water jacket in the cylinder? Otherwise this sounds like an interesting engine haven't seen many L heads around lately other than the Wall 50 cc. I look forward to this build, and will be following it.
Art


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## Goldflash (Jun 21, 2013)

Further Thoughts. 
The Brit Twins ( apart from Matchless and AJS ) did not use a center main bearing on the crank. 
The main bearings were either roller or ball bearings in most cases apart from the timing side bearing on the BSA Twins which was a bush and the achilles heel of that design. 
These ball or roller bearings were lubricated by the oil mist and droplets that were present in the crankcase 
If you use ball bearings they will allow for a bit of misalignment


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## kuhncw (Jun 21, 2013)

Interesting engine and I'm looking forward to your build.  Maybe I missed it, but what material is the block made from?

I second the recommendation to go with cast iron rings and no more than two rings per cylinder.  You could retain the piston pins with Teflon buttons.

Regards,

Chuck


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## Jasonb (Jun 21, 2013)

I would also go for iron rings BUT only of its an iron block or you intend to sleeve what I suspect is an Ali block but your head design is not ideal for keeping a liner in place.

You may also want to look at your crank web shape as there is no counterbalance with the plain round profile if going with the 360deg option.

J


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## jwcnc1911 (Jun 21, 2013)

Goldflash said:


> Further Thoughts.
> The Brit Twins ( apart from Matchless and AJS ) did not use a center main bearing on the crank.
> The main bearings were either roller or ball bearings in most cases apart from the timing side bearing on the BSA Twins which was a bush and the achilles heel of that design.
> These ball or roller bearings were lubricated by the oil mist and droplets that were present in the crankcase
> If you use ball bearings they will allow for a bit of misalignment



Goldstar, this is interesting.  Where did you find this rendering?


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## smpstech (Jun 21, 2013)

Thanks for the feedback guys. These are the exact things I was worried about. 

To answer a few questions:

I plan on making the block and head out of Cast Iron. All things considered, I will probably change the pistons to only use 1 Cast Iron piston ring, as what I've read has said that Cast Iron rings and Cast Iron cylinders go together well. The crankshaft, connecting rods, and piston will be aluminum. 

I was weary of Cast Iron rings not because of the machining process but because of the heat treating. :hDe: But thinking about it I believe my college does have an oven capable of the temperatures needed in the material sciences lab. 

And regarding the camshaft duration, I was basing those off of full size camshafts. But considering these little engines like to rev much higher than the full size counterparts, longer duration would make much more sense.


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## johnny1320 (Jun 21, 2013)

smpstech said:


> the crankshaft, connecting rods, and piston will be aluminum.


 
If this is a IC engine I would not recomend an Aluminum crankshaft


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## Draw-Tech (Jun 21, 2013)

Just to get my 2 cents worth, I agree with everybody on cast iron rings, just to mention that I believe that Teflon when heated to much produces a toxic gas. Correct me if I'm wrong.
Jack


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## smpstech (Jun 21, 2013)

johnny1320 said:


> If this is a IC engine I would not recomend an Aluminum crankshaft



Steel? Or maybe Cast Iron?


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## Terryt (Jun 21, 2013)

Hi:

Very nice.

Do you know if this can be made on a 3-D printer and if so how big would the printer need to be?

Thanks,

Terryt


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## smpstech (Jun 21, 2013)

I suppose it could, its only something like 2" by 2 1/2" by 2" big. 

Just about any consumer 3D printer out there would be able to print it, like a Makerbot. Don't expect too much precision but it would be great for mocking things up.

I've actually toyed with the idea of getting a 3D printer and using it to do some sort of...lost plastic casting. Not sure if the plastic would have any sort of adverse effect on the metal being poured and it would probably melt much too slowly.


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## johnny1320 (Jun 21, 2013)

smpstech said:


> Steel? Or maybe Cast Iron?


 Steel for sure, 4130, 4340, anealed


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## kuhncw (Jun 21, 2013)

Right.  Steel for the crank and 1144 makes a good crank.  

You mentioned relying on the coolant in the cylinder head to cool the block.  You might consider adding cylinder liners to the design which would let you cut out material from the block to make a water jacket around the upper one third of the cylinder liner.  The cylinder walls probably need direct cooling more than the head needs it.  The liners also give you a more forgiving design if you'd happen to make an error while machining the bores.  A new liner can be made quickly compared to a new block. 

You commented about Teflon giving off a dangerous gas if heated.  If this comment is about using Teflon pads to hold the piston pins in place,  cylinder temperature in the range of pin bore travel  are probably not high enough to cause a problem.  If this is a concern, you could use brass or aluminum pads to retain the piston pin.

I'm looking forward to seeing more of your design.  Perhaps some sections through the porting in the block.

Regards,

Chuck


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## ShedBoy (Jun 21, 2013)

Looks to be a great little engine. Aluminium will be a bit soft for a crank.

I would have the crank pins 90° apart. It helps reduce a lot of the vibration of a 360° or 180° crank. These 2 animations explain it better.
Standard  setup





Rephased 





Bert Munro modified a brit twin by cutting the crank through the centre and twisting it 90° to give it better balance. I found a pic of a norton crank




I know we are not building speed machine but it just helps to stop them bouncing off the table. 
Just my 5 cents worth (I have run out of copper)

Brock


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## 123RWO (Jun 21, 2013)

There is nothing wrong with a 180 deg. crank on a parallel twin.   The Honda CB350 had one and nobody can argue that it was not good running machine.   No doubt there were other motorcycles, that used that set-up, but I don't have personal knowledge of which ones did.

RWO


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## Goldflash (Jun 22, 2013)

Considerations. Side Valve engines. Side valve engines run hot in the region of the exhaust port which in the case of a side valve engine is in the cylinder block. 
cooling in this region is very important. Therefore you should consider having water cooling in the cylinder block and using cast iron or good quality steel sleeves. 
The cylinder heads would most probably work ok without water cooling as long as they had well machined fins as most of the heat generated in the combustion process is going out the exhaust port. 
I would not try to go over a compression ratio of 6.5 to 1 as side valves can actually be choked by excessive compression ratio. Good breathing and gas flow is more important to get good performance.  
Had a bit of experience with tuned Side Valve V twins ( Indian ) and you can actually be quite radical on cam timing and valve lift.


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## Hopper (Jun 22, 2013)

I would not go much over 6:1 compression on a flathead. Less than that and the restriction to breathing in the area between the valves and the bore outweighs the performance gain of the higher compression.

If you want ideas on tuning/designing flatheads, Google "Harley KR". Harley had the 750cc KR flathead racer lapping Daytona at 150mph in 1968.
An outfit called Victory Library sells some excellent publications on tuning up old flatties. Lots of good info on combustion chamber design (very critical in these engines) and cam timing.
Another website called the Beauty of Speed has some good flathead info too. As does KRXLRTT.COM

If you use the 90-degree offset crankpins (ie a 270 degree crank) it gives a loverly loping v-twin exhaust note due to the uneven firing intervals, as well as running smoother. 
Triumph is doing this with some of its new twins (the America model I think), and Yamaha did it with the TDM800 I think, and Laverda sometime in the 90s. Lot of guys doing it to Nortons in the classic race scene these days.


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## Goldflash (Jun 22, 2013)

Triumph TRW 500 CC Twin Side Valve. Made for the British army.


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## Rivergypsy (Jun 22, 2013)

Just going back to the 3D printing comments, there is a print material suitable for using for lost wax casting IIRC. I've also got some info from Objet on how to do this at work, so I'll try and remember to difg it out and post it when I get back there on Monday.

Looking forward to seeing how you go with this - good luck!


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## smpstech (Jun 22, 2013)

OK so a few updates.

I lowered the compression by cleaning up the combustion chamber design. It sits at about 5.5:1 now. I hope this will also help reduce the heat generated by combustion a bit. 

The camshaft profile has been changed. It now has a 240 degree duration, as per stevehucks suggestion, and I also fattened up the nose a bit. 






Regarding the engine block cooling. Unfortunately, I do not have much room to allow for water jackets inside sleeves. The hottest side of the engine block will be the side with the ports on it as that is where the exhaust gases will be passing through. I plan on making the valve chest cover and intake/exhaust manifold as one piece and will act as a heat spreader and heat sink as it will have fins machined into it. on the opposite side of the engine where the cut out is, I may not cut that piece out entirely and instead opt for fins there too.


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## ShedBoy (Jun 22, 2013)

RWO said:


> There is nothing wrong with a 180 deg. crank on a parallel twin.   The Honda CB350 had one and nobody can argue that it was not good running machine.   No doubt there were other motorcycles, that used that set-up, but I don't have personal knowledge of which ones did.
> 
> RWO


Didn't say there was anything wrong with them just that other types are smoother. Not trying to take anything from a 180° crank.
Up until about the mid 90's most parallel twins were 180°. 

Brock


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## stevehuckss396 (Jun 22, 2013)

Looks great!  When are we going to start building.


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## Art K (Jun 22, 2013)

Steve,
If you're not careful you will have the engine built before smpstech starts on his.
Art


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## neseng (Jun 22, 2013)

.......A bit larger all round but similar to your design ideas in some ways.  It is a side valve, air cooled, 10 hp, twin cylinder, 360 deg, 3 bearing crank, petrol fueled, magneto ignition, 6:1 compression ratio.  Bore 85mm, stroke 82.5mm, 468 cc per cylinder, ign 12 deg BTDC, inlet valve 6 deg before TDC to 30 deg after BDC, exhaust valve 41 deg before TDC to 19 deg after BDC.  There you go, you can chew on those figures for a while!






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Cheers,      neseng


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## smpstech (Jun 23, 2013)

Art K said:


> Steve,
> If you're not careful you will have the engine built before smpstech starts on his.
> Art



Ha, probably. Machining begins in September is all goes well.


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## Goldflash (Jun 23, 2013)

Have a look at the Westbury Seagull 10 CC side valve twin on the web site below it should give you some ideas 

http://www.modelenginenews.org/etw/seagull/


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## stevehuckss396 (Jun 23, 2013)

Art K said:


> Steve,
> If you're not careful you will have the engine built before smpstech starts on his.
> Art



I think it's kind of cool. I would build one.


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## Hopper (Jun 24, 2013)

Some interesting stuff on flathead cam tuning here:
http://www.harleykrxlrtt.com/technical_info_on_kr_cams.htm

And the ultimate combustion chamber design is probably this:
http://www.harleykrxlrtt.com/images/01p-1965-krtt-head-barrel-2.jpg


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## smpstech (Jun 24, 2013)

Rivergypsy said:


> Just going back to the 3D printing comments, there is a print material suitable for using for lost wax casting IIRC. I've also got some info from Objet on how to do this at work, so I'll try and remember to difg it out and post it when I get back there on Monday.
> 
> Looking forward to seeing how you go with this - good luck!



Apparently PLA plastic will work, which is pretty much the standard filament used by most consumer 3d printers. It has the lowest melting point and is the cheapest, so it makes sense and sounds like something that might be worth looking into in the future.


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## Metal_slicer (Sep 6, 2013)

smpstech,

I love the design! I have been trying to design a simple 2 cyliner engine with the exact dimensions you have. A 2" x 2" x 2.5" block of aluminum. This is a good size for my Sherline mill. Seems I always start to run out of room for the valves and intake and exhaust ports. I like the simple approach of having the cam on the side vs having it  overhead.

Any latest images of your design?


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## smpstech (Sep 10, 2013)

That is indeed why I went with the flathead engine design. I wanted an engine that will be able to be ran for long periods of time, possibly at higher RPMs and with a load so cooling and lubrication were key points. With all the valve train in the block and open to the oil pan with splash lubrication, almost everything that needs lubrication is at the bottom where the connecting rods can fling oil around. The valves in the block mean there is just so much more room for the spark plug and larger valves as well as having more material around everything for greater strength. 

And as for the design, it is largely unchanged. Hopefully I can get the first chips flying in about a week or so. I am still wrestling with the block cooling, I may use coolant passages, but was thinking of a aluminum intake manifold/valvechest cover that would act as a heatsink for the hotter side of the block. The exhaust manifold would most likely have to be steel to sustain longer run times. If it was a piece of the "dual purpose cover" it would transfer more heat into it which is kind of the opposite of what I want to do.


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## gus (Sep 12, 2013)

Sad. Lister and Petters Plants are no more in existence. Used both to power air compressors. 
Lister engines run forever.


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