Off set cylinder

ben4221

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Sep 17, 2017
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31
Hi all just thought I'd put up a few pics of my latest engine build, going to offset the jug so that con rod is at a proper angle during compression stroke, as far as I'm aware no one has attempted this mod before so any input would be much aprieciated. I'm planning on getting a stroked out crank with a long rod I've looked but can't find any strokers in Aus so if anyone could recommend a good American crank with with 3 or 4mm extra stroke and 40mm rod that would be great
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Spare_Parts

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Nov 29, 2017
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I'm lost. What is this proper angle you speak of? Looks like you are just rotating the cylinder forward.
 

ben4221

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Joined
Sep 17, 2017
Messages
31
The first photo shows proper angle notice the angle of the ruler is vertical with little end offset to the intake side, the second photo shows stock angle with the little end of con rod directly above big end notice the angle not vertica
 

Will'smotobikes19

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Apr 9, 2018
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1,578
Don't know how well changing the jug angle will work I'm guessing you can weld aluminum or (aluminium). What I want to see is a 2 cylinder inline twin CG. No shoddy work maybe even a redesigned crankcase and crank.
 
Joined
Sep 26, 2018
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Moving the cylinder back shouldn't yield anything power wise. If anything, you will lose power/efficiency, you'll screw with timing relative to the crank, and I wouldn't be surprised if you increase piston slap.

Actually, could it even run? Where would the piston be at TDC vs the crank? Wouldn't you need to retard timing more? I know Nissan did the opposite so the power stroke was more efficient in the variable compression engine...
 

ben4221

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Joined
Sep 17, 2017
Messages
31
Moving the cylinder back shouldn't yield anything power wise. If anything, you will lose power/efficiency, you'll screw with timing relative to the crank, and I wouldn't be surprised if you increase piston slap.

Actually, could it even run? Where would the piston be at TDC vs the crank? Wouldn't you need to retard timing more? I know Nissan did the opposite so the power stroke was more efficient in the variable compression engine...
yeah your right moving the cylinder back by it self wont yield anything but its a great geometry to make a high powered semi reliable engine, as for timing it will be way out so ill just make some new marks on the magnet and move it to where ever it runs. the timing curve shouldn't be the same too.

ive heard of 4 stroke 4 cylinder engines running 90psi of boost reliably with offset crank shafts (same principle as offset cylinder) so i thought it would be a good base for a high compression 2 stroke engine to run on methanol.

This pic should help to better understand, look at the angle of the con rods, in the right hand one its on a much better angle during power stroke when it has maximum force pushing down on it. yes it will be on a worse angel when its coming back up during compression stroke but its only under very slight rotating force from the weight of the crank shaft spinning pushing it back up not a high pressure flame explosion like power stroke, hope that explains it a bit better




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