Hey fellas are the dampener springs on the drive and transmission different on a M20 to a M21?

email (option): pumbriaco@sbcglobal.net

I don't understand what you are asking? Could you refrays it? But apart from the crankshaft and piston. Most of the M20/M21 is the same. Ron

email (option): ronpier@talk21.com

Hi Paul..If you mean the crankshaft shock absorber spring and the clutch spring (on the single spring clutch) they are the same for both models...Ian

email (option): ian@wright52.plus.com

Yeah thanks fellas the crankshaft shock absorber spring and the clutch spring.
I have a M21 rod in my M20 engine( There's a plate under the barrel so know it's a "stroker). So It has a little more power now. But if i accelerate to quickly it feels like that crankshaft sprocket skips like crazy. And in 4th gear too. I'm not sure how to remedy that. Any Ideas?

email (option): pumbriaco@sbcglobal.net

First thing to check is that the shock absorber spring is fully compressed. Then lock it.

email (option): Gasboy@btinternet.com

Yeah I checked that already. The springs are compressed and bolted down tight. That's why I'm stumped.

email (option): pumbriaco@sbcglobal.net

Paul I'm intrigued about the plate under your barrel. With the correct M21 piston there is no need for the plate. I'm guessing it's been done with a standard M20 piston or something else Ron

email (option): ronpier@talk21.com

Hi Paul...That's to stop you breaking the conrod again.. ...
You need to check the crankshaft shock absorber nut..this should be tightened up all the way until it 'bottoms out' on the sleeve that carries the engine sprocket...Then, using an aluminium drift and hammer 'knock it up' tight...
If you don't do this it will either come undone or if not fully tightened initially it won't be exerting enough pressure on the spring.
If the shock absorber still 'ratchets' over after you have done this you need a new crankshaft spring.
When the nut is fully tightened, slowly turn the engine over using the kickstart until it comes up to compression...The compression pressure should stop the piston momentarily and the crankshaft shock absorber will operate...One cam will move against the other and should move 1/4-1/3rd of the way 'up the slope' of the other cam, at which point spring pressure should overcome compression pressure and the engine will turn over...
The mechanism is not designed to 'ratchet over' at any stage of its operation....I'd like more info. on the plate under the barrel as well..Your engine must have some non standard parts fitted..either piston or conrod or both..How thick is the plate?..Ian

email (option): ian@wright52.plus.com

Yeah I may need a new spring I'll have to take off the primary and take another look.

The plate is under the barrel to makeup the extra length of the M21 rod that replaced the M20 rod that was in there. The original rod busted below the wrist pin and for the life of me I couldn't find an M20 rod. So I installed a M21 rod which has a longer stroke. I didn't have a M21 barrel so I had to extend the length of my M20 barrel.


Your pal
Paul

email (option): pumbriaco@sbcglobal.net

No Paul. The M20 and M21 rod is exactly the same. It is the crankshaft throw that is different. (The big end is in a different location relative to the centre of the crank) All you need to make 600cc is M21 flywheels and an M21 piston. Everything else apart from differences with carb and gearing is the same. Even those can remain the same. Ron

email (option): ronpier@talk21.com

Oh OK. I worded it wrong then. I have an M21 flywheel in an M20 barrel and piston.

email (option): pumbriaco@sbcglobal.net

get an M21 piston and you won't need a "stroker" plate

email (option): n.gentner@bigpond.com

Paul, just as a matter of interest, how thick is your barrel spacer plate? Ron

email (option): ronpier@talk21.com

Is an M21 piston shorter then a M20 piston Neale?

email (option): pumbriaco@sbcglobal.net

Yeah Ron the Plate is roughly 1cm thick. Aluminum plate.

email (option): pumbriaco@sbcglobal.net

Thanks Paul. I was chatting to Ian the other day and he worked out that an M21 piston is 9mm shorter than an M20. Which coincides with your plate thickness. If you haven't fully assembled the engine, It will definitely pay you to source an M21 piston and therefore give you another 100cc in standard form.
The other issue is your tappet lengths. Is there enough adjustment left?

Cheers Ron

email (option): ronpier@talk21.com