david rosenthal wrote:
Interesting. some of the piston/brgs could be explained. broken crank/rods????????
Consider this
1 the clutch bake plate and pressure plate are bolted together and attached to the flywheel with 3 metal strips.
2 the dia. of the backplate is 225mm
3 the weight of the back plate and pressure plate is 7kgs
4 engine running at 6000 rpm ie 100 revs /sec
the circumference of the back plate is travelling at 71 meters/sec
when the clutch is used the back plate moves and as there is NO positive location to crank or flywheel andmoves off center and the whole crank/flywheel goes out of balance.
This out of balance force can be calculated by using a formula called centripetal force and the vibration transmitted thru all the reciprocating parts[crank/rods/pistons and brgs] is calculated with torsional vibration formula. all IC engs have torsional vibration and critical noduals, the point at which maximum stress occurs.
I was shown a practical demo of this years ago. One of the engineers where I was working had a min eng set up on test bench. He cut a hole in clutch housing to see bolts in pressure plate. Maked around this area with chalk. Ran eng to 5000 rpm and using a strobe light we watched the bolt. Then activated the clutch, you could see the bolt moving around every time the clutch was engaged and dis-engaged. It quite often did not return to original position. This meant that this whole 7kg mass was going out of balance.
This out of balance force is like bending a piece of metal, the amount of deflection and the no. of times determins when it will break.
What is the point of balancing a crank/rods/flywheel whe you have this out of balance force occuring unless the reciprocating mass can be positively located and included in the balancing.
Man these engines are good for the abuse we give them
Good analysis there David, I'm wondering if the later Verto clutch setup is any better?
These have the pressure plate/flywheel setup reversed, where the pressure plate is bolted to the crank, and the `flywheel' floats... it is all still hung a long way out from the rear main bearing. I bet that doesn't help crank durability either!
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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
).
Stupid kids. 
