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Peek-a-boo racing block, enjoy!


Deilke53

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On 5/5/2021 at 10:45 AM, Deilke53 said:

Sure, every step always is a good policy.

 

Read a couple interesting forum threads on 4cyl knifing.  I think I'm blaming crank flex from using 8500 as my new normal.

 

Did you balance the rotating assembly? 

72'  2002 turbo build - under construction...

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2 hours ago, evil02 said:

Read a couple interesting forum threads on 4cyl knifing.  I think I'm blaming crank flex from using 8500 as my new normal.

I think I'd find out what Byron (preyupy) is doing and do that. Byron has built any number of race engines and has seen more than his share of rotary disassembly.

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If everybody in the room is thinking the same thing, then someone is not thinking.

 

George S Patton 

Planning the Normandy Break out 1944

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If the underside of the pistons are all colored the same and wrist pins, no sign it was hotter than the others I say you lost a rod bearing. Preassemble bearings in rods then measure with a bore gage. Some brands will have more clearance than others near the parting line. Plastigage just measures the gap 90 degrees to that. Measure the rod bore without bearings also. If the remaining 3 are still straight and round its further proof the rods are good metal and not the problem. 

 

The light crank can be a problem just because its easier to use it like a sportbike. Back in the 2 stroke gp days riders who shut the throttle abruptly at the end of long straights lost more cranks than those who smoothly rolled it off. The sudden no damping at tdc from combustion pressure on the piston puts a load on the rod bearings. 

 

Thanks for the pictures and build another, measure more 

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8500 is a lot! I don’t know what cam, valves, and carburetors you are running  but to get a 2 liter M10 to actually make power past 8000 rpm is a good trick. Did you have it on a dyno? I’ve seen a lot of them that people have said they normally run past 8500 and when we actually run them on a dyno we find they are all done making power at 7800-8000 and the last 500 rpm is just noise and abuse. 
 

I have also found that an engine with a 7500 rpm rev limit has a 25-30% longer life between rebuilds than an 8000 rpm engine. 

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1970 1602 (purchased 12/1974)

1974 2002 Turbo

1988 M5

1986 Euro 325iC

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