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914World.com _ 914World Garage _ Plastigage tolerance

Posted by: Vacca Rabite May 14 2009, 12:40 PM

I need to use plastigage on my crank to see what the clearance is.

What am I aiming for? How much is too much?

Zach

Posted by: SLITS May 14 2009, 12:59 PM

Haynes .... Page 11

Mains ... #1 & #3 ... 0.0016-0.007"
#2 .......... 0.0011 - 0.0066"
#4 ......... 0.0019 - 0.0074"

Rods .... 0.0008 - 0.006" RADIAL

Other than this, I know nothing!

Posted by: Jake Raby May 14 2009, 06:55 PM

Those specs are worthless!! They give a full five thou of tolerance and a 914 engine with .006 main and rod bearing clearance will have ZERO oil pressure!!

Look for a max of .003 on the mains and .0025 on the rods, I like even less than this...

And plastigage is NOT a precision measurement device.. The only way to do this is with a micrometer and a bore gauge... If you send the parts to me for balancing we'll do it for you.

To check the main clearance the bearings have to be installed into the case and the case has to be torqued....

Posted by: charliew May 14 2009, 09:52 PM

Or you can use the plastigauge and try to learn how the shade tree guys like me do it. I like to compare my mike readings to the plastigauge. The inside id of the mains are hard for me to do with a bore gauge. Plastigauge kinda rounds off the amounts but it really gets pretty close. To me it's actually easier to mike the clearances rather than torqueing it together with the plastigauge on all the mains and then taking it apart and not tearing the plastigauge up getting it back apart. The rods are easy.