Telling Crankshafts apart

[Diseazd]

If you have an L series crankshaft by itself, how do you determine whether it is an L26...L28 or an L24 without measuring the stroke? In other words, are there any marks or numbers to simplify the process?

[MikeW]

If there are no marks or numbers I wonder if there's a weight difference? Presumably the longer the stroke the heavier the crankshaft.

[ozconnection]

The L26 and L28 crank is the same item.....look for a number cast into one of the crank counterweights. IIRC its N42

A diesel crank will be VO7

The L24 will be P30 IIRC

And heck, I can't remember what the L20A one is without popping out to the shed, sorry.

But I hope this helps.

[Diseazd]

That'll help. The reason I ask, is because I'm building an L24 (72). I bought the motor used, so I don't know the history. I put the bottom end together assuming all was original ( it didn't look like it had ever been apart) and when I installed the .040 over 240Z Nissan pistons, they came out of the deck by .035 inches. The machine shop decked the block .008 of an inch and assures me no more, but the piston is out .035 of an inch. I pulled a rod and they are 240Z rods. Is it possible someone had installed (by mistake) an L26-L28 crank?

[MikeW]

The stroke went from 73.7mm (L24) to 78.0 mm (L26/L28) which is 0.170 inches, far more than the 0.035 inches that you're seeing.

[Diseazd]

Which means that the engine block must have been decked before......but .035 of an inch? .......WOW!

[MikeW]

Precisely. I honestly don't know enough about rebuilding to know what's acceptable but I knew you'd come to the inevitable conclusion on your own - as you've already done. All I was able to do was steer you away from the notion that it could possibly be an L26/L28 crank in there.

[oldhemi]

Compare your new and old pistons and see whats up! I know that you gotta pop one out, but I am pretty sure that you will end up popping them all out anyway.

[Diseazd]

You're right about that! The number on the crank is E3141. I pulled a piston.....both rod and piston were L24 (long rods). I'll pull all pistons and dump this block in the garbage!!! It's beautiful with it's new paint and brass freeze plugs. What a shame! Guy

[ozconnection]

Don't waste the block!!!!!!!

There are 2mm (80 thou) and the like headgaskets out there that would solve your problem. Kameari make them, or you could find a custom thickness copper gasket that'll get you outa trouble.

What is the casting code on your block outa interest?

[MikeW]

It looks like MSA carries the 2mm gasket for $314.95:

http://www.thezstore.com/page/TZS/PROD/PEM09/10-2453

How thick is the stock gasket? I seem to recall mine being more than 1mm but that was 20+ years ago when I replaced it.

[Diseazd]

As I understand it you can have the flat top of the piston out of the block by .015 with the stock gasket which crushes to .050 inches. The clearance needs to be .035 inch minimum. I believe that the gasket that MSA sells is for a bored out L28 and is 2mm. If anyone knows where I can get a 2mm gasket for a .040 over L24 I sure would appreciate your help. 2mm would be .080 less .035 out of the block would be .045 clearance. Thanks Guy P.S. It's a P30 block

Edited April 27, 2010 by Diseazd