First of all, I read this forum daily and have learned tons about the Y block from you folks.  Your knowledge is far beyond any other group of people on other forums , and your willingness to help without making us unlearned feel like idiots is much better than on some of the forums I read.

Now to the problem.  I took my 312 to the machine and had it bored .040 and zero decked.  The rods were rebushed on the little end and resized on the big end.  The crank had already been turned .010 on the mains and .030 on the rod journals so it was just polished.  When I got it back and started assembly, the pistons in cylinders 2,3,4,7 and 8 were sticking out of the hole any where from .005 to .015...., so I thought that maybe somehow they resized them wrong and some were shorter than the others and the short ones were used to measure the deck height.  I took it all back and the machinist told me that he measured the rods, checked them for straightness and they are OK.  He says that the difference is in the stroke of the journals that are long.  He says that if the crank had been turned a couple of times to get the .030 that maybe someone got the journals offset causing a longer stroke, and that some of the cranks came from the factory with not so good tolerances which doesn't help.  Can this be so?  Has anybody else had this problem?  Help and suggestions would be greatly appreciated.  I have built small block and big block Ford before and never had this problem.  I don't want to put this thing together and have to do it over.

Sorry for the long post, but I needed to get all the info out there for you guys to chew on.  Thanks for any help.

Butch

Manchester, TN

Butch Lawson

Manchester,  TN

Butch:

I never thought of it, but yes, with sloppy setup, the throws could be ground with different stroke.  However, if some pistons are out of the block .015 and some 0, then the stroke would have to be .030 long one some throws, which means to grind the throws .030 would mean all the material would have to be taken off one side of the journal.  That surely didn't happen.

Try taking one of the 0 deck rod/piston assemblies and putting them in the holes that the pistons come out of the block.  If they are 0 in those holes also, then the crank stroke is probably not the problem, but either the compression height of the pistons vary or the rod lengths vary.  If I were building this engine, I would measure how far each piston sticks out and machine that much off the top of the piston.  I'm assuming they are flat tops.

John in Selma, IN

John - "The Hoosier Hurricane"

Thanks John.  That was the solution of the machinist also.  He had the pistons cut when I went back.  I think I'll take your suggestion and put the #1 piston in a couple of other holes and see if it sticks up any, and try one that has been cut in the #1 cylinder and see what it looks like.  I used speed pro pistons.  I would think that there wouldn't be that much difference in the set.  Do you think that it could have happened when they resized the rods?  Maybe got offcenter when they resized?  I really don't want to button this thing up until I find out what it is.  Guess I'll spend a couple of days measuring everything.

Butch Lawson

Manchester,  TN

Don't get too caught up on it, Butch.  Only the most meticulously built race engines will have everything perfect.  Get your pistons so that they are 0 to .005 out depending on the head gaskets.  It will be fine.  I notice that many crank grinders have a service where they will equalize the throws.  I'm sure this is not done on most rebuilds.


Lawrenceville, GA

Thanks Charlie.  It's more a matter of curiosity now.    It's one of those things that keeps rolling around in my mind.  I just gotta know before I can rest. 

Butch Lawson

Manchester,  TN

I just had a full assembly done. One of the pistons was a different brand and was a little high in the hole. It was also lighter. They fly cut the top of the piston to match the others (0 deck) and added some heavy metal to the pin for the balance. Crank was square though. Gotta watch these so called "machinists" sometimes. Chuck in NH

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

John: Is it possible that the block decks are not parallel with the crank? I've seen this problem mentioned somewhere. Possibly in Y-Block Magazine..

Paul

I'd be checking the the rod lengths and deck heights VERY carefully. You may be able to mix and match long rods with short pistons and vice versa to get everything close enough to use. Were the pins resized in the pistons, did they screw that up? John's trying to tell you that the crank issue is not likely the whole problem.

      The stroke can be checked by installing any one piston in each hole and rotating the assembly. If it's off .030" that won't be hard to measure. One thing to kinda check yourself, If you find a throw that's off, it will also be off the same amount on the opposite side of the block, same crank throw. 

Frank/Rebop

Bristol, In ( by Elkhart) 

It’s not unusual for the strokes to vary from journal to journal even on a factory crankshaft but as has already been mentioned, you’ve likely got more going on than just a stroke variance by itself.  If the stroke variance isn’t checked when the crankshaft is turned, then the problem is compounded when the journals are ground undersize.  And turning the crankshaft multiple times also adds to the amount of variance that can exist depending upon the individual doing the grinding.

 

Seeing as how the pistons have already been cut to remedy the problem, you’re technically good to go.  But if wanting to clarify where the problem originated, then you’ll need to to verify the stroke on the individual journals and go from there.  Remeasure your rods for length and see what the length variance is.  This is something you can do yourself with a set of dial calipers in lieu of more sophisicated rod measuring equipment.  If piston tops hadn’t already been cut to compensate for the variance and assuming there is some rod length differences, then you'd put the short rods on the long strokes and long rods on the short strokes.

 

Based on the numbers you posted, there is the strong possibility that the decks are not square with the mains.  Do you have the original and exact deck height measurements by cylinder as this may help in determining if it’s all stroke related or is a combination of deck cut, rod length, and stroke variance.

Lorena, Texas (South of Waco)

Update!!  I finally got everything back from the machinist again and he says its a combination of rod length, crank throws, and the deck was not exactly parallel with the mains, Just like you said Ted.  Whew!! My first complete Y build couldn't be really simple.  (or maybe it's me that's simple)  I think I'll take Charlie's advice and put it together and not worry.  Thanks for everyone's help and thoughts.  Maybe someday I can get enough experience to help someone else.  It looks like the static compression will be around 9.7:1.  Think I can run 87 octane?

Butch Lawson

Manchester,  TN