I have been looking for engine build kits on ebay and such and have noticed there are many difference sizing options for the pistons, cam bears and crank bearings and so on. What I want to know if how to determine which sizes I will need for my engine and what parts I need to measure to determine the correct size. I see sizes like 0.010, 0.020, 0.030, etc. What determines an oversized or undersized bearing, from what it should be stock? I know the block I purchased has been bored 0.030, so I should get 0.030 over pistons, correct? But what about the others? All info. appreciated. THANKS

 

if your machinist has turned your crank down "10/10"
that means you need .010" oversize main bearings
and .010" oversize rod bearings

cam bearings should just be a normal size
your rings should match your pistons of course, so .030" oversize there too

if you're getting a new crank, get std bearings.

you already have the block .030" over? ok, then when you get your .030" pistons, put one in, and a feeler gauge, and measure the clearance. Certain pistons need a different clearance, (forged vs hypers for example), that's why my machinst wouldn't bore my block, unless he had the pistons in hand to use...

 

what does std stand for? What are std bearings? I don't have a crank yet, so i guess it'll be easier. whats usually the stock crank measurements for a crank?

 

You've got that backwards man, if your machinist turns the crank down .010, you will need .010 undersize bearings, not over. Oversized bearing are used when boring the housing.

 

what housing is bored for oversized bearings? any pics? also, what does std stand for? std bearings?

 

If you have a main bearing housing (mains) that is out of round, they will bore the housing out, to make it round again, thus necessitating oversized bearings. Undersized bearings have a smaller inner diameter, oversize bearings have a larger outer diameter.

STD is an abbreviation for a standard bearing.

 

Okay, so if I mic the main bearing housing, what would be a normal number (make one up) and then whatever that number is the sized bearing to get. Im not sure what a normal sized housing is, if i knew that and then measured it with a mic then i would know if its standered (stock) or not.

 

You need to look at the back of the bearing in the block now, and see what it says first. It will give you a good idea. If there are no bearings, search the net, or get a shop manual that lists the manufacturers specs for the block. Find out what it should be, and then check it. Either use a dial bore gauge (expensive) or a telescoping gauge and a mic. I really cant tell you off the top of my head what it should be. You need to measure the bore in 3 places. One directly accross, from the middle of the cap to the middle of the bore on the block side. Then go to the parting line and measure it across both ways, just above it to just below it. YOu need to know if the housing is out of round. This is standard procedure in rebuilding. The same should be done to the rods also, with and without bearings in place, while torqued. You do it with bearings in place, and then mic the crank. Some simple math with tell you your clearances.

 

I always mix that up.... I think that if the crank is turned .010" SMALLER, then you'd need bearings that have a smaller ID, which is more material, therefore a "oversize" bearing.... well whatever...


If you don't have a crank, and you'll probably be buying a new crank, it should be the normal stock size (I don't know what that is off the top of my head...), and then you'd buy std bearings (std = stock size)....

of course you'd want to measure it all up as well. Bore gauge etc, or plastigauge. I'm using plastigauge personally, it's cheap, like me

 

I will use plastiguauge while measuaring, just for insurance. The only downside to plastigauge though, is you cannot tell out of round, just taper and overall clearance.

 

Best thing to do is to take the block to a competent machine shop and let them check it for you. I've been building motors for years, and still don't trust myself on checking things like that, I take it to my machinist and he does what is needed to make it right and gets me the right parts.

 

The machinist doesn't do anything you can't do, if you've got the right tools.

 

Except having a whole lot more experience in using the tools.

 

There's only one way to get experience.

 

Its all about insurance. If I measure everything twice, take my stuff in to be done, the machinist will check it too, hopefully. Then when it comes back, I will check it again. DO NOT TRUST THE MACHINE SHOP! Not saying that you dont have a trusty machinist, but anyone can make a mistake, and its not worth destroying an engine. No matter how confident you are, its worth it to measure it all before assembly.

 

This is true, especially with the newer equipment all it takes is punching a number in wrong and whoops, there goes a crank or cylinder bore. I can honestly say that out of all the engines I've taken to him, I have never plastigauged any of them after getting it back and all are still surviving with no problems, even the LT1 which was one of the first ones he had done, guess it's all a matter of trust.

Plus he doesn't use any of the new computerized equipment and has been doing this for over 40 years and the equipment is older than he is, and can probably get it closer than the new equipment does....like I said, it's all a matter of trust.

 

Agreed, most of the times there will be no mistakes. It just sucks when you have 6 or 7 grand riding on it, and there is one. An experienced machinist will usually measure after he is done anyway.

 

Thanks everyone for the info. Ill keep everyone posted!