gsxr1216

so i dropped the pan off my motor today and checked all the main and rod beairngs on it. theres a few that are looking like they have some wear on the coating so since i have it all apart and out of the boat i want to replace them all now so i dont have to mess with this 5 years from now. i wrote down all the GM bearing # and clearance size that was stamped on the bearing shells itself and after doing a few quick web searches i came up with nothing on the numbers??

are the OEM bearings not made anymore?

am i looking in the wrong spot to find the OEM bearings that use the 1990 part #'s?

does anyone cross reference the OEM GM4 bearing shell #'s to other makes like federal mogul? if so do the other makes come in at proper size to OEM or will i be buying the supposed same bearing and plastiguage it and find it to tight or loose and be ordering more bearings to get the right fit?

thanks!

JeremyAnderson

Why not some Clevite bearings?

gsxr1216

those are fine also as long as i can get a direct replacement for my OEM part, do you have any cross reference to the OEM numbers??

BillK

gs,
The ONLY place you can get the oem bearings are either from a GM ($$) dealership or Mercruiser ($$$$). A lot of times the original bearings are "select fit" with a .001 or other size bearing in one or more posittions. Those size bearings are available from Clevite but you need someone with an interchange book to order them.

Personally, I would have you take your bearings to a good machine shop that does performance work and have them figure out what you have and order the Clevite bearings to match. Unfortunaltely, a lot of times the thickness of the aftermarket bearings does not exactly match the thickness of the oem bearings The last 502 Mercruiser I had apart had the GM bearings in them and I swear they were King bearings. That is what I ordered to replace them and by looking at them and measuring them, I am almost certain they were the same. I am not sure who is making GM's bearings now. I have a Clevite interchange that shows the correct bearing numbers to replace the GM bearing numbers, but I do not blindly trust it without having the OEM bearings to measure.

I know this really does not help you a lot, but it is the correct way to order the bearings.

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

gsxr1216

some of my main bearings had .0006" marked on them and a few had .0012" on them. all of them were GM4 bearings, i assume the gm4 was since its a gen Iv motor? any idea where i can get a look at the this interchange book oniline???

my rod bearings were kinda strange, every odd rod# had a gm4 2621313 then 46D932, and every even rod# had a GM4 2621313 then 63R932 on them, i thought i would find some difference in them just like the main bearings since i find it hard to beleive they are all identical on each even and odd number!

BillK

gs,
GM4 is the bearing material. As far as I know, the Clevite interchange is not available on line. You must have the printed book. Also, like I said in my previous post ..... the interchange does not assure you that you will get exactly the same thickness bearing. The ONLY way to assure that is to measure your existing bearings with a bearing micrometer, then compare them to the replacement bearings that you purchase and hope they are the same. GM used those bearings to make up for the lousy production grinding tolerances on the crankshafts. If you buy an actual GM bearing, it "should" be the same thickness and give you the same clearance, BUT no engine builder worth his salt that I know of would just assume that without measuring the bearings or measuring the actual clearances while assembling the engine. Pretty much impossible to do correctly with the engine still together

If you want to get the engine back as close as possible to the way it came from the factory, you need to buy the GM bearings, period. I dont think Clevite has a .0006 or a .0012 bearing. Your crankshaft (or rods) must have really been a mess when they ground it There is still no guarantee that they replacement bearings will be identical to your 21 year old ones

So ..... now you see why good engine builders charge the type of prices they do

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

gsxr1216

any bearing i ordered i planed on measuring, and using plastiguage to make sure it was in spec, i just didnt think getting a stock oem bearing would be a such project for a stock engine rebuild.....


as for engine builder prices, I'm aware of them. i race a motorcycle that goes 8.17 in the 1/4 mile and i dont have all the machinery i need to do all the machine work myself so i have had to spend some $$$ to say the least!

GPM

Maybe you should take the crank and rods to a machine shop have them checked and then make the decision on the bearings. They may need reconditioned. Just an opinion.

scottw

iTrader: (1)

1988 to 1992 454 Magnum.



http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr= 19378&ivar=images/CRUISER/19378/35.png&inbr=961&bnbr=190&bdesc=CRANKSHAFT%2C+PISTO NS+AND+CONNECTING+RODS

Baja226sport

iTrader: (28)

This may very well be a good idea. Correct me if I am wrong, and I very well may be, but I was under the impression that rod bolts were only good to be torqued one time.

The factory bolts from GM I was told were "torque to yield" bolts that strectch and should not be used twice.

Again, I could be wrong on this. I know this is a fact for the buick 3.8 V6 as I had an issue with this in my Grand National, but not sure about a Big Block Chevy Marine motor.