ACE1252

I've pulled the heads off my engine and got the pistons out as well. However I am puzzled on the bearings sizes. This is my first time dealing with engine bearings, so please bare with me if I'm missing something.

The bearings have the following numbers....

Mains - 18019643 - 0.0006
Thrust - GM-A-400 - 0.001
Rods - GM-45 18021941

When I look up these part numbers on GM parts sites I come up with nothing.

Are these bearings sizes standard? The 0.0006 seems like an odd under/over size. Which leads to the question....are they over or under? All the bearing shells were of the same numbers....no mismatched shells on any mains. Also, no + or - next to the 0.0006 or 0.001.

I've got a 2"-3" micrometer on order to check the crank journals.

Has anyone actually got the above bearings from GM before? All the bearing clearances were in spec when I checked them and what I'd like to do is just get exact replacements for them.

I have not been able to find a smoking gun on my original problem. So my plan is to replace the bearings and oil pump to see if the problem goes away. If it does...my plan then is to get a new 355 or 383 short block and have my spare set of heads ported for it. I will then set my stock short block aside for a spare in case I have problems down the road with my stroker(seems like a good idea to keep a spare short block ready in case I blow something at the track one day).

As a reminder....I pulled this thing apart for a strange oil pressure drop between 3000 and 5000 rpms at WOT. Below are links to my threads on it...video in the first one(takes a couple of mins to load...~30megs). With bearing clearances and pictures in the second thread.

https://www.camaroz28.com/forums/sho...d.php?t=703486
https://www.camaroz28.com/forums/sho...d.php?t=713070

MachinistOne

I never even look at the numbers on the GM bearings, they never correlate...

You need to have your crank mic'd to determine if it will be ok at STD size or if it needs to be ground to .010", if it will work sizing wise, the machine shop can polish a couple tenths out to make the surface finish perfect again.

The bearings will be Clevite MS909P on the mains and CB663P on the rods. If the crank is ground to .010" under the numbers get a -10 on the end.

Get a new oil pump and block the adapter bypass.

OneShoe50

I've ssen this on a couple of stock GM engines. My LT1 rear main was a -.001, all the others were STD. Seems during assembly they (GM) will use numerous different size main bearings to meet clearance specs with all the +/- tolerances used during manufacturing. And swapping bearings is quicker and cheaper than sorting through a stack of crankshafts to find one that is .000 perfect.

IMO .0006 or six ten thousands of an inch shows why most small blocks with even poor maintanance will usually last 100,000+ miles, attention to details during assembly!

No, I don't work for GM

ACE1252

Cool deal. Thanks guys!

What would you recommend for cam bearings?

rskrause

Both posts are right on. I use the Durabond cam bearings.

Rich

MachinistOne

Durabond.

For a stock rebuild the standard CH-8 set will be fine, if you're running a bigger cam that takes higher pressure springs I would go with the CHP-8 set and for soild roller or extreme hydraulic roller apps I use the coated CHP-8T

ACE1252

Guys,

Just measured my crankshaft. Mains and the rod journals(had to guesstimate on the ten thousandths).

Mains
#1 - 2.4489
#2 - 2.4485
#3 - 2.4485
#4 - 2.4485
#5 - 2.4485

Rod Journals(measured middle of where rod was riding...#'d by cylinder)
#1 - 2.0986
#2 - 2.0986
#3 - 2.0987
#4 - 2.0987
#5 - 2.0987
#6 - 2.0987
#7 - 2.0987
#8 - 2.0987

Opinions or comments? The thing seems to be in very good condition.

Oh, another question....
If I needed to get a set of std and -0.001 to mix and match shells to get my clearances....which shell needs to be on the bottom or top? For example, do I put the std on the top and then the -0.001 on the bottom or vice-versa?

EDIT:
Did some research on the bearing shells. Looks like the thicker bearing goes on the surface with the highest load. So for main bearings, you would install the thicker shell in the lower half. For rod bearings, the thicker shell goes in the top half of the rod.

Some useful links....
http://www.enginebearings.com/it_bearinginstall.asp
http://www.ellweinengines.com/ERE11/ERE11.htm

ACE1252

I've just ordered all my bearing sets(MS909P, MS909P1, CB663P(x8), CB663P1(x8), and CHP-8).

Another question.....

When dealing with the thrust alignment, do I need I to snug all the main caps and give the crank a light tap from the front to align the thrust surfaces?

brucer

the bearings are matched halves.. you dont mix bearings over .0005..
and for a .0005 i dont think i would even mess with it.. .0005 isnt going to make or break you with what your crank measured.

pay attention to the oil holes.

i never tap or beat the crank front to back.. i'll push and pull on it, then i spin the crank, it should spin pretty easy.. the thrust is a bearing surface also, so i treat it like one.. i check thrust with a dial indicator

ACE1252

I've seen several recommendations of mixing in a 0.001 shell. I also did note that in the Clevite article, they said what you recommended(not more than 0.0005). Any more opinions on if I can mix a 0.001 shell?

ACE1252

Oh wait....I've just read that half a 0.001 set would be 0.0005. Hehe, damn you'd think I could do math. Can't believe I missed that.

MachinistOne

We mix shells all the time to get our clearances where desired. Only mix in one increment of .0005" up and down, so you can mix a std with an HX, or down with an H-1, but don't mix an H-1 with an HX. Despite what Clevite says we don't throw out half sets of bearings just to use the .0005" thicker shell on the bottom or top and I've not yet met another builder who does - it makes absolutely no difference which side the thicker shell goes in other than keeping it consistent with the mains, IE all the STD's upper or all the H-1's lower.

I set the thrust first, none of the other caps in place. Lay the crank and measure the thrust, that should get listed as "Block end-play", then put the thrust cap on and lightly snug the bolts. Now you seat the thrust by prying the crank to the back of the motor first to even up the pressure on the bearing halves, then you will pry it to it's final forward position as the crank will see forward pressure during it's running, so that's the position that you want to load the thrust bearing to. I use an old screwdriver that I modified to tap into place in-between a crank throw and the block to pre-load it forward, lightly smack the back of the crank and then torque down the thrust cap and re-check your end-play. If there is more than a .001" change in end-play with the thrust cap in place you need to look for a misalignment issue such as the thrust cap being clipped out of square during a line hone job.

ACE1252

Thank you very much! I appreciate all the help.

ACE1252

Just for kicks and thrills, I have looked up the factory manual spec on where the oiling holes for the cam bearings are supposed to go. I also verified this by checking the oiling hole locations in my stock engine.

With the block right side up as installed in the car. These are the factory locations....

#1 - holes at 1 and 5 o'clock
#2 - hole at 5 o'clock
#3 - hole at 5 o'clock
#4 - hole at 5 o'clock
#5 - hole at 12 o'clock

The book "How to Rebuild Small Block Chevy LT1/LT4 Engines" states totally different positions. Here they are....

#1 - holes at 10 and 2 o'clock
#2 - hole at 2-3 o'clock
#3 - hole at 2-3 o'clock
#4 - hole at 2-3 o'clock
#5 - hole at 2-3 o'clock

Is there any good reason to change from the factory recommendations? The LT1 rebuild book states nothing on the factory locations, but does say that the 10-2 and 2-3 o'clock locations create a better oil wedge. Is this true?

dangalla

for what its worth to you i checked my factory service manual and it lists the same locations as you found in the service manual you used, not the rebuilding chevy book

but i would wait for these guys