main bearings clearances

hepcat

Registered User
Well i am just starting to get my motor back to gether.

I need the specs for oil clearances on main and rod bearings.

I had to grind the crank .010 under, rods and main. I then put the crank in dry of course and used some plastigage and got
.003in or .076mm for the first three main bearings in front and then I got .004in or .102mm for the last one at the rear.

Does this seem close?


thanks

hepcat75
 
Last edited:
main bearings

Good question.

I'm in the same stage of assembly.
What bearings are you using? I ordered Clevite 77 bearings part number MS1782P. They don't match my main caps where the anti rotation notches are. So I went back to autozone and they said that was the right part number so we ordered another set of the same part number just to make sure the first set wasn't boxed wrong. The second set was the same. ??:confused:

I can't put this thing together without main bearings and I can't find a set that fits!

I checked my block and it is definately the SC block. I wonder if my machine shope mixed up my main caps with a different block when they align honed the block.

Can anyone tell me if that is the right part number?

Oh yea,... and the clearances would be helpful too.
 
clearance guide from clevite.

When measuring bearing measurements, they should always be taken at 90-degrees to the parting line to determine the minimum clearance. If measuring the bearing wall thickness, use a special micrometer with a ball anvil to fit the curvature of the bearing ID. The best way to determine bearing clearance is to measure the bearing ID with the bearings installed in the housing and the bolts torqued to the specified assembly torque. Use a dial bore gauge to measure the bearing ID at 90-degrees to the parting line, then subtract shaft size from bearing ID to determine the clearance. If the dial bore gauge is zeroed at the actual diameter of the crankshaft journal to be installed, the dial bore gauge will then read clearance directly and the subtraction calculation can be eliminated. About .001" clearance per inch of shaft diameter is a good rule of thumb. Increasing that by about .0005" will add a little margin of safety when starting out, especially for rods. Example: .001" X 2.100 = .0021" then add .0005", so starting out set clearance at .0026" for a 2.100 shaft.
 
clearances

i am using sealed power from advanced auto parts. So far i just done the main bearings and ounce I got that right then I would start with the rods.

Since my clearances are to much what If I went to a .050 over main bearings or would that be to much.

I don't have access to the right tools for measuring the mains and crank.

Dan what you said for that last clearance or .0026 I do beleave that is what the book said but I don't always trust them. So I am here.

Well I don't want my crank wearing these bearings out anytime soon So I want the best I can do now.

Any thoughts or trying another brank of bearings?

Thanks I am really in a bind and I have to move out in the next four weeks so I have to get this thing running.

Hepcat75
 
clearances

What would be the max clearance you guys would run on the 3.8. Maybe I didn't use the plastigage right. I put it on a dry crank on top in the middle and then torqued it the main cap to 75.

Need some advice because I don't want to ruin this motor because of a oil clearance problem.

any help or advice appriciated.

Raymond
 
if they are really ground that small you USUALLY can get .001" oversize bearings that will fix the problem
 
hepcat. my 1990 shop manual shows the mains to be
SC no 1,2,3 0.0005 - 0.0023 in.

SC no 4 0.0010 - 0.0028 in.


My crank was just polished and it came in at 0.0010 for 1,2,3 and 0.0015 for no 4.

Before I used bigger bearings I would make sure that I was getting a good measurment.....


Slysc. The main caps are marked with triangles for the location.

I am using the same bearings as you and they fit fine. I would not say I had the thrust bearing in the wrong spot (rear) instead of 3. Maybe I did.... but I'm not telling.

in my engine 1,2 use bearing marked 3187 and 3 and 4 used the ones marked 3188.




did you compare your bearings to the old ones you pulled out of the engine?
 
bearings clearance

Well I am going to try some new bearings at 25mm over and see if that makes a difference since One of my bearings the stor gave me had been in a crank before.

I noticed that one of the bearings ( sealed power ) was not finished and didn't know where that one went So I tried that one in front and the crank wouldn't bottom out on the bearing because it was hitting the sides. So I put that one in the back and that is the one that was used before and gave me .004 for an oil clearance.

Well how many pieces of plastigage do you guys use to check clearance?

Well I will try it again when my new bearings come it.

Ow boy I hope I can get some better clearance with some different bearings.

Thanks all for helping me become a better sc fanatic.

Raymond
 
clearance

Just had a though when I took out my rod bearings and noticed oil under the bearings.

So whith that thought should I put oil under my mains and rod bearings for the extra lift to get the oil clearance better between the crank and all.

Thoughts on this please

Sounds stupid but you never know and I know there was oil under all my bearings in the first place so until I dried them off.

Thanks for the thoughts

Raymond
 
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