Technical Hey guys, got another amateur question about my 235 engine. Main bearing question

I got this engine torn down to change out all the seals, inspect everything, clean and paint etc... The main bearings all have these score marks that are just deep enough to feel with my fingernail. The crankshaft has corresponding discoloration, but I can’t feel it with my fingered or nails. I’m going to replace these bearings, but should I have the crankshaft turned as well?

Sorry for what may be a stupid question, but this is my first time diving into the deep end of an engine, so I have lots of possibly stupid questions





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What do the upper shells look like?
Those look like a little damage from some trash going through at some point.
If the crank looks good ,,,no reason to have it turned,,,maybe polished,,,up to you?
Do you plan to spend a lot on this rebuild?,,,,,there can always be plenty of things to spend money on.
Post more pics of the other bearings and crank journals,,,that will help as well.

By the way,,,did you already clean the rear main cap,,,,,that old rope seal looks really good.
If the entire bottom end is that clean,,,you might have a really good engine to start with.

Tommy

 

Those bearings have seen dirt and debris .
Worth while replacing.
Take a pic of the crank .
Might get away with just bearings and a polish.
Pull the entire engine apart, disassemble the oil pump look for wear and dirt and clean clean clean everything !

Was there a lot of sludge in the pan? Under the valve cover?

Did theengine runbefore you tore it down?

 

Make sure you mark everything so yo can put it back where it came from, and facing the correct way.
As was already said, it’s seen a little trash but not much really. I would guess the crank looks good also, but pictures are nice. Good luck.

 

That is an example of the bearings doing their job. Being the softer metal compound of the two (crank/bearing) they absorbed the consequences of the debris and kept the crank from serious harm. Replace the bearings and polish the crank, you’re good to go.
r


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This is probably the important question...my guess is that since you took it apart to replace seals, you didn't plan on rebuilding the engine, you want to run it for a while

I would not even replace the bearings (they're kind of expensive). I'd just replace the seals, and drive it, assuming that the rest of it is in decent condition.

Before they had full flow oil filtering, there was always a bit of trash running through the oil system. There is not nearly enough wear there to warrant replacing anything.

 

Locate a new shim package before re-assembly. The factory shims after one or more disassembly are a bitch to work with. Bearings show no real wear, just debris from dirty assembly.
Since this is your first trip into the bottom of a Chev 6, it's time for a factory issue '49 - '54 shop manual. Best investment you'll ever make ...

 

Thanks for the replies guys, the rope seal is new, I just replaced it. The engine ran like a top before teardown. This all started with switching to dual exhaust, and drilling and tapping the snout to stop my balancer noise. But the engine was ugly, so I thought I’d just take everything off the engine and paint it in the bay. Then though “oh, I’ll just wedge a block of wood between the crossmember and the front of the engine so I can take the mounts off”.
Then I thought “huh, only 8 bolts and a few linkages and I can just pull it out”.
Now the engine is out, transmission is at the shop getting rebuilt, torque tube is coming out this week for a rebuild and 3.55:1 gears.

The pistons are clean, cylinder walls are like mirrors, no scoring or anything.

The bearing tops look just like the bottoms. Front and rear look almost new, centers have those scratches.
Whoever had this car before me had this engine rebuilt, because the pistons are stamped .040.
I’m out right now but I’ll post more pics when I get home.


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Here’s the old main seal. Somebody mixed and matched parts. That too half was in backwards, with the lip facing the back of the engine. It leaked a LOT.

As far as marking everything, it’s all marked, down to the bolt. I’m obsessive about putting things exactly where they came from.


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Ok, so here the crankshaft journals

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Shim Kit


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And that my friends is what we call project creep...
r


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Haha... my dad warned me. When I told him I was pulling the head he said “just pull the engine. You’re gonna end up doing it anyway.” I was a little scared at first, as I’ve always had him there helping, or supervising on things like this, but he can’t physically help this time, just had foot and hand surgery.
The more I tear into it the more I realize I know what I’m doing. at least on an engine this simple.


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the crank is beautiful, I would just put it back together.

Can you find a rubber rear main seal? I would use one, if possible...

 

That would be ideal, but Tom Langdon says the seal surface on these cranks weren’t machined concentric with the bearing, and to use a rubber 1 piece seal requires some pretty expensive machining.


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I agree, run it with new seals.

 

Man,,,I have never seen a half and half rear main before,,,half rope and half neoprene.
I think Jim meant to use. Regular neoprene 2 piece seal.
At least that was how I took it.

Yes,,the crank journals look fine,,,go with it.

Tommy

 

I guess you can try the rope seal...I'd try the rubber seal first, then change to rope if it won't seal. But that's only because I'm not very good at installing rope seals.

 

Hi. You are on the right track and I am glad to see you have contact with Tom Langdon. Had a conversation or two with him back when I did my 235 engine. Purchased a few things from him. My avitar is of my 1957 235 engine. It is 0.060 over with everything inside new except the crank. Cam is Clifford 268 grind and he said that was the most for I should run for a non racing street car. Intake and shorty tube headers are Clifford along with the dual 2 barrell Weber carbs. Since photo I have changed out the chrome rocker cover to a finned aluminum Thickston old style. This engine is in my 46 Chevy coupe and is not currently on the road due to being rear ended.
You will like the 355 gearing as I got 20+ MPG with that & this engine with 700r16 Coker classic radials and the original tranny. Good luck with yours. jimmie