The Stovebolt Site Forums The Shop Area Engine Shop main bearing replacement

So, as the in frame engine refresher saga continues, I purchased 6 new pistons to replace the cracked ones along with the rings. I want to change out teh main bearings since I am already there. The truck has 40,000 some odd miles on it. I intend to loosen the main caps a bit and try to pull the crankshaft down enough to "cheat" the old bearings out and slide the new ones in. I have removed the driveshaft and unbolted the 4 speed trans and slid it back far enough to disengage the input shaft from the clutch. Is this gonna work or will I cause damage to something? I realize there is the potential of the timing gears not re-engaging corectly and being "out of time". Just wanted to run this by you guys first and see what ideas or potential problems you might think of. Brian

What year is the engine? The 216's and splash-oiler 235's have dowel pins in the upper main bearing shells that engage holes in the block, so the crankshaft would have to drop WAY down. The later-model 235's have anti-rotate tabs on the ends of the bearings, and those would be a lot simpler to change. Be sure to get the right size bearings. If they're undesize, the dimension should be stamped on the back of the bearings- - -.010, .020, .030, etc.
Jerry

If I were you I would pull the engine and do the rebuild on the engine on an engine stand,you already have the trans out.If you pull the engine you'll be able to do a much better job doing the bearings and pistons,rings,etc.
Pete

I did my mains in place and I did drop the crank some. Mine is a 216 with the dowels. I removed the front cover to give room for the drop and also observe the timing gear. If you don't have the dowels you should be able to drop the cranks very slightly and change the bearings. I would rotate the upper shell so that the tab comes out first. The thrust bearing is probably the hardest to change because of the sides.

If you check the clearance and it is not excessive, I would leave them in place. You can get an idea of ahwt kind of shape they are in by looking at the bottom halves.

I agree with Pete52... Pull the engine and stand up to do all that work, On your back is very hard on ones body.And you will get a better job! Just my 2 pennies worth.

Fellas, sorry to leave out the engine size. It is a 235 out of our 55.2 3600. After our oil pan was removed, I saw the oil pump and realized it was not a splash system. The only reason I don't want to remove the engine is because everything I need to do can be done while in the truck and the truck is not in my garage right now. So, getting the cherry picker over to the truck, trying to roll it in the dirt, would make for alot of F bombs being thrown around.
The bearings will have to be slid out tab side first, yes. I am glad to see that one of you have done this successfully. Just gonna take some patience I feel. The trucks engine sat for a long time without being started. When I got it, I was able to get it started and it ran fine, but even tho I changed the oil first, I was REALLY gummy. Barely, made it the top of the pushrods. I want to Shoot Brakleen into the oil journals of the crank and then blow them out with compressed air. And just wanted to start out with fresh bearings all around. (except the cam.) You should have seen the lifters when I cleaned them out...OOOOOHHHH. Bad.

I think that if you re-read your last sentence.
"You should have seen the lifters when I cleaned them out...OOOOOHHHH. Bad."
That should be reason enough to get a plan to take the engine out and get it properly cleaned. Your spending a fair chunk of money on pistons and other parts, its a small detour in the long run.

If it's that gummy, you're wasting your time trying to clean it up in the frame. It's your time and money, obviously, but doing a halfway job is not something I'd reccomend. There are dozens of places you won't be able to clean, and as soon as the oil hits the crud, it will circulate it all over ther new parts.

BTW, splash oiler engines also have an oil pump. The main bearings get pressure-lubricated. The rods have dippers bolted onto the bottom and they dip into oil-filled troughs in the pan. At higher speeds, the tubes that fill the troughs squirt oil directly into the rod dippers. Any engine newer than 1953 should be a full-pressure design with oil passageways drilled through the crankshaft to supply the rods with pressurized oil.
Jerry

The 216's also have pressurized oil to the cam bearings (via the crank bearings/journals) and to the rocker arm shaft. As said above, the rod big ends get "pressurized" by force of dippers moving through troughs and via oil nozzles.

I would be worried about oil sludge and crude in the cam bearing passages and oil distribution passage running front to back of engine (cam bearing oil return passage on way up to rocker shaft).

I appreciate all of the wise replies and concerns. THey all make great mechanical sense. But I like the challenge of doing it in the truck, plus the lack of shop space, engine stand availability right now, etc....
So last night I finally got the crankshaft out. Learned a couple new things along the way. (THis is the first 235 engine I have disassembled)
1. The thrust bearing is on the 3rd main cap back, not the rear heavy cap like I have seen in the past.

2. The bearings have a little round nub on the back of them to hold them from spinning in the block. This was new to me as well, also the reason for totally removing the crank, just easier.

3 Chevrolet used alot of screw head bolts when assembling their engines. WHY?? THey suck and are so easy to strip out. Definitely gonna replace most of them with a hex head bolts!

4. Chevrolet has alot of faith in pinch bolts holding in their oil pumps.

5. I found thin foil spacers between all of the main caps and the block, I guess this was Chevrolets' way of shimming the bearings for clearances? Should I put these back in with the new bearings? Or should I just plasti-gage it when I assemble it to check if I need them?

This morning I am going to use a whole case of BRAKLEEN to degrease and clean out the engines oil passages, journals, etc. Then its onto re-assembly, finally. I pretty much have the entire engine apart. If I can, I will post some pics later, but engine pics can be pretty boring.

Good luck- - - - -you're making things a LOT more difficult than necessary, and almost guaranteeing that the job will be a disaster. I'm out of this thread!
Jerry

I'd suggest that you go back and re read the posts on this thread. If you want to do it your way why keep asking questions? I'm not trying to be a smart arse here but if you keep going your direction you are going its going to be a bust.

Brian,

The slotted screws are the famous stovebolts. Loose them at your peril! :>)

You really should read the engine section in the shop manual before you put the motor back together. The shims are critical as they set the oil clearance between the crank and bearing. Since you have the crank out, why not have the journals measured so that you can be sure of what you are working with?

Here are some links to the old Chevy car manual project:

1954 truck manual

1955 second series shop manual

I took a look at the engine section of these two manuals and noticed that the 1955 second series engine did not use shims on the main bearings. So you might want to double check what engine you have too.

Good luck!

Kurt

Dude don't listen to Kurt!
You don't want those old bolts. Their just a few short years from rusting up on you so just drop me a PM and I'll send you my address and take them off your hands for you.

and just curious... how much that case of Brakleen set you back?

I am still in on this thread. I didn't have the room to pull my 216 years ago and I did everything in place. More than likely you will need the shims and probably more with the new bearings. It would be good to read the manual on this procedure.

The case of Brakleen ran me 61.99 after tax. But if I don't use it all, I will put it on the shelf in the shop. I have been reading the manual on this procedure over and over.
I may not have all the funds or fancy tools available to me that some of the other bolters have here, or the ample room to take everything out of the truck and do it "textbook". But I do have the ambition and patience to do it another way. If anyone wants to bash me or try to discourage me, have at it... your just wasting your time. I want to get this truck finished so badly, my girlfriend wakes me up every nite cuz I am talkin in my sleep about it. LOL... Probably find the naysayers have never laid in the dirt or stones on their back at night, in the winter, changing out U-joints because their vehicle HAD to be fixed by morning to get to work. And had it work fine when done. There is a certain kind of satifaction from that PITA work that they will never experience.
I have plenty of plasti-gage and will check my bearing clearances when I install the crank. If I need more shims, I will have to source some material for that. Thank you to those fellow bolters whom understand that sometimes the motor must be left in and a little extra elbow grease will be needed.
I spent most of the morning cleaning up the bell housing, clutch parts, front cover and parts, main caps and bolts. When assembly begins, I want everything ready. Brian

I think most of us have layed on our backs way too much already and the punishment from it have made it a "no way" platform for us to talk about because many of us can no longer get back up as well as we used to.
I would plastiguage.
Good luck.

Brian,

Take it slowly and carefully. Read the manual as many times as is necessary.

Most of us undertand your situation, and many of us have been in it.

I knew you were reading the Shop Manual, but, at times your amazement at what you were "discovering" made it look like you might be flying blind.

Go ahead, keep asking questions. Good luck - take it as slow as you need to.

I buy brass shim material in a tube from CarQuest. I keep .001" and .002" on hand.

Brian,

I just gotta laugh.

I rebuilt my first 235 on my back, in the dirt, during the winter, in the dark with the engine still in the vehicle. And my girlfriend was wondering why I wasn't instead inside being warm an cozy with her? Anyway, that was in 1972.

That engine ran pretty good for about 6 months.

Just sayin' and I would not have traded one second of the experience for the world.

More power to ya.

Kurt

I tend to jumble the laying under neath experiences up over time.
I can think of several I wouldn't mind trading several hours of though...

Brian, your candoworkaroundgetitdone spirit is what most folks don't know that's what they mean when they talk about whats missing from "Their" America....

Now, if you'll just get those bolts in a bag....

I remember my car buried in snow up to the top of the fenders. I dug a hole down below the left front tire and went head first into it to pull the starter. I got the starter out, and there I was, stuck with my feet above me and my head under the car in a hole in a snowbank with a starter in my hands. Talk about claustraphobia!