Rolling in new main bearings - SBC -by just dropping the pan ??

I'm running a 91 TBI 305 in my 49 GMC.

The 305 was low mileage, probably 60-70K, the odo wasn't working, and the car had been sitting for a couple of years.

Anyway, the motor runs great, and I've put about 5K on it in the 49.

But.

The oil pressure has been getting gradually worse.

I dropped the pan, pulled the oil pump and a couple of main and rod caps. The gears in the oil pump show some galling, along with the bearings, even though the clearance on the mains still show .002

My buddies say the upper mains should be easy to replace, but I can't get them to come out, and even if I did, I don't think that I could get new ones in.

Is there any tricks?

At this point I'm thinking, replace the lower main bearings, all new rod bearings, and new oil pump and ****on her back up.

What would you guys do?

Thanks,
Rich

 

Ive done it, in a 73 Z28

 

Any tricks?

Pull all the main caps?

I can get them started, but they're tight as hell.

 

That used to be easy to do. I have changed a few.

Parts stores used to sell small pieces (I forgot what they are called) that look like short dowels with a swedged "nail-head" at an angle that would fit the same angle as the drilled oil p***age in the crank.

The soft aluminum plug would fit into the crank oil hole. The flat "nail-head" section of it that stood out from the oil hole would be just the same thickness as the bearing shell.

As you rotated the crank about 1/2 turn the "dowel with the nail head" would push the bearing shell around with the crank so the bearing shell would drop into your hand. You installed the new bearing shell the same way- rotate the crank and it slips right into position.

I still have an ***ortment of my 30 year old ones on my tool shelf.

I would say check with your local machine shops, parts stores and tool suppliers to see if anyone still carries them.
They make the job so simple and easy.

 

You can do it with a cotter pin, just bend the end(round end) of the cotter pin over to for a right angle, stick the cotter pin in a oil feed hole the little bent over part should sit flat on crank, rotate the old bearing out, (you will need to look at main cap to see where the tabs are) remember the tab has to leave the block first. The just oil new bearings and install the opposite way. done this many times, super simple once you do the first one. Do one journal at a time and pull just that main cap when needed.

 

Yep, what they said. Works on almost any engine.

 

ooops

 

RODSTER...It can be done, but one should have some experiance. now if you still won't to do it. i'll tell you how. first JUST loosen the main caps, ALL of them, DO NOT take them OFF. the crank will probably come down a bit. just make damned sure you only loosen the caps. after the crankshaft slides enough to roll the main bearings OUT. now LISTEN this is important, when you roll the bearings in THE NEW ONES, make sure the bearings that TOUCH the block are the ones with a hole in the center of bearing. WHY? because the hole let's OIL come in around the crank. wait untell all the bearings are in before TIGHTNING. ALSO these main bearings MUST be torqued to a specfic number. if your scared as hell at this time, you should be. because this REALY is not the way this kind of thing should be done. but you ask how, do i recommend such? NO! because i'am wondering why you think the mains need to be replaced, and i must say only a GOOD mechanic should do this. am i trying to talk you out of this? YOUR DAMNED RIGHT...POP.

 

Oh hell.

Just do it.

JH

 

Would it help to unbolt the torque converter from the flexplate, to allow the crank to drop slightly at the rear?

Rich

 

Yes, it would, and drop the v-belt (s) off of the crank pulley.

 

Yeah, that's what I was thinking too.

I'm gunna try that tonight, we'll see how it goes

Rich

 

The cotter pin trick always worked for me. But loosen all the main caps even if you do them one at a time. This will give the crank a little room to drop down.

Bob

 

I'm surprised that no one has mentioned checking the bearing clearance using plastigage. It's always been available at the real auto parts stores. Auto repair manuals usually contain a tutorial. Also should mention that if you see any hint of copper tint in the bearing it probably is worn past the limit.

 

this will not fix your problem.
IMO.

 

Wouldn't just an oil pump be suficient?

 

I plastigaged a couple of the mains, they appeared to be .002 clearance

There's a lot of scoring on the bearings, but non are showing copper.

Well, I'm listening ????

 

You state in the original post that oil pressure is getting worse. What pressure did you start with (hot and cold) and what is it now (hot and cold)? Also how many miles on the oil? is the 5K on one oil change? If so it could be the oil is breaking down and just getting thin.

 

I seem to recall the oil pressure was OK originally, 60 cold, 20 hot idle, 40 hot down the road.

Now, it's still good cold, 50-60, but around 5-10 hot idle, 15-20 hot down the road.

The oil was just changed a few hundred miles ago.

 

If you have the crank out you can get the upper half of the mains out. Its still a half ***ed overhaul but you gotta do what ya gotta do. never the less its half half ***ed to just change the bottom half of the insert.

Take the time to worry the uppers out.

 

what about the thrust bearing ? both the upper and lower needs to be masaged for proper crankshaft endplay ! you said that the oil pump gears were galled ?if so, all of those metal shavings are in the motor,and in the lifters !

 

ooops

 

We used to do that when we were kids, and just used a nail in the oil hole to spin them out. Worked OK. Never knew there were real tools to do it. Back then there was even parts stores that would come to your shop and cut (polish) your crank while still in the car. Didn't get to see them do it , but remember pulling the snow plow off a tractor so the guys could come in that night. We plowed with it later that week, and everything was fine.

 

by the time this thread is over,you could of had the motor out and new bearings and rings in and ready to drop the motor back in !

 

If the mains are 'grooved', (but only have .002" clearance) the loss of oil pressure would be highly likely attributed to worn connecting rod bearings.
These should be the first thing you check / replace. (check with plastigage.)

 

I'd add a high volume oil pump. The extra flow will help mask the problem.

 

A good heavy screw driver and a hammer will start the bearing moving, and the PIN in the chank hole will do the rest. Its easy and well worth it. With a new oil pump and bearing you will be good to go for many miles. Iceman

 

RODSTER...like i said ONLY a good mechanic should do this. WHY? because he can READ all of the bearings and oil pump wear, actually maby you need this experance. hell it's only time and money, well there's the screwed up engine thing...POP.

 

Man, that's ALOT of work for half an overhaul. If it was me, I'd pull it and do the job RIGHT.

 

Well, I got em in.

New mains, new rod bearings, new pump.

I have 30 lbs hot at 70 mph, I'd hoped for better, but I can live with these numbers.

Rich