Main Bearing Replacement

[Stretch]

As part of the plan to continue improving my car I've contemplated replacing the engine main bearings from time to time. The manual says the crankshaft has to be removed which requires removal of the engine. Does anyone know a way to remove the bearings without removing the engine? For instance can the upper half of a bearing shell be rotated out with the crankshaft in place?

 

[Dave Russell]

Stretch,

You might be able to replace the main bearings without removing the crank but it would be pretty difficult. Then there is the center main thrust bearings to deal with.

Why do you want to replace just the bearings? Chances that if the mains are worn enough to cause trouble the rod & cam bearings & most everything else including piston rings needs replacing also.

Unless there are extenuating circumstances, I think that it would be a waste of time to just replace bearings & the chances of screwing something up are great.

If the engine is that bad, it needs to be pulled & rebuilt. If not that bad, just live with it for a while.
D

 

[Stretch]

Engine is not bad but oil presssure is on low side. Last winter I rebuilt the rocker arm assembly with no improvement in oil pressure. I've just been making improvements in stages and really don't want to pull the engine right now. Bottom line is I like to tinker.

 

[Dave Russell]

Stretch,

OK, give it a try. Should be an interesting experiment. Be sure to do the rod bearings also. Then the only remaining cause of low pressure would be the cam bearings.

I have done things like this in the "distant" past. If you can't get all of the main shells out just replace as many as you can. Anything will help some. I wouldn't expect 50,000 miles more out of it but you never know.

As far as performance & reliability, it will depend a lot on how good & how even the compression is now.

Have fun,
D

 

[ThomP]

The other thing you might consider before replacing the mains is the oil pump. When I rebuilt my engine, the oil pump "looked" good upon inspection, so I didn't replace it. After I fired the engine, I had oil pressure, just not good oil pressure (~20 lbs at idle and 35-40 lbs at speed). This worried me, because the engine was new, so I replaced the oil pump. The difference was dramatic: ~30-35 lbs at idle and 50-60 lbs at speed.

It's also easier to replace than the mains and it just may be your culprit. Happy tinkering.

 

[piman]

Hello Stretch,
there is a little trick to removing main bearing shells which is to put a split pin into the journal oil drilling and rotate the crank pushing the shell out (from the non tab side obviously).

Alec

 

[Bob Claffie]

I'd vote for the pump, too. The main bearings are the first thing in the engine to get oil and the last to fail. If not the pump try something simpler like the rod bearings. Anyway, what's the point of slipping in new mains without measuring the journals! Bob

 

[Stretch]

I appreciate the tips. I have a friend who races sprint cars. He's replaced main bearings in his race engine in the manner discussed without pulling the crankshaft. I believe the journals can also be measured for wear so I can do the proper checks, but just replacing the bearing will still regain some clearance lost to wear. The oil pump intrigues me more, though, now that two people have mentioned it. Looks like parts are available. Has anyone rebuilt one of these with good success?

 

[Pete Haburt]

Stretch;
I replaced the oil pump gears in my 61 BT7 as mine were scored, and it made a huge difference.
Added 15lbs at idle and at cruising(hot). I now have 38psi idle, 58psi above around 2500 rpm.
Pete H.