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Old 05-06-2018, 01:53 PM   #1
Chris Haynes
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Default Center main bearing

My A knocked out the center main bearing. I am in the process of tearing it down and pulling the engine now.I do understand the there has always been a problem with keeping a good oil supply to this bearing. I have a core engine I bought some years ago that had an oil line going from the pump directly to the center main.
My question is, should I use this same technique on my current engine?
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Old 05-06-2018, 02:18 PM   #2
Jim Brierley
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Default Re: Center main bearing

If the rest of the oiling system is stock, yes I would run that line. 3/16" tubing is all that is necessary, it gets oil to that main much more quickly than without it.
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Old 05-06-2018, 02:26 PM   #3
Kohnke Rebabbitting
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Default Re: Center main bearing

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Originally Posted by Chris Haynes View Post
My A knocked out the center main bearing. I am in the process of tearing it down and pulling the engine now.I do understand the there has always been a problem with keeping a good oil supply to this bearing. I have a core engine I bought some years ago that had an oil line going from the pump directly to the center main.
My question is, should I use this same technique on my current engine?

The problem with those are, the little pipes crack from the vibration.


The real stress on the center main is the heavy flywheel, they should be lightened.


There may be some that say they have never had a problem with a oil line to the center main, and I have never installed one, but the ones I have rebuilt over were all broke, if brass, or copper, and cracked if steel line was used, your choice.


Herm.
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Old 05-06-2018, 06:23 PM   #4
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Default Re: Center main bearing

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Originally Posted by Kohnke Rebabbitting View Post
The problem with those are, the little pipes crack from the vibration.


The real stress on the center main is the heavy flywheel, they should be lightened.


There may be some that say they have never had a problem with a oil line to the center main, and I have never installed one, but the ones I have rebuilt over were all broke, if brass, or copper, and cracked if steel line was used, your choice.


Herm.
I'll preface this by saying that I have pressure fed the centre main on all of my engines and have not had any problems.
Herm, Why did those engines you rebuilt need to be rebuilt? Was it through normal wear and tear or was it the failure of the centre bearing. If so, did it fail because of the cracked line?
FWIW, I use inserted bearings, lightened flywheel and direct feed to the bearing (25psi in one engine.)
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Old 05-06-2018, 11:23 PM   #5
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Default Re: Center main bearing

Dennis Piranios has a kit for center main oiling, all the parts including taps, cheap, takes oil from the block passage not the pump. Have used it for years, no problem.
http://modelaparts.net/special.htm/p...entermain.html
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Old 05-07-2018, 12:53 AM   #6
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Default Re: Center main bearing

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I'll preface this by saying that I have pressure fed the centre main on all of my engines and have not had any problems.
Herm, Why did those engines you rebuilt need to be rebuilt? Was it through normal wear and tear or was it the failure of the centre bearing. If so, did it fail because of the cracked line?
FWIW, I use inserted bearings, lightened flywheel and direct feed to the bearing (25psi in one engine.)

Oil coming out the broken tube, shorted the bearings, all went bad.


Herm.
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Old 05-07-2018, 12:54 AM   #7
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Default Re: Center main bearing

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Originally Posted by PC/SR View Post
Dennis Piranios has a kit for center main oiling, all the parts including taps, cheap, takes oil from the block passage not the pump. Have used it for years, no problem.
http://modelaparts.net/special.htm/p...entermain.html

That sounds better.


Herm.
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Old 05-07-2018, 06:50 AM   #8
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Default Re: Center main bearing

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Originally Posted by Kohnke Rebabbitting View Post
Oil coming out the broken tube, shorted the bearings, all went bad.


Herm.
Yeh, That's the scenario I suspected.
As I said, I have pressure fed the middle main. I'm unsure whether the engine would have survived what I have done with it (towing at 50 mph for tens of thousands of miles) without it. I've heard of guys getting 50,000 miles plus out of an inserted engine and using nothing but the original oiling system. They would have been only a solo car though.
I drilled and tapped for a fitting in the vertical "shank" of the oil pump and ran a line horizontally to the bearing cap just below the block. Hope I explained that clearly enough! In one engine, I used a replumbed V8 pump and the other, one of those high volume, high pressure aluminium bodied pumps that were around a while ago with the built in 50 psi valve. On that one, I made a pressure relief valve for 25 psi because I believe 50 is too much pressure on the pump drive.
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Old 05-07-2018, 07:33 AM   #9
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Default Re: Center main bearing

Unlike the front and rear main bearings, the center main reacts loads from all 4 cylinders. The rear main bearing reacts the flywheel, clutch loads and some of the loads from Cylinders 3 & 4.
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Old 05-07-2018, 08:16 AM   #10
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Default Re: Center main bearing

Might take a look at secrets magazine ap 2010. page 14.
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Old 05-09-2018, 12:12 AM   #11
Chris Haynes
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Default Re: Center main bearing

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Originally Posted by PC/SR View Post
Dennis Piranios has a kit for center main oiling, all the parts including taps, cheap, takes oil from the block passage not the pump. Have used it for years, no problem.
http://modelaparts.net/special.htm/p...entermain.html
Whike he didn't list a kit he does tell you what parts are needed. It does look pretty simple. However his price for drilling and tapping two holes is a bit steep.
PRESSURE OIL CENTER MAIN BEARING,LABOR $125.00
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Old 05-09-2018, 06:25 AM   #12
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Default Re: Center main bearing

The crankshaft pressure is down, so adding the oil hole to the bottom as pictured is the worst place to add oil, unless you cut an oil passage into the babbit, and I wouldn't want to do that to the bottom babbit.
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Old 05-10-2018, 11:39 PM   #13
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Default Re: Center main bearing

I have been studying this picture and wondering if oil passage could be drilled in the block delivering oil higher on the bearing and not having a line subject to breaking.

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Old 05-11-2018, 06:43 AM   #14
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Default Re: Center main bearing

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The crankshaft pressure is down, so adding the oil hole to the bottom as pictured is the worst place to add oil, unless you cut an oil passage into the babbit, and I wouldn't want to do that to the bottom babbit.
I agree with Tom. It is not going to do much on the bottom. 3 lbs of oil pressure is not going to lift the crank and get oil under the crank. All the cars I have worked on feed the oil in from the top. There is a reason for that.
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Old 05-11-2018, 08:37 AM   #15
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Default Re: Center main bearing

If I was worried about adding direct oil pressure to the main bearings, I'd make feed pipes to fit the tubes in the valve chamber.
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Old 05-11-2018, 08:51 AM   #16
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Default Re: Center main bearing

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I have been studying this picture and wondering if oil passage could be drilled in the block delivering oil higher on the bearing and not having a line subject to breaking.
I was wondering the same thing, I would hazard a guess that it depends on if the centre web is thick enough to drill through.
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Old 05-11-2018, 08:55 AM   #17
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Default Re: Center main bearing

BTW, many think the center babbit fails due to lack of oil, but I think it fails due to high RPM and lack of counterweights.
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Old 05-11-2018, 10:53 AM   #18
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Default Re: Center main bearing

Pirinnos (sp) has the center main kit for sale for $12. Call direct to order 940-382-2742. The web site is hard to figure out and get around in,
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Old 05-11-2018, 11:07 AM   #19
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Default Re: Center main bearing

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Originally Posted by Tom Wesenberg View Post
If I was worried about adding direct oil pressure to the main bearings, I'd make feed pipes to fit the tubes in the valve chamber.
That is how I did it on my over head. then I run a small line to the cam bearings.
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Old 05-11-2018, 11:51 AM   #20
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Default Re: Center main bearing

It may not be the best spot to put it but it works.
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