# Rear Main Bearing Failure ????????



## D1147 (Sep 3, 2009)

I had my 1969 ram air III engine built by a reputable pontiac builder. Installed engine, primed oiling system. It fired almost immediately and ran for about 30 min @2000-2500 rpm. I changed oil and took it on a test drive, all went well. On the second test drive I heard a slight rod knock after about 20 miles total. I pulled engine and took it back to the builder. We pulled main and rod caps, rear main bearing was trashed and had sent bearing material into #8 rod bearing which caused rod knock. Engine was torn down and cleaned. All clearances and oil passages were checked. Turned crank and replaced bearings, rechecked clearances, reassembled and ran on dyno for bout 20 pulls. All went well, cut open oil filter and it looked great. So I reinstalled engine in car, and fired it up all went fine. After about 15 miles of driving it started knocking agian. Oil used is rotella 15-40 with a pint of GM E.O.S. supplement. ( 1969 gto ram air III with manual trans) What gives, any input would be great.


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## Rukee (Feb 8, 2007)

What kind of max HP and RPM's are you guys running in this thing?


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## freethinker (Nov 14, 2009)

D1147 said:


> I had my 1969 ram air III engine built by a reputable pontiac builder. Installed engine, primed oiling system. It fired almost immediately and ran for about 30 min @2000-2500 rpm. I changed oil and took it on a test drive, all went well. On the second test drive I heard a slight rod knock after about 20 miles total. I pulled engine and took it back to the builder. We pulled main and rod caps, rear main bearing was trashed and had sent bearing material into #8 rod bearing which caused rod knock. Engine was torn down and cleaned. All clearances and oil passages were checked. Turned crank and replaced bearings, rechecked clearances, reassembled and ran on dyno for bout 20 pulls. All went well, cut open oil filter and it looked great. So I reinstalled engine in car, and fired it up all went fine. After about 15 miles of driving it started knocking agian. Oil used is rotella 15-40 with a pint of GM E.O.S. supplement. ( 1969 gto ram air III with manual trans) What gives, any input would be great.




main bearing failures are a lack of lubrication problem. if your pump/pan/pickup all check out look at your lifters. the pontiac block combined lifter oiling and main bearing oiling. that means that if your lifters somehow leak too much oil it will bleed oil away from the main bearings. this was a common problem and it a reason why there are so few numbers matching gtos out there. they all blew up with rod failure problems. this weakness is why a stock pontiac should never be turned over 6200 rpm.


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## D1147 (Sep 3, 2009)

Max Hp Is 370, It Was Ran Up To About 6000 Rpm On The Dyno.


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## geeteeohguy (Feb 2, 2008)

Freethinker is right on the money. Your oil galleries need to have all the plugs in place, and need to be clean, there needs to be no oil bleed off and there needs to be enough oil in the sump at the pickup at all times. Pontiacs can over oil on the top end, and starve the lower end. You can get oil foaming at high RPM. Get online and look at the Jim Hand articles, Nunzi Romano stuff, etc. There is a lot of info on beefing up your oiling system. That said, I think something is wrong. I've been using stock Clevite77 or Michigan 77 bearings and regular Melling or TRW oil pumps for decades in these engines, and have yet to have a bearing failure. I DO keep it under 5500RPM, though. Your choice of oil with the EOS is appropriate. You have an oiling issue if your clearances are ok like you say. With proper lubrication, bearings in a Pontiac V8 can go well over 200k miles.


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## D1147 (Sep 3, 2009)

Thanks For The Responses. I Will Relay The Info To The Builder. If Anyone Has Anthing To Add Please Feel Free, Any And All Help Is Great. Thanks


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## freethinker (Nov 14, 2009)

D1147 said:


> Max Hp Is 370, It Was Ran Up To About 6000 Rpm On The Dyno.


Kauffman Racing Equipment
here is what a restrictor kit looks like for a pontiac. every serious pontiac performance engine must use these. it is not something you can easily do now. the engine must be stripped and tank cleaned after you install these because they require tapping threads in your lifter oil holes.
some other things from my memory bank: always use full groved main bearings, beef the oil pressure spring to 50 psi range, do not use cheap short oil filters they are too restrictive, if you can find a super duty oil pump use it. they were higher volume.


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## sjh67gto (Nov 30, 2009)

*bearing failure*



D1147 said:


> I had my 1969 ram air III engine built by a reputable pontiac builder. Installed engine, primed oiling system. It fired almost immediately and ran for about 30 min @2000-2500 rpm. I changed oil and took it on a test drive, all went well. On the second test drive I heard a slight rod knock after about 20 miles total. I pulled engine and took it back to the builder. We pulled main and rod caps, rear main bearing was trashed and had sent bearing material into #8 rod bearing which caused rod knock. Engine was torn down and cleaned. All clearances and oil passages were checked. Turned crank and replaced bearings, rechecked clearances, reassembled and ran on dyno for bout 20 pulls. All went well, cut open oil filter and it looked great. So I reinstalled engine in car, and fired it up all went fine. After about 15 miles of driving it started knocking agian. Oil used is rotella 15-40 with a pint of GM E.O.S. supplement. ( 1969 gto ram air III with manual trans) What gives, any input would be great.


I found out the hard way like you. DON"T rev over 5500 rpm and run the oil level one quart over full. I have done this and get along just fine.


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## 05GTO (Oct 6, 2004)

D1147 said:


> Oil used is rotella 15-40 with a pint of GM E.O.S. supplement. ( 1969 gto ram air III with manual trans) What gives, any input would be great.


Shell's Rotella 15W40 should have sufficient amounts of zinc (1200 ppm) and phosphorous (1100 ppm) to run your flat tappet lifters and cam without adding GM's E.O.S. and if your builder upgraded to rollers you shouldn't need either.

JMHO,


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## 646904GTO (Feb 10, 2008)

freethinker said:


> Kauffman Racing Equipment
> here is what a restrictor kit looks like for a pontiac. every serious pontiac performance engine must use these. it is not something you can easily do now. the engine must be stripped and tank cleaned after you install these because they require tapping threads in your lifter oil holes.
> some other things from my memory bank: always use full groved main bearings, beef the oil pressure spring to 50 psi range, do not use cheap short oil filters they are too restrictive, if you can find a super duty oil pump use it. they were higher volume.


I have (home made) restrictors in all my Pontiacs, been doing that way for 30 years. They are 1/4-28 thread and 1/16"(.062) holes. Also always use full circle oiling main bearings and a HIGH PRESSURE oil pump not a high volume pump. The Pontiac engine is known for pumping all its oil 'upstairs' with prolonged high RPM's. We circle track raced the Pontiac successfully with these methods for many years. The engines seldom went below 3800 RPM under racing conditions. The upper RPM was 6400. Since your engine was clean after the dyno run and its the rear main that is failing it makes me wonder if there is something to look at the back of the engine. Did the dyno use the same flywheel? Is it zero balanced? Is the pilot bearing a bearing instead of a bushing? The Pontiac engine doesn't do well with bushings in that location. Is the input shaft true or bearing good on the transmission? The thing that bothers me most is the oil pump delivers the oil from the rear of the block toward the front. Most bearing failure issues I have seen were from the middle or forward areas. Also if it is a starvation issue there is usually telltale grooves on the crankshaft surfaces that you can see as dark lines and feel with a finger nail scrape. One thing you could check before reassembly is to lay the crank in on the top bearing with a light coat of oil and no rear main seal. Set up a dial indicator on the rear main journal and rotate the crankshaft. It is not common but I have seen bent cranks before. Hope this helps.


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