Rear Main BP blow out

Bill Edstrom

Bill Edstrom

Member
I just finished getting my engine rebuilt with a new B cam, new crankshaft, and a Synder 5.5 head. Last week i went on a tour with the Up North Wisconsin, club. I had about a 150 miles on the engine at the start of the trip. The engine ran great during the tour execpt on the way back after 700 miles on the engine. The engine just stopped running at an intersection and then started after just sitting there. We then drove about 50 miles to a lunch stop where I took time to check the wiring and found a loose connection at the amp meter But before we got to the lunch stop I stepped on the brake to slow down and there was a loud backfire which I think was probably caused by the loose connection reduceing the spark voltage and causing incomplete commbustion. Anyway at the lunch stop the is oil running out of the fly wheel hsg like the BP oilspill. I checked the oil and I was a quart low so I added a quart of oil and we drove about 40 miles to a cheeze mart where we stopped and the oil was still runing out and I was low on oil again so I added another quart and requested that we stop in about 40 miles so I could check the oil level and replinish it. At stop the oil level was full and remained full for the next 100 miles when I arrived home. There has been a little oil from the hsg that has drained on the floor but nothing that is alarming.

I sorry for the long story but I thought it necessary to provide at much information
as possible. I suspect there was blowby which increased pressure in the crankcase forceing oil out thru the rear main. Could the backfire have caused a blowby that would cause this much leakage? Could someone tell us how blowby occurs? I would think that after 700 miles the piston rings would be seated.
I don't want to drop the pan to check main but of course I will to inspect it.

Any help to understand what happened will really be appreciated. Thanks

Bill Edstrom
 
I would check with the builder before doing any kind of major work like removing a main cap. Doing something may void any warranty if there was one.
 
Rings that are not seated in a "new" engine can cause excess blow by and oil leaks.
Are the plugs showing any signs of oil burning? If so the rings may not be seated yet.

The back fire is most likely cause by a lean or rich fuel mixture. Check for intake system leaks and/or low float level in the carb.

In addition to a poor electrical connection, a non or poorly vented gas cap will cause stalling, which cures it's self in a few minutes. Then it will stall again further down the road.

Just My W.A.G at the problem.
JIS
 
Jerry in Shasta said:
Rings that are not seated in a "new" engine can cause excess blow by and oil leaks.
Are the plugs showing any signs of oil burning? If so the rings may not be seated yet.
Click to expand...

I agree!

I think I would continue to run it, keeping watch of the oil level and the leak. The fact that it quit leaking indicates the rings may be seating in. I think if there was some problem with the rear main bearing itself, it would not have stopped leaking.

Keep the oil level up but do not overfill it. If you start to hear any unusual noises or the leak returns, you may want to look further.

This is what I would do for now.

Chris
 
The loose electrical connection may be unrelated to the oil loss problem. It is possible that at the 700 mile point you had finally driven it hard and long enough to cause the pistons to heat hotter than they had ever been before.

Just one piston with insufficient clearance, or one ring with too little end clearance could have scored a cylinder wall or scuffed the side of the piston causing the rings to stick in their lands. The resulting loss of seal and excessive blowby would cause the oil out the rear. After more mileage the rings may have partially worked loose or reseated reducing the problem, but if that was the case, the damage is done.

Do a cylinder leakdown test at both TDC and BDC if you have that tool, elsewise do a compression test. If you have one that is way low, it is a rebuilder's error. In any case I would follow up with a bore scope examination of the cylinder walls. Pay particular attention to #4. That one always runs the hottest.
 
I'm sure you have checked this but..........The oil cap fits right and isn't blocking the crankcase ventilation? Internal pressure will blow the oil through the rear main seal/baffle.
 
Bill when you find out for sure what the problem is and the solution please post again to let us know. I'm sure I am not the only one interested in this. thanks Joe
 
The aluminum rear bearing labrynth seals are poorly manufactured. It is extremely important the the ends of this seal is perfectly machined with the surface of the block underneath the main bearing. I like to use a very thin wipe of Anerobic sealer in this area, or wherever you have metal to metal contact requiring sealing. A wipe of non-hardening Permatex is also recommended for under the aluminum seal to the engine block.
 
:rolleyes: Bill , hope you find the problem and let us know. I just hit 60 miles on my 180A. I'll take it easy until 200 mile's .[I keep it under 40 :D ] for now. Are you making it to Hershey or is that a stupid question:confused: Good luck with your engine. James Rogers and MikeK,, thank you for your inputs they are always good reading and very helpful.:)
 
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