Reply With QuoteAlso the oil pressure is very stable.
My buddy has a 455 olds in a jetboat and his motor spits oil out the breather over 4000 rpms. We done a compression test and heres what we came up with.
Cylinders# 1 and 2 -120psi
Cylinders# 3 and 4 -100psi
Cylinders# 5 and 6 -90psi
Cylinder# 7 - 100psi
Cylinder# 8 - 120psi
How does this look? I dont really know much about olds so I told him I would turn to you guys. What should we do? Where should we start?
thanks guys,
Also the oil pressure is very stable.
junk, Throw it in the trash, No JK its time to rebuild befor it dies completely. Rule of thumb 10% difference off the average. your average is 105 so your range is 95- 115, some people even run that tighter especially when your running big horsepower. as for the oil out the breathers it is probably bleeding off so much compression into the crankcase that it is blowing it out the only place possible. Your motor is dieing fast.
I don't think cranking compresson has anything to do with ring seal and blow-by. An engine can have good/equal cranking compresson and still have poor leak-down and excessive blow-by. This is checked on an engine dyno with an accurate manometer while the engine is running under load.
You could do a leakdown test to see if the cylinders are leaking compression past the rings or through the valves. Your a little outside the 10 percent "rule-of-thumb", but if it still runs smooth I wouldn't worry about it too much unless your chasing big HP numbers, which in that case you would need more compression. 100 to 120 cranking compression only = around 8:1 compression ratio.
Check and make sure the valve covers have oil baffles under the breathers. The olds like to send a lot of oil to the top and can get to splashing around pretty good in the v/c. Some cheap breathers just leek, you might try another style .
A real simple test to check for sevear blowby. Unplug the pcv valve and plug the v/c hole, then with the motor idling remove the breather and put your hand loosely over the hole and see if you can feel any pulses or air escaping from the engine. If it is worn real bad you will be able to feel the pressure coming out.
You have a problem in one hole for sure. Take the spark from the low hole, squirt in some oil, and run the compression test again. If it goes up, you have a broken ring. If not, valves, or a crack in the head.
As to a cheap blow-by test, plug up all the vents (PVC, breather, etc...) and put a half full balloon over an easy opening. If it surges, all is good. If it inflates for a while (use a big balloon) you have issues. :-)
We went out today and I noticed that he had milky oil.I am thinking blown head gasket. But one thing he has alot of water going through his OTT headers. If there was too much water would it go into the heads and hit the cylnders? Thanks for the info guys, also I will help him do the simple tests that you guys told me sometime this week.
Have you checked the exhaust manifold. if it is cracked on the inside it may be responsible for getting water back into the cylinder. Also a blown head gasket can do the same thing.
Good luck http://free.***boat.net/ubb/smile.gif
396 i just had the same problem with my olds having water in the oil. A leak down test and compression tests showed that nothing was out of order. (the cylinders all showed 170psi during the compression tests) But, the shitty turkey tray intake manifold gasket was the culprit. That's where my leak was and it was a big one. It filled the whole pan up with water. I had lots of water coming out of the headers at idle and the T-fitting had nothing to do with it. I changed that gasket to a regular one and have not had a problem since. I would start there.
cyclone I here you on that one, same shit happened to me now the block is in the shop and the new crank and pistons rods are getting balanced. 4weeks and waiting , I'll have all this crap back in by the fourth of July. Spent a week restoring my dad's 68 Hallett, new paint,seats,carpet and a trick 455. The best thing to buy is a by-pass kit for olds motors. I got one from HI-Tech in KS. Money well spent $90 for the valve. Next week my little Taylor will be looking for a challange.
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