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Old 03-10-2004, 05:15 PM
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pontiac 455 high oil pressure

Fresh rebuild on a 70 model 455 / 462 in a 65 lemans. seems to have very high oil pressure 30-40lbs idle 70lbs down the road 65m.p.h. engine shows no sign of compression blow by. but blows oil dip stick out of the tube an inch or 2. Recently began leaking oil out rear seal during heavy acceleration. Help!! anyone heard of this and does this engine have an oil pressure regulator system, Thanks
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Old 03-10-2004, 06:31 PM
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do you have a pcv valve??
or any crankcase ventilation?
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Old 03-11-2004, 04:30 AM
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Yes, good vacuum to pcv and two large breather caps on the valve covers.
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Old 03-11-2004, 05:52 AM
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This is normal oil pressure on a combination like yoursand nothing to worry about. Pontiacs are known for rear mail seal leakage and unless you used a Viton seal from BOP your going to have leakage out of the rope seal. As far as the dipstick I believe that if your engine has the windage tray that the lower portion of the dipstick tube may have been left out and the throws on the crankshaft are hitting the dipstick itsself and knocking it back out, due to the dipstick not going on down into the oilpan correctly and just going to the top of the windage tray and turning.
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Old 03-11-2004, 02:03 PM
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Red face

Well, I've got the same symptoms with my fresh 455 and have had to pull the motor each winter for the last 3 years to fix my leaky rear main. My dipstick blows out under full throttle too. This time I decided to send it to antoher machine shop for a tear down inspection and rebuild because I think my rings didn't seat thereby causing too much crank case pressure. I have a breather in each of my valve covers and a PCV valve in my valley pan which is then attached to my carb spacer plate. I should know by early next week if it's what I suspect. I'll keep you informed if you like.

I agree with Grusome that your oil pressure is good.
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Old 03-11-2004, 03:00 PM
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Yes, 6567GTO please keep me informed on what you find out. It looks like I might be pulling it out this weekend. I have talked to some local pontiac heads, as well as this thread. It seems to be a somewhat common problem, but I really don't know if it is compression blow by related, I'll be looking forward to hearing what you findout. Thanks
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Old 03-11-2004, 03:48 PM
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I've had the same problem with my Pontiac 350. Well, not the rear main problem, but sometimes at long, WOT passes, I've blown my dipstick out as well. I haven't seen anything on the tip of the dipstick to suspect any mechanical interferenc (I couldn't imagine the reason that it'd only happen at WOT if it was mechanical anyway) so I'm almost postive that's not it. I think I may take an extra dipstick, and drill some small holes in the top, and stick a small amount of foam around the top to see if that'd help at all. Maybe that's goofy, but I don't know what else to do.
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Old 03-11-2004, 04:08 PM
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Here's something you could try. Not sure if this will work, it's an old trick...

Drain your oil and change your filter but refill with NON Detergent oil. NAPA sells it. Then when you drive your car, try and run the rpm's up and down in one gear. If you know what I mean, "gear it". Rev it up and then let off on the gas. This might help get rid of any glazing of the cylinders and rings and hpoefully seat them. It's worth a try
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Old 03-12-2004, 07:14 AM
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Alright, once again I'm humbled and in the learning phase, (note that I don't call myself an engine builder master, but an engine builder mentee). Anyway, what is a nondetergent oil, and what do you mean by "gear it". What I get from "gear it" is leave it in first and rev it, but get out of it without shifting, so that your engine is still turning due to your tires still turning. What exactly is the point of this, and how does it help seat the rings? Granted, it doesn't help me right now, but I'm always in the mood to learn from the elders.
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Old 03-12-2004, 09:10 AM
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The oil pressure sounds good to me (especially for a Pontiac) and the leaky rear seal is a chronic problem with them. Rope seals have to be 100% perfect or they will leak. You have to be careful putting the neoprene replacements in because they are more for racing engines that the builder wants to reduce drag. Rope seals were used in engines mainly because the seal housing areas were not precision machined and thus the rope seal would "fill in the gaps".

As far as blowing your dipstick out, that really is nothing more than excessive crankcase pressure that comes from cylinder pressure blowing past the rings. It may stop after you have some miles on the engine. Generally, the rings will finish the hone job that the machinist could not do and this should subside over time. The better the cylinder finish that can be put on a cylinder the quicker everything will seat.
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Old 03-12-2004, 09:26 AM
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I'm not an expert, just telling you what I've heard. Varying the throttle helps to seat the rings better from what I'm told. Non- detergent oils have less slippery additives in them allowing more friction between the cylinder walls and rings for better seating.

Then there are those that use synthetic oils for breaking in engines and swear by it. I guess it depends on the rings used and the hone pattern and coarseness.
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Old 03-12-2004, 05:32 PM
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6567GTO you are right about the type of rings used and and what grit hone was used to do the cylinders. I remember using a standard 800 grit stone on my hone several years ago and installing Moly rings, took about 2 months for the rings to seat (this was before I knew better) Also something else that can cause exceessive cylinder pressure is not staggering the gaps on the rings I have known this to happen before, but this will also cause blowby. But for some reason I never had problems with blowing the dipstick back out.
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Old 03-13-2004, 07:03 AM
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Thanks everyone for alot of good information. I guess I am at the decision point. Everything else about the engine is awsome "tirefryer" is exactly right. The engine has 150-200 miles on it. I live about 15 miles from town. If I take the hiway and drive 70 mph, I get about a 2 foot spot on the shop floor. Is it worth putting up with it and trying to put some time on the motor, or is it time for the Viton seal????
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Old 07-10-2004, 06:09 AM
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Well I am getting ready to pull the engine, I have talked to several locals and get about 70/30% for going rubber over rope. What do you guys think, rubber or rope, Thanks for the input I hope to only do this one more time.
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Old 07-10-2004, 07:03 AM
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Man, I hate to give the wrong advice if it fails again but I just used the rubber one again myself. So I guess I'd vote for that. I think I'm gonna switch my pcv location from the valley pan to the valve cover too.
Good luck.
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