427 390HP Low Oil Pressure? Tech question

[Dick W.]

Re: 427 390HP Low Oil Pressure? Tech question

From all your descriptions of the noise, it is a slight piston slap when cold. This is not unusual with forged pistons. Every 427 and 454 that I have had has had piston slap, some worse than others. Our '72 has had that cold rattle for over 20 years. I would not worry about it. If it is still there 150,000 miles from now, you might think about doing something about it.

[Duke W.]

Re: 427 390HP Low Oil Pressure? Tech question

IP = instrument panel.

Even though your oil pressure is less than spec, I dont' think any harm will come to the engine in normal driving.

The noise sounds like cold piston slap rather than a bearing. I have the same "problem" with my Cosworth Vega. There is one noisy piston when cold, and it's quite noticeable under load. By the time the temp gage moves up above the first graduation of 100F it goes away, so it's very similar to your situation. I try to minimize the load until it goes away - just use the least throttle possible in the first couple of minutes of driving.

I assume the bores were honed and using standard size pistons might have increased the clearance enough to cause some cold slap on one or more pistons, but it doesn't sound serious enough to tear the engine down. You could be chasing a ghost. Does the shpt that rebuilt the engine have records of piston to bore clearance?

Is the oil pump the original or was it replaced when the engine was rebuilt? If so what is the mfg/part number?

What was the hot oil pressure @ 2000 prior to the rebuild?

What does the shop that rebuilt the engine have to say?

Is the IP oil gage max. graduation 80 or 60 psi ?

Duke

[Neil S.]

Re: 427 390HP Low Oil Pressure? Tech question

Duke, The oil gage goes up to 70 psi. I did not receive or have any specs on the motor, and the engine builder did not save his report. The oil pump is a stock type new pump, I believe Melling 77. Oil pressure prior to rebuild is not known. Just another thought, If the oil pump screen is too close to the pan will it affect pressure? What should the distance be between the pickup pump screen and the pan? I think you are right about the piston slap, and mabe I am worrying too much about this. Anymore thoughts?

[Philip C.]

Re: 427 390HP Low Oil Pressure? Tech question

The noise your hearing sounds like something a piston pin. Phil 8063 P/S HATE this new (copied) technical board

[Duke W.]

Re: 427 390HP Low Oil Pressure? Tech question

So you are saying that the maximum labeled pressure on your gage is "70"?

I'm only familiar with "60" and "80" psi gages.

I doubt if the pickup being too close to the pan is a problem unless the bottom of the pan appears pushed up. With the pan off it would be pretty easy to take the measurements and compute the distance, which I expect should be not less than about half and inch and no more than an inch. This "problem" killed a lot of Vega engines. The early models lacked jounce travel, and if bottomed out the low hanging pan could be pushed up into the pickup, which would starve the engine of oil.

My '77 vintage P & A catalog lists 3904827 as the replacement pump for all '65-'72 big blocks except SHP and HD. SHP is 3904826, and HD shows two different numbers. The listed relief springs are 3860378 exc. SHP/HD, 3876866 for SHP/HD, so clearly the L-36/68 had a different pump setup than SHP and HD - likely a lower value relief spring. "HD" refers to L-88/ZL-1 ,and the two listed pumps probably have longer gears (higher volume) with the same relief spring as SHP.

I think 40 psi hot @ 2000 and 15-20 hot at about 600 RPM idle is perfectly acceptable for a road engine, and if anecdotal evidence from known original L-36/68s is the same then you have nothing to worry about. These values are typical for 327s except late '63 and later mechanical lifter small blocks, which had 55-60 psi springs versus 40-45 for all other small blocks.

The issue is further confused by the AMA specs listing only one spec, which covers a very broad range of 50-75 rather than 40-45 or 55-60 for small blocks depending on the configuration.

As an aside, in other recent discussions with people whose engines were rebuilt by commercial shops all the parts were lumped together as "parts" with a single price for the lot. This is very sloppy administration, and raises suspicion of their shop work.

If you have an engine rebuilt by a commercial shop INSIST that you be provided with a detailed invoice of all parts including manufacturer and part number. I would specify parts to use and require my approval for all parts used. This is not an unreasonable request when you are spending several thousand dollars on an engine rebuild!

Duke

[Ray G.]

Re: 427 390HP Low Oil Pressure? Tech question

Hello;
The noise you describe may be the front main caused by the PS belt pulling the crank to the left side. Actually making the main bearing shells move in the block and main bearing cap.
There was a offset front main available from Chevrolet at the time to solve this noise. It never really caused any harm, but the back side of the bearing shells had wear marks just enough to be noticeable.
Don't remember if it was on SB & BB, or both. Maybe someone else who turned wrenches in the '60s remembers.
Hope this helps.

Ray

PS. If you use plastigauge support the crank up against the top half of the bearing.

[Neil S.]

Re: 427 390HP Low Oil Pressure? Tech question

Yes Duke, My 69 oil gage reads "70" at maximum. I have sorted through everyones input and decided that this IS just the way the engine's built and also think you are right Duke about chasing ghosts for the noise. It has gone 5,000 miles without any changes, and will probably go another 100,000. Extremely good informationfrom all of you. Thanks everyone for your input!