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Old 03-15-2009, 07:56 PM
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oil pressure trouble ?

Ok its on a 355 sbc solid lifter cam, double hump heads, 9.8 compression stock oil pump. Ok motor was rebuilt last summer and its in a street strip 55 wagon. I race points with it during race season and last year after fresh rebuild it ran great carried 25 psi at idle warn and 55 psi going down the strip, its got about 40 passes on it. I drove it some over the winter not much tho. Saturday was a test and tune on the first pass i noticed it losing oil pressure it would drop to 20psi at half track and hold there till i lifted and it would slam to 60 psi. I added a court of oil thinking maybe the pickup came off and second pass it was worse you could see it dropping in the burnt and when you lift off the gas it comes back to normal. So when i got home i put a new mecahanical oil psi gauge and no luck then i dropped pan and things looked great pick up was still attached and i pulled oil pump looked fine, i had a high volume pump new in the box so i put it on just to try it, and it got worse when it idles with around 25psi and cruising it carrys 35 psi and when you stomp the throttle and hold it down it slowly drops to around 15 to 20 psi and comes back up when you lift. The only thing that was changed over the winter was a new distributor.Im lost please all help would be appreciated.

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Old 03-15-2009, 10:21 PM
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I would check the dist. you replaced. The lifter oil galley runs thru the dist shaft - if the machining is not right on the shaft, oil could be by passing causing low pres. Also check galley plugs on front - if loose or missing this will cause low pres.
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Old 03-16-2009, 12:07 AM
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Change the oil filter. I had this happen to me on my 400SBC. It was the oil filter.
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Old 03-16-2009, 04:21 AM
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thanks for the info, the distributor is a new mallory magnetic pickup, also when i changed the filter it had great oil pressure right away then when back to doing it again, can the bypass where the oil filter screws on be causing this? Thanks.
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Old 03-16-2009, 06:00 AM
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The bypass gets a pipe plug installed in it on my engines.

Along about '86 this filter mount was changed to a different style.
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Old 03-16-2009, 01:21 PM
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Quote:
Originally Posted by bracketracer
thanks for the info, the distributor is a new mallory magnetic pickup, also when i changed the filter it had great oil pressure right away then when back to doing it again, can the bypass where the oil filter screws on be causing this? Thanks.
Yes it could. When I did mine I removed the oil filter adapter and inspected it also and it seemed ok so I stuck it back in with a new GM Delco oil filter and its been fine ever since. (6600rpm)
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Old 03-16-2009, 05:12 PM
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ok guys so i checked the oil filter adapter and put a different brand oil filter on it. still same results. Ok a old drag racing guy told me that he had a cracked crank shaft do exactly what im talking about, had great oil psi until under a load and the crank flexing opend up the crack and lost oil psi and soon as you lift its back to normal. Ive had alot of grief with this motor, it was built by a man that builds race motors and has built atleast 40 percent of the motors at the track, when i first bought it it was fresh got ten passes on it and it wiped out six rod bearings , now with only 40 or so passes this happend, is it possible this crank could have been the reason for the first bearing failure? Thanks for all the help its frustrating.
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Old 03-16-2009, 05:21 PM
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This theory could hold water IF the crank's forged steel. They will flex (to a point ) w/o breaking, unlike a cast crank that cannot withstand flex nearly as well.

Just for s&g, can you reinstall the original distributor (including the old oil pump drive) and test for oil pressure?
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Old 03-16-2009, 07:15 PM
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yes i can try that tommorow and see if that does anything, ive also noticed a little vibration at 3800 and on up? Wasnt there till this problem occured.
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Old 03-16-2009, 09:21 PM
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Quote:
Originally Posted by bracketracer
yes i can try that tommorow and see if that does anything, ive also noticed a little vibration at 3800 and on up? Wasnt there till this problem occured.

Oil pump loose. Did you check the front galley plugs???
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Old 03-17-2009, 06:50 AM
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the oil pump was tight, and i havent had a chance to check oil galley plugs, the engine builder wants me to pull it out and bring it back. This will be the fourth time its been in and out of the car, when does a person say thats it and go else where? Ive had to pay money every time weve had it apart no warantees on work but some free labor. Last time he had it apart he wouldnt let me come and get it because he didnt want his name tarnished, so it took another complette rebuild so it cost me almost full price less 300 of labor. Ive paid to have this thing built twice and this will be number three. Thanks for your help
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Old 03-17-2009, 07:02 AM
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Quote:
Originally Posted by bracketracer
Last time he had it apart he wouldnt let me come and get it because he didnt want his name tarnished, so it took another complette rebuild so it cost me almost full price less 300 of labor.
???

Sounds like it's time to declare "malarkey" on this hack.

It's YOUR engine, if he were to hold me up like that, more than his name would get tarnished! LOL

Time to move on, cut your losses, and find another wrench, IMHO.
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Old 03-17-2009, 07:29 AM
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I may have missed something, but it sounds like this oil pressure issue is only present under acceleration. Is it possible that the pickup may not be sitting deep enough in the pan and under acceleration the oil is moving away from it causing it to suck air instead of oil? Though it may also have contributed to your original bearing failure.
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Old 03-17-2009, 10:58 AM
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Quote:
Originally Posted by bracketracer
the oil pump was tight, and i havent had a chance to check oil galley plugs, the engine builder wants me to pull it out and bring it back. This will be the fourth time its been in and out of the car, when does a person say thats it and go else where? Ive had to pay money every time weve had it apart no warantees on work but some free labor. Last time he had it apart he wouldnt let me come and get it because he didnt want his name tarnished, so it took another complette rebuild so it cost me almost full price less 300 of labor. Ive paid to have this thing built twice and this will be number three. Thanks for your help
"When does a person say thats it.....". The simple answer is build you own engine. Building/assembling is very easy and with all the information available (including the very knowledgeable members of this site) you have all the resources needed. If you don't have them, invest a few hundered dollars in some measuring/building tools and go for it. You can't do any worse then your present situation!
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Old 03-17-2009, 08:38 PM
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Thanks guys for all your help, im sure the pickup sets deep enuff in the oil its a deep 7 quart pan, what does it meen when someone asked if it could be cavatating the oil pump? I run 10w 30 so its not real thick. Your rite there is alot of great information on this site and i plan on tearing it down and checking it out myself and going from there, ive done alot on top end builds and cam swaps and such just never tackled the bottom end. Thanks again
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