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Author Topic:   oil pressure?
Dirt Full Roller

Total posts: 27
posted July 15, 2001 12:05 AM
k just though i run this past everyone and see if it rings any bells. i run a 406 in modified. when i start the engine it carry's 60-70psi hot or cold idle or reving. however on the track when i pick up the throttle my press will drop to 40 psi and stay there upon slowing the pressure will continue to drop until i kick the car out of gear and give it just a little razz. then bam 60-70 psi. i run a milodon diamond stripper tray and 7 quart trap door pan and pick up with a pu depth of 3/8 inch hv oil pump. tryed new pump and guage also tried over filling the oil by 2 quarts to see if it was a return problem no diff. not then last night with no warning i blew the hill out of it. no power loss noticible just sudden vibration and fire.uppon dissasembly the 2 center pins on the crank appeared to have been starved for oil all other m and r bearings in great shape. mind you i ran this engine about 10 nights messing with the op problem. eagle rods need oil too. any help is much appreciated. thanks in advance. jlfastride.

Dirt Freak

Total posts: 219
posted July 15, 2001 03:26 AM
I would say the crank was broke......I would think this motor was at the very least running with a cracked crank. Under racing condition it would flex the crank creating a big gap for oil to come out......this showed up as a drop in oil pressure. I have seen cars run with broken cranks before, if it's behind the 2nd main.......broke off at a sharp edge......or a v shape.........
did this motor have the same problem since it was new.......or was the crank maged the last time it was apart? or did the problem with oil prssure start when you broke a tranny or rear gear? I say the crank was broke, It just now came apart.

Dirt Full Roller

Total posts: 27
posted July 17, 2001 10:09 PM
crank was magged at begining of season im not sure when the problem started as i tend to forget about the guage while racing. however i haven't broken a trans or gear or shaft all year. thanks.

Dirt Full Roller

Total posts: 27
posted July 17, 2001 10:12 PM
almost forgot crank is still in one peice. visible however fails the ding test though that's not accurate all the time it sounds like a peice of lead.

Dirt Full Roller

Total posts: 29
posted July 21, 2001 09:13 AM
Had the same problem once with the same setup. Had crank turned and put back together and sold it,the two center mains were trashed,after the fact i was told the side clearance on the eagle rods could be the problem( dont know how true this is)If you find out anything else out let me know.

Dirt Roller

Total posts: 7
posted August 26, 2001 11:42 AM
My personal truck does the same thing, but it goes from 40 and work its way down as the motor gets up to temp. I pull up to the stop light and it goes to zero, pop it in neutral back to 15 psi. hit the highway and its steady at 30 psi. I been driving it like that for 1 and a half years. But it hasn't ever seen 7 grand. take it till she pops for me.

Dirt Administrator

Total posts: 3279
posted August 26, 2001 12:57 PM UIN: 16262997
The crankshaft is junk if it doesnt ping. The harmonics on the crank will cause some serious problems if it has a defect like this. What happens is that the harmonics will match a component that is attached because of the different frequencies that are put out throughout the RPM range. This will cause a major problem. If it matches any rod, pin, valvespring, or whatever, it will cause some serious internal vibrations and heat. This will kill a motor quicker than you can crank it. I personally had this happen to me, and checked the crankshaft harmonic signature. It showed us that it was defective. It somehow matched the harmonics in the wrist pin or the rod and broke 4 c-clips that were holding the wrist pins. Which of course, caused failure. I just wanted to let you know this because we have been doing a lot of testing on this and can determine if that is the case. If the crank will not ping, it is junk.


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