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Old 05-07-2018, 10:13 AM
Per Per is offline
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Join Date: May 2018
Location: Norway
Posts: 2
Confused V8 noise, power loss, oil pressure

1969 model 383has a strange set of symptoms:
- Tinny, clattery noise with a frequency following engine rpm
- Only comes in once engine is above 80C, and disappears again if tem falls below 85C
- When listening with a rod stethoscope the noise is strong and clear at the rear of block where the valley pan is bolted down with a clamp and three small hex head bolts. Equally strong at the oil pressure low switch right at the rear of the block. And nearly as strong at the very rear of the valley pan itself.
- Oil changed
- Oil pump replaced (HPNV)
- Lifters replaced
- Oil pressure is 80 psi cold, ca 45psi hot at idle and 80 psi at say 2000rpm
- Once warm'ish oil pressure needle vibrates a bit at all times, when the clattering is there it fluctuates very quickly with ca 30psi peak-to-peak at idle. With rising revs the frequency increases and peak-to-peak reduces to ca 10psi at 3000rpm
- Mechanical gauge connected via plastic tube at the rear of the block.
- Ran it on the starter with valve covers removed, there is oil at all rockers
- Running a hot engine on the starter the pressure needle drops ca once per 1 or 2 rounds of the crank.
- After a local run to get it up to temp I did not nurse it home. This time I gave it a full welly. And lo and behold the higher the rpm the worse the power loss. Thus I believe the theory of oil starved lifters is very likely.
- The noise is very loud and clattery. Rising and falling in frequency along with the vibrating pressure gauge and now proven power loss.

BUT:
The lifters are fed from the main oil galleries. The camshaft is fed from the RH oil gallery. The rocker shafts are fed from camshaft bearing no 4.

The oil pressure gauge is fed from the cross feed from RH to LH oil gallery.

And the gauge shows 80psi at about 2500rpm even when noise etc. are at their worst. I simply cannot understand how the lifters can be oil starved under those circumstances.

If the feed to the rocker shaft(s) is what causes the rythmic drop then the oil galleries should be able to feed the lifters without any problems considering pressurenever falls below 45psi.

Otherwise the engine starts easily, idles nicely, pulls strongly, responds well to the throttle as long as the temp is below 80C..

Any good ideas?
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Old 05-07-2018, 03:03 PM
burnnotice burnnotice is offline
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Join Date: May 2018
Location: washington dc
Age: 50
Posts: 7
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sounds like rockers and lifter issue. check all lifter lash and lifters.
if the noise is below idle and goes away and clunky usually bottom end. yours sounds like a lifter and rocker issue. pull the valve covers check rockers for lash. if ok put the car in neutral and then rotate the crank 90 degrees and check lash. do this 8 times. when you are at zero lash. back off each rocker 3/4 turn. verify acceptable lash. button up valves. if problem persists. pull the push rods check length. if push rods check out check lifters.you can narrow it down with a mechanics stethoscope and check each cylinder for the noise at idle.
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fed , lifters , noise , oil , pressure

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