Thread: 4 year old rebuild in Corvette - now tapping or knocking...leaking oil

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Have a 61 Vette with a newer totally rebuilt 327 block, Edelbrock top end stuff. It seemed to be running high oil pressure for awhile (55-60 cold, 35-50 hot)...higher than it did right after rebuild.

Last week I noticed big oil leak under car (never leaked before). There was oil sitting up on the intake manifold as well. I retightened valve covers, filled with oil and it doesn't seem to leak up top...having a hard time see where leaking is coming from.

There is a NEW tapping sound...checked lifters and they seem tight. Any easy way to check to see if it's in a rod somewhere?

Here's video so you can hear it:https://youtu.be/35-uWjpaKYY

any ideas appreciated....hate to break it down to much as it's pretty newly built.

Remove valve covers and see if pushrods spin while engine running--if not cam is wiped out

Originally Posted by lrsmith62

Have a 61 Vette with a newer totally rebuilt 327 block, Edelbrock top end stuff. It seemed to be running high oil pressure for awhile (55-60 cold, 35-50 hot)...higher than it did right after rebuild.

Last week I noticed big oil leak under car (never leaked before). There was oil sitting up on the intake manifold as well. I retightened valve covers, filled with oil and it doesn't seem to leak up top...having a hard time see where leaking is coming from.

There is a NEW tapping sound...checked lifters and they seem tight. Any easy way to check to see if it's in a rod somewhere?

Here's video so you can hear it:https://youtu.be/35-uWjpaKYY

any ideas appreciated....hate to break it down to much as it's pretty newly built.

I did tighten the lifters on the tapping cylinder and was able to quieten it but didn't want to tighten to much and possibly hurt things more. Noticed that one lifter is not oiling very well...whereas the others are. Could that help inform what's going on?

chect to see if pushrods are spinning as the motor runs------a flat tappet camshaft is ground on a slight taper to cause the lifters to turn ----if its not spinning. the cam/lifter is worn-happens a lot with todays oil on new rebuilds

First, welcome to CHR. I typed a reply earlier, but it didn't post and I lost it.... My first thought was that you lost a lobe on the cam, and your statement about tightening one lifter to reduce the noise points to that even more. I'd drain the oil and check for very fine metal dust in the oil, and maybe cut the filter apart and check in the folds of the filter media, too. I assume that the rebuild of the 327 did not include a conversion to roller lifters, right?

On the leak, look at the "China Wall" gasket surface across the back. They're known to blow out, which is why using a thick bead of silicone has become the preferred method of sealing vs the rubber gasket.

Just out of curiosity, are you running a road draft tube and the oil filler in the intake manifold?

NTFDAY....as a matter of fact, yes, I'm running original draft tube and filler neck in the Edelbrock intake. Interesting question....why?

On CAM, it's a new cam replaced during the build. Engine had an aggressive racing cam and it was a pain to try and dial in, so we purchased a new cam from Edelbrock to specks with the engine. I guess I'd be shocked that the cam is worn our since I have less than 2500-3500 miles on this engine.

Originally Posted by lrsmith62

I guess I'd be shocked that the cam is worn our since I have less than 2500-3500 miles on this engine.

Today's motor oils no longer have zinc and phosphorus additives, which were there to deal with high pressure, point load friction, specifically cam to lifter friction. They were omitted when OEM's found that catalytic converters were getting plugged with heavy metal deposits, rendering them useless, and since OEMs had switched to roller cams they had no concern with changing the oils we can buy. If the cam is not broken in 100% perfectly, i.e. immediate start without extended crank, 2000 rpm for twenty minutes with no idling, a wear pattern can start that stops lifter rotation, and wipes a lobe quickly, often less than 2000 miles. Running a racing oil, like Brad Penn's or Joe Gibbs can work, but it's still a gamble.

I don't remember the exact specs/time, but we did do an intentional break in on the engine and I seem to remember running it for 30 min at 2000. The guy that helped me rebuild the engine was an ex-GM mechanic and a hot-rodder.

Additional info:
- I went back and adjusted all valves. Did the GM instructions, while running engine, loosening to tap/noise and then doing 3/4 turn back tight. Did for all valves including the #8 cylinder that seems to be giving the noise. Still a bit of tapping, so it's not the rockers (not rollers btw)
- checked carefully the push rods and all are rotating at a normal rate it seems
- dried all the oil off of the back (exhaust) rocker for #8 cyl. and it didn't re-oil when started. This has to mean something...no oil even though push rod is turning?
- took push rods out of #8 and they look straight and normal to me.

Originally Posted by lrsmith62

NTFDAY....as a matter of fact, yes, I'm running original draft tube and filler neck in the Edelbrock intake. Interesting question....why?

The engine has to have a way to breathe and I've seen those who will delete the road draft tube and put a closed breather on the oil filler tube. They won't run a pcv system because they don't want to hack up the finned Corvette valve covers. That will cause a massive pressure in the crankcase pushing oil out wherever a place can be found.
I experienced that on a cherry 57 Ford in 1964 in California. After a 1000 miles or so the dipstick blew out, dented the hood, covered the right side of the windshield in oil and wiped out the bearings.

Can you see through the pushrods out of #8, or can you run a piece of safety wire through them unrestricted? I'd still drain the oil and check for metal. If you wiped a lobe that's a bunch of microscopic abrasive flowing through the engine, so you're looking at a total teardown. I wouldn't waste a nickel on building a flat tappet cam engine today. It's been said that it's not "IF" it will fail, but only "When" it will fail.

If you didn't wipe a lobe? It's a pretty healthy knock from the video, so chances are you're gonna be taking it down, at least enough to get #8 pulled out....

gotcha....I'm not running a pcv system, but do have the draft tube and the filler cap is vented around the bottom side of it.

Originally Posted by lrsmith62

It seemed to be running high oil pressure for awhile (55-60 cold, 35-50 hot)...higher than it did right after rebuild.

Sudden increases in oil pressure usually indicates a restriction to the oiling system and can be as detrimental as low oil pressure. Something has gone wrong, check the oil and filter (as suggested by rspears) before you continue to do further damage.

#8 exhaust tappet is the first to get oil so if it isn't and others are-------bad tappet, plugged pushrod, etc-You might be able to fish it out thru dist hole in manifold-however since you have a leaky manifold your going to need to fix that but would suggest you check out the tappet first-

for cylinder noise-you can short out spark to cylinders one by one to see if noise goes away or changes------if # 8 becomes quiet or changes siq amount? probably need to pull pan also-oh wait-oil leak

Here is video after valve adjustment....top end noise lessened but still tapping for sure. Also, engine not running as smooth as it used to....a little sluggish on idle every 30 sec. or so.

https://youtu.be/sb02Ul1NNLs

Push rod not clogged....so I guess I'll drain and look for metal, probably also pull intake and check tappet, pull pan and check #8 bearing as well to make sure it's not spinning. Need to re-seal everything anyway. Bah humbug....this is why we like old cars, right