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

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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.

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

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....

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

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.

A local guy here in town made it less than 30 miles down the road on a new crate motor with a flat tappet cam, pulled over on the side of the road after it wouldn't run and pulled the valve cover, rockers where barely moving, didn't put any zinc or use oil with zinc and it went flat that quickly. I hope all goes well for you as we have all been down the road your going! Best of Luck Matt

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.