And It Still Leaks!

[BMERDOC]

I had trouble tuning the 400 in my new to me 68. I finally chased it down to leaking intake gaskets. So I replaced the gaskets tonight and the left side still leaks. I did every thing right. I have never seen or heard of a warped manifold. I'm thinking the heads were shaved and the intake wasn't. It only seems to be leaking on the right side of the motor but after start up and confirmation of the still existing problem I packed it up and left.

So what have you guys seen? Would you agree that at least the right head may be shaved?

[1972RedNeck]

Do you have a cast iron or aluminum manifold? I have seen warped aluminum manifolds.

[BMERDOC]

Its a cast iron 2bbl. manifold. Heavy SOB. I guess I can take it back off and put a straight edge on it. It'll have to come off one way or the other

[s_nova69]

It is common to have a bad seal on the intake with a shaved head. It would be worse if one head was shaved and the other not.

It would be nearly impossible to know if it has been shaved without taking it off and cc'ing the chambers.

Solution: you could try to reseal the intake again and use a generous portion of silicon around the ports on both sides of the gasket. That has worked in the past for me.

Worst case u pull the heads to see what's up and then u can shave/mill the intake ( new or old) to match the heads.

Or find some new heads and intake and upgrade
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[FLEET72]

Are you using the front and rear end gaskets for the lifter valley?

[50bomb]

make sure that you put extra sealant glue on the back corners on the back of block cause the intake manifold gaskets usually don't cover those corners well. My grandpa had that problem and we did what I mention and its doesnt leak anymore.

[geezer#99]

Put a flashlight in the lifter valley and put the intake on without gaskets. Easy to see where the mis-alignment is.

[68gmsee]

I am tinkering with a 350 and replaced the intake gaskets a couple of weeks ago. I had two sets of gaskets. One form about 10 years ago I had bought but never used and a new set that I just bought three weeks ago. Both were Felpro.

What I noticed is that the older set rubber end pieces were made of a slightly firmer rubber and the new ones were soft and flimsy. The reason I even noticed the difference is that when I tightened the intake to specs the rubber end gasket in the back bulged out and almost squeezed itself off the engine block and intake. I took the intake off, opened the older set and used the older rubber ends pieces. Had no problems. Quality is not like it used to be.

[sean1969c10]

Have the gasket surfaces been buffed off with a 3m roll-lock disc? I know they claim that they won't hurt anything but I can't tell you how many manifolds, heads and blocks I have had to surface because of those "cookies" in the hands of heavy handed guys. when this happens, the edges of the intake ports and water ports get rolled over and the gaskets aren't able to seal. Just my .02c

[MusicMan70]

I had a small puddle of oil on my passenger side of the factory intake by the carb. I took out the adjacent intake manifold bolt and put sealant on it. No more puddle.

[VA72C10]

If you find it's something with the intake I have a nice used single plane for a 4bbl....I also have a factory intake and 4bbl quadrajet I'd make a good deal on....especially if you'll help me button up the new 350 I got

[BMERDOC]

Thanks for everyones input! I will be pulling the intake again on Monday. I'm gonna straight edge the right side of the manifold and try Geezer#99's trick to see how well it works. I didn't use the end gaskets out of the kit. I used a nice bead of RTV on each end and let it skin up a bit before I installed the manifold. I can't speak for anyone who came before me but I Roll-Locked the mating surfaces. I'm used to roll lockin aluminum so I feel good there. I had hoped to just slap some intake gaskets on but it looks like I'm gonna have to slow down this time and make sure every bolt and thread is clean, surfaces are flat and the rest of the prep is done correctly. If I find out that the manifold is warped we may be talkin Jonathan.

[davepl]

Are we talking vacuum or oil leak? I'm assuming oil leak, so:

I use RTV-only on the ends as well, as do most people I think. I'm not clear from your post exactly where on the left side its leaking, that info might help jog someone's memory.

Do you have a functioning PCV? If you wind up with positive crankcrase pressure, it makes leak-proofing an engine that much harder.

[BMERDOC]

Oops! Sorry Dave! Vacuum leak. It can't muster over 15 in. Hg. If I spray carb clean along the sides of the manifold where it meets the cylinder heads the right side leaks by cyls 2, 4 and 8. It didn't seem to leak on the left side (odd bank).