The Stovebolt Site Forums The Shop Area Engine Shop Timing cover leaking oil

Does anyone now the best way to prevent the two bolts on the bottom of the timing cover for a chevy 235 from leaking oil? Mine has been leaking for a while because I did not put sealant on those two bolts, live and learn. Which would be better thread sealant or RTV or something else? I am speaking of the two bolts at the bottom that go from the inside by the crank into the timing cover. I am sure there are some motorheads here that can help me.

Mike, the two bolts from the inside of the pan that secure the bottom of the timing cover are held in place with a sort of French lock tab plate. So if you used the plate, its unlikely that the bolts have come loose and are now leaking. And its not common at all for oil, that much oil anyhow, to be wicking the threads.

You may have had a gasket failure, or a seal failure. The thing is, to actually access these two bolts, you have to pull the pan. To get to the thread part of the bolts at the outside of the timing cover, to goop on rtv, you have to pull the harmonic balancer. So you have sort of chicken and egg issue. Is it the bolts or is it a seal or gasket. Me, I am not totally sold that its those little bolts that are leaking, unless you think you put them in loose or with out the locking tab and they got loose.

Mike: If the engine is removed from the truck for repair, would you recommend the modification that moves those two bolts that can only be accessed by removing the oil pan to bolts going in from under the timing cover? I've done this on a GMC engine and I think the procedure would work on a 235 Chevy as well.

Update: Bolter SlimSix (Andy) did a nice write up with pictures on this modification 20+ years ago on the OldGMCtrucks web site. He states "this same procedure applies to the Chev 216's, 235's and 261's".

I do it for all my motors. Case in point, a couple of years ago I had a bad leak at the front of my 261. I assumed it was the seal. Turns out it was the timing cover gasket. Because I had done the modification, I did not have to remove the pan to remove the timing cover.

Keep in mind the reason for the bolts through from the inside had to do with in chassis maintenance on earlier motors. When the crank and bearings wore out a bit and the clearance because excessive, you did an in-chassis maintenance and removed shims or replaced bearings. So you could pull the pan, remove the lower timing cover bolts, remove the front main cap and do the service without having to tear down the front of the motor.

Not really a thing after 56 and the introduction of precision bearings. No adjustment for those bearings.

I will also say that in addition to modifying the timing cover for outside bolts, I always drill the snout of all my cranks for a balancer bolt. Keeps the balancer in place god forbit it gets even a little loose and starts working itself on the cranks snout ruining the snout and the balancer, but also because it makes installing the crank gear and balancer, and removing the balancer soooooo much easier and less chance for damaging the crank thrust bearing when installing the balancer with the block of wood and hammer method.

These days, its more likely that I am messing with these old motors by myself so finding someone to hold a pinch bar against the crank while I hammer is not as easy as it once was.

Did you use a speedi-sleeve on the harmonic balancer shaft? Even a little bit of roughness can cause failure of the spring-compressed seal there. I've even had trouble when I've polished that shaft. Just a thought. This can and will make for a pretty good oil leak.