I recently rebuilt my 355. The block has the casting number 638, so it is a one piece rear main seal. I have replaced the oil pan gasket twice and still can't get it to seal up. It always leaks where the oil pan and timing chain cover meet. The first gasket was the jegs one piece gasket. The second was a felpro one piece gasket. Brand new GM oil pan, and a brand new timing chain cover. I am looking for a multi piece gasket kit for my engine but can't find one anywhere. And pulling the engine out to replace the oil pan gasket definitely isn't fun, so hopefully this will be my last time.

 

Are you putting some RTV at the corners? I didn't until I actually read the directions LOL Some just use RTV and no gasket, modern RTV like grey or the right stuff is good but I'd not wanna separate or deal with that clean up myself.

 

I did. I even bought the caulk tube of the right stuff to throw on there. After the felpro gasket leaked, I dropped the pan, pulled the timing chain cover and lathered the oil pan gasket in the right stuff. Only for it to leak more.

 

Did you clean the gasket of all the oil? Are you letting it cure long enough? You sure it's not something else leaking the the damper seal? Does your engine have a lot of blow-by? I think you'd be able to tell you have the wrong cover/pan combo, it was pretty noticeable when I tried to use an older pan. What pan are you using?

If your rings didn't seat after the rebuild then it's gonna leak.

 

I pulled the motor out to replace the gasket. That was when I put the new timing chain cover on it as well. So no oil was in the engine at all. Gasket surfaces were cleaned. Also I put a speedi sleeve on the balancer to eliminate that leaking as well

 

This is the wrong way to do it, I had the same problem on both my cars, oil leak at front where timing cover meets pan after gasket changes.. On both of them I cleaned up the area as best can be and just took a tube of gasket maker and my finger and stuffed it in the seam across the whole area, haven't had a leak there again, did this years ago..

 

Sure it's the pan gasket?



Got a bolt in this hole right here? If not, put in a short one with a drop of sealer on the threads.

 

Check the oil pan with a straight edge to make sure the gasket surfaces are flat; it may have been damaged at some point between you and where it was manufactured. Front covers are not all equal either; a cheapo Chinese knock-off may leak no matter how much gasket sealer you stuff behind it.

Keep in mind that just piling silicone sealer in there is the wrong way to go; excessive amounts of that stuff will find their way into oil passages and the oil pan where they can clog the pickup. As you might imagine, catastrophic engine failure is the result.

 

Does the later model blocks, 87 and on, use the same timing chain cover? I mean obviously the bolt pattern is the same because it fits on there, but is where it meets the pan/gasket the same?

 

Yup, all the same, since they change to the thicker front gasket in around 69. Except I think for the very latest, maybe 96-up, acoupla the screws are in different places.

I should also mention, if your TC or OP is "krome", GET RID OF IT. or at the very least, grind / sand / something ALL the "krome" off of ALL the sealing surfaces.

 

It is one of the mr Gasket ones. I planned on picking up a proform one, but it says 55-85 is the fitment years.

 

They started welding the timing tab on in 86, so "technically", one without a tab won't be a perfect "fit".

Other than that they're the same.

 

That reminds me I had a brand new pan from a good manufacturer that most the holes were dimpled. I've sen this problem before but it was on used pans that were over tightened and why the one piece gasket has those metal inserts. If your pan is dimpled, I just use a ball peen hammer and something solid clamped in my vise on the other side. Think I used a piece of solid rod last time w/e I had laying round that fit between the rail lip and pan wall.

edit: Also why newer pans have those load spreaders that run the entire length of the pan.

 

Speaking of that, my pan is flat and not dimpled, however I do have the load spreaders on there. Should those not be used with a one piece gasket?