RESTO 650 Exhaust Manifold Gasket Failure

[wabash]

Tried searching and didn’t find so figured I’d start a thread. On two skis now, both 94 GTXs I’ve had a gasket fail at the exhaust manifold to cylinder connection. A piece of the gasket blows out and it leaks exhaust. The first one was a couple years after rebuild the other about 10. Is this a common problem? Any tips things to look for special procedure different from the manual? Everything’s been done by the book other than I don’t believe I used OEM gaskets during the rebuilds. Could be bad gaskets? Age? Getting ready to fix this second one just looking for tips before I dig in.

 

[wabash]

Well I think I might have found the issue. In both cases I had used aftermarket gaskets. They looked to be good quality thick stock type gaskets but you never know with aftermarket. I noticed in both cases the manifold bolts were not tight. Snug but not tight. It appears the gaskets had relaxed over time. Also I had used RTV Ultra Copper to thin coat the gaskets as a precaution. This may have been a mistake. The area where the gasket blew out had zero residual gasket or RTV sticking to the metal as if the oil or gas had cleaned it right off. SO I’m putting the new OEM gaskets in dry.

 

[mikidymac]

Good gaskets, proper thread lock and torque. No sealant should be needed.

 

[wabash]

Yes about a 1/2” piece on a corner near a bolt hole was blown out. Same thing happened on the other machine a couple years ago. I’ve not had gasket blow outs on anything I’ve worked on. Couple things to note. Other than the Ultra Copper on the gaskets I follow the book to the T. Blue thread locker clean surfaces and proper torque. I guarantee it wasn’t because of those issues. When removing the manifold the bolts felt relaxed as far as torque. Book doesn’t call for a lot of torque though. But I noted that the area that was blown out was clean. The metal surfaces had no trace of RTV or stuck on gasket material. Also the split washers were relaxed. I kinda hate the idea of using no sealer on these because they also seal the cooling water ports but I guess I’ll put em on dry and go for it.

 

[wabash]

When exhaust header pipes are installed, there must be no stress on that joint, this a common mistake in the installation, if there is, eventually engine vibration, and heat will allow a small leak. Over time, ( on the earlier motors, 720's, etc), a part of the gasket can be blown away due to the hot exhaust. On the later larger motors, it results in exhaust and water leaks,, but the gasket it not blown away.

Please explain because I don’t believe this was the case.

 

[AKnarrowback]

I rebuilt motors on older DOOs a lot and used to put a light coat of "gasket dressing", loctite red something or other in an aerosol can. After observing the rebuilds over the years I can say it was not needed. Put all your gaskets on dry. Use only oem gaskets.

I would always put the cylinders and exhaust manifold on finger tight and give things a wiggle to make sure the three parts mated good at the exhaust gaskets. I would run through the torque pattern a few times using a nut driver hand tool to let things settle in even more then I would do the full torque pattern, first to half torque then two full passes at full torque. Torque specs are not only for making sure the bolts are tight but also for making sure the parts seat into place, that is why there is a pattern for some parts. I have seen people torque things into place putting full torque on the first bolt while the others aren't even finger tight, their rebuilds always had a high failure rate. I won't say I'm an expert, but I never had any of my rebuilds fail.

A little loctite on the threads doesn't hurt either, just a couple drops though.

 

[wabash]

Torque pattern alignment and seating were all done properly. That was not the cause of failure. Somewhere between using the Ultra Copper and the gaskets relaxing was the cause. Torque is only 25 nm on these bolts but they were definitely not that when I took them off. So I went back with OEM dry. And of course blue thread locker. I read the book and I follow it unless someone has a compelling argument to do something better.

 

[AKnarrowback]

Sounds good.