Permanernt silicone valve coverggasket-fume problem solved

[MAC10]

Last season I installed a permanent silicone valve cover gasket. A very logical and economical thing to do, for good reasons including cost of replacing paper gaskets.

But, I began to struggle to solve a mysterious exhaust fume problem behind my windjammer fairing. I thoroughly inspected the headers, mufflers, gaskets and seals. Re-welded the muffler joint, and replaced all four header gaskets, and the two outside pipe seals, re assembled using copper exhaust system rtv. Added hose clamps to the valve cover to air box breather hose. Sealed and tightened everything.

The problem disappearred for the first hour of highway riding, but then re-appeared and got worse to the point where I had to carry my head high or to the side to get fresh air. I could smell it any time I accelerated. Not fun, and dangerous, as carbon monoxide exposure is cumulative. There is no safe level.

The last thing I forgot about. The silicone gasket is relatively thick and springy, if that is a word. When I checked the bolts holding the valve cover, the bolts were quite loose. Tightened them down to a firm hand tight, and the exhaust fume problem is solved. A paper gasket doesn't have this problem because it is hard, thin, and goes on with gasket cement. An unforeseen problem with a silicone gasket.

The silicone gasket takes a lot of compressing. Mine is new and hadn't quite "bedded in" yet, and when it got hot, was allowing gases to burp out. Right under the tank, where the fumes would re circulate in the still air behind the fairing.

I will keep an eye on those bolts, and routinely re tighten them.

 

[tkent02]

A paper gasket doesn't have this problem because it is hard, thin, and goes on with gasket cement.

Only if you are selling the bike to someone you really hate.
It goes on with a bit of grease so it can be taken off again without ruining it.

Congrats on the fix.

 

[MAC10]

Point taken tkent! That is one reason I went with the silicone version.

 

[chuck hahn]

Heres what causing the real problem.

Those OH SO MGOOD REUSABLE silicone gaskets cant be tightened down properly or they will crush and split..making a leaky mess.

This means you cant tighten the bolts to specs and they vibrate loose. Sorry to tell you, but your problem is gonna return. The solution is to add a drop of SEMI permanent thread locker or something equivalent that will hold the bolts where you leave them.

 

[MAC10]

I agree Chuck. Right now I have anti seize on the bolts, which works fine with normal gaskets. On these springy thick silicone ones, they eventually work loose because of the play. Extra time and maintenance to keep them tight. Convenience has a price.

How much risk is there of seizing bolts in the soft aluminum? Which threadlocker to use?

 

[chuck hahn]

That's why I stated SEMI permanent.. The red is a done deal.

 

[farmall]

Only if you are selling the bike to someone you really hate.
It goes on with a bit of grease so it can be taken off again without ruining it.

Or leaving chunks behind forcing you to scrape 'em off.

Grease or vaseline is the way to go for paper gaskets on the majority of surfaces. Besides working well, vaseline is clear.

Vaseline is also what to use on O-rings and seals which contact petroleum. It's been USAF practice for decades to have "butt putty" on bench stock.