Don't Use Silicone On Gaskets

[ATC King]

Gaskets cost less than engine rebuilds.


If the stock gasket didn't have any additional sealer, it's not needed, and worse is it may cause expensive damage.


Generally, engine side cover gaskets are put on dry. A little wipe of oil doesn't hurt and may help them come off better later on. Silicone, besides being a pain to clean up, is a liquid and bolted between two surfaces it'll go all over places it shouldn't.

I don't know how many times I've seen this junk and every time I work on something where someone has used it I belt out choice words when I encounter it.

A previous owner had just about managed to destroy this engine by being cheap. Besides that, there were loose and broken parts. It very much looks methed up. If it wasn't someone on drugs, they were brain dead anyway.

The case has a passage for the transmission oil supply and they pretty much plugged that up.



The oil pickup screen was destroyed. It had become so clogged it distorted.


I also had a fun time removing all the silicone worms.



This engine runs, but I'm certain there's a lot of damage that has drastically shortened it's useful lifespan.

It'll get put back together and run until a big bore kit is put in. That's the owners plan. It has already been rode like this for a while, so we're going to run it until the smoke or noise becomes too much.

[Dirtcrasher]

It seems that most people have no clue how to use silicone. If both surfaces are flat, and free of defects, it takes a very small amount of sealant to seal the mating surfaces.

3 Bond, Yamabond, Hondabond, used very thin seems to be the best sealant I've used on engine cases.

There's no need for so much silicone, it does far more harm than good.

[ATC King]

For a better perspective of the thought process behind this past job, there are roofing marks on one part I'm replacing, a part bolted to the crankshaft, and it was very, very noticeably broken.

They definitely had no clue how to use a , mush less, silicone.


Luckily, the handful of parts that needed replaced were less than $50.


This job started out with just replacing both side cover gaskets because of leaks. Maybe if they used more silicone it wouldn't have.

[El Camexican]

I wouldn’t write silicon off completely if properly used. Back when I had to pull clutch and valve covers off multiple times per year I would start with brand new OEM valve and clutch cover gaskets and lightly coat both sides of them with silicone and hang them to cure. I could then re-use that gasket all season. The only thing that ever went wrong was if I got it hung up on an alignment dowel and tore it, and even then, I would just have to add a dab of silicone in that spot to keep using it.

I have no idea what they cost now, but 25 years ago a valve cover gasket for four cylinder Suzuki was C$65, and the clutch cover was nine bucks.

I wouldn’t do this with anything that was meant to stay together for more than a year, but this method allowed me to buy a lot more beer back then.

[ATC King]

You used silicone as a release agent, of sorts. I can see where that would work for a racing application but wouldn't be optimal for general use.

Lots of engines don't have an actual clutch cover to facilitate quick clutch replacement, the side cover is the clutch cover and that'd be a lot of gasket surface cleaning if removing and installing several times in a year.

A concern I'd have with dressing a OEM gasket would be tolerances on any parts supported on the case and cover and what shims may be in there to keep tolerances correct. A thousandth of and inch is a thousandth of an inch. If there's no parts between the case and cover that would be upset by that, then there shouldn't be an issue.


What I was addressing was the use of silicone in lieu of a gasket or to 'repair' badly torn one in critical areas.

I've got plenty of different RTVs I keep on hand, each designed for their own purpose, along with the Hondabond and Yamabond. Used correctly, they're great products. Pretty much anything is better than working with gaskets made from tree bark. I'm glad those days are past.

[Scootertrash]

It seems that most people have no clue how to use silicone. If both surfaces are flat, and free of defects, it takes a very small amount of sealant to seal the mating surfaces.

3 Bond, Yamabond, Hondabond, used very thin seems to be the best sealant I've used on engine cases.

There's no need for so much silicone, it does far more harm than good.

This

most shadetree "mechanics" use far too much.