Air leaks at the spark plug or decomp threads...

[PogoInTheWoods]

What's the sealant of choice for these occasional leaks? I've run across a few and have used everything from LocTite to Dirko to even JBWeld to re-establish a hogged out seat on one plug thread fix that also needed a heli-coil. I've also let a couple slide by that weren't all that bad and didn't detect any noticeable performance issues like you would expect from a bad seal or other type of case or intake leak. Also hafta wonder how many saws that were tested through the plug hole actually have a leak there once a plug is installed.

Just did a MS361 rebuild with an aftermarket top end and have leaks at both the decomp and plug threads with a brand new dual washer decomp substitute bolt and brand new NGK dual washer plug installed. Gotta wonder how common it is with the AM kits (but overlooked), too.

Kinda frustrating to say the least.

 

[TreeLife]

Toss some Teflon tape on thar and try it again...

 

[Czed]

Motoseal hasn't failed me yet.

 

[BuckthornBonnie]

Are the leaks way out of spec?

They're probably tuned out on most saws... not sure about comp loss, tho.

My personal preference would probably be a Dirko-like material. I use it on decomp plugs all the time. 518 may not be the best.

But isn't the seal broken each time the spark plug is removed?

 

[Lee H]

Hard to find a sealant that will take the heat. If threads are loose enough
to cause a compression leak I would repair the threads. A temporary repair
will eventually fail.

 

[Homemade]

My vote is for teflon tape. I know it holds up to steam fittings where pipe dope will melt out.


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[drf256]

My vote is some thick grease.

Too much teflon tape could insulate the plug.

But like Lee said, fix it right, once.

 

[drf256]

FWIW

Any vac leak above the upper transfers won't affect tune, or ruin a saw.

 

[Homemade]

I was referring to the decomp plug. If the spark plug is leaking, then the threads are junk and it will need a time sert or helicoil. or the washer is junk and you need a new plug.


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[cus_deluxe]

Anti-sieze lube

 

[stihl livin]

^^^this right here^^^

Use the high temp nickel or copper stuff. When I was at the paper mill we used Teflon and anti seize and that was with steam.

 

[PogoInTheWoods]

Some good input, guys. 'Preciate it.

Dirko HT is good to 500+ degrees and also retains its elasticity for fairly easy removal/cleanup. I've been successful with it on the couple of occasions I've gone that route. The anti-sieze approach makes sense. Sounds like it sorta depends on what you generally have on hand otherwise, eh?

Even good threads are gonna leak. Gasket (washer) seats are gonna get roughed up. Plugs get pulled and checked and reused all the time. Washers get flattened and leak. Was just curious if there was a common sealing approach..., or if folks even worried about it at all unless it was severe.

I'm real picky about the results of my vac/pressure testing when it comes to case (bottom end) and intake integrity. I'll let a minimal top end leak slide on occasion (depending on the saw and general use considerations), but would rather be tight all the way around on every saw..., just because they should be.

 

[Basher]

I have found the seat area the plug squish washer tightens down on to be really rough and sometimes not square to the plug thread bore so the washers cannot make a tight seal. A flycut on the endmill solved that issue, these AM jugs are not well machined.