Decomp Blew Out

Shanesaw80 · Dec 10, 2019

Hey guys while running my saw yesterday I had my decomp blow out and strip all the threads. First time something like this has happened to me, scared the *s-word out of myself for a second when it happened, quite the noise lol After talking with a couple of guys they both suggested drilling and tapping the threads to the next size up and plugging the decomp which sounds easy enough. I'm just wondering if any of you guys have done this before and if so what size and thread of tap did you use? Any info is greatly appreciated!

Shanesaw80 · Dec 11, 2019

Does anyone happen to know what size and thread the stock decomp is, that way I have a starting point?

Bjorn · Dec 11, 2019

You can use one like this, and then put a new decomp in.

qurotro · Dec 11, 2019

Thread should be M10x1.0.

Shanesaw80 · Dec 11, 2019

Bjorn said:
View attachment 212044 You can use one like this, and then put a new decomp in.

You trust a helicoil enough to put in the cylinder head?

Bjorn · Dec 11, 2019

Yes I do, sealants on the treads an it Will be tight. I Done it on the spark plug treads in many cylinders.

Al Smith · Dec 11, 2019

Well if you cut to the chase the new hole size and thread would be whatever size the replacement decomp would be .

Al Smith · Dec 11, 2019

BTW a simple way to find tap hole size is major diameter minus one thread spacing,not to confused with thread count For example a plug hole generally is M14-1.25 so the tap hole is M12.75 .On SAE 3/8"- 16 would be 5/16" . As simple as that is most tool and die makers have to use a chart .

srcarr52 · Dec 11, 2019

Shanesaw80 said:
You trust a helicoil enough to put in the cylinder head?

Heli-coils work well on decomp threads. Since it's a small pitch the final hole is still small enough that the decomp crush washer seals.

KS Plainsman · Dec 21, 2019

Al Smith said:
BTW a simple way to find tap hole size is major diameter minus one thread spacing,not to confused with thread count For example a plug hole generally is M14-1.25 so the tap hole is M12.75 .On SAE 3/8"- 16 would be 5/16" . As simple as that is most tool and die makers have to use a chart .

That's a great tip Sir! Thanks, I didn't realize that!

Deets066 · Dec 22, 2019

I believe they make a time-Sert for that size too. I trust those over the helicoils. @drf256 may have some input on em, I believe he has used em in plug holes

drf256 · Dec 22, 2019

Deets066 said:
I believe they make a time-Sert for that size too. I trust those over the helicoils. @drf256 may have some input on em, I believe he has used em in plug holes

Never did a decomp hole with a timesert.

Ive used the Stanley branded timesert-like plug hole repair I bought off amazon for plug holes. I did buy M14 timesert, but never the kit. The biggest issue is keeping the axis of the hole exactly 90* in all directions to the plug pad on the cylinder.

Shawn is the man for plug hole repair. I’d trust his advice without reservation.

For a decomp hole I’d just find the next size up, tap it, and plug it.

Al Smith · Dec 22, 2019

I'd go with the next size larger myself rather than a coil .

Bjorn · Dec 22, 2019

There are many ways to plug a hole.

Decomp Blew Out

Shanesaw80

Tree Assassin

Shanesaw80

Tree Assassin

Bjorn

Pinnacle OPE Member

qurotro

Cookie Cutter

Shanesaw80

Tree Assassin

Bjorn

Pinnacle OPE Member

Al Smith

Here For The Long Haul!

Al Smith

Here For The Long Haul!

srcarr52

Shop rat, backyard slice cutter.

KS Plainsman

Here For The Long Haul!

Deets066

AKA Deetsey

drf256

Dr. Richard Cranium

Al Smith

Here For The Long Haul!

Bjorn

Pinnacle OPE Member

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