Head bolt torque spec

Tom R S · Sep 30, 2023

Hi Guys,
Quite off topic here but I'm wondering if anyone knows what the head on a Johnson 20 hp outboard should be torqued to.
Replacing head due to stripped out sparkplug hole.

chuck machinist · Sep 30, 2023

(quoted from post at 17:00:06 09/30/23) Hi Guys,
Quite off topic here but I'm wondering if anyone knows what the head on a Johnson 20 hp outboard should be torqued to.
Replacing head due to stripped out sparkplug hole.

3/8 studs 18to 20ftlbs start at 10lbs in a cross pattern then 15lbs finish at 20ftlbs. cm

Hemmjo · Oct 1, 2023

Perfect place for heli-coil repair.

Steve@Advance · Oct 1, 2023

Best I remember they would be 1/4-20 or 5/16-18.

Can't remember using a torque wrench on them, just judgment feel They are
pretty forgiving, even reused head gaskets without a problem.

More important is to get everything clean, chase the holes, wire brush the
bolts, use antiseize, especially if going in salt water.

Tom R S · Oct 1, 2023

If a helicoil is used, do you have to use a smaller shank sparkplug?

Jim.ME · Oct 1, 2023

It would use the same size plug as before. You drill and tap oversize for the heli-coil and when installed the heli-coil brings it back to original.

Heli-coils will work, however if I had a good head, I would use it, not a heli-coil in the old head. Heli-coils have been known to stick to the plugs and come out on a plug during plug changes.

wore out · Oct 1, 2023

(quoted from post at 03:37:33 10/01/23) Perfect place for heli-coil repair.

I like Heli-coils for many repairs, but for a stripped sparkplug hole TIME-SERTS or their generic equivalent are a LOT better.

rustred · Oct 1, 2023

My opinion , its the worst place. I hate helicoils , just garbage.

chuck machinist · Oct 2, 2023

(quoted from post at 20:23:20 10/01/23) My opinion , its the worst place. I hate helicoils , just garbage.

I think Heli coils are the next best thing since French toast. I have had great success with them. Chuck Machinist

Dave G9N · Oct 8, 2023

(quoted from post at 12:23:20 10/01/23) My opinion , its the worst place. I hate helicoils , just garbage.

ou are certainly entitled to your opinion, which is likely the result of having had a bad experience with helicoils.

My experience has been pretty good with helicoils. If they do come out with the plug or get buggered up, they are not difficult to replace. Most kits come with a drill, tap and several helicoils, so you should have a few spares once you have installed one. Anti-seize is your friend here if you want the plugs to reliably come out of an aluminum head. I used to own several Corvairs, which had aluminum heads that ran 375 (air cooled engine), so any screw without anti seize might as well have been welded in.

Head bolt torque spec

Tom R S

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chuck machinist

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Hemmjo

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Steve@Advance

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Tom R S

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Jim.ME

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wore out

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rustred

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chuck machinist

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Dave G9N

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