stripped spark plug hole

**bill mason** · 05-14-2020, 05:39 AM

Not enough thread to hold heli coil. Can head head be heliarch welded and new threads tapped into it? Or any other fix?

Stay healthy have fun

**kellytheaker** · 05-14-2020, 06:22 AM

Time sert seems to be the fix from my look see . Give them a little read on the forum that comes up below this thread

**mike schmidt** · 05-14-2020, 06:36 AM

Drill and tap it 1/4" NPT. Screw in a brass pipe plug or reducer fitting really hard. Maybe a dab of green Loctite. Mill it off flush on both sides. Drill and tap it 14mm. Used this method to fix a bunch of the old Mercury "Stock Outboard" racing motors.

If you weld it, you take the heat treat out of the aluminum. Goes from T-6 to T-0 (dead soft). Not what you want on a race motor. Any kind of insert will act as a glow plug, because they are made of some form of steel and don't transfer the heat like aluminum. Brass transfers heat very similar to aluminum.

**Bateman** · 05-14-2020, 06:51 AM

Time sert worked well for me more than once.

My current boat has 2 cylinders running them.

**Dave Strong** · 05-14-2020, 10:39 AM

Time Sert

Dave

**Chaz** · 05-14-2020, 09:38 PM

Originally Posted by mike schmidt

Drill and tap it 1/4" NPT. Screw in a brass pipe plug or reducer fitting really hard. Maybe a dab of green Loctite. Mill it off flush on both sides. Drill and tap it 14mm. Used this method to fix a bunch of the old Mercury "Stock Outboard" racing motors.

Well lets apply some basic's here :

The correct bit for 1/4" NPTM is .4375 or 7/16"

The correct bit for 14 x 1.25 mm is .500 or 1/2"

It seems to me that all the work you do to put in a plug would go to waste when you drill it all out, or in the case of a stripped plug hole .. the 1/4 NPT tap would fall thru the hole before you even get started …

Those of us with ADD shoot the hole .492 with a bit and ream the final size to .499 and wind up with tight threads because of the tap used. Do your homework on taps , you'll learn why that is ..

If you weld it, you take the heat treat out of the aluminum. Goes from T-6 to T-0 (dead soft). Not what you want on a race motor. Any kind of insert will act as a glow plug, because they are made of some form of steel and don't transfer the heat like aluminum. Brass transfers heat very similar to aluminum.

I would also suggest that you buy a cheap spring loaded center punch .. and Ka-chink some actual T-6 material .. and then some outboard head and block castings to see the difference.
Out of the literally hundreds and hundreds of sparkplug holes I have welded , not one has ever pulled the threads out from being too soft .. I think the problem is not being able to weld a hole shut that has the same depth as diameter and keep the air pockets out ..

Think the seats fell out after welding the bores …

The studs pull out of this 911 Turbo head after welding the floors ..

How much heat do you think it takes to close these chambers up ..

How many plug holes failures do you think these heads have had …

Do you think this step turned "dead soft" and broke the first time someone stepped on it .. ???

I can go on and on …

**powerabout** · 05-14-2020, 09:42 PM

I thnk lots of plugs stripped because the heads were not hard as they should have been in the first place

**bill mason** · 05-15-2020, 05:50 AM

Thanks for quick reply guys. Much appreciated.

stay healthy have fun

**Chaz** · 05-15-2020, 10:20 AM

Originally Posted by powerabout

I thnk lots of plugs stripped because the heads were not hard as they should have been in the first place

Put down the half inch breaker bar and buy a quality inch/pound torque wrench … you'll be amazed at how much better the aluminum has become …

**Dave Strong** · 05-15-2020, 10:30 AM

Originally Posted by Chaz

Put down the half inch breaker bar and buy a quality inch/pound torque wrench … you'll be amazed at how much better the aluminum has become …

That old 1/2 turn after finger tight on gasket plugs only applies to the first time.

Dave

**Chaz** · 05-15-2020, 10:34 AM

Originally Posted by Dave Strong

That old 1/2 turn after finger tight on gasket plugs only applies to the first time.

Dave

That must mean on a used plug … ya go a full turn …

**InjectorService** · 05-15-2020, 12:10 PM

Originally Posted by Chaz

That must mean on a used plug … ya go a full turn …

The nice thing is once you've gone full turn once, it is easy to go full turn again!

**Instigator** · 05-15-2020, 03:05 PM

There is also a new tool out that goes through the plug hole, then expands to cut threads as you extract it and the shavings to be able to do one w/o pulling a head.
Probably designed for the new hi tech car motors that are so labor intensive.

Like a grand to put a water pump on a new Ford 4 or 6 banger!
I think 8 or 9 hrs flat rate!

**Dave Strong** · 05-15-2020, 04:16 PM

Originally Posted by Instigator

There is also a new tool out that goes through the plug hole, then expands to cut threads as you extract it and the shavings to be able to do one w/o pulling a head.
Probably designed for the new hi tech car motors that are so labor intensive.

Like a grand to put a water pump on a new Ford 4 or 6 banger!
I think 8 or 9 hrs flat rate!

Had those when i was at GM, special Cadillac and Corvette special tools. This leaving plugs in an aluminum head for 80k is nuts, threads tend to come with the plug.

Dave

**sonicss33** · 05-15-2020, 04:18 PM

Originally Posted by Instigator

There is also a new tool out that goes through the plug hole, then expands to cut threads as you extract it and the shavings to be able to do one w/o pulling a head.
Probably designed for the new hi tech car motors that are so labor intensive.

Like a grand to put a water pump on a new Ford 4 or 6 banger!
I think 8 or 9 hrs flat rate!

I think what you talking about is “Lock Stitch”. It is the only method approved by Ford for warranty repairs on the spark plugs that blow out. The proper alloys match the Ford heads and expand and contract at the same rate.