stripped spark plug hole...

So, it's not a Kawasaki, but I manage to have a Honda 350 with a stripped spark plug hole.

I REALLY don't want to pull the head, mainly because it's not my bike and I'm reviving it for a friend. Aside from finding a new head off ebay or something, what are my options?

Put in an insert. Use lots of grease on the tap. The cuttings will stick to the grease.

The initial threads may be cross-threaded (often resulting from some earlier ham-fisted plug installation) making it impossible to get a plug properly started into the hole.

Often, there's a lot of good undamaged thread remaining deeper inside the hole past the shallower cross-threaded area.

The challenge then becomes how to perfectly re-thread the shallow cross-threads to sync perfectly with the deeper good section.

It may be possible to re-cut the cross-threads by starting at the deep end with a reverse tap, also known as a back tap.

The reverse tap inserts all the way through the spark plug hole, and then the tool's deep end expands to begin tracking along the good threads from the deep end, and re-cuts the cross-threaded section as the tool proceeds upward and out of the hole.

It's akin to having the head off, and re-threading the hole in the normal manner starting with the good threads on the piston side of the plug hole.
A reverse tap accomplishes the same result, but without needing to remove the head.

Here's a pic of the reverse threading tool.



Good Fortune!

Thanks Patton, I never knew what a back tap was or what it was for. A good tool to have in the arsenal.
Wayne

OK guys, thanks for your help. Tried to get motor out of frame, but someone welded the shifter on, hence can't take the sprocket cover off, hence no motor out of frame, hence no head off motor to do this job, therefor, pissed off Andy. It's all back together now and I'll grease the tap up and use air while drilling/tapping to blow shavings out.

The real question...I have a steel timesert...Can I use it, or should I get an aluminum one?

I've used those repair/insert kits before with good results.

whatever you do, bring that cylinder up to TDC and lock it there. In case anything falls in and so you can vacuum out any debris.

Kidkawie,
I agree. I think my plan was to have it positioned just a hair after the intake stroke, that way the intake valve is opened, but not full open. The piston would be slightly lower too (that way I don't hit piston or valve with bit or tap). I planned on having my shop vac or aircompressor blowing air into the intake and hopefully out the spark plug hole as I drill and tap. Afterwards I planned to slowly rotate back to TDC and vacuum out any remaining debris. I also planned on greasing up the tap so the shavings stick to it.

What about the steel insert in the aluminum head? that ok?

apbling wrote: ...Tried to get motor out of frame, but someone welded the shifter on, hence can't take the sprocket cover off, hence no motor out of frame, hence no head off motor to do this job...The real question...I have a steel timesert...Can I use it, or should I get an aluminum one?

Engine head may be readily removed with engine remaining in the frame.

Where a timesert is needed to replace and serve as threads in an aluminum engine, would use a timesert made of steel. I didn't know timeserts constructed of aluminum were available.

Good Fortune!

I did this on my KZ1000 several years ago. Used a shopvac to suck up shavings as the tapping took place, plus sucked everything out of the cylinder. Fortunately my dad (a professional mechanic) has a cool little fiber optic scope that let us look around inside the cylinder and on top of the piston to make sure we got everything out.

It has been in for many years and many miles, with plugs going in and out and I have had no issues with it.

apbling wrote: What about the steel insert in the aluminum head? that ok?

No prob, spark plugs are steel. You need to locktite the insert in place.

excellent, sounds great and I have all my tools. I have access to a little camera scope, but it's a little big to fit in the hole...

Yes, blue loctite was in my plans.

Patton - Head cannot be removed. It's a 73 Honda CL 350 and the studs run from the case, through the jugs and cam cover. All that can be removed in frame is the cam cover.

apbling wrote: ...Patton - Head cannot be removed. It's a 73 Honda CL 350 and the studs run from the case, through the jugs and cam cover. All that can be removed in frame is the cam cover.

Thanks, apbling!
Should have remembered that. :ohmy:

If needed, here's a link that provides a free downloadable Factory Shop Manual.
www.mediafire.com/?5f3menxnmzm

Good Fortune!