Topic: Spark plug hole threads are stripped. What do I do?

[Dr. Honda]

Thanks for all the responses.

I ended up pulling the head to have a better look at it.  The threads are only messed up half way down.  The spining that was happening was the plug screwing through the stripped threads and then not lining up with the good threads and just turning.  So I ordered a back tap off ebay, that should straighten it out good enough, there will be plenty of good threads for the plug to bite. 

Heres the link to my build in the project forum if you want to see the project.

http://forums.sohc4.net/index.php?topic=78283.0

thanks again for all the help.

[camelman]

If you use a tap coat in thick grease. this will catch 99% of the shavings.

 
Someone wrote:
" The sparkplug will not seal against a cheap helicoil, and you will get blowby every time that cylinder compresses and/or fires"

Say Wha? I tapped and helicoiled my ford truck and I've put 10,000 hard miles on it no problems since. Including a trip halfway across the US and Canada @ 14 hour days and towing my boat 1000 miles roundtrip over two mountain passes each way. And the timesert is nothing more than a fancy over priced helicoil (same idea same result) but at 10X the cost.

The one good thing is the SOHC4 head is relatively easy to take off, unlike my F150.

I know this thread is done, but I just want to clarify the issue I had.  The end of the helicoil has to be flattened where the spark plug washer contacts it.  That is where I got blowby.  I didn't do the helicoil myself, and just assumed it was done right.  I ended up doubling the washers (one slightly larger one against the cylinder head) to get a seal.  The blowby didn't come from the threads, it came from where the spark plug washer didn't contact the head well.  I'm sure there are better options for helicoils too.  I think the one I had installed wasn't appropriate for the task.

[crazypj]

camelman, Helicoil probably wasn't done right and wasn't 'square' to surface
 The end should be one full thread below surface, something a bunch of people get wrong

[MCRider]

camelman, Helicoil probably wasn't done right and wasn't 'square' to surface
 The end should be one full thread below surface, something a bunch of people get wrong

In my experience the "drive tang" of the helicoil may break off before the coil is down far enough, creating a second problem. I know this has to do with hole preparation before turning the coil in, but it has happened to me and I thought i was prepped pretty well. Then you have to snip off what's left, which may not be flush with the top of the hole. Or drag the whole coil out of the hole and start over.

[crazypj]

Only time I've seen drive tang break off premature is when hole wasn't tapped deep enough and it bound up on the taper section left by tap. You have to have 'full thread' for at least length of helicoil plus two threads (they get smaller diameter but 'longer' when installed)

[MCRider]

Only time I've seen drive tang break off premature is when hole wasn't tapped deep enough and it bound up on the taper section left by tap. You have to have 'full thread' for at least length of helicoil plus two threads (they get smaller diameter but 'longer' when installed)

That's what i meant by hole prep. I'd never heard of the extra 2 threads, but makes sense. My prep may not have been good enough. Hence the warning, if the tang does break, its a problem.

[Duanob]

I know this thread is done, but I just want to clarify the issue I had.  The end of the helicoil has to be flattened where the spark plug washer contacts it.  That is where I got blowby.  I didn't do the helicoil myself, and just assumed it was done right.  I ended up doubling the washers (one slightly larger one against the cylinder head) to get a seal.  The blowby didn't come from the threads, it came from where the spark plug washer didn't contact the head well.  I'm sure there are better options for helicoils too.  I think the one I had installed wasn't appropriate for the task.

There are two types of insert plug contact: Crush washer and V-angle seats. getting them mixed up could cause serious blow by. Older cars use the washer, newer cars like my ford use the angled seat. I think I like the washer as it adds pressure to the plug so it won't loosen up. On my truck I have to retorque the plugs about once a year for peace of mind. Otherwise due to expansion and contraction of aluminum head material, they can back out to the point of only a few threads holding them, then they blow, then you have to re-tap and use the insert. Unfortunately a common problem with Ford. Good thing Ford doesn't make a motorcycle!