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Should spark plug inserts be used at all on LS heads?
I have an LS2 that I picked up with a cross-threaded spark plug hole. And I was thinking of repairing it using a Time Sert. But is this REALLY a good idea? Or should the head be replaced. Of concern is the red circled area shown below.
That wall is VERY thin, and will only be made thinner when the hole is enlarged to accommodate the insert (interestingly enough, I can find NO pictures of this). To make matters worse, this is the area where the insert will be tightened up against the internal threads to hold the insert in. It just seems like this weakened, thin metal might eventually break off. Is this something that I (or anyone else considering an insert to repair a damaged thread) need to be concerned with? Should I just replace the head? Or am I just overthinking what could go wrong with my motor?
Last edited by StorminMatt; Jun 16, 2017 at 05:38 AM.
Have you tried chasing the thread first from the inside out? Did someone actually cross thread it the whole length or just part way?
I would be more inclined to use a full length heli-coil for home repair or contact a good head shop like AI and get their input before attempting any repair.
That head looks like bad things happened to the spark plug when it was running..
This is actually a different head from the one that is actually on the motor with the bad spark plug threads. This one is a 243 head I picked up cheap with no valves or springs last fall. Apparently, they were used on a 6.0 blower motor. It DOES look like they have been ported, though.
Time-Sert. You know, you don't have to use an insert that's the full 3/4" length. You can use a shorter one that leaves the chamber-exposed portion of the hole intact. Then run a tap through the full depth, using the insert as a tap guide. The Time-Sert WILL NOT come out.
Time-Sert. You know, you don't have to use an insert that's the full 3/4" length. You can use a shorter one that leaves the chamber-exposed portion of the hole intact. Then run a tap through the full depth, using the insert as a tap guide. The Time-Sert WILL NOT come out.
Not possible, at least with the tooling provided. The way that the step tap and seat cutter work, you must tap a new hole all the way through. You can always USE a shorter insert. But it will still leave a VERY thin wall. To do things as you say would require fairly accurate use of machine tools. And the trouble and expense of having that done would probably not be justified vs just buying used 243 heads.
Find a good air cooled VW machine shop,, this is every day for them. There are some inserts that require a machine shop but you end up with a steel lines spark plug hole, don't know how savvy the shops are these days But I used to have all the spark-plug holes done as well as the holes in the case for the head studs.
I suppose another good question to ask is just how many threads are required to hold in a spark plug? In other words, if a hole has half of its threads, is this good enough?
Thread depth has to equal the diameter of the spark plug...
It isn't. I have maybe 6-7 good threads (or roughly 7.5-8.75mm). Then again, I would figure that there is at least SOME chance that the damaged threads may be able to contribute to holding in the plug to some degree once chased. It is just impossible to know whether it will be enough.
Last edited by StorminMatt; Jun 21, 2017 at 06:22 AM.
Here is what I did. I took a reamer the size of the hole before it was threaded and ran it from the bottom to the top. Then I got the next size and did the same thing until the threads were gone.
I flipped the head and ran a few reamers from the top down part of the way until it was opened up to the keensert size. That was 10 years ago and close to 130k miles.
The time sert preserves the taper where the spark plug seals, think I would go that route myself. You will need to be careful on the machining though. After seeing the photo, I would fix this prior to using the head and not try chasing threads and then blowing out a plug.
The early Ford V10 engines had a big problem with blowing spark plugs out, you might research how Ford repaired those heads in the field.
Here is what I did. I took a reamer the size of the hole before it was threaded and ran it from the bottom to the top. Then I got the next size and did the same thing until the threads were gone.
I flipped the head and ran a few reamers from the top down part of the way until it was opened up to the keensert size. That was 10 years ago and close to 130k miles.
HSS reamers on ebay are cheap.
Those Keenserts are HUGE - MUCH bigger than a Timesert. Was there anything left of the spark plug boss that extends into the combustion chamber after you reamed the hole? Do you have any pics?
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Should spark plug inserts be used at all on LS heads? 
Not possible, at least with the tooling provided. The way that the step tap and seat cutter work, you must tap a new hole all the way through. You can always USE a shorter insert. But it will still leave a VERY thin wall. To do things as you say would require fairly accurate use of machine tools. And the trouble and expense of having that done would probably not be justified vs just buying used 243 heads. 
