I ordered a pair of rebuilt cylinder heads for my '08 Legacy (SOHC N/A version)
One of the new heads has a helicoil or similar installed in the spark plug hole. Looks like a neat enough job.
Is this concerning or is it fine/normal? I'm not sure what the industry norms are for rebuilt heads. In the past I always had my own heads rebuilt by local machine shops, so this never came up.
I don't want to be too fussy, but I also don't want to be insufficiently fussy- the heads are off and theoretically easy to return now. If there's an issue down the road it's going to be much bigger hassle. I'm hoping to hear from folks with more experience with this!
It wouldn't bother me as long as it was done in a tidy manner.
I used to pay extra money when I bought VW engine cases to get the ones that had helicoils where the studs all screwed in.
Aren't there a bunch of Ford engines out there where you should be more concerned if there *aren't* helicoils in the spark plug threads? 
I also wouldn't be worried if it appears well-done, but I would be sure to run iridium plugs in that engine to minimize the number of plug changes needed in the future, just in case...
GameboyRMH said:
Aren't there a bunch of Ford engines out there where you should be more concerned if there *aren't* helicoils in the spark plug threads?
I also wouldn't be worried if it appears well-done, but I would be sure to run iridium plugs in that engine to minimize the number of plug changes needed in the future, just in case...
It'll be fine unless it isn't. :-) I was hoping I could just whip sparkplugs in and out with reckless abandon, rather than wondering if this time was going to be the time the plug seized to the helicoil and ripped it out of the head. Realistically, there's most likely only 50K miles left to go in the bottom end of this engine, at that point it will have 200K, so maybe it's a non-issue?
wspohn
UltraDork
5/10/24 2:07 p.m.
That is a bonus, not a flaw.
I raced a quite rare DOHC MG engine and insisted that they install steel helicoils in all the plug holes - the alloy they were cast in was fairly soft and easy to cross-thread in a race situation when everything may be done in a hurry - eliminating at least one failure mode was worth it.
Must be an MGA twin cam you're referring to? Those were so cool.
Get the good plugs, they last 100K miles. Seriously, look at the helicoil very closely, magnifing glass close and if it looks ok run with it.
Done right they are often an improvement. The LH6 5.3 I have now has all 20 head bolt threads in the block with Time-serts in them, should be good for a long time.
Before installing the heads test fit the plugs to spec’d torque, use anti-seize too.
My off road racing VW engines had heli-coil plug holes and they never were a problem.
I might be tempted to go ahead and do the other 3 too. Just use a light coat of antisieze on the threads of the plugs
Hey,
I have run several 215 aluminum Buicks with Helicoiled spark plug threads.
One of the installations was a bare head on the workbench, the other was done with the motor in the car.
I installed all of the Helicoils. I did not have any problems with the parts or the installation.
YMMV.
Rog
IIRC some aftermarket aluminum cylinder heads are factory Helicoiled as they thought it would be more durable than threads into aluminum.
It seems like the consensus is "Yay." I always put antisieze on the plug threads anyway, that's a given. I like the idea of bench fitting the plugs to see if the helicoil holds. In the hopefully unlikely event the insert doesn't hold, it 's much better to discover it before installing the heads...
Thanks to everyone who chimed in!
I had a plug strip out on a two liter boxer (airplane) engine. Then I noticed it was already helicoiled. 
I bought a helicoil repair kit, it's over sized to repair the repair and it includes Time-Sert inserts. I like these better, visually it appears to give a better seal. IIRC it cost ~$400 but worth it.
If your helicoil jets out, give me a call, this is a fix to the fix.
