Spark Plug Issue

[Thomas]

While doing a tuneup today I came across a problem. I was installing new plugs and when doing the number 4 cylinder in stopped half way in. I screwed it out and tried again but it stopped again. I tried the old plug and the same thing. Not sure what happened to the thread but I don't want to force the issue. Not sure but I was thinking of chasing the thread (14mm x 1.25). Is it OK to do with the head in place or am I better off to pull the head off? Thanks Tom

[somevwguy]

I had the same thing happen to me, I don't remember what size tap I used, but I took a spark plug to a machine shop and they had one the same size. I covered it in grease to catch most of shavings and did it with the head on because with the type IV I would of had to pull the motor out of the car.

[BUSDADDY]

Head off is best, but grease on the thread chaser (any FLAPS will have one) or a shop vac in reverse blowing pressure into the exhaust (turn the engine until that exhaust valve opens) will keep the majority of the chips out of the cylinder. It kinda depends on just how bad the threads are chewed up, since it's out of the car now it'll be easier to install a thread insert if you have to.