That was unexpected

I recently purchased a 1970 skylark with a modified 455 engine (car belonged to the late Dennis Connell). After jumping through hoops with the DMV, I was able to get it on the road when I noticed a lot of hesitation. Fuel pressure was correct for the EFI system so I decided to change the spark plugs (lot of carbon buildup, so I thought I was on the right track).

Although I applied slow and steady pressure, it looks like each cylinder head will need one spark plug hole rethreaded. These are TA Performance aluminum heads, and while they make a kit to rethread I’m nervous about reinstalling the heads especially regarding the pushrods and adjusting the lash of the rocker arms. There’s actually a classic car restoration shop about 20 minutes away and I’m contemplating having the professionals do it. Thoughts?

 

Where are you located?

 

Connecticut. Shop has been in business for over 20 years and has a very good reputation. Understand that I’ve been waiting for this car for a long time and the last thing I want to do is damage the engine as I have no experience with these adjustments.

 

Before you go pulling things apart..

Is the hole that needs repair in each head accessible with it assembled?

Will a plug screw into the damaged threads, but just not tighten?.. have you tried it? I have been there and done this.. for many years, TA ran the spark plug holes on the low side of the spec.. the plugs would not screw in by hand. They then tended to gall when trying to remove them, taking a bunch of aluminum with them on the way out. There always seemed to be one that was worst than the others..

There are several options here, from thread chasers to spark plug taps, to kits that put a heli-coil in the head. All of which can be done on the car, with the engine assembled. If you have access and room to do it.. Obviously number 6 cylinder on that setup will be an issue, due to the AC box. WE want to keep any metal debris out of the crankcase at all costs, but in the sealed cylinders is a different story.. best to keep it clean, but a couple chips typically will just exit thru the exhaust, and cause no issue.

If it screws in, but won't tighten, don't be afraid to put some locktite 242 on it... the worst thing that is going to happen is it blows out.. which is no big deal. If it were my car, I might even put some epoxy on the base of the plug/gasket, to hold it it.

Then you can drive and enjoy the car, maybe for years, and then get set up to do the major repair, which is to install a heli-coil. That is best done with the head off, in a machine shop to precisely locate and angle the plug correctly.

If your not comfortable doing it, then take the car to several different shops, and get a professional opinion on your exact situation. Hopefully you can find an honest shop, who does not just want to separate you from a large chunk of your money.

But spark plug issues do not equal automatic engine tear down. Not always..

JW

 

Agree - had a stripped thread on a 6 cyl Jag engine. The holes are on top of the alum head centered over the piston. We just greased the tap to catch most chips and put the heli-coil in. No problem.

 

I spent almost 3 hours trying to get the spark plug started as well as with various angles. I even asked my wife to try it as her hands are much smaller than mine. I thought about trying to re-thread it while the head is still on the engine but it’s a tight space getting to the number seven cylinder on the driver side and number six was almost impossible with the AC box.

The previous owner had use a combination of AC Delco and Bosch spark plugs didn’t know about NGK but will keep that in mind. I also enjoyed reading a post on a different website stating that the reason these holes lose their threading is because the spark plug was in the engine for too long or have been changed to many times .

 

Just bought one as that was the only way I could figure to get to the spark plugs on the passenger side by the AC box. Thank you everybody for the information.