Spark plug thread disintegrated on no 2. All the others are fine. I can just about make out some of the thread but not enough to grip a plug. Any do's or don'ts, best repair kit to buy would be greatly appreciated as I will be tackling the repair myself. It's a 1968 MK2 240

 

https://uk.rs-online.com/web/p/threa...E&gclsrc=aw.ds

I've never done this job, so can't advise, but hopefully others will chime in.

 

Is the head off or is it on the engine ?

 

Hi Jeff

Still on the engine. I was just starting to tune the SU carbs and realised I hadn't changed the plugs. All play has now stopped until I get peoples thoughts based on experience of re-threading these old engines.

 

I think the biggest concern here is getting any aluminum bits into the combustion chamber no matter what you do.

Here's a video on the tool that Fraser linked you too _ I would use a good quality cutting lube, you don't want to gall the aluminum.

Personally if it was my car, I would use this as an excuse to do the valves, I would then do all the threads when the head is out.

I would even go so far as to make my own inserts, but that would require a lathe and a bit of skill to make an interference fit thread so the insert stays put.
Using lock tight wouldn't work because of the heat involved.
Maybe JB Weld, I don't know.

About 40 seconds in.

https://www.google.ca/url?sa=t&rct=j...wplj_qTTLJt1ZY

 

Here's another one where the guy uses an actual insert rather then the heli-coil type.
I think any aluminum bits that were left in there would simply get blown out into the exhaust.

 

The engine had a complete rebuild in 2012. I've owned it for the past 5 years and probably only driven 500 miles max. It's been sorn and dry stored most the time. House move and life intervened. No work needed head and valve wise so the thought of taking the heads off is the last option.

 

Removing the heads is just me being OCD and a perfectionist.
I've done so much major engine work over the years that removing a head isn't that big of a deal for me anymore.

I sure others will post, Homer Simpson will more then likely have something to add.

 

One of the first engines I removed and replaced was a 351 Windsor from a 1969 Mustang. It was out side my house in the street. I had to have the engine hoist almost over the wing to allow for the twist in the lifting arm as the camber in the road was so great. Over 40 years ago now but back then you did what you had too when and where ever you could. Happy days.

 

The danger in doing that sort of job with the head in situ is the risk of metal shavings falling in to the combustion chamber - If it were me I'd remove the head (Cheaper than having to rebuild the engine when the swarf
gets into the oilways). Good luck !

 

A genuine Helicoil does the job perfectly. We have done it in situ a number of times on friends Jag engines, Alfa engines etc. Cut the thread with a sharp tap & suitable lubricant. Wind in & snap off the Helicoil as directed. DON'T let a piece of Helicoil fall into the cylinder. It's hard as hell. (you would have to fish it out with a magnet). Use a vacuum tube to vacuum out any aluminium swarf. Should a small piece of aluminium remain in the cylinder it is soft, will do no harm & blow out the exhaust.

If you have any concerns get in a Helicoil service technician that does it every day. Not expensive ~ here at least. They just drive around from customer to customer putting in Helicoils day in & day out.

 

Thanks for this Glyn. I've just watched a YTube and a guy had to try and get not one but TWO helicoils out of the cylinder that had gone right through! I'm considering using the inserts with a shoulder.

 

My recommendation is to look at using a Wurth time sert kit . They have a special shoulder and the Insert is screwed in and then formed in place with a modified thread tap.

this means no breaking off the tang of the helicoil. We use this system for cast magnesium.

 

Hi Ron,
If I was going to do put an insert in with the head in place, I would use grease on the tap and not oil. That is what I was taught. The grease will hold the chips a lot better than oil. I wouldn't cut the threads all at once, I would back the tap out about half way and clean the tap. Then put fresh grease on it and finish cutting the threads. Also get a borescope and check the cylinder for chips before claiming victory. You may want to have the piston in that cylinder 1/2 way up on the exhaust strokes before you start cutting threads. So that if you blow the cylinder out the chips can go out the exhaust and not into the intake manifold to be suck in later.

Best of luck, let us know how it turns out.

 

The Helicoil guys here use high temp LOCTITE® 2620™ Threadlocker on Helicoils. They are not going anywhere.

 

This damage could not be helicoiled in place - no room for tools. Head removal could have allowed a heli coil, and I should have. Wasted a lot of MK2 time on the Chevy van and new heads


My van, not the Jag.

 

Hi Bob. That's a good idea. Thank for this. I've looked at the cylinder head with a camera so I should be able to see any debris. Lots of YTube say that the minute pieces of swarf should not be a problem. Probably going to use a reverse thread cutter too. Think I may stand more of a chance of keeping the tool in line. I'm going to suck, blow and whatever to clear it out. Incidentally I've found out that cylinder 6 has s helicoil in. I feel encouraged by all the responses I've had so thanks to everyone.
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And the plot thickens! Cleared debris away from no. 6 spark plug and found it has a helicoil in! It's not sitting flush at the top and I thought these should be installed a nats below. Is this correct? Should I leave well alone?

 

Does the plug crush washer achieve a seal? If it does I would leave well alone as long as the plug shows no sign of overheating.

 

Got to wait until I've repaired No.2 to test. Going to be interesting