Spark plug thread repair

[233sqn]

just blown a plug clean out of my 1725 Ali head Rootes engine.....anyone had any experience of using the Draper Spark Plug repair kit?

Can it be done in situ?

advice welcomed!!

[classic chris]

Hi, I had exactly the same thing happen to my mark 2, I used a complete kit that i got off ebay, reccomended by someone on the old forum. You retap a new thread then put an insert in , worked a treat. I did it all in situ , no problems at all. I'll pop out to the workshop tomorrow and find the make.
Hope this helps.

Chris

[johnc]

I can't help with the problem but I am alarmed that a plug could be blown out of the head.
I am about to fire up my Rapier fitted with a 1725 engine after a total rebuild and don't want a Champion missile bouncing around the garage,how did it happen and how can it be avoided?
If you do need to replace the head I do have a spare standard (non Holbay) head but as I'm in France it's of little use,but they do crop up quite often on e-bay or try one of the Rootes clubs (Sunbeam -Apline,Rapier etc.etc.)
Best of Luck
Johnc

[JPB]

....If you do need to replace the head I do have a spare standard (non Holbay) head but as I'm in France it's of little use,but they do crop up quite often on e-bay or try one of the Rootes clubs (Sunbeam -Apline,Rapier etc.etc.)
Best of Luck
Johnc

Bear in mind that the order of the ports, hence the camshafts and manifolds, are different between the ali and iron heads on these, so to swap over from one to the other, you'd need to fabricate a fresh bit of exhaust front pipe and keep the head together with the manifolds that belong. That's typically when you'd discover that the camshaft isn't a straight swap and give up in disgust before simply swapping the engine and mounts over.
I discovered that the hard way with this:

Which ended up with an all-iron engine and hand made exhaust system to overcome that particular hurdle.

A plug won't routinely blow out unless the thread in the aluminium is damaged or it hasn't been tightened quite enough after replacement. DO NOT overtighten the plugs in an alloy head as that's usually what strips the thread in the first place.

[Wicksy]

The Draper kit is a form of "helicoil" thread insert whch has been around for almost as long as parts have been bolted together.
Can you use it in situ
Yes if you are very careful and can prevent swarf and metalic debris and the broken off tang dropping into the cylinder head.
Coiled up greased cord fed through the plug hole can catch the swarf from the drilling and tapping operation and coating the drill and tap with grease will also make most of it stick to the tools.
The tang or driver for the coil has to be snapped off after insertion so having a decent pair of long nosed pliers of the correct size is useful although If you are unlucky enough for this tang to drop into the cylinder head the coiled cord should catch it.
I have fitted many helicoil inserts over the years and have to say that it is a relativly straitforward job and works as well or better than the original thread - the key is carrying out all the steps properly with the correctly sized drill tap and insert.
Good luck and take your time - the main problem is the tang breaking off when the coil is only partially inserted and then having to remove the coil and start again; poor tapping is the usual cause.

[Wicksy]

PS. Just seen a pic of the Draper kit on Amazon and it does not seem to incude a drill so the operation would be a shortcut of the full procedure - I would chance it though, better than taking the head off

[233sqn]

I managed to win a Draper kit on EBay for just over £20…. Much better than the £40 -£50 they seem to go for!!

Although I haven’t actually seen it in the flesh yet, nor any instructions, looking at various pictures on the net I concluded;

• You don’t need to drill…. The tap is stepped with a sort of tapered reamer between steps to take the hole out to the correct tapping size. Mine is an Ali head too, so probably easier to do

• The inserts don’t have tangs (as far as I can see in the pictures)

• You get an “expander tool”….. I can’t work out what that is for!!

There is another insert set available on EBay… goes for around £5, and uses a more solid insert but what appears to be the same tap. There is a video of it in use on you tube. It shows the insert being screwed onto the spark plug, then the whole screws into the head.