Spark Plug Hole Too Big

Rob Hoehn /

I just got myself a 76 Batavus VA Deluxe. Thing rocks.

Somebody cross-threaded the spark plug threads and had it drilled out and re-threaded bigger. The old spark plug that is on it has some kind of spacer thingy to make it fit the bigger hole. Any ideas where to get another spacer? Now that I think of it I bet that spacer is supposed to stay in the head and not come out with the spark plug. Can't I just have a machine shop weld some metal in there and have it re-threaded at the right diameter?


Re: Spark Plug Hole Too Big

There are these things, I think are called

Re: Spark Plug Hole Too Big

Chris Robertson /

Helicoils are the way to go. I had to do this to one of my mopeds before.

It is dead easy to do. Here's the steps:

1. Remove the cylinder head.

2. Tap out the old spark plug hole to a larger diameter using the provided tap.

3. Thread in the Helicoil insert with some sealant (sealant not included).

4. Hit the insert a couple of times with the provided tool and a hammer to lock it into place.

5. Put the plug in.

It is super easy to do. However the kits are kind of expensive (I paid CDN$60 for mine at the local NAPA). Lots of motorcycle shops will put in a Helicoil for you for much less than this (I seem to remember them quoting me CDN$30).

You are right that the "spacer" is probably a Helicoil that's come loose (whoever installed it probably forgot to use sealant or didn't hit the insert hard enough during the whacking stage). Look around for Helicoil inserts, and maybe you can avoid having to buy the whole kit.

If you decide to do it yourself let me know and I'll consult my kit and tell you what kind of sealant to use.


Thread Inserts

There are also "Thread Inserts" for spark plugs... which are a a little different from Heli-Coils.

They are more or less a solid "sleeve" with threads on both the insides and outsides.

Whereas the Heli-Coil is a "coil".

Auto Parts stores carry both... ask them which is easier.

Re: Thread Inserts (Sav-A-Thread)

Chris Robertson /

Hi Fred:

It turns out I was talking out of my ass! I checked the package and I was using a product called "Sav-A-Thread" which sounds exactly like what you described (inserts with threads on inside and outside). Sav-A-Thread rocks! I must now confess I've never even seen a "Helicoil".

Rob: Replace any reference I made to "Helicoil" in my first message with "Sav-A-Thread".



Re: Spark Plug Hole Too Big

Ron Brown /


You should be able to unscrew the insert from your spark plug and re-use it with the correct sealant.

Try to find out what kind it is by taking it to an auto parts then follow the directions.

If it is difficult to get off the plug, you may be able to clean it and the thread in the head, then screw it in, wait a day or so and unscrew the plug, but make sure you use the reccomended sealer.


Re: Spark Plug Hole Too Big

get another head 4 a few bucks . seam easier. unless your looking for education .

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