Spark plug thread chaser?

[Buzetti]

Help!, I have a problem with one of my spark plugs.

I thought I would pop the plugs out and get and idea on how my engine is running/ tune.

Previously, the plugs have been changed by my garage – I have never removed them myself previously. But, removing, inspecting and replacing 6 spark plugs - what could possibly go wrong?

Well, working from the front of the engine, first plug came out and went back in fine.

Next plug - seemed very tight on removal - and now won't tighten down more than about two thirds of the way.

I have tried cleaning/ lubricating the threads and have been very careful not to cross-thread - but to no avail. Tried a different plug - same problem

So, I am guessing the thread is damaged - I am thinking I need to get hold of a 'spark plug thread chaser' tool in 14mm size?

Does that sound the right approach?

If so, any tips on how to use the tool please? I am particularly concerned about debris/ swarf from the 'chasing' ending up in the cylinder – who can I prevent that from happening please?

How much ‘force’ does the tool need to get to the bottom of the thread?

Any comments/ advice/ tips/ dangers would be very gratefully received
Many thanks in anticipation

[piman]

Hello Buzetti,

that would seem to be the next course of action. You can buy a chaser relatively cheaply or evn easier, if you have a grinder is to grind some grooves down an old spark plug.

To help reduce the debris (I would say impossible to entirely eliminate with the head on) grease the chaser to capture the debris. Screw it in, ensuring it is vertical in the hole, screw in a couple of turns, then back off a turn continuing until you reach the bottom. Take it carefully and don't force it.
I use a smear of copperslip type grease on my plugs to ensure they don't get too tight, just keep it away from the tip.

Alec

[Buzetti]

Thanks Alec - I have ordered a chaser tool and will take it very carefully....

I guess I may find the need to use some force (given the plug gets completely stuck) - what is rthe worst that can happen do you think?

Is this a common problem with a 50 year old aluminimum head I wonder?

[piman]

Hello Buzetti,

It should not take as much force as you think, basically the plug is tight because the thread has built up some debris on the threads, the chaser has lands that allows this debris to escape as you screw it in. To retain most of the debris will probably need a few goes of screwing in a couple of tuurne then removing it to wipe off the rubbish, re grease and go again. I would not be too concerned about what falls in the cylinder as it is soft and will soon be blown out once the engine runs.

The worst scenario is stripping the thread which will entail having a heli coil insert fited.

Alec

[Buzetti]

Thanks Alec.

Bought a Clarke spark plug chaser off e Bay, plus a tube of copper grease.

Greased-up the chaser with Vaseline and started to work my way gently put persistently down the thread - using my small Halfords ratchet and a spark plug socket -back and forth, back and forth - the threads got quite tight about half way down and I was pretty nervous about possibly making the matter worse, but I applied a little more firm pressure and just went down a bit further each time, until I reached the bottom (couple of hours careful work) - not much obvious 'debris' but to be on the safe site, stuck a tube down the hole and sucked it out with my mouth (!) - a few bits of crud came up, but no obvious metal shavings.

A dab of copper grease on the plug and in she went, nice and smooth, all the way (finger tight most of the way, finished off with a gentle tug on the ratchet - but not too tight)

Problem solved with a £5 tool (which was a nicely made item for a fiver) and a couple of hours patience - I was terrified about having to helicoil and possibly remove the head!

Ignition on,tick tick from the fuel pump, a dab of choke and she fired on all 6 first turn!

Ordered my new fuel tank (from Norman Motors) in celebration!

Cheers

Buzz

[piman]

Hello Buzz,

good job, being careful, as you did, is the key. It is normal to be able to screw the plug all the way by hand so it seems you've sorted that problem:-).

Alec