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MG TD TF 1500 - Tidbit I wanted to confirm (off topic)

I am rebuilding a 4 cylinder Continental motor in a commercial air compressor. One of the spark plugs left its threads in the head.

I took one of the other plugs to the auto store to get a tap to chase the threads and I find out the threads are metric. This is a 1960's compressor built in the US.

The guy at the parts store said all spark plugs are metric?

Is that correct?
Bruce Cunha

Yep
Most are 14mm now, some older engines were 18mm
Motorbikes and outboards etc 10mm or 12mm
And then they measure the length of the threads in inches, like 1/2" reach or 3/4" reach etc
Bit weird really, like tyre sizes, width in mm and rim size in inches
Cheers
willy
William Revit

I guess it depends on how old the plugs you're talking about are. 1960s, yes I would imagine those are metric.
Steve Simmons

Rather than a tap, look for a spark plug thread chaser. They are commonly available for those who manage to cross thread a plug. Any larger auto parts store should have them. A tap has the chance to cut into the metal in the head which you don't want to do.
e.g.
https://www.amazon.com/Spark-Thread-Chaser-JTC-1618/dp/B072LRP9WZ/ref=sr_1_49_sspa?dchild=1&keywords=spark+plug+thread+chaser&qid=1586026589&sr=8-49-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFGNlhCSEdHMjlISVMmZW5jcnlwdGVkSWQ9QTA0OTAwODczQk5IMks2RTJWRFNWJmVuY3J5cHRlZEFkSWQ9QTA4MTkzNDFBTFNTVEpFM08yUVkmd2lkZ2V0TmFtZT1zcF9hdGZfbmV4dCZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=
Lew Palmer

I agree with Lew. A tap may cause more damage than it fixes. I bought my spark plug thread chaser at my neighborhood Advance Auto Parts. It has both popular sizes of threads. I had my head off, so I chased it from the inside out.

Lonnie
TF7211
LM Cook

I agree, a chaser is always a good idea. Better to re-form the threads than take metal away from them.
Steve Simmons

Thanks all. Yes, the auto shop sold me a sparkplug thread chaser, not a tap.
Bruce Cunha

Rather than a tap, look for a spark plug thread chaser. They are commonly available for those who manage to cross thread a plug. Any larger auto parts store should have them. A tap has the chance to cut into the metal in the head which you don't want to do.
Lew Palmer

Just out of interest, how much does that Amazon thread chaser cost?

I clicked on the link, but it says they don’t ship to the UK, so it’s not showing the price.
Dave O'Neill 2

Dave,
There are loads of them on fleabay!
https://www.ebay.co.uk/itm/WM-Tools-Spark-Plug-Re-Thread-Chaser-Tap-Set-10mm-14mm-Damaged-Repair-Cleaning/201647968092?hash=item2ef327cf5c:g:lHUAAOSwD5ZZ210v
Regards
Declan
Declan Burns

Just out of interest, how much does that Amazon thread chaser cost?

$8.40 Dave. $7.41 Carriage

Mike
TF-8257
M Brand

This thread was discussed between 04/04/2020 and 07/04/2020

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