Plug thread size different on same engine

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Jun 11, 2015 | 07:54 PM

nukeone01

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From: Ohio

Plug thread size different on same engine

I have a 2003 1200 custom sportster. When I started to check spark plugs I found one plug was a larger thread and the plugs were different. I'm new to Harley's but I'm almost positive this isn't the way it should be. Has anybody seen this before? If so what can be done to correct this problem besides buying a new head?

Jun 11, 2015 | 08:03 PM

Harleycruiser

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From: North Florida

Quote:

Originally Posted by nukeone01

Someone has stripped the treads and re-tapped to a larger plug.
There are tread repair inserts like helicoil and time sert, or you could have the head welded and re cut, or strip the other and drill it larger.
That Or ride it, that would not bother me at all.

Jun 11, 2015 | 08:05 PM

senna

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From: San Jose

Someone probably stripped the threads and just went to the larger (14mm IIRC) thread size.

You could research thread serts or similar and see what size thread a 12mm repair sleeve threads into.

Jun 11, 2015 | 08:14 PM

nukeone01

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From: Ohio

Quote:

Originally Posted by Harleycruiser

Thanks what would be the two plug numbers u would use?

Jun 11, 2015 | 08:18 PM

nukeone01

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From: Ohio

Quote:

Originally Posted by senna

Someone probably stripped the threads and just went to the larger (14mm IIRC) thread size.

You could research thread serts or similar and see what size thread a 12mm repair sleeve threads into.

Thanks what two numbers would u use for the new plugs?

Jun 11, 2015 | 08:45 PM

senna

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From: San Jose

Quote:

Originally Posted by nukeone01

Thanks what two numbers would u use for the new plugs?

Not knowing what size your cyl head has been oversized to, I would find the correct insert to reduce the thread back to factory size, 12mm I believe.

The kits can get expensive. so for a one time job you might seek out a local shop that could do the repair. Might be cheaper in the long run.

This is a sample of the repair kits

http://www.timesert.com/html/sparkplug.html

Jun 11, 2015 | 08:49 PM

Harleycruiser

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Joined: Apr 2012

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From: North Florida

Quote:

Originally Posted by nukeone01

Thanks what would be the two plug numbers u would use?

Stock plugs are champion, I would find a supplier that sold them and ask them to get the same heat range resistance etc, in the different thread size.
Stock is RA8HC.
What is in there now?

Last edited by Harleycruiser; Jun 11, 2015 at 08:52 PM.