Bob Lister 142 #1 Posted November 22, 2022 I have a 67 JD 112 with a HH100. It had a blown head gasket that ruined the head. I got a used head for it but the spark plug hole is 9/16 instead of 1/2" What plug will I need to use this head? 1 Share this post Link to post Share on other sites
Snoopy11 5,718 #2 Posted November 22, 2022 3 minutes ago, Bob Lister said: I got a used head for it ...and I doubt you know what model engine the used cylinder head came off of? Hmm... I have heard of people using 14 to 12 millimeter thread adapters... never used one myself though... Don 1 Share this post Link to post Share on other sites
Jeff-C175 7,206 #3 Posted November 22, 2022 (edited) 3 hours ago, Bob Lister said: What plug will I need to use this head? Maybe take a look at the spec for the original plug, heat range, 'reach', etc and see if you can match them up to a plug with the correct thread. So the "J" is what was on the HH100, but I don't see a 12mm thread with 0.375" reach... There is a 10mm thread with 0.375" though, circled in red {wait... you said the threads on the replacement were LARGER! so forget this} Edited November 22, 2022 by Jeff-C175 Share this post Link to post Share on other sites
Bob Lister 142 #4 Posted November 22, 2022 1 minute ago, Jeff-C175 said: Maybe take a look at the spec for the original plug, heat range, 'reach', etc and see if you can match them up to a plug with the correct thread. I think that may be the best starting point. All I know about the head is that it came off a raider 10 Share this post Link to post Share on other sites
Achto 29,388 #5 Posted November 22, 2022 3 hours ago, Bob Lister said: I got a used head for it but the spark plug hole is 9/16 instead of 1/2" Is it possible that some one installed a thread repair insert in the head and it has came out? This would explain the oversize hole. 1 Share this post Link to post Share on other sites
Jeff-C175 7,206 #6 Posted November 22, 2022 3 hours ago, Bob Lister said: the spark plug hole is 9/16 instead of 1/2" Something odd here... I looked as best as I could at Tecumseh heads and can't find a one that uses anything but the 14mm threads. You say the threads are BIGGER? 5 minutes ago, Achto said: some one installed a thread repair insert in the head and it has came out? This would explain the oversize hole. Good thought! Share this post Link to post Share on other sites
Achto 29,388 #7 Posted November 22, 2022 12 minutes ago, Jeff-C175 said: looked as best as I could at Tecumseh heads and can't find a one that uses anything but the 14mm threads. 14mm would be close to 9/16, 13mm would be close to 1/2" Share this post Link to post Share on other sites
Jeff-C175 7,206 #8 Posted November 22, 2022 1 minute ago, Achto said: 14mm would be close to 9/16, 13mm would be close to 1/2" Bob may have been 'eyeballing' the measurement though... 1 Share this post Link to post Share on other sites
