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All was going well today as I prepared for a first engine start... and then. The bottom plugs were never installed and the lower plug holes were only covered up to this time. Spun the engine up with no bottom plugs installed to get the oil pressure up and it worked great. Then I installed in the bottom plugs for the first time and the aft plug holes in both heads stripped out before I even got up to 6 Ft. Lbs of torque. Pulled the heads and sure enough, deep in the hole the threads were barely machined into the head. Will call Sonex Monday but it will likely require inserts to repair the poor machining. M12-1.25 17.5 MM long timeserts would seem to be the only reasonable resolution now. Don't think I would even trust a new set of these MoFoCo heads at this point.

See the top of the Sonex Foundation home page for a loan of the tool :-)

http://www.sonexfoundation.com/

Sorry to see that cylinder head issues are still a thing. Here's a post I made with my head issues back in 2015. I had to replace both heads from the kit for 2 different reasons.

http://www.rynoth.com/wordpress/waiex/2 ... ad-issues/

Call Sonex. I encountered the same thing with my mofoco heads. Sonex totally covered me and sent me two new heads very quickly. The new heads (not mofoco) were of much higher quality (not just the threads).

I also had valve issues with my first set of mofoco heads. Sonex replaced them with another set of mofocos. I did put plugs in, and torque them with no issues, so I skipped the timserts.

I ordered new heads and got Mofoco heads from Sonex. I spun a spark plug and Sonex had me send them back to them. They replaced the heads with ones that had Timeserts in all the spark plug holes. These torqued up and have been fine. Sonex took care of me at no cost so give them a chance.

Talked to Sonex yesterday and they are sending me replacement heads. I regret the loss of time and effort on my part but I must say that Sonex has been very helpful and are standing by thier products. Kudos to Kerry and the entire Sonex team for thie gracious and timely help. I also believe that Sonex has stopped providing the Mofoco heads now.

I though the hissing sound heard when turning the engine over was a leaky valve but today I realized it's the spark plugs. 3 of them were leaking and when I tried to tighten them, the thread gave out completely. I guess I'm in the market for the thread repair kit, too...

Interestingly it's both top and bottom, so it can't just be the extra holes that are bad. Or someone previously used too much torque.

I'm actually really surprised the install manual specifies 12ft-lbf. All automotive spark plugs I've ever used specified "finger tight and then 1/2 turn" or something similar on first install when the crush washer compresses, and "finger tight and 1/8 turn" or something on reinstalls. As I recall, the required torque for that is way below 12 ft-lbf.

lutorm wrote:I'm actually really surprised the install manual specifies 12ft-lbf. All automotive spark plugs I've ever used specified "finger tight and then 1/2 turn" or something similar on first install when the crush washer compresses, and "finger tight and 1/8 turn" or something on reinstalls. As I recall, the required torque for that is way below 12 ft-lbf.

Yes, I never torque the spark plugs. I tried that once and snapped the insulator! Finger tight, then a half turn is about right.

Well, crap, I just realized half the sparkplugs in my heads, including one of the stripped ones, have already been repaired with some shitty helicoil work that's not even concentric to the seat. No wonder they leaked. Co-owner/builder knows nothing about repaired spark plugs so how this happened is a bit of a mystery. I wonder if the shop that did a valve job stripped the plugs and just repaired them without telling anyone. That or my co-owner has amnesia... But this sucks, because I don't think the time-sert will repair a previously helicoiled thread.