I think you should fix that Heli-coil insert for one of proper size which does not extend into the cylinder (mine was about 5/16 no more )
it should line up with the plug base. clean the threads of any oily deposit, reinstall properly with red locktite , punch it in with the punch tool
I would wait a few hours then install that sparkplug
I agree…That exposed helicoil could turn into a hot spot and lead to preignition damage. I’m guessing the crap in the water plugged your cooling passages also. But, I would surely inspect the impeller housing closely, and replace it it is gouged/grooved excessively. I would certainly replace the impeller with an OEM new one also…
Hmmm, one other possibility…..Perhaps the impeller has spun on its metal (or plastic) hub. So, the hub may have been spinning, but the rubber impeller was not….Have a close look at where the rubber bonds to the hub for separattion…
You have the head off, any signs of scuffing/scoring on the cylinder walls? Probably not, these engines are pretty robust and can take a beating. If you are really concerned, you may want to pull off the intake bypass covers which will expose the intake side of the pistons…I do NOT recommend pulling off the exhaust cover, that is a big and messy job.
Once you have determined everything seems OK internally, you may want to give the cylinders a 50 cent hone job with a fine piece of emery/crocus cloth….Sure, not very professional, but we are not dealing with tight tolerances or jet engines parts here…Rough up the cylinders, then clean out any dust with spray ignition cleaner, be sure to oil the cylinder walls liberally afterwards. Did the head gasket appear to be “blown”? Replace it even it it “looks OK”. Be sure to check the cylinder deck and head for flatness…These parts are aluminum and easily distorted during an overheat. I’m guessing this great old QD will be purring again for next season.
One more thing…You mentioned green oily residue, which usually is “normal”. But, be sure to change the gear lube and check for water….No sense reinstalling a leaky gearcase…
