I've been ignoring issues on my savage engine and now due to a significant oil leak on the head it's time to address them.  In addition to the oil leak there is a crappy epoxy repair on the left side engine cover that will be addressed as well.

The head is removed.  I found the infamous oil plug was in place and appeared not to be the cause of the leak.  Best I can tell is the leak came from a less than stellar job on the head cover sealant application or perhaps a blind threaded hole in the head near the spark plug that is no longer blind, there is a bit of daylight coming through the bottom of the hole.  No idea how it got that but given the menagerie of bolts that fasten the head someone might have tried one that was too long at one time or another.

But the best is yet to come.  On disassembly of the head cover many of the bolts were way over torqued but several seemed to be under torqued.  Two of them are the long ones that go into the cylinder and the third went into the head near the intake port.  (sorry, no pics of that) The ones that went into the head are stripped and the one nearest the intake port actually cracked the head!

So that's the first question.  It looks like the readily available helicoils are about 9mm long.  Does anyone have advice on what length helicoil to use on the 6mm threaded holes in the cylinder?  It's the two blind threaded holes nearest the timing chain tunnel that are the problem.

My plan for the crack in the head is to use a burr to remove the broken section all the way down to the threaded bore and re-fill it with weld, re-drill and re-tap.  I'll strip the head bare before all that grinding and welding.  And probably open the exhaust port area as well while it's all apart.

That's a very nice repair.  
You can prevent this porosity by not applying filler material straight away, but first degassing the aluminum with your flame and only then adding material, otherwise you will always have holes at the transition.

I would use as long helcoils as the situation allows.
But a helicoil is 40% stronger than normal thread, so you need less long thread than original. (in theory)

zevenenergie wrote on 03/27/24 at 12:46:46:


Thanks.  I have learned to warm up the weld area slowly at like 1/3 of the power it takes to create a puddle for awhile.  I should have could have warmed it up longer in hindsight but I was worried about putting too much heat into the assembly.  It didn't heat up excessively so I could have pre-heated longer.

I tackled the big weld today.  I couldn't direct enough heat to the bottom of the hole to really fill it in very well so I widened the weld at the base to compensate.  It got a bit globby but I'd rather have too much than not enough to hold.  Last two pics are a simple guide to bore out and tap in prep for helicoils.