Thread insert for cylinder stud

[raz]

For some reason one of my cylinder studs ate the block threads and ceased doing its job. I torqued it myself a couple of years ago and I re-torqued them after a while with no problem. I guess the reason could be my torque wrench is too cheap and miscalibrated so it was too hard. I'm sure it didn't break at torquing but maybe it was so borderline it broke later at heat cycling. Is that even possible? Anyway I need to fix it.

 

I do most everything myself except valve jobs and tires, unless someone talks me out of it. So here is my plan. I haven't actually done anything yet, just planning, so you have the chance to save me.

 

First, I need to drill by hand without making things worse. So I thought I should make a jig. Then I realized the barrel could be used as a jig, but its holes are 12 mm and drill is 10.4 mm so it's not very exact. But the head's holes are 10.5 mm or something, it's perfect!

 

I wound the crank so the conrod was below surface, then gently placed the head there without the barrel. It seems to work just fine:

So, like this I can drill some 15 mm down, and the last couple of mm's should be easy from there. Apart from that I need to take good care of material falling into the ditch pump, is this a sane plan?

 

Question number two: The length of threads is 28 mm. Either I need to find longer Recoil inserts, or maybe I could use two of them? Anyone tried that? I reckon I could mount the first all the way down, wind in a second until that one is a mm below surface and set it there. Any comments are welcome.

[GuzziMoto]

I see no reason why you could not use multiple inserts. I have done it. As for the jug or head as a guide/jig, I would think that would work if your drill bit is long enough to drill what you need out of the block while sticking out past the head. But the idea scares me unless you have a plan to keep the drill bit from carving up the head (some sort of centering spacer?). Maybe some epoxy on the drill bit to cover any of the drill bit flutes that you don't need (i.e., only have the part needed for drilling into the block and the rest filled in with epoxy). Just keep pulling the bit out if needed to clean the shavings out. I personally have never used an insert for anything more serious then an exhaust stud (I used two in a row). But I have known people to use them for all sorts of important things and I have more faith in a heli-coil then I do in aluminum threads.

Good luck.

[Tom M]

Timesert makes a steel 24mm insert that might work for you. I've never used one but a lot of folks prefer these over helicoils.

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

 

If you stick with the helicoil plan I would look for a 12mm OD / 10.5mm ID sleeve to fit in the stud hole in the jug. Then you could use the jug for your drill fixture without risking damage to the head. That said, even if you did oval out one hole in the head a little I can't see where it would hurt anything. There would just be a little more clearance around that one stud.

 

Pack the flutes on the drill bit with grease to catch the chips and obviously do everything possible to keep the chips from falling into the sump.

 

Good luck!

[gstallons]

You say "Recoil" Is that a brand name? Here in the U.S. the brand is Heli-Coil. There is a company here also "Timesert". Expensive and the best. If at all possible I would use one insert instead of two.

[pete roper]

If the thread has stripped out in the block this is going to be fraught with problems..

 

Whichever way you tackle it the head and barrel will have to come off to allow insertion of the coil or timesert, (Which are made by Wurth.).

 

The problem is that if you get the drill/insert even slightly off line the inaccuracy/deflection will be greatly multiplied by the top of the stud!

 

Obviously the best way would be to remove the engine and set it up on a jig on a drill press but most people don't have access to stuff to do/make such things.

 

If you remove the head and then use sleeves and the sother studd nuts to hold the barrel in placeyou could probably use the studd hole in the cylinder as a guide to keep the drill true. When you have drilled the case that way you can then remove the barrel and CAREFULLY tap the hole and then put in the thread repair but this too is still fraught with risk.

 

Whichever way you attempt it be VERY carefull as if it goes wrong it will be a bear to fix.

 

Pete

[pasotibbs]

I see no reason why you could not use multiple inserts. I have done it. As for the jug or head as a guide/jig, I would think that would work if your drill bit is long enough to drill what you need out of the block while sticking out past the head. But the idea scares me unless you have a plan to keep the drill bit from carving up the head (some sort of centering spacer?). Maybe some epoxy on the drill bit to cover any of the drill bit flutes that you don't need (i.e., only have the part needed for drilling into the block and the rest filled in with epoxy). Just keep pulling the bit out if needed to clean the shavings out. I personally have never used an insert for anything more serious then an exhaust stud (I used two in a row). But I have known people to use them for all sorts of important things and I have more faith in a heli-coil then I do in aluminum threads.

Good luck.

 

I was once told that heli-coils were developed during WW2 because the alloy threads holding Spifire wings on failed in high speed dives

Not sure if its true or not ?

[raz]

You say "Recoil" Is that a brand name? Here in the U.S. the brand is Heli-Coil. There is a company here also "Timesert". Expensive and the best. If at all possible I would use one insert instead of two.

Recoil is just like Helicoil but (apparently) Australian. There are very similar German alternatives too (V-coil I think). I'd guess the quality of those are similar, but they are all very expensive. I found a dirt cheap brand too (you can guess the origin) but that one I don't dare using. Not for this application anyway.

[raz]

OK, done now. All went fine. For jig I used the head (secured by two bolts) while drilling, and the jug for the first few turns of the tap. Then free hand tapping, without taking one single breath (that I recall) for the whole operation.

 

Two coil inserts just fit (number two made contact with the first one just after clearing the surface). End result is perfect. I'll just need to make sure the engine surface didn't raise a thou around the hole (although that would probably be off the gasket or mating surfaces anyway)

 

Thank you all. Man, do I need a drink.

[gstallons]

I know this after-the-fact. you always want he insert to end up one thread below the surafce of the part you have repaired. You might (if you feel man enough) take a burr and grind off enough to be below the mating surface ?

[raz]

Yes I know. I thought it would go deeper. I'll just leave it though, it's down enough I can't see it when stud bolt is there, and the hole in the jug is larger anyway.

[fotoguzzi]

OK, done now. All went fine. For jig I used the head (secured by two bolts) while drilling, and the jug for the first few turns of the tap. Then free hand tapping, without taking one single breath (that I recall) for the whole operation.

 

Two coil inserts just fit (number two made contact with the first one just after clearing the surface). End result is perfect. I'll just need to make sure the engine surface didn't raise a thou around the hole (although that would probably be off the gasket or mating surfaces anyway)

 

Thank you all. Man, do I need a drink.

you are a hero! well done and you have guts.