Went to confirm the head torque on my newly rebuilt 12 motor, and wound up stripping a bolt. That was sure a bummer, but then, it happen 2 more times to 2 other head bolt locations before I finally got it all back together and finally got the torques properly qualified...whew! All 3 holes that failed had previously been heli-coiled, where there appeared to be no visual damage to these helicoils? When I drilled these helicoils out, all 3 shattered into pieces. Having no idea of when these earlier helicoils had been installed, I have to wonder whether these failures were the result of metal fatigue. I've both used and removed helicoils in other applications, and do not recall any where a drilled out coil actually shattered.
The last time I had a stripped head bolt in one of my blacks, I was out of the right thread Helicoils, so I took it to a machinist. He installed the new (to Me) helical that is built like a cup. I really like the idea and plan to do that again if I need to.
Has any one got any opinions on the new cup style????
If there are no bad sports on the cup style, I think I will stock up on them.
Threaded inserts are a common alternative to helicoils.
Keensert is a common Cup style as described. A negative to these is that the service drill and tap are significantly larger diameter than the helicoil application. The more common helicoil failure occurs when the insert pulls out....a Keensert will not pull out.
Once it's fixed, I'd use studs. You could even use acorn nuts.
I wonder if there are 7/16 x 1/2 studs?
Unless you have an high compression head you should only need to torque to 35 to 45 LBS esp the early blocks (like your 12). I would suspect that in the past someone has tried to go to 50 or 60 range and pulled the threads.
Studs are extraordinarily inconvenient in a Model T because they require you remove the firewall to install or remove the cylinder head. I've used head bolts on (names of the 25 or more brands of engines I've worked on over the past 40 + years as a mechanic) and have yet to wish any of them had studs instead.
Ralph: I don't understand how studs would be any more resistant to pulling out under load than bolts. Perhaps I'm not understanding the proposed application?
Mark: Got the stock 11-12 Fingerprint head using 40 ft/lbs torque. That certainly does not mean that someone earlier did not aggravate this by over-torquing.
Jim Thode has the fix. I have used the type of inserts shown in his illustration and also an insert very similar to those called "Keenserts".
Keenserts are just like the ones in the photo above except they have three hardened lock pins attached that when the insert is screwed into the hole, the three pins are driven down between the insert and the original hole thereby locking the insert in.
When I worked in aircraft tooling, we used those for threaded holes in soft metals like aluminum. This way, a threaded fastener could be repeatedly inserted and removed without the fear of pulling out the threads in the soft metal.
I believe Kenserts are available from McMaster-Carr.
Scott, studs can use all the threads in the block, while common model T head bolts only uses perhaps 2/3 of the available block threads? Check with a bolt through a head plus a gasket, not much thread to engage the brittle cast iron there.. But beware of too long bolts that bottoms out in the holes, they'll strip out for sure. With studs you can safely use all the threads
Why not install studs after head is in place?
The project is a restoration, so studs would not be a solution here, even if purely for aesthetic reasons. I'm sure there are still other ways to skin this cat, but I believe a basic approach is to adhere to the reasonable torque values mentioned here. Hopefully will not have to take this apart again, but if I do, I'd likely again replace the helicoil with another helicoil as was done here.
There is another advantage to using keenserts/keyserts. They are available in different outside diameters for the same inside diameter. So there is no need to make bigger holes than required to make a fix.
I once bought a 1913 block which had been drilled out and 1/2" studs used in place of the original bolts. I was going to drill out each hole, fit a solid plug, and redrill and tap the plugs. By using thinner walled keyserts, I could just use a slightly larger drill on the 1/2" holes and wind the keyserts straight in. The little drive in pegs lock them in well.
Hope this helps.
Allan from down under.