Don Terrill’s Speed-Talk

The carbs have a rubber bushed support rod, but the typical soft mounts between carbs and manifold aren't needed.

BTW, I printed a couple ring squaring tools today. Thanks to whoever suggested that ... great idea.

here's a view of the model of the ring squaring tool I had came up with, for a reference I tried to attach the .STL but says that filetype is not allowed here this puts the ring about 3/4" down the bore. You're going to have a difficult time printing that design in one piece with FDM because of the...

The problem with epoxy is its coefficient of expansion. If that's your choice of repair method, I'd recommend looking for for one that is aluminum filled to match expansion rates as closely as possible.

This is an excellent candidate for a weld repair. Clean the surface all the way to the bottom of the flaw with a cabide burr, weld (100% penetration), finish the weld within 0.010 then peen the weld with a round nose punch. Unless it's peened, a weld will have a residual tensile stess ... which coul...

Ok, good luck! :D if the press fit is on the high end of sanity, might do you good to use a lube such as..... standard silver anti-sieze, or coating the parts in soot, are the best lubes i know of for steel in aluminum press fits. I've had good luck with cutting oil for aluminum. I prevents aluminu...

Case is nicely chamfered as are the bearings, I have a delrin driver, nothing to hold them together though A chamfer is not good enough. Break the sharp edges of the chamfers with some 320 grit wet-or-dry paper ... 0.005 in radius is enough ... and you won't have any shaving of the aluminum case.

The contract edge always goes to the bottom. Put a set on a piston and slide it up and down a couple times. Pull it out and look at the face of the rings. You should be able to tell which edge is touching the bore.

Walter R. Malik wrote: ↑

Thu May 16, 2019 9:17 am

It make little sense to use a bolt or stud which takes more torque to stretch it, than the metal it is going into will handle.

True, but cost is the only downside to using the higher grade fastener. The modulus is the same so the stretch will be the same at a given torque.

Never would have imagined that cause, but it makes perfect sense now! I suppose the larger OD of the Helicoil left such a thin wall between it and the (oversize?) valve seat recess that it cracked and blew through.. PS: What's holding the valve open? The distance from plug to valve seat was already...

Roundybout wrote: ↑

Sun May 12, 2019 7:30 pm

Does that plug hole have the threads repaired with an insert?

Yes, a Helicoil. Not particularly well done.

Finished the weekend with no other issues. Cranking compression was down on that cylinder (80 psi vs 220) but never got worse. The replacement plug started showing the same type of damage after one 30 minute session. After removing the head, the cause was pretty obvious ...
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The bottom 3 threads are burned ... 1/2 normal height. At the location of the damage, it's burned to the root.

Looking through a borescope, there's no damage to the piston to indicate mechanical damage. I can't see the valve seat, but the damage is right next to the exhaust valve, which shows no signs of distress.

We've installed a new plug and will run it tomorrow ... checking after each session.

It's the correct plug for the engine ... I've built dozens of these. I haven't seen the engine myself, only photos from the client. I'm guessing it was loose, possibly arcing to the head? He said it unscrewed easily, that he didn't notice the damage until they were all out. The engine is in a vintag...

This plug was removed from a good running vintage sports car after 3 race weekends. The other three are normal. Any idea what could cause this type of damage?