Upshur's opposed twin engine

[Mike1]

Brian, As in my post "127" the head is aluminium but I made the insert in steel the insert never came loose due to thermal difference's
Mike.

 

[gbritnell]

OK here's how you fix a stripped 1/4-32 thread. Drill and tap the hole 3/8-24. 5/16-24 won't give you enough metal at the thread root to re-tap to 1/4-32. Now take a piece of steel or aluminum and cut the 3/8 thread on it with a die. The starting side of a die has a chamfer or lead on it. This will leave an imperfect thread where the die stops. Cut the threaded piece off leaving enough to grab with vise grips. Tighten the threaded stud into the threaded hole using Loctite. When it gets to the imperfect thread it will start to bind up in the hole. Tighten it reasonably tight. It will never leak or come loose. Set up your head and mill off the extra stock then drill and retap for 1/4-32 thread.

 

[Longboy]

"......I've been thinking about making my own threaded insert to repair the damaged sparkplug threads on one cylinder head. It looks like I can make a piece 3/8" outside diameter with 3/8"-16 thread and a hole through the center with a 1/4"-32 thread, tap a 3/8" thread into the cylinder head and screw in the insert along with some J.B.Weld on the threads.".......

That is the correct solution to resize mis- sized threaded holes. Especially into the combustion chamber, an oversized threaded plug with a sealant. This also works if you need to relocate off your original spark plug position or change the spark plug angle into the chamber when you redrill and tap.

 

[Brian Rupnow]

Today I was busy like the beaver. I made four rocker arms, which are just about at the limit of "littleness" for me to make. Then I made four pushrods, which are posed for the picture, but I haven't actually made the cams yet.

 

[pileskis]

Today I was busy like the beaver. I made four rocker arms, which are just about at the limit of "littleness" for me to make. Then I made four pushrods, which are posed for the picture, but I haven't actually made the cams yet.

Do those pushrods follow the plans as far as diameter?
They look disproportionately large.
If not, extra mass is not desirable.

 

[Brian Rupnow]

Yes, that is what the plans call for.---Brian

 

[Vietti]

For what its worth, I have had good luck using knitting needles for push rods. They are hollow, come in a variety of cool anodized colors and are light and strong. Simply use the pointed end in the rocker and press a ball shaped stub in the push rod end.

 

[Brian Rupnow]

Thank you, Vietti. That is a very novel idea. My engines are only ran at low speed, so I don't anticipate issues with the pushrods. I will keep your suggestion in mind for future engines.---Brian

 

[Nerd1000]

A die? Blasphemy! He has a lathe.

Anyone who single point cuts a thread when they could have used a tap or die has waaaaay too much time on their hands.

I say this as someone who has single point cut a lot of threads.

What's even better is when you can cold form the thread with a fluteless tap. No stopping to clear chips, just send it all the way in, back out and on to the next one.

 

[Jasonb]

You don't need a fluteless tap for that. Just use a spiral flute or spiral point. First lifts the spiral of swarf out the top of the hole, second pushes it forwards and is used for through holes, neither are backed off to break the swarf. Very good for hand tapping not just machine tapping. And works in all metals.

Same with Dies, if you get a "gun nose" one that will push the swarf forwards.

 

[danallen]

Anyone who single point cuts a thread when they could have used a tap or die has waaaaay too much time on their hands.

This is true provided you first have the die you need and second have a way to hold and start it perfectly square to the part being threaded. Then you have to fiddle with the adjustment on the die.

 

[gbritnell]

So where are you with repairing the stripped thread! Just saying!

 

[Brian Rupnow]

I'm getting down to the short strokes on this engine. I still have to make cams, valves, and an ignition point system. The valves are a bit more delicate than those I have built in the past. The valves are 0.094" diameter. All the valves I have made are 0.125" diameter. When will I repair the stripped sparkplug hole?--sometime in the next 3 or 4 days. As the weather gets nicer, I'm losing my interest in spending every day in my shop. I go in for knee replacement surgery on the 23 of this month, and I certainly hope to have this engine up and running before that.