Horizontal Air Cooled Engine

[Brian Rupnow]

I have not reached a decision yet. I am waiting for the sparkplug I ordered to show up. If the sparkplug isn't 8 mm thread, I perhaps can turn the threads off, leaving a 5/16" or 8 mm plain end that I can then thread to 5/16". I have also thought about j.b. weld, and a dozen other things, but I'll get the sparkplug I ordered first.

 

[Zeb]

Something to add to the insert plug option mentioned might be to make it an interference fit. Similar to how valve guides go in with some heat and dry ice.

 

[Steamchick]

IMHO I don't think JBweld or other epoxies can be anything other than a bodge job. Not of the standard of your workmanship. If there is insignificant room to over-bore thread and fit an insert, then the simple repair for aluminium is a blow-lamp ally weld rod. I used to you the heavily zinc based rods, but there are now some very cheap (€&@y) alloy rods that are 90+% aluminium, but melt flow and take to your aluminium below the melting point of your aluminium.
I have used it as a solder on 1mm thick aluminium, 3mm thick, and other small jobs. I have used the zinc-aluminium mixtures to fill holes in thicker ally.
But try an insert first if possible. Least risk to your existing job.
K2

 

[dsage]

If you thread the insert, the JB weld is just a permanent thread sealant. You don't even see it when it's done. Except for a very fine ring the diameter of the insert. Same for loctite.

 

[Brian Rupnow]

I have spent the last two days designing some light automation for an old customer. My new sparkplug will be here on Saturday, and if it doesn't have an 8mm thread I am going to buy a 1/4"-32 helicoil kit from a source provided by Brian Lawrence from Calgary. Tomorrow I will begin the task of making rings for a 7/8" diameter piston. I have the grey cast iron material, but will have to build a new heat treat fixture to accommodate the new ring size. The rings will have the same cross section as the ones I made earlier this year for my T-head engine.

 

[minh-thanh]

Hi Brian !
Why don't you make spark plugs with 8 x 1 mm or 8 x 1.25 mm ?

 

[johwen]

Very Easy to make as I have described before John

 

[Brian Rupnow]

Todays job was to make a whole armada of 7/8" rings. The material is fine grained grey cast iron, same as I made my other 1" rings from. The o.d. of the ring is turned to 0.875" diameter and polished with 200 grit aluminum oxide strip and a fine India stone, to the best finish I can get. The i.d. is drilled and bored out to leave the rings 0.038" wide axially, which is what I was aiming for. The rings are then parted off, and with some luck will all be slightly greater than 0.045" width, which is the width of the ring grooves in my piston. They will be finished on both sides with some 600 grit aluminum oxide paste on a sheet of glass, rubbing round and round until they are a sliding fit into the ring grooves in the piston. After they are "sized" for width, I will break them in my bench vise. I don't like the fancy fixture which I made to split them because it has a tendency to bend the rings. The last rings I made were cut with a sharp cold chisel, but I felt that doing that deformed the ring on both sides of the cut.

 

[Brian Rupnow]

Okay---Just to set the record straight---My rings came off the lathe about 0.003" to 0.004" too wide (as I had planned). I tried polishing that 0.003" to 0.004" off using 600 grit compound on a piece of glass, but it took so long I thought I might not live long enough to get all the rings done.---So---I used a sheet of 600 grit paper laying on a finished cast iron surface, and my handy dandy piece of steel with a 0.875" dia. x 0.025" deep hole in it to hang onto the rings with while I polished them. That went more quickly, but even so it took a lot of scrubbing in circles before the rings came down to 0.044" thick and would fit into the 0.045" grooves in my piston.

 

[MRA]

I am intrigued how you are going to snap them 'just so'. Hope you show that bit!

 

[Brian Rupnow]

MRA--I misled you.
This was something new---The material didn't want to break in the vice. Damn stuff wanted to bend, which is unusual. When I seen that it didn't just snap quickly like other rings have made, I sharpened up my big cold chisel and cut them with the chisel and a pall peen hammer. Whack---and it was done. All the rings in this picture are finished, deburred, and split. Tomorrow I will machine a heat treat fixture and into the heat treat oven they go.---Brian

 

[Nerd1000]

MRA--I misled you.
This was something new---The material didn't want to break in the vice. Damn stuff wanted to bend, which is unusual. When I seen that it didn't just snap quickly like other rings have made, I sharpened up my big cold chisel and cut them with the chisel and a pall peen hammer. Whack---and it was done. All the rings in this picture are finished, deburred, and split. Tomorrow I will machine a heat treat fixture and into the heat treat oven they go.---Brian

Is it possible that you got ductile iron rather than grey cast iron? It would be more inclined to bend than snap.

 

[Jasonb]

I was thinking the same when I saw that swarf from drilling out the waste, looks more like ductile iron.

If it is the same bar you used for the others that may also explain why the Trimble cutter was deforming the ring around the split.

 

[Brian Rupnow]

Could very well be. I've broken rings in my vice in the past, and they always cracked under light sideways pressure. I have never n one bend before.

 

[Brian Rupnow]

A couple of picture worthy things going on here. One picture shows a good way of filing the ends of the ring at the ring gap. That is an ignition points file gripped in the vice, and a ring spread over it. I grip the ring with thumb and forefinger of each hand and slide it back and forth on the file, keeping it "square" to the file. Give it 20 strokes and try it for fit in the cylinder--You are aiming for a gap of 0.004" between the ring ends when the ring is slid into the cylinder. Keep track of the number of strokes you take, because whatever it took for that first ring will work for all the rest of the rings. The other picture shows the heat treat fixture I machined this morning, made specifically for 7/8" rings. The drawing I am working from specifies a 0.131" diameter spreader rod. Closest I had was an 0.135" drill, so thats what I used, and the drill will be sacrificed as my spreader rod. Once the cap is bolted on, compressing all of the rings to ensure that they are all laying flat and tight next to each other, the fixture and rings go into my heat treat furnace for 4 hours.

 

[CFLBob]

The drawing I am working from specifies a 0.131" diameter spreader rod. Closest I had was an 0.035" drill, so thats what I used, and the drill will be sacrificed as my spreader rod.

Is that a typo? Those are a tenth of an inch different? I mean is it supposed to be 0.131 and 0.135 or .031 and .035?

 

[Brian Rupnow]

That was a typo Bob.--thanks. I fixed it.---Brian

 

[Brian Rupnow]

Bad on me---I ordered an M8 sparkplug from A.C. Delco, assuming it would have an M8 thread on it.---it doesn't. It has a 10 mm thread on it. However, all is not lost. As we speak, Stephen Hucks is making me a "one of" sparkplug with a 5/16"-24 threaded end. As luck would have it, I do have a 5/16"-24 tap and die as part of a set I inherited from my dad.

 

[Brian Rupnow]

After four hours at 1100 degrees F and then an overnight cooling off period, the fixture comes out of the oven looking like this. There is a lot of black crud on the outside of the fixture (Don't know what it is) but it cleans off very easily. When the fixture is taken apart, the rings come off easily, but they are all stuck together. A bit of finessing with a jacknife gets them apart, and as you can see in the picture they have all taken a set to the new gap of 0.135".

 

[Nerd1000]

The black stuff is probably mill scale, a mixture of iron oxides formed at high temperatures.