Re: patching (alloy) cylinder bores

IF (note capitals!) IF the score can be chemically cleaned sufficiently well to fill it with chemical metal, that's what I'd do. It's described as being at the bottom, so if it is beyond piston ring reach, I'd try it as it is.

Regards,

Kim Siddorn

Hmm, I'll take a look and see how far down it is - but the engine wouldn't run any more because it was losing too much compression. I'm not bothered if it ends up way down on power and can only be used for light duties, but it might be useful to have a portable IC engine kicking around the place, and it seems a shame to scrap the lot.

cheers

Jules

As much as anything else, it occurred to me that if the plastic metal failed in use, it would not do much (if any) damage.

I did do it once before on the bore of a 750 Honda where the impecunious owner had had a circlip failure. It wasn't easy to get the scrage clean and keyed, but once done it was relatively easy to fill it. We used a glazed cardboard tube as a "piston" and inflated a balloon inside the tube to force the Day's Plastic Metal into place whilst it went off. We then took it down to our tame rebore man who honed it out. It not only worked, but was still giving no trouble 10,000 miles later, although we thought that it was beginning to smoke a bit on opening up off a roundabout.

Regards,

Kim Siddorn

True. I like the cardboard / balloon trick - sounds like a good plan. No idea where I could get it honed around here, though; I wonder if there's anything soft enough (but which would still withstand the heat in use) that I could fill it with and finish it myself just so it was "good enough". I'm not sure what temp various modern epoxies will withstand, for instance.

One other possibility might be to use it as an air pump rather than an engine - the carb, magneto and governor are all rather worn-out anyway. I've got a spare electric motor I could drive it with, and a big stack of surplus bricks from around the old wood furnace. Homebrew forge, perhaps :-)

cheers

Jules

Many epoxy resins will take 600c for a short time & if the groove is below initial combustion height, I see no problem.

Regards,

Kim Siddorn

Thanks Kim - I put some epoxy in there yesterday, so will give it a try and see what happens :-)

How did the repair go Jules?

Regards,

Kim Siddorn

So far, so good! I finally had some time earlier to finish reassembly. It only sat half-assembled on the bench for about a month ;-)

Anyway, I did a couple of "live" tests, and no problems so far (well, not compression-related ones; I was running without an exhaust because the mounting holes in the block have stripped threads, and I shut everything off at the point where the 20 year old fuel line sprung a leak :-)

Whether it'll run for any length of time is another matter - it'll be interesting to see if the oil or the heat kills the epoxy, but prior to the epoxy it wouldn't start at all due to bore damage. The fact that it was run up to temp, allowed to cool, and then started right up again is promising.

I need to buy some better engine mount bolts and some replacement fuel line before I can do any kind of long test (and tune the carb, and rig up a silencer somehow)

cheers

Jules

I just had a way out idea. I'm half kidding here. If it was a cast iron bore, you might be able to make a mercury amalgam and use it to fill the scrape, like dentists use for fillings. You could scrape it into shape before it sets hard. Pick the right metal for the amalgam and you might get a high enough melting point. Now that would be cool. But with an aluminium cylinder, the mercury would probably eat it.

Chris

I've never heard of that being done with amalgam, but the same idea was certainly used with rust joint cement (iron turnings and sal ammoniac, some recipes with red or white lead too)

I've an RAF pamphlet here just called "Corrosion". It has some splendid photos of the perils of mercury in manometers and barometers, particularly its effects on steel pipework that has been assembled with aluminium crush washers rather than copper. Great vermiform extrusions of aluminium amalgam squirting out everywhere.