Piston Rings Question(2)

[graham-xrf]

I am hoping there are some engine experts here.
The picture is of of pair of pretty rough looking vintage (1930s thru 1940s) pistons from motor cycles of that era. The engines were 350cc air-cooled horizontally opposed types. Given #1 is not the same as #2, I don't expect they came from the same bike model, but they both do come from the same casting as the ones I mentioned in the "Pistons problemo!" thread. One has a ring set I have never seen before, and I don't understand how it works.

These messed up pistons are +0.030", which means there is some scope for them to be cleaned up donor parts in a +0.020" bore, basically by removing 0.005". That is, except for the rings. I know nothing about rings technology of the time, and I would like to discover what these are.

Piston #1 is looking more modern, I think, though my originals had the oil control ring down on the skirt near the bottom.

Piston #2 is the complete mystery. The 3 x 1/32" rings in the second slot have gaps 1/8", and then 1/4" cut at an angle, for the first and third. The second of the set, "in between has zero gap, the slit also at the (about) 20° angle. By itself, the slit is quite hard to find, until you flex the ring.

The wider, third ring in Piston #2, just above the wrist pin is a set of 5 x 1/32" rings, all with 1/4" gaps, spread about the circumference. I did find the series of oiling holes under the set of 5, though they were carbon clogged, and that may have had something to do with the overheated bore scoring "event". I would much appreciate any information about these strange (to me) ring things.

 

[pdentrem]

To me some of the rings have been overheated and the tension is all gone. Time for a new set.
Pierre

 

[pdentrem]

In the good old days, the compressions rings would be cast iron. Some rings were made to fit in the ring slot where an anti rotation pin would stop the rings from spinning. Usually Honda engines I have seen, no idea of other makes.
The top ring has the scraping edge at the top, while the second ring (today) would be scraping the oil back down. Some second rings were ground flat to the cylinder.
Oil control rings with spacer are ground flat to the cylinder as well.

Ring packs are designed with many needs, and are specific to engine and expected use. Cast iron, moly rings, chrome rings, step rings with filler, L - shaped rings and the list is long. Ring gaps are also varied due to expected temperature. Hotter the engine, the larger the ring gap. Boosted engines gap is .007” per inch of diameter is a typical call out.

Should call ring suppliers, more than one, as their ideas differ.
Pierre

 

[matthewsx]

Honestly, I don't think I'd use those in any engine that I wanted to run for more than a few minutes. I'm kinda a do it right person when it comes to engine internals, I've seen what happens when you try to just get one more rebuild out of worn/damaged parts.

John

 

[extropic]

We have a master motorcycle performance innovator (among other technical skills) who has recently become a member of H-M.
Think of this equivalent to the Bat Signal.

@tonyfoale , I couldn't help but think of you. I don't mean to put you on the spot, but I'm sure the OP would appreciate your input.

 

[Deleted member 69715]

I am not the expert mentioned. But what manufacturer is the bike in question? Is the bore capable of being honed out, or is it a grenade? If you can answer these questions take that info to piston builders who can manufacture suitable replacements from suitable material. Ask Hastings about the rings for those things. Different piston in each cylinder? I would sincerely love to hear the backstory on that.
Please keep us posted as this progresses.

 

[tonyfoale]

Deleted. irrelevant.

 

[tonyfoale]

Different piston in each cylinder? I would sincerely love to hear the backstory on that.
Please keep us posted as this progresses.

Two engines not two pistons in one engine?

 

[tonyfoale]

Deleted, irrelevant.

 

[graham-xrf]

Honestly, I don't think I'd use those in any engine that I wanted to run for more than a few minutes. I'm kinda a do it right person when it comes to engine internals, I've seen what happens when you try to just get one more rebuild out of worn/damaged parts.

John

Indeed I agree, and given the beautiful +0.020" re-bore, and head with valve guide inserts, it would go together like new. It should have been with new pistons, but the pistons (importer) supplied the wrong pistons. They took back the returns, but it leaves me somewhat up the creek. There exists a design for casting at JP Pistons in Australia, from where these come, but I think they don't want the business. They asked AUD$600 (each) + shipping etc., and then I get UK 20% VAT on top. Add it all up, do exchange rates, and we get to a number that certainly stops the entire effort. Also, the investment in re-bore and head job is then wasted.

This is not really a "one more". It's the first actual re-bore. All previous was of the "clean up and re-assemble with new gaskets" sort.

The messed up piston(s) happen to be oversized. The idea is that they only contribute their correct shape cast metal. The outsides get machined to a correct taper, and then the skirts below the wrist pin, at right angles to the pin axis are slightly relieved to make the correct "oval".

I have even considered TIG welding up the ring slots, and then re-cutting to copy the positions and ring sets that came out of the original. One would need 4032 TIG filler rods, which has 12% silicon + a friendly TIG expert. Who knows where both those can be found?

Another option might be to use electro-less nickel strike on the originals, as precursor to a layer of copper under a final surface of some metal suitable to be in a nickel-iron alloy bore. The piston surfaces are not supposed to contact the bore anyway, being held off by rings and oil film, but I suppose they always do at some point, because they wear.