Piston question

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Biscuit said:
If the pistons measure satisfactorily you could consider getting the top land squared up and fitted with a steel spacer. This used to be quite common a repair and a machine shop that's been around for a while will know exactly what the procedure is. Basically, the ring groove is cut suitably oversize enough to square it up and a thin steel spacer is installed in the bottom of the newly cut groove. This spacer is much like one of the thin oil ring expanders but fits very precisely in the groove tightly enough to not move. It provides a perfectly flat surface for the new ring to seat/seal against and restores correct clearance. Two plusses, the machining cost is a lot less than new pistons and that steel ring-land insert will never wear out so ring clearance will stay virtually the same for life.
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It would be interesting to have "oversize" rings - thicker - so the ring lands could be machined to restore original side clearance specs with the thicker rings.
 
YukoNorton said:
It would be interesting to have "oversize" rings - thicker - so the ring lands could be machined to restore original side clearance specs with the thicker rings.
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I'm not sure about that, it would undoubtedly work but thicker rings would also cause more friction and harder to source special rings. With the procedure for the groove restore, it takes very little cutting to square up the groove. The machinist takes the measurement needed for correct ring clearance + the measurement of the thickness of the steel band. The groove is cut to the resulting measurement and when the steel band is installed factory ring clearance is re-established.
 
Widening the ring grooves for larger rings or to install a shim ring may have it's place with an item that cannot be readily replaced and you really need it; say pistons for a 1950's vintage Russian dozer in the arctic circle of Far East Russia, but for something as readily available as replacement pistons for a Commando, you cannot beat the price of OEM. Besides all that, after reworking the ring grooves and rings; you still have a piston with warn skirts. Yes, I know others have knurled the skirts but when everything is said and done, unless your machinist is being paid at Bangladesh wages, it's better (more cost effective and better quality) to replace with OEM or something even better.

I do remember paging through a vintage automotive service manual (Chiltons?) where they described the "insert shim ring" and "knurling piston skirts" to recondition - that's apparently the way they did it 70 to 90 years ago. Even today I would be hard pressed to find a reason to recondition grooves and skirts. Even if it were a unique machine, there are so many over the counter piston options that can be made to work. We had a 1942 BSA M20 that needed a piston and we made do with an industrial engine piston - worked like a charm.

Even with attempting a 100 point restoration where pistons are no longer available I would go to JE and have them make the pistons.
 
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Dances with Shrapnel said:
I do remember paging through a vintage automotive service manual (Chiltons?) where they described the "insert shim ring" and "knurling piston skirts" to recondition - that's apparently the way they did it 70 to 90 years ago. Even today I would be hard pressed to find a reason to recondition grooves and skirts. Even if it were a unique machine, there are so many over the counter piston options that can be made to work. We had a 1942 BSA M20 that needed a piston and we made do with an industrial engine piston - worked like a charm.


.[/ven with QUOTE]
Well that's kind of a snotty retort if I may say so. I am not yet a hundred years old and yes although the technology may have been around for a while, it works. As I mentioned "IF the pistons otherwise measure well" it is a way to go, and the fact still is, a piston with a steel spacer will outlast an all aluminum piston in regards to ring groove wear. And actually may slow bore wear too because as the groove in a piston wears, it's ring is fluttering up and down. Besides pumping oil, that is a cause of bore wear too. That alone is a reason to consider the work over new. Again, IF the bore and piston measures well. There are other methods that may indeed "work like a charm" but to say reconditioning a piston is not a viable option is just close minded.
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Well that's kind of a snotty retort if I may say so. I am not yet a hundred years old and yes although the technology may have been around for a while, it works. As I mentioned "IF the pistons otherwise measure well" it is a way to go, and the fact still is, a piston with a steel spacer will outlast an all aluminum piston in regards to ring groove wear. And actually may slow bore wear too because as the groove in a piston wears, it's ring is fluttering up and down. Besides pumping oil, that is a cause of bore wear too. That alone is a reason to consider the work over new. Again, IF the bore and piston measures well. There are other methods that may indeed "work like a charm" but to say reconditioning a piston is not a viable option is just close minded.
 
Hurt feelings? Really?

Never said it was not viable; the question is why when there are more viable and commonly practiced options. Sure, casting up and machining one’s own pistons is viable if ones time is not worth much. Never said machining and inserting a shim or wider/thicker heavier rings would not work as it was done back in the day.

If someone is a gifted and skilled machinist then have at it IF the pistons with something like 90,000 miles on them are still serviceable.

It’s really a matter of context. I never saw it done nor heard it done for a Norton twin.

Really a bit off topic from the OP’s issues.
 
I don't really think off topic at all. Peter R was asking or wondering what course of action to take after concluding that although the pistons and bores measured up fine, the top grooves were worn. Knowing of an alternative to simply buying new, I put it out there that groove restoration was a possibility. Casting up and machining one's own piston is a bit of an over the top comparison (unless of course you're Burt Munro). What I am referring to is still a bit more main stream than that. Though I never had this done for a Norton engine, I did get this done years ago (as well as knurling the skirts as a matter of fact) of a 650 Thunder Bolt. It works. Again,,, IF everything else measures up perfectly or nearly so. The best way to go IMO would be to go to a +20 overbore along with + 20 pistons and the barrels honed to give .0045" skirt clearance. That would equal perfect in all respects. We can probably agree on that. Unless I am way off base in my estimate of money saved by restoring the ring grooves over purchasing new pistons though,I think just plunking new pistons into even slightly worn bores is a waste of new aluminum.

And really Dances, this is fun, it is nice talking with you. - Pete
 
Plus, it gets recycled. So the only thing that’s wasted is the resources to process it!

FWIW, I thought the ring land recovery method was interesting, I’d never heard of it before.

But also FWIW and IMHO, I wouldn’t entertain it on pistons that are so cheap and readily available.

Interestingly, the DiamonDyze hard anodising treatment that I recently used also coats the ring lands and claims to protect against this wear (to protect new pistons, not reclaim old ones). It’s also possible to have pistons Teflon coated, with a thick enough coating to take up some extra slack in bore clearances.

But, when all said and done, this motor has done 90,000km. Personally I’d get the bore measured by an expert as I find it hard to imagine that there is not enough wear to require a rebore after this mileage. Which is certainly not unreasonable after such good service.
 
The Phil Irving "Tuning for Speed" suggestion was to square up and slightly enlarge the ring groove and fit two thinned-down rings into one groove.
 
Triton Thrasher said:
The Phil Irving "Tuning for Speed" suggestion was to square up and slightly enlarge the ring groove and fit two thinned-down rings into one groove.
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Now that is clever! You can then have a sort of "Total Seal" ring pack where the ring gaps (should) overlap. Really what Biscuit is saying but taking it a step further though you would lose the benefit of a hard surface in which the ring would bear against though the spacer ring concept would still be flapping against an alloy ring land so maybe there's no benefit there. Phil Irving published Tuning for Speed around 1949; nearly 70 years ago!

Lots of clever tricks though I wonder how appropriate they are with something like a Commando with relatively high mean piston speed. I always had this concept that the steel ring insert "fix" was more applicable to older more agrarian style auto engines and industrial engines where mean piston speeds are relatively low. I can't help but think that this "fix" is stuffing more and more mass in the ring groove where there should be less and less.

I can see where you might do a piston/ring repair where you are repairing something like an AJAX, Cooper-Bessemer or Worthington industrial engine where a replacement piston is probably costly if not unobtanium. In these instances I can see where the ring groove repair would make sense; especially if you were in the Arctic Circle in Far East Russia.
 
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I was thinking of just squaring up the lands with only a 1 thou or 2 thou cut, then install a set of +0.002 or +0.004 thicker rings (if a manufacturer makes oversize pistons and rings, why not make 'oversize = thicker' rings), you would be back on the road for the cost of new rings and a hour of machine time. What about coating the piston after the rings have been squared up - with nickel. When I was in a machine shop building industrial aluminum pistons, the owner decided to nickel plate them all to reduce wear, including the completed ones on the shelf, so I had to recut them all by 0.0015" (diameter -0.003, ring groove width +0.003). This would combat piston wear, increase diameter of the piston by a few thou, which would allow just honing of the cylinder to restore original clearances. Could be an option, not sure if it would only be applicable for vintage machines near the Arctic Circle though (lol). The expense may not be cost effective due to the readily available replacement parts, but it is interesting.

Here is a bit of info I found:

The technique of electroless nickel plating has been used widely in race engines for a long time. Electroless nickel is a family of coatings rather than a single coating, and a number of electroless nickel 'composite' coatings are available. Even where the coating is a plain nickel coating rather than a composite, there are different types of coating...Perhaps one of the best-known applications of electroless nickel coatings is on pistons. In engines that are especially prone to combustion knock - that is, where very high compression ratios are used, or where the engine is supercharged or turbocharged - electroless nickel coatings can mitigate knock damage. The coating has been widely used in turbocharged rally engines for a number of years, and the main area of application is the piston crown and top land.
https://www.highpowermedia.com/blog/3331/electroless-nickel
 
If you really want to reuse the original pistons, the simplest solution would be to machine the top groove for 5/64", or even 3/32" rings (stock Commando has 1/16" top and second grooves). Both are available from Hastings and other suppliers to fit 73 mm bore size. I'd go with new pistons myself, mostly because of the mileage on the originals, assuming that the other ring grooves are also probaby worn. But if you have the tools, or a good machine shop that works cheap, this would be the cheapest solution. You do need to take care that the finish on the groove surfaces is very smooth, but a good machinist with a sharp tool can do that.

If the bore isn't worn, I wouldn't consider knurling the pistons. It works, but doesn't really last all that long.

Ken
 
Brendan S said:
Noted as well. And I thought it was damp where you live. You must take great care of your stuff.
Brendan
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True, although the bike has never been restored, it was well maintained troughout its life, although upon a closer look it is showing its age ,the red paintwork of the tank has faded, and the paint of the frame shows blemishes at some places, but since there are few Commando's around with original factory paint I would like to keep it that way al long as possible.
 
Peter R said:
True, although the bike has never been restored, it was well maintained troughout its life, although upon a closer look it is showing its age ,the red paintwork of the tank has faded, and the paint of the frame shows blemishes at some places, but since there are few Commando's around with original factory paint I would like to keep it that way al long as possible.
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Quite right sir!

Now then, have you decided upon a course of action for the piston question ?
 
Fast Eddie said:
Quite right sir!

Now then, have you decided upon a course of action for the piston question ?
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The ring land recovery as described here above, seems no viable option to me, although I have heard of this method before, it is discribed in Phil Irving's book Tunung For Speed, I doubt if there are local engineering companies willing or able to do this job, I will have the cylinders honed/deglazed and take it from there. The valve guides also show wear, and will have to be replaced while the head is off, it's a RH4 head by the way, and not showing cracks at the inlet ports, so carefull work is needed here.
 
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