I have posted frequently on many forums about Hepolites and aftermarket pistons, so dont recall if I recited my screeds here or not in other discussions but Ill try to hit the high points and move on.
Hepolites were a OEM supplier of a cast piston. Keeping in mind CAST being an operative word. Generally okay and revered by many, I have used many sets and sold even more. However I never placed them very highly as some peoples prices may suggest. (There is some fanboys out there of them) I still have a few sets in original EARLY packaging so, Surely the early types. Hepolites over the years had different packaging so you can guess-timate the era of manufacturing by its packing. The original company was bought up by a US company, they did nothing with it, then broke it into pieces and sold off. There is other vendors now making poor quality parts under that name, I believe under license. Poor quality is a relative term because I never felt the originals were never more than a cheaply made part, however that low benchmark sunk even lower with the knock offs.
### I grew up building hot rod American V8s... So a cast piston was a cheap part and not worthy of any self respecting engine builder. Forged pistons were the minimum benchmark, But economies of scale are much different, And I have had car guys getting into classic British were shocked at some of the prices for pistons. For an approx comparison some years back I ordered a set of Cast Small Block Chevy 350 pistons for a grocery getter. Less than $100 for 8 pistons, pins and rings. For a set of much better Hypereutectic Was $160 and premium Forged was $275 FOR a FULL SET of 8! I had a guy ask about Original Hepolites for a 1961 Triumph Bonnie and he was incensed at the price at the time of $220 for a set of 2. (He opted for some cycle crafts I had for $90.00) Now days, some are using all kinds of interesting materials as manufacturing has evolved. A lot of discussion about Billet, and unthinkable before, but apparently its working out great. MAP cycle is selling Billets for a range of applications. Good reports I hear. ###
Now, when using Hepolites of the original company I have seen a great deal of quality variables. Pistons are graded and the better ones are matched up, When you turn them over NOS should have small painted dots.. green, red, blue etc. This means that L-R they are somewhat consistent. Castings can vary widely so they pair up sets to match. However its not uncommon to get a set that varies considerably by weight. Up to several grams. They can also vary by sizing. CONSIDERABLY between L-R and some Hepo's are absurdly mismatched to proper dimensions. So, when boring a cyl,, Its mandatory to label them L-R and hand fitted to each bore to correct dimensions as the piston ODs vary with Hepos in most cases.
Verify yourself, Throw them on a scale and measure with mics & calipers. Math is Brutal!
With Hepo rings,, again depends upon era manuf,, Some were quite good, (Considering) However later years not so much.
I have NO experience with JP. However I find the expansion joints on the skirts shocking! Holy hell that would keep me up at night! I have seen many decades of mayhem on the Nortons where such joints were a sure fire way to seperate the crown of a piston from the skirts with much damage. Even the later versions with just the holes would break with regularity. Many pictures online of blown up Nortons with these and the INOA tech digest expressly warns about this. I have heard of similar on other makes. Although I have seen a FEW race motors with holes drilled in the thrust face skirts for lightening, But in general a piston is like an egg,, It derives its strength from its integrity of the shell structure so a big slot, seems counterintuitive. Other than some 2 strokes have never seen that pencil out. (Expansion joints)
Now for 2 decades I was a huge fanboy of CycleCraft pistons. For a casting, they were excellent quality. The finish and casting quality was excellent. More importantly I found very consistent piston weights L-R and dimensionally they were so consistent I never found any out of spec. In some apps.. BSA A65 they were heavier than originals for example.. So rebalancing is important, But I like to balance everything so a minor issue. However the supplied rings were garbage.. I always used Hepo rings, Hastings or a few others.
I only found one instance of the piston weights being off in 25 years of using them and we caught it early. I believe that was an anomoly. I DID find the supplied pins varied but we always weighted them and machined the IDs of the pins to get a consistent weight. The supplied clips are a spring type and depending on what shows up, I never had a problem but in many cases I used special circlips I ordered for piece of mind. (There was a raging argument on a NotRun site about bad circlips and grooves)
So, When I was building a LOT of motors (Mostly Triumphs) I would take in 4-6 cyls at a time. (20-40-60-80 in a few cases) and drop off one set of pistons for each size with my cyl guy. The consistency of the cycle crafts was so good, I never had an issue with sizing. If it was for Hepolites?? hell no!! We carefully controlled each cyl and the pistons to get the holes sized exactly.
I only built a few Motorcycle engines with high end forged pistons, as its a different world than car engines. The reality is few people actually race or push these vintage bikes hard enough to justify it, so Cast pistons are usually adequate. However when I hear someone gushing excessively about a Cast Hepolite being the top of the game its amusing. Its still JUST a casting. And in the world of metallurgy a casting is subpar to other materials.
**One note on sizing. I still have some old dealer stock with 10 thou increments, but its very hard to find pistons and rings in those ranges. Back in the day they were supplied in 10 over, 20-30-40-50-60-70 and even 80 over. I have run Triumph 650s with 80s with no issues and high mileage covered because there was enough meat in the cyl. However I had a few cyls that were scrap at 60. Nortons twins the cyls were so irregular you take a serious risk at even 20 over, 40 is exceptional and 60 is a miracle! (Dirt inclusions, dross, casting voids and cracking are the usual rejection issues)
Manufacturers typically only offer ins 20-40-60 these days unless you can find some old dealer stock, then HOPE there is matching rings. ALSO note over the years, some pistons changed Ring designs,, which is a whole different topic, But the ring grooves HAVE to be checked they are suitable for the rings and vice versa
Check ring groove WIDTH and DEPTH!
I have had conversations with some of the largest US wholesalers and its painful for them to stock pistons for the more common BSA-Norton-Triumph as to get pistons made now requires huge orders in each size to get them done. Often these wholesalers will work together. (MAP-JRC-Walridge-British ONLY-and Healys operation-Coventry Spares). You guys are not riding enough and ordering enough. It can take YEARS to sell off enough pistons to justify a re-order. BSA A10s are considered so obscure very few people will bother to stock parts for them. BSA A7??? Ha! Good luck with that!