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Pistons for a Domi 99 - good ones, bad ones?

Submitted by tony_wood on Tuesday, 14 May, 2019 - 11:13
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Heavy Twins

Hi.

I’m going to be needing some new pistons once my barrels have been repaired. I’ve heard lots of different opinions about various brands. I’ve been warned about GPR ones - someone said that the pistons are ok but the rings are rubbish. Someone else said that he’d had problems with JP pistons and I’ve been advised not to go anywhere near Hepolite ones unless they are genuine old stock. (I was told that Hepolite are now made somewhere in the Far East and are of dubious quality).

So, if I take all those opinions and distil them, the only pistons I should get are genuine NOS Hepolites - and where am I going to find those?

One guy I spoke to said he uses Triumph pistons in his Domi, but that just sounds odd as the Triumph ones don’t have the valve pockets set at an angle across the piston’s top face.

I’d be interested to hear what other Domi 99 owners are using and any expertises (good or bad) they might have had.

Thanks

Regards

Tony

Submitted by robert_tuck on Tuesday, 14 May, 2019 - 15:00

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I managed to find some old stock 650ss pistons for my 99  ,had to use my 99 pins and rings from anywhere, They have been good.  You may be able to find some SH old (99or650) pistons and bore to suit them.

Submitted by david_cooper on Tuesday, 14 May, 2019 - 16:03

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I notice that the cost of liners (£60 a pair from RGM) is far less than pistons (£175).  I don't know the likely machining costs to fit and bore, but it might seriously affect the decision for anyone who has some old pistons...

 

Submitted by tony_wood on Tuesday, 14 May, 2019 - 18:58

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Hi David,

I discussed using liners with a couple of engineering companies that specialise in engine work when I was thinking of having my damaged barrels lined but there was a lot of concern about the very thin spigots that would be left after the cylinders had been bored out to take the liners. General opinion was that it was a bit risky. That’s why I went for a different set of barrels.

regards

Tony

hello  well good piston are  BHB  if you can find them but they're out there like  Hepolite  Pistons marked with  AE auto parts inside the bottom skirt  RGM as only GMP  Piston  some say they're not bad if you like Lead Bricks    so go hunt  for some good pistons   yours anna j

 

Submitted by tony_wood on Tuesday, 14 May, 2019 - 19:02

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Hi Robert. I’d like to find some +10 pistons but then I’m not sure I’d find the correct rings. It seems odd that finding good quality pistons for Nortons is so difficult - I can’t believe there’s not a demand out there.

regards

Tony

Submitted by robert_tuck on Wednesday, 15 May, 2019 - 05:59

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Rings will not be a problem.Probably the best place to find some used but sound pistons is on this  site. Do not bore the barrels till you have your pistons. You should however get the barrels properly measured to see what they will clean up to.

Submitted by john_shorter on Wednesday, 15 May, 2019 - 15:52

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I have had no need to fit liners, although I considered it. However, I was under the impression, possibly wrong, that top end of the liner protruded from the barrel, forming a new spigot.

Submitted by robert_tuck on Wednesday, 15 May, 2019 - 18:17

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You would think that a stepped liner that would give a new spigot would be availiable for the older twins, It would also ensure that the liner could not slip down. Perhaps no one thinks it important to do a proper job.Dissapointing.

Submitted by david_cooper on Wednesday, 15 May, 2019 - 18:47

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The RGM liner looks like the one you want, complete with spigot. 

My Dommie was lined by PO but inside the original spigot. The spigot is of course a little wider and more robust on the 500 bikes.

Submitted by robert_tuck on Friday, 17 May, 2019 - 07:49

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Happily the  bare  and disregarded  old stock 650 AE pistons I found are working well in my 99. I have switched to a fully synthetic oil ( with no ill effects)  to give them the best chance of a long life ,along with an air filter. Perhaps this is the way forward.

 



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