Hello there, I need to rebore my Mk3 to sixty thou and the question has arisen what piston to use.
We have forged and cast pistons and several different makes of piston at all different prices to choose from. I was going to use Hepolite, but told not to. Then I read that for normal running of the bike, cast pistons totally adequate. Forged pistons to be used for racing and if your going to thrash the bike a bit. Plus forged pistons are a bit noisier "rattle a bit" as clearances are different.
The Hepolites are cheap compared to other cast pistons that I have priced. So at the end of it all I am getting a bit dizzy reading all the info.
So to make me a bit more dizzy I would appreciated the members thought's and experience on this matter.
Bill
Nothing wrong with Hepolites…
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Wow, what some advice,…
Wow, what some advice, thrash an 850 - how? it will rev out about 1K rpm less than a 750 unless it has a large valve job. Forged pistons, other than the Omega's and maybe JS pistons whom I'm not sure supplies them in standard for the 850 there is no one else making forged pistons.
Forged pistons rattle more - total tosh, if made from the correct alloy they can be fitted with tight clearances, ideal for a water cooled engine but not ideal in an aircooled engine, so a little extra is wise, but they still don't rattle as the clearances used for the cast pistons are the same.
Pistons aside, a poor rebore and fitting will not allow any piston to last long. Also, be careful with JCC pistons, as they come from different channels of supply and the rings differ and this gives the pistons itself a bad name. The worst rings on the market are no longer being made thank goodness, they were awful. Whatever you fit these days, providing it is fitted correctly will last many miles.
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Forged Pistons
The +0.040" JE forged pistons in my Mk3 aren't noisy at all even after 27k busy miles and 0.005" clearances, the best for power and torque with the JE alloy.
JE a more expensive option but way lighter than stock, have high quality thin ring sets and positive gudgeon location with simple wire lock retainers.
Jim Schmidt in the USA sells them for standard conrod 750 and 850 Commandos.
Some replacement Commando pistons had a problem with ring sets and poorly designed gudgeon circlips coming loose causing serious engine damage as in this recent NOC example. Could be why you were advised not to use them.
https://www.nortonownersclub.org/forum/jcc-pistons
You may want to research the Access Norton forum which has many posts on this subject and possible fixes to avoid big problems.
Before the JE set I bought some +0.060" modern Hepolites, much heavier and found white corrosion on both pistons. Got a full refund and ordered the JEs.
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Nothing wrong with Hepolites, they are made by JCC and are a nice piston. I have used them many times. approx 30K miles on the set fitted in my Mk3. What was the reason you were told not to use them? Was it a dealer who doesn't stock hepolites and wants to sell you his more expensive pistons?