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Wanted NH HC piston +20 or +30

Posted: Tue Jan 14, 2014 6:47 am
by brenton.roy
Hi All, I'm building an NH motor for my son and am after a high Comp piston.
The only ones available in the +20 range via Drags or JP seem to be 6.3:1.
Thanks, Brenton

Posted: Tue Jan 14, 2014 8:57 am
by Nick.Wilson
Try CP-Carrillo over in the states. They make pistons and con rods. I will be getting a set of con rods made by them for my Square Four.


Posted: Tue Jan 14, 2014 11:52 am
by Bob.Murphy
Have you tried 'British Only Austria' ??

The ad' doesn't say what the compression ratio is - but it might be worth an e-mail ??

(Unless you know from the Part Numbers).


Re: Wanted NH HC piston +20 or +30

Posted: Tue Jan 14, 2014 12:51 pm
by brenton.roy
Thanks blokes.
Bob, I think these are JP pistons, so the low comp type.
Nick, have you had a quote for the rods? I know that Carillo and Arias will make forged pistons, but I'm a bit scared about the cost!

Posted: Tue Jan 14, 2014 6:05 pm
by robin.parker
Hi Brenton, Also from the US of A , try "Wiseco", looking at it another way, there ought!! to be a fair few 350 HC pistons knocking around on shelves and under benches, which, I guess is why you posted .
Good luck.

Posted: Tue Jan 14, 2014 9:44 pm
by Nick.Wilson
I got a quote for the rods, for the set of 4 it was $1512. Expensive, to say the least, but they are made out of chromoly.

Re: Wanted NH HC piston +20 or +30

Posted: Wed Jan 15, 2014 8:20 am
by david.anderson
I guess you have seen that Drags have Italian GPM 8.5 pistons in standard size only. You may be able to go direct to the manufacturer GPM for oversize pistons (although I have been told that GPM are now being made in China?)
Apart from that JP do make specials and they are close to you. Somewhere I have an old diecut Y alloy hi com piston that is standard bore. It has been seized badly but could be copied. It worked well in the 48nh when I first built it, apart from excess piston slap. In fact the bike registered 100mph on the speedo with that piston (PA speedo gears and chronometric speedo). I did not check the com but I believe it is about 9. It is visibly less than the Hepolite 10 and more than the 8.5 GPM that I have. There was no pinking at all. If you want to borrow it to be copied you are welcome.
The 48nh has been sleeved back to standard and is running an 8.5 GPM.
The problem with chrome moly rods is that they are heavier than the originals. This will increase vibration and increase the flexure in the crankshafts which are already known to flex excessivley. A few years ago there was a gent selling carillo rods by advertising in Cheval. A friend bought a set but complains that it transformed his vibration free 4 to being not so pleasant to ride.

Posted: Wed Jan 15, 2014 8:54 am
by brenton.roy
Thanks (again) David,
I'll talk to Peter at JP's re what he has lying around or could adapt. Stephen (son) has been there twice, but they have been closed the past couple of days.
The barrel is pretty good and unsleeved standard, no scoring but a bit of a top lip. I did think about taking a punt on a standard piston.
Thanks for the offer of your piston to copy.
The club spares list mentions a +10 with 'good compression' I'll ask what this means..
You never know, someone might have one in a box somewhere...

Posted: Wed Jan 15, 2014 10:53 am
by Nick.Wilson
Thanks for that information David. I might still give them a try, just to see what the person building my engine can do. If not i might look into the rods that dragonfly have.

Posted: Fri Jan 24, 2014 12:11 pm
by brenton.roy
Happy days.. After taking up David's offer of a piston, I have now discovered a +20 at your piston dealer Thornton's.
I see now why the UK people are so positive about them. Reasonable price, quick service. Duncan, the rep wrote back straight away.
The piston they have is 2 1/4" from centre of pin to top of crown.