Ariel Owners Motorcycle Club

Check the pin length. I think on the FH the JP pin is shorter, consequently the circlips are closer together and the Hepolite pin is too long to fit in the JP piston.

SG

Sort of......

Essentialy .002" oversize. Just ease it with an adjustable reamer. and you'll have a good bush fit. Nev

But the other way, would you do that ?
lighter 'thinner' Hepolite pin in the JP ?

JP spec for pin for VB piston, OD = 0.8125
https://www.norndaautomotive.com.au/jp- ... 0(1936-59)
Which is...20.638mm?
Poor quality control, get it replaced with another one??

SG

Taper bored Pins are better. Sometimes I bore them out myself. The less reciprocating weight the better.. Nev

nevhunter wrote: Thu Dec 05, 2024 6:47 am Taper bored Pins are better. Sometimes I bore them out myself. The less reciprocating weight the better.. Nev

Thank you, I completely agree about reciprocating weight. I have a new VH +.060 piston set ordered and will compare the pins once I have the new one in hand. My tapered pin OD 0.8105", weighs 72 grams. The Heplex 11497 piston that was in my engine has a CR or 5.7:1, therefore I will be increasing the compression ratio from 5,7:1 to 7.5:1 so would the higher CR be the reason for the thicker/heavier pin?

Looking at the Hepolite doc, the low compression piston uses exactly the same gudgeon pin as the highest tuned HS model (and all 20.61mm dia!).
The full specs carry across two pages and it's necessary to use the line numbers to marry up the details.
line no. comp ratio gudgeon pin
29 8.7:1 4310A
36 (concave) 4310A
37 7.5:1 4310A
38 8:1 4310A
39 6.8:1 4310A

What I have noticed is the small variation in specified bore sizes for the 500 single engine - 81.787mm, 81.8mm and 81.812mm.
(The smallest size is for the alloy-barrelled HS, so it's smaller allow for greater expansion of the alloy cylinder barrel? That's going to be a bit controversial here I suspect.... )

SG

The Hepolite pin diameter being on specification, it slides in the JP without any effort.
The JP pin only goes in by -ofcourse- heating the JP piston.
I assume that it is not wise to use this Hepolite pin (because of it's weight advantage) in the JP piston.
The JP piston quality might be o.k. but they dont keep the OEM

I'd only KEEP a non-taper bore pin for cost reasons, The pin is case hardened and not easy to bore out when already finished. Better done at the production stage. A small comp ratio increase wouldn't make much difference. Revs are a bigger factor. The tension and a BSA Gold Star rod is about 6 tons at 6,000 rpm . Most OEM piston pins for Cars are just Mild steel bored parallel.. A single cylinder Powerplant is a bit of an oddity especially when It;s mounted direct in the frame. Not likely to be used in cars.. Nev