Which pistons are available for my ariel

[Vincent.vanGinneke]

Hello, Pete Kemp had a nice collection of 500 pistons with him at the rally, dont know if he still has some. I bought one NOS Std. Hepolite from him.
However, Omega from Oak Barn Road, Halesowen West Midlands B62 9DW have pistons for Vincents.
info@omegapistons.com or www.omegapistons.com
The one I have for my Comet is a +20 (ref: 1019, 8.0:1 ratio) . It measures 84.5mm the pin is 7/8" whereas the Ariel pin is 13/16" both have more or less the same pin to crown distance (Comet ± 21mm Ariel ± 20 mm) The Comet piston has a much shorter skirt; ±59mm compared to the Ariel Hepolite with 72mm.
Hope this is of any use, regards, Vincent (aka "The Dutch Branch")

[john.whiting]

I finally got around to checking out Harley piston prices. XLH 3 3/16 std to 60 over. US$ 115 with rings and pin. [thats for a pair]. Big end kit about $350[includes two new conrods.]Check out the V-Twin Mfg site. Would you want to buy a kit to build a replica 1947 Ariel?You can buy one for a 47 knucklehead. Regards John.

[robin.parker]

Still worrying about this!!
Has anyone had a look at a BMW R75 (airhead) piston, I've just looked up the spec, as far as I can, 82mm bore, gudgeon pin is 22mm diameter. I'd like to get hold of one to measure the height. I don't think the complication of Nicasil bore/soft rings had arisen during the life of the R75.

[admin]

Were any (later) R75's made with nicasil bores ?
I thought it was the later (80's) ones .. the R75 only goes up to early series /7 (and there were few of those)

[Vincent.vanGinneke]

R75 with nikasil bores? Aha! now that could well be the reason for Rommel to ditch in El Alamein....

[dave.owen]

I'm using a BSA Gold Star piston 85mm in my '30 ,might be too high CR for later engines as I think the combustion chamber shape changed(less domed) in later years.Only mod is a small end bush 3/4 " ID

Dave

[robin.parker]

Hi John,
As I said, the complications of Nicasil bores and soft rings didn't arise during the model life of the R75 (/5/6or/7)
On another tack, isn't boring our to 85mm pushing things a bit with our VH's non too strong cylinder base flange, I have mates who feel it's neccessary to realign all the head and barrel stud centres and fit BSA style through bolts.
Anyway if you guys round on me and tell me 85mm is safe, then surely that makes the (fairly affordable) 84mm Vincent piston a good choice.
Kind Regards.

[nevhunter]

The 350's are the weakest and often broke off when raced. The 500's have a much stronger base. (excessively thick really) and are a bit thicker in the bore and I am "happy" to sleeve them so, as the sleeve doesn't add to the tensile strength of the cylinder, I reckon you are safe to a 2 mm overbore. A few racing 500's here had through studs/bolts, but nothing lines up perfectly. If you analyse what is required and are happy, then go ahead, but for ordinary road work and authenticity, I wouldn't go down that road.
IF you put a plate under the base, the pushrods end up being shorter effectively by the same length which the adjusters might cope with but the pushrod cover tube length, will not crush the rubbers correctly. You may have trouble with the exhaust valve lifter as well.
The original design has the gudgeon pin quite high up, so there are not many period pistons have the same dimensions there. . The oversize Harley Sportster. (1,0000 cc low comp) style will fit OK and most of that stuff is very cheap
The lighter the piston you use will, if balanced correctly, give the smoothest running engine, so it's woth trying to keep the weight down.....Nev

[john.whiting]

Some early 30s ohv motors had an 85mm bore as standard[as did the ohv 500 KOC JAP].Possibly the sloper.I dont think the later longstroke motor would take a bore that big.Regards John.

[nevhunter]

People I know in New Zealand get pistons made by Venolia and Arias and Wiseco i
(All in the USA)
These are all high quality products and are generally forged. While forged pistons used to run lot's more clearance in aircooled motors I believe the later alloys permit running less clearance. I'm not a person who likes to run these motors with "smallish" clearances anyhow.
The recommendation for the type of piston often run just after war war here in australia. (solid skirt.) was .0035 " per inch of piston diameter which makes the figure for a VH around 10 thou. which will make a small amount of noise when started cold. Split skirt with "W" slot can run much less but is not recommended for racing.
This is getting a bit long winded, but surely SOMEONE should get some made. We have only had JP once the "old stock" stuff got scarce.
The JP piston will work OK (even though it is heavier than desired. It certainly won't break.) if you give it the right clearance and I wouldn't go for as much ovality as some of the grinds give you as the piston can only dissipate heat through the skirt contact with the cylinder wall in the main. There is not enough oil circulating in a standard Ariel single to significantly cool the piston and generally high volume oil pumps do not do a good job as the design of the scavenge oil system is inadequate, the oil accumulates in the crankcase and absorbs power and makes the engine run very hot. ( And leak oil everywhere)... Nev