Choosing replacement piston brand..

chasdev · Post by **chasdev** » Tue Feb 22, 2011 9:28 pm

I'm finally nearing the point of buying oversize pistons for my G9 and there are several choices floating around out there.
Would Hepolite be considered top choice, and if not them what would be (provided there is a detectable difference between brands)?
I've read about having to run increased clearance with some brands and I would prefer to not do so, if a brand exists that will allow more normal sizing of the bores.
Can anyone describe those offered by the spares scheme in terms of clearance required and/or any other direct observations relating to quality or fitment?Edited by - chasdev on 22 Feb 2011 9:30:52 PM

wilko · Post by **wilko** » Tue Feb 22, 2011 10:29 pm

Try hanging out for the original wirewound pistons. Occasionally they come up on ebay.

paul knapp · Post by **paul knapp** » Tue Feb 22, 2011 10:52 pm

Original cold clearances were in between .0005" to .0015" for your G9. Unless you can find new old stock pistons, you are going to have to run after market pistons with extra clearance. The main problem I encounted with my '51 Model 20 by doing this, beside the extra rattle when cold, was the weight, which I over came by machining out the I.D. of the heavy skirt, and removing extra metal around the gudgeon pin boss by using a rotary burr. I managed to get the weight down to within 6 grams of the original wire wound ones. Though, in hind sight, I now wish I had the crank balanced at the time.
These were locally made J.P. pistons
http://www.jp.com.au/JPPistons.html
and upon J.P.'s recommendation, since I run the bike in temperatures up to 40 Deg. the cylinders were bored to give .004" clearance.
I have had no problems so far.
Also, J.P. pistons are re-boxed in other manufacturers boxes in other countries out side of OZ.
(from the owner of J.P.)

Paul

Groily · Post by **Groily** » Wed Feb 23, 2011 9:47 am

I did get a good not-new pair of +20 Hepolites from AMC Classic Spares last year - always worth a try - but ring sets are hard for all bar modern substitutes. FW Thorntons helped me out, but the radial thickness of the compression rings available meant relieving the piston grooves a few thou. Ring height was correct.
Next time I'll probably go the modern route with the extra bore clearance, as frankly it is easier despite the issues Paul mentions.

chasdev · Post by **chasdev** » Wed Feb 23, 2011 11:33 am

I think I found a set of new-old-stock Hepolites in second oversize, but they may be higher compression than standard (which I don't want).
Can anyone translate Hepolite part numbers, the number seems to be 43267?
Also, will 1956 and up pistons fit earlier version twins?Edited by - chasdev on 23 Feb 2011 11:34:49 AM

alanjennings · Post by **alanjennings** » Wed Feb 23, 2011 5:56 pm

My model 20 is ready fore a rebore, but I keep putting it off!-not because I'm mean, but I hear of so many problems with modern "pattern parts"! All 1-make clubs seem to have this problem, with my Morinis it is the same. The V----t club has know got good replacement pistons-but they don't come cheap, but you pays your money and "smile" if the quality is good!

itma · Post by **itma** » Wed Feb 23, 2011 6:11 pm

just go for hepolite,often on ebay usa

Gerard Harrison · Post by **Gerard Harrison** » Thu Feb 24, 2011 1:32 pm

Have you tried Rabers Parts Mart in Los Angeles yet?....

Link: http://www.rabers.com/

they have a fairly extensive array of NOS bits...and some obscure ones as well.

I just got a pair of NOS Hepo's in .030 from them for my Atlas motor

They have a look-up/search capability you can plug your part numbers into

Mike is quite helpful on the old British stuff

Don Madden · Post by **Don Madden** » Thu Feb 24, 2011 5:02 pm

Err, Rabers is in San Jose, a few hundred miles north of L.A. but a very good shop. I usually drop by during my annual pilgramage to the All-Brit Clubman's Show, held a couple of miles away. Cheers, Don.

Gerard Harrison · Post by **Gerard Harrison** » Sat Feb 26, 2011 5:03 am

Right you are! Don't know why I relocated them to L.A., I'll blame old age. Link is good tho.
and they are my first stop for obscure original NOS parts

(Threadjack alert), Walridge is selling new production (oversize) P11/Matchless Scrambles pattern tanks in steel. I believe under their "new products" section w/photosEdited by - Gerard Harrison on 26 Feb 2011 05:05:17 AM