[Karl Childers]

.....Something that I'll be doing this winter and I'm looking at H's offerings and trying to make up my mind which way to go. The cheapest option is to just get a forged piston and keep the iron barrel as it has only about 2,500 miles on it and most likely will not need a re-bore. The alloy barrel appeals to me more so I see two options there, go with the 500 barrel and forged 84mm piston and keep my nice friendly compression ratio and same performance level I have now or go instead with the 535 kit and it's higher compression ratio that I would either initially offset the cam by moving it a tooth or go with a (de) compression plate. I'm not planning to replace the crankshaft this year it's just not in the budget, in the meantime I don't want to stress the stock crank with a high CR. The most important goal to me right now is to get a reliable piston in the motor but if I do at a later date want the better crankshaft and a little more performance I'm thinking I should get the 535 kit. I'm looking for opinions on what get for this phase as well as other options I might consider.

[AzCal Retred]

My dos centavos - You are a mature, experienced, mechanically sympathetic rider, shop at the "Big 'n Tall" store, and there's no substitute for cubic inches. I vote for these parts:
PART No. 200074C  ;  BIG BORE KIT, (ALLOY BARREL - INDIAN MADE) with forged 8.5:1 piston  ;  £319.00
PART No. 200480  ;  COMPRESSION PLATE (ALLOY), 500cc, 2mm  ;  £12.50

All that is about $440 USD, the shipping is likely $60 more, so $500 gets you a "man" motor. The forged piston has some hairy valve recesses milled into the top. A Dremel and maybe 30 minutes could smooth these out, notching back the compression a bit and removing some pre-ignition carbon collectors. The $15 USD compression plate is backup if cranking compression won't settle down to a polite 125-130 or so after the rings break in. As you say, the intake cam can always be retarded a tooth as well, and you'd have enough compression to make a perceptible difference. Maybe tighten up/replace the centripetal ignition advance springs to keep "full retard" properly located to prevent surprises when kickstarting.   

I think the iron barrel is OK where it's always about 50F, but it just adds something else to worry about. If you want, I'll give you my old iron barrel and you can use one of these 0.040" over Bullet Whisperer recommended pistons. $120 USD, mebbe $150 by the time it hits your door, a $60 local bore job and you have a nice 500cc running at perhaps 7.5/1, according to BW. You can always drill out or notch the fins on the barrel to increase exposed surface area like we did in the wayback. So about $200 or so out of pocket would get you a better piston and improved CR, but heat transfer won't be as good as alloy. As long as you aren't flogging it hard it 's likely all good though at New Mexico mountain temps.
PART No. 42877/40  ;  PISTON, 84mm +40, 9:1, C/W RINGS  ;  £88.00 (about $120 USD)

Cheers - ACR -

[Karl Childers]

Thanks, as always I'm relatively new to these motors and don't want to make a misstep due to lack of knowledge, I'd hate to turn the engine into a grenade. The 535 upgrade with an alloy barrel is really what I want so now I feel better about getting it! While on this subject a couple of things come to mind, one is if I did have to use a compression plate do they need a base gasket on each side or does  of the plate seal itself? The other is painting the alloy barrel, I really like the black look of the iron one and I'd like to replicate that if the paint will hold up reasonably well, is this something others have done? I'm thinking VHT header paint should do the trick but have no experience with this particular part.

[AzCal Retred]

The emissivity of black paint is more than bare aluminum, it radiates more in the infrared and enhances net heat loss. Every Japanese 2-stroke I ever saw had a black painted motor, and you just know those boys have numbers to back up their choices.

Ace says you don't need a base gasket, just goober some Motoseal or other non-hardening gasket goop on there. Myself I'd Motoseal the top of the compression plate to the bottom of the cylinder, then slap a well greased base gasket on so removal would be easy later.

I'm sure the 535 kit won't frag a good crank if you don't spend a lot of time lugging the engine. I see lugging as 1000 - 1500 RPM under load. That's a big advantage of a $1400 custom rolling element crank, it's relatively immune to oil pressure issues, it just needs "some". But Bullet Whisperer has had good luck with stock cranks. If the crank is marginal, the 535 may put it over the top, but it would just accelerate what's going to happen anyway. Price Part Cycles has a stock crank with a rolling element conrod bearing  for about $600 if it comes to that.

[Mr_84]

KC I've been pondering this quite a bit lately too, I'm thinking I'm just going for forged 500cc in the alloy barrel low comp piston with no base gasket. Yesterday I had a parcel arrive from Price part in the UK with my Samrat rockers in it ,took awhile to get here but I'm happy I have them they are quite neat looking little units ,a bit of unobtianium these days. Also doing the comp valve kit and alloy push rods so no real gain in performance for me but a bit more reliable I guess

[AzCal Retred]

I put the 6.5/1 forged piston/steel rings/alloy barrel combo in mine. About 500 miles and the piston & rings were sealing well, good power like I'd always imagined it would. The "Nivea" problem went away, I guess when the rings actually seal the combustion byproduct water vapor actually stays on top of the piston & just exits via the exhaust valve instead of blending with the oil and being whipped into mayo.

Replacing the piston is for the reasons you mention, removing an incipient failure. I know the OEM pistons are very soft, and AdrianII says they can both drop a skirt and have the top separate off. Either option is likely to frag your engine, so a piston/barrel is cheap.

The forged units are much "tougher" and more thermally stable. The classic soft seizure is what happened to me on the OEM unit - a long gradual uphill in 4th, the engine "just" pulling it at maybe 2500 RPM. Power drops, the engine starts to bog, the piston outgrows the cylinder & wipes soft alloy into the ring lands, severely degrading sealing ability. Mine cooled enough to run the 20 miles home, but you could tell it was damaged. The same grade on the forged unit is worry free.

Pricepart sell a nominally 7.5/1 87mm piston with a 535 alloy barrel, maybe 250 Pounds, I think that would be a good basis for an engine. I think if you aren't a teenager you'll be fine. Chuffing about between 2000- 4000 RPM shouldn't hurt anything and you'll have plenty of oil flow. Midrange should be even better for keeping up with traffic & even the occasional pass. The H's lightened alloy pushrods rods seem the ticket, reducing actual reciprocating weight by 50% has to really cut down on inertial loads. The alloy valve spring retainers are a good idea, but unless you are "buzzing" the motor you don't need heavy competition springs, they just load up the valve train, adding back valve train wear that your Samrats & light pushrods just pulled out.