a resize works as well but for quick and easy the "removing a shim" method works just fine , sticking with the same percentage nitro which in most of our cases is 30%

To each their own. If I see any kind of decrease in power and the "quick and easy head shim removal" could possibly need to be done, I'm just pulling the sleeve out for a $10 pinch from my local guy. $20 tops if you have to ship it to a guy you dont know. Not worth risking a $160 dollar matched piston and sleeve for me to yank out a shim. Like I said, To each their own.

out of curiousity what makes you think removing a head shim will cause the p/s set to become "unmatched"

I never under stood sleeve pinching, trying to compress hard as glass chrome doesn't seem a good solution. lap honing a new piston to fit is the best solution, I have personally done that. but manufacturers won't sell us just a piston...

But I would have to agree with the other guys who say just drop a shim. I doubt pre-ignition is going to happen if the overall amount of compression at TDC is going to be about the same. I guess the way to really find out is a compression test between a freshly broken in motor vs a worn motor with removed shims. houston, done this? would you have a suitable subjects to do such a test?

A thing I have noticed in regards to carbon buildup, don't clean it off! especially the little carbon ring that develops around the cylinder. every motor where I cleaned that stuff off always ran weaker than if I left it alone. It does no harm, in fact probably aids a compression seal. and the carbon on the piston head retain heat for better ignition.

Thanks Newland for the insight on tuning. I think myself have been running the top too lean since we have come back outside. I always had the impression (told by others) you needed to run the low end richer. eager to try a different approach.

Since we are doing the opinion thing I will give mine. All of my motors run a tighter clearance then factory and have more compression and power. From what I can tell compression ratio has nothing to do with engine life. Improper tuning and dirt is the enemy!

I do not think the carbon layer does reach 0.1mm thickness but the carbon layer has a more important function, it act as an heatshield for the piston. Overheating pistons do get weak, the carbon layer does alow the engine adjusted to more performance without overheating the piston.

Expansion is the word why manufacturers do not sell sepperate pistons. Manufacturers do change materials which can have different expansion rates. With that you want a sleeve that folows the piston best. It is impossible to tell which piston does fit the sleeve and if you do combine different specs piston and sleeve you can notice that right away in several ways but not an perfect running engine

it maybe just me ... but i would think the carbon buildup will get soft when up to operating temps... do a test yourself.. take you carbon coated button and just put a little heat on it with some nitro... so i don't see ho what can help with proper tuning because the piston and button will have an inconsistent surface... maybe i'm wrong.. just like the carbon build up in tune pipes... if its not clean you loose performance...

but i maybe wrong... either way i use to clean the carbon off my engine parts if needed when i inspect my engine.. which is like every half gallon to a gallon ( depending on the conditions i was running in prior).. now that i switch fuels, carbon buildup is very negligible...

I clean everything except the sides of the piston/rings and the seal at the top of the sleeve

I'm not over heating anything, I was making a point. What's this have to do with the price of tea in china?

I was talking about pulling the shim and running the same nitro %. I can drive a couple miles and have it pinched. Even If It took a while for me to send it out and have the work done I still would. I would know before that though if it was losing power and would nip that in the bud long before there would be a shim removal option going through my head.

When the engine is near its end of life you could remove one shim to compensate the compression with the compression loss/leak. Another trick is to use a cooling head with more cooling capacity.

Hope I don't writes something you guys already has written:

Carbon build-up also happens with:

too cold plug
too low nitro percent
too low compression ratio

the ignition are in all cases too late.

I've seen several engines with tuning issues and carbon build-up due to too cold plug. Once I/they changed to a warmer plug, every issue disappeared. Many Danish guys runs Byron 25% fuel. Nice clear/gold piston and exhaust with the right ignition and total black with the opposite.

I have had several sleeves pinched and have worked just as good, if not better then a fully broken in new sleeve. I have several theories for this, the main one being that a seal has already been made with the P/S. So basically you are tightening a already perfect seal other then match a set from the get go. Plus you do not have to do the full break in procedure and can get some heavy heat cycling down in almost race conditions if it is a good pinch job, making for a very good sealed matched set. Like i said better then some sleeve sets i have done brand spanking new.

Some services are better then others, i have used a few different ones and rcrenew is by far the best and most consistant. perfect pinch, peak power and compression that tunes so easy it's ridiculous.

With many new engines an extra shim is included. By installing this shim you reduce compression and retard the timing of the engine. This eases the stress on the rotating assembly during break in, especially with the heavy pinch engines. After the break in procedure you remove that shim and it puts the engine back to the factory optimal compression ratio and ignition timing. No what alot of us do is run a gallon or so with this shimming and them pull another shim. This then increases compression and further advances the timing. At this point there usually isnt any fear of pre det but if there is its fixed with a colder plug. We try and squeeze every little bit out of the engines, run warmer than most people would but at the same time still get 8+ gallons and 13+ minute runtimes... To each their own though...

Yes, we actually include a blueprint sheet with every JS engine that shows your current head clearance, thickness of shims and quantity of shims for breakin, after breakin is completed (1.5-2gals) and 90% of the metal pinch is gone there is another chart with a recomendation of which shims and how many to remove for optimal race tune, power and efficiency. You dont even need any measuring tools.

2 gallons? wow. but then again i have only had o.s./werks/picco. 2 gal of breakin, no thanks i will pay someone to do that.