pistons

[natemoen]

There is a guy on ebay that always has ring sets (all 4 pistons) for 40. I got a set a few months ago. Don't remember they sellers name though. Every time I look though there seems to be a couple ring sets though.

[natemoen]

This is the guy I got my rings from. He has at least 4 sets of ring on ebay right now of various oversized measurements. These are 1st over, 45 bucks shipped.

http://cgi.ebay.com/ebaymotors/FOUR-...Q5fAccessories

[Rickrod3]

Even the 1st oversize rings are hard to find (and about $50 per piston when you can), so don't count on doing this; Tarzan lucked out and found a set. The 'big bore' kits are the only readily-available piston/ring sets still out there, and at $600 for the kit and another $100+ for the boring, not the cheapest fix either. That's why good used cylinder/piston sets are still worth money...

I agree with used cylinder and piston sets being worth the money.
Just wanted to know how the first oversize worked out.
I'm a little concerned about oil consumption when I put this motor back I would like to make the best repair for the money.

[natemoen]

Likelihood of you finding 1st over piston is about 0%. First over rings could be filed down and used on standard bore piston as long as the cylinders are still straight.

[crazy steve]

Well, personally I'd be more than a bit uncomfortable using 1st oversize rings in a standard bore. This is basically a .010" oversize set and is designed to be used with a matching .010-over piston/bore. All the 'oversize rings/standard bore' sets I've seen for other motors are only .005" over. While you can file the end-gap to make them fit, this also has the effect of increasing ring tension (pressure against the cylinder) which can cause accelerated ring/bore wear. Guys have got away with this, but I wouldn't do it...

You could get correct-oversize pistons (Arias, Probe, others will make them for you), but at probably $200+ each, still not an inexpensive option.

But the choices here are severely limited, so 'ya gotta do what ya gotta do...'

[Geezer]

I don't think this was mention already but if you're getting low compression on a test. Add 2 or 3 cc of thin oil (ATF or 10w30) to each cylinder, spin it over without the plugs for a few seconds then rerun the test as per the manual.

If compression comes up a lot, you need rings. On the other hand if compression only comes up a little or no improvement then it's a valve problem.

Sometimes on a bike with leaky guide seals, carbon will build up on the backs of the valves from not running the engine hard enough to burn it off. Let go long enough and valves will burn but caught early, you can run the pi$$ out of it and burn the carbon off. If this is the case. find a long, steep freeway up hill section and run it hard at red line in 2nd and 3rd gears for a while. Then ride home, let it cool down and test it again.

Geezer

[tarzan]

Well, personally I'd be more than a bit uncomfortable using 1st oversize rings in a standard bore. This is basically a .010" oversize set and is designed to be used with a matching .010-over piston/bore. All the 'oversize rings/standard bore' sets I've seen for other motors are only .005" over. While you can file the end-gap to make them fit, this also has the effect of increasing ring tension (pressure against the cylinder) which can cause accelerated ring/bore wear. Guys have got away with this, but I wouldn't do it...

I disagree with this.I used first oversize.The cylinders were well within standard spec.I honed the cylinders and filed the end gaps and installed all rings.The rings are fine.I dont know why filing end gaps would increase ring tension,you often have to file ring on new rings.I have never had a problem.
My XS had great compression and didn't smoke. If you are talking about the major diameter of the ring not being the exact same diameter of the bore,it never will be anyway.Anyway the amount we are talking about is negligible anyway.

[crazy steve]

I disagree with this. I used first oversize.The cylinders were well within standard spec. I honed the cylinders and filed the end gaps and installed all rings.The rings are fine.I don't know why filing end gaps would increase ring tension,you often have to file ring on new rings.I have never had a problem.
My XS had great compression and didn't smoke. If you are talking about the major diameter of the ring not being the exact same diameter of the bore, it never will be anyway. Anyway the amount we are talking about is negligible anyway.

I didn't say you couldn't do it, I said I wouldn't.

Filing the rings for end gap won't increase ring tension per se. It's fitting rings that are machined for a .010" larger bore that does that. Whether or not that's 'negligible', well, if you installed bearings or pistons that far off I wouldn't expect them to last too long. They made the different-sized sets for a reason...

As to the 'great compression and didn't smoke', well sure. Higher ring tension means a better cylinder seal. But (as always) there's a tradeoff. This is something drag racers have done in the past (before the advent of 'gas porting' and 'gapless' rings) and they were willing to accept faster ring wear; they replaced rings often anyway. But you run the risk of having the rings doing too good of a job and not leaving enough oil on the cylinder walls to properly lubricate, leading to possible scuffed pistons/walls, broken rings or even a seized motor. Higher ring tension also caused a measurable increase in internal friction and heat. Eventually they discarded this method (for the above reasons) and went to 'gas-ported' pistons. This is a series of tiny holes drilled from the piston top to the groove behind the top 'normal' ring, allowing combustion pressure to force the ring against the cylinder. This worked much better, as you only had increased 'tension' during the firing stroke, allowing the ring to work 'normally' the rest of the time, but even this sharply increased ring wear. These were all (except for gapless rings, which retained 'stock' tension) 'race-only' mods, as longevity in street use was poor.

Oversize rings can work, but these are the risks and downsides....

[Geezer]

You can use any of the 4 oversizes rings in the standard bore if the end gaps are ground to the correct specs.

Yes they will have more tension against the bore but that's nothing compared to the pressure exerted from combustion pressure. Rings don't hold back combustion pressure from spring tension alone, but rather this pressure gets behind the rings and pushes them out against the cylinder wall while pushing down on the bottom of the ring groove.

I think this is one of the more misunderstood aspects of engine theory...

Geezer

[Jerry]

I still have a set of Venolia-brand Alcoa forged 11:1 racing pistons, no rings, brand-new that I bought a few years back. Boxes say 80mm...don't know if that is stock or oversize. $50.00 plus shipping from 81601.











No wrist pins, either. Venolia is still in business, but I have never contacted them to find out if they still have rings, wrist pins, or other XS11 parts.

[natemoen]

Off the top of my head I think stock bore is something like 71.5mm so 80mm would be way oversized. I think the 1196 big bore is only 75mm

[Geezer]

Those 80mm pistons would require new sleeves for certain. I would measure them to find out for sure if they're 80mm or just in the wrong boxes...

Geezer

[crazy steve]

Ok, all this talk of fitting oversize rings, etc got my curiosity up. My knowledge is limited by what I used to read in the car mags and a few mis-planned experiments in years past. So I asked a real expert....

I emailed Kevin at Total Seal (their tech guy), and he actually called me on the phone. First, the issue of oversize rings. He said you can get away with doing this, although he said that going more than .010" over (1st oversize) can cause real problems with uneven ring wear, and he wouldn't really recommend even the first oversize. He said that too-large rings tend to go 'oval' and wear unevenly; the maximum recommended oversize in a stock bore is .005" . He said for the larger oversizes, he'd put 'em in and then sell the vehicle..

But the more interesting part of the conversation was that he was pretty sure he could come up with a full ring set with off-the-shelf parts. This would be a 'custom' set (assembled for this combo) which if I recall correctly was the problem when this was tried before; there were no 'factory' sets that quite matched up. For ring/groove sizes, I used info from this thread: http://www.xs11.com/forum/showthread...n+rings&page=3.. but as the groove dimensions were pulled off a used piston, he needs to verify the ring grooves by precise means (pin gauges). So, is there enough interest in a correct ring set that somebody who has a good loose piston would be willing to mail it to them? For cost, he said no more than $120 worst case but said 'I can probably do better than that when I know what's needed'. Maybe a 'group buy' could knock the price even lower... any takers? These sets may even contain their 'gapless' top ring for a performance boost.

He knows a little about XS11s; he remarked that his dad had a Midnight Special and he was 'impressed' with it's performance...

[Geezer]

This info is different than what I was taught in mechanics school and what I've seen in rebuilding engines. In my experience all rings tend to wear oval or elliptical in shape.

I don't have a bike apart to supply a piston but if the price was right, I'd be willing to get in on the group buy to have a set on hand. I was thinking next winter (2011/2012) I would tear down the top end on my bike and freshen it up with a new set of stainless valves. Adding in new rings at the same time would sweeten the deal...

I bought a set of .5mm Yamaha oversize rings cheap on eBay and I was hoping to find a set of pistons to go with them. Strangely enough right now the pistons are easier to find than the rings.

Geezer

[natemoen]

Absolutely I would be in on a buy for rings. It would be even better if it could happen by Luke February or march at the absolute latest so I could have them in before next.riding season otherwise I have to do the 1st overs that I have.

Would you need anything to get this going?