Ring clearances

[(F5)]

So we're pulling apart a mate's 07 EC300 last night. Done a bunch of hours, but probably less than mine I did a few months back.

Piston didn't look that worn, but it was a different make to the one I'd pulled out of mine. Very similar but
1. had black coating on some of the areas with silver (unplated) border
2. ribs under crown different
3. skirt was finished differently on the inside.

Otherwise it looked real damm close. I assume one of them was a Vertex

Mine was considerable more worn. Neither was a Woosner (which is what I put back in). No evidence it had been apart before.

ok so back to the queer part. Mine had worn rings, the closed end gap was like 1mm. Std for the 300 is 0.5-0.8mm

So slotted his in a reasonable ways. . . 0.3mm! Hells teeth!

I would have though being that tight they would have bound on each end & bulged the ring into the ex port. Can't see any scraping damage at all.

This makes a bit of a mockery of the ring end finishing I've done on other bikes. Who else has seen such close fitment on their GGs?

Surprised that it is so tight & not worn for the time he has put on it. Looked a very low hour bike when he got it.

 

[Jakobi]

I think my 2010 EC300 had 0.4mm ring gap after 75hrs on the stock piston. Strangely enough it had piston slap. Dropped a Wossner in with 0.5mm which did another 80 something hours before I went to the 250. Those rings came out at 0.55mm.

 

[(F5)]

The std Wiseco in my 200 came out looking mint, & the rings that the previous owner had put it (said it didn't need them, didn't believe him) came out as new spec after 3 years of my thrashing so started to believe him.

Still 0.3 seems super tight for a 72mm bore.

 

[Jakobi]

Its on spec with Wisecos recommendations for a top ring.

72 millimetres = 2.83464567 inches
2.84 x 0.004" = 0.01136 inches = 0.288544 millimetres

 

[(F5)]

Hmm, actually you're quite right. Still seems pretty tight. GG manual over cautious perhaps.

 

[Jakobi]

Yeah I went over cautious with the first top end on the 300 and set mine at 0.5mm. Even with the 250 I used Wiseco recommendations and then added a touch more.

If they came out at 0.3mm though depending on how many hours on the top end, you'd have to wonder how tight they were when they were fresh.

 

[(F5)]

well yeah exactly the question in my mind as I was measuring them. Too tight & they must bulge, or at least scrape the bore of oil. You'd think that would wear them a bit more. Sheesh I don't know.

 

[desertgasser300]

At the sake of sounding ignorant, how would I check my ring tolerences?

 

[Jakobi]

At the sake of sounding ignorant, how would I check my ring tolerences?

When you have the cylinder off the bike and the rings off the piston you carefully compress the ring and place it inside the cylinder. Turn the piston upside down and then use it to push the ring down an inch or two. The piston levels the ring. Then use feeler guages between the ends to measure the gap.

 

[Jakobi]

well yeah exactly the question in my mind as I was measuring them. Too tight & they must bulge, or at least scrape the bore of oil. You'd think that would wear them a bit more. Sheesh I don't know.

Mmm. Hows the clylinder look? Like I said, I went pretty tight on my 250 engine. Well just over wiseco recommendations.

 

[(F5)]

pretty mint, no scraping at all really.

PS found gasket stripper works better than oven cleaner on PVs

 

[Jakobi]

Gasket stripper works a ripper! Costs more than oven cleaner but gets the job done quick and easy!

 

[(F5)]

just did my mates 300 & set them at .5. Safest & don't want to take chances with his bike.

Man I need to get my head mod sorted out to reduce the silly 2mm squish. but it can wait

 

[Wheelieman69]

Ring gaps

I am working on a 1999 xc250 (possibly a 2000)
I believe this is a wosner piston
Top ring end gap is .015 mm
Bottom ring end gap .010 mm

Cylinder wall is nice n smooth no gouges marked more on the exhaust side

Piston has marks on the side but pretty good looking still

After reading up these end gaps seem super tight and this is after an entire season of riding the bike and pretty hard too ! Maybe 80-110 hrs

Should I just put everything back together and ride on or open the end gaps before putting it back together ???

Bike ran really well all summer then the flywheel nut backed off pinning the fw and breaking the key. I decided to see what the top end looked like while I was wrenching. No damage to anything thankfully just replaced $10 key and adding a 8 oz fww as well see how it changes her. First gasser and I love it !
Pictures to come shortly..

 

[pscook]

I am working on a 1999 xc250 (possibly a 2000)
I believe this is a wosner piston
Top ring end gap is .015 mm
Bottom ring end gap .010 mm

I question these numbers. Why? 0.015mm = 0.0006". I am pretty confident that you won't get a feeler gauge thinner than 0.002" into any gap, let alone one that is that small. I believe that you are measuring in inches, so you have a metric gap of 0.381mm on the top ring, and 0.254mm on the bottom ring.

If you look at post #10, Jake gives a good representation of a good gap. I think you are fine with your numbers, assuming that you switched measurement modes.

 

[Jakobi]

I'm guessing he meant .015" and .010" (0.38mm and 0.25mm)

That would make more sense. Still on the lower end of spec. Maybe last rebuild someone forgot to spec the end gaps. In saying that if it was built with tight tolerences and never seen many revs, kept a clean air filter, a quality oil, and never been drowned, it wouldn't be unheard of. The first set of rings I pulled out of my 300 at 75hrs came out with 0.4mm gap. The next one saw 85hrs and came out also only at 0.5mm and had seen much more throttle application. I'll be pulling the current 250 piston down soon and be interested to see how much wear they've had. Its at 100hrs now and has been ridden harder than I ever had any of the 300 top ends.

 

[Wheelieman69]

yes jakobi that must be. but my feeler gauges say mm on them so thats why i put that???dgcues@hotmail.com
hers some pics
how do you know when the barrel needs to be redone as well ?

 

[Jakobi]

The real way is to have someone with the right tools mic the barrel and make sure its still round etc. The backyard mechanic usually just gives it a good cleaning with an abrasive pad to remove the glaze. If you've worn entirely through the cross hatching then its seen some time. If you can still see them its usually good enough to go another round. Thats assuming no obvious damage. Cracks, flaking, scoring etc.

 

[(F5)]

I've just lost tips of rings on an aircooled 52mm bore that had the gap in the boost-port. Evidence was it was bulging when hot (airs get a lot hotter it has to be said). but that was set at 0.3mm. I'd always gap the rings now to be sure. its a big bore & 0.5mm isn't going to cause any performance drop off.

Light rub of scotchbrite & if not grey ally showing through you should be right for this age bike where you're not chasing 0.1hp.

 

[Wheelieman69]

Thanks f5
I used the scotch brite and all seems good. I'll send out for nickasil and rb mod next time apart.