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Post by Jim on May 13, 2017 8:22:29 GMT -5
0.005" isn't bad. I used to rebore when it got around 0.006", but even then it was more to make it quiet than because it needed it. When the big end rod bearing gets near its wear limit, you get more noise from the pistons at idle too. My piston clearance is under 0.003" now, but it's noisy at idle because the rod bearings are getting loose.
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Post by acceleration on May 13, 2017 15:53:35 GMT -5
Cylinders that are straight and round are really important.And always best to check with a dial bore gauge during the boring and honing.Not rush through the process as so many seem to do ? But check as you are cutting the cylinder and when honing it, in steps, to make sure they are straight ? Many piston to wall failures are a result of cylinder not being round and straight.And clearancing gets the blame ? I remember back in the mid 70'S when I called DENCO to get a catalog (which I still have) and order some parts.They were kind enough to take the time to give some advice on what to do and what parts to use.They didn't just try to sell me some parts. I recall being told that on their race bikes they ran the piston to wall quite loose because they made the most power like that.They also told me that they would change rings at the track when they were racing, they could tell when the rings were getting weak because the ET/MPH would start to fall off.Said they would change rings at the track and not even deglaze the cylinder !! And said it wasn't needed if the cylinders were good.That the rings would seat,I did buy some parts and man those race clutch springs were really killer.Could never get used to them.Really hard to pull.But the clutch didn't slip !!
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Post by lc on May 16, 2017 22:12:47 GMT -5
Leo posted this on one of he Kaw triple forums:
"Have meanwhile fitted Al-liners in two sets of H2 cylinders. The first set some 10 years ago with 0.04 mm clearance. This is for both roadracing and long distance travel (700 mi/day). At the time 88 RWHP with VM34's. By now 100 RWHP. First with Wiseco's, then back to stock Kaw pistons because those have stronger skirts. Another set H2 was worn out 2nd oversize, now back to tight 2 nd oversize (0.05 play) with stock cast iron sleeves. This is my Lush-tune engine with now 112 RWHP. A 3rd set is a worn out 2nd oversize H1 bridged inlet cylinders, now back to a quiet set with tight 0.04 mm play thanks to Powerseal-coating. Never had anything come loose. Did suffer three nippers over the years: 1 due to leaky basegasket, 1x faulty one-way-oilvale, 1x empty oiltank. Every time just the piston required replacement along with a two stroke diamong hone."
.04mm (h1) .00157in and .05mm (h2) .00197in
I emailed Wossner. They told me the coating is .0003in thick. (appears to wear off).
J
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Post by Jim on May 16, 2017 23:42:17 GMT -5
I figured the coating was really a break in thing. After a couple thousand miles, it's only in the low spots of the machined surface, and there's very little skirt wear.
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Post by acceleration on May 17, 2017 7:42:32 GMT -5
We have used coatings on pistons for bikes and have applied it to pistons here in the shop.You have to hit the skirt with aluminum oxide giving it a shot blast to prep the surface for the coating to stick, apply it and then let it dry for 24 hours and then bake it at 350 or so degrees so that the coating cures.You can put it on "as is" it does not stick as well and wears off.Wiesco does not do that ?IE: Just applies the coating to the new smooth surface on the skirts ? And that is probably why it wears off quickly.Wossner too ? It sounds kind of scary to shot blast the skirt of the pistons.But it works.It roughens up the surface and gives it some bite for the coating to stick to.Last set I looked at to see how it was holding up ? It did wear shiny but didn't wear right off, but was smooth and shiny from running.Put the Teflon type coating on the skirts and thermal barrier on the piston tops.Measuring the piston and then checking the cylinder with a dial bore gauge and then arrive at your piston to wall clearance.You can actually build up the piston skirt to tighten it up in the bore if you find that it is loose.But you can only build it up so much.
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Post by roco on Jul 28, 2017 18:25:39 GMT -5
It's the old story every machinist is an expert, I had disaster after disaster using wosners and wiseco pistons, they ran great and sounded good till about 1500 mile then the dreaded rattles started. Part of the problem is the soft cast iron cylinders that wear just by looking at them in the end I had the cylinders nickasil coated and bored with a clearance of .002 yes .002 thou, many heat cycles and riding it sensibly it has now done 5200 mile and still tight. Nickasil is extremely porous and holds oil well. Another sensible thing to do is to upgrade your cylinders and heads with a squish band of 18/20 mm this will stop the preignition and the engine will run much cooler allowing to run one or two ranges hotter stopping plug fouling.
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Post by Jim on Jul 28, 2017 18:57:36 GMT -5
It's the old story every machinist is an expert, I had disaster after disaster using wosners and wiseco pistons, they ran great and sounded good till about 1500 mile then the dreaded rattles started. In recent years I've learned to embrace the rattle, rather than worry about it. With dino oil, stock plugs, and the stock pump set to stock specs I haven't fouled a plug in my H2 in the last ten years.
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Post by givr on Jul 28, 2017 19:32:47 GMT -5
Precision cycle bored my h2 cyls and checked all the wossners. There were all exactly the same diameter. Went with wossner recommendation for clearance and that engine ran absolutely perfect.
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Post by roco on Dec 23, 2017 20:38:56 GMT -5
Again for my 2 bobs worth my H2 which was nickasil plated and set at 2 thou.002 and Wiseco pistons is still strong with no piston rattle at 10800 mile I see no need to pull the cylinders and check anything I will have a look at 20000 mile this bike is used for weekend burn ups and long trips up to 400 mile is cruises happyly at any speed I want any body interested I can run thru the things that I did to get it to this point .
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jyrgnorway
2nd Gear
H2B CAFE, H2B, H1B, F8 BISON, Z1000ELR, RD500
Posts: 468
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Post by jyrgnorway on Dec 24, 2017 17:29:13 GMT -5
Roco: yes, please Jørgen
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Post by JA-Moo on Dec 24, 2017 20:03:29 GMT -5
Wossner coating is just a break in coating really. I go by factory clearance myself.
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