Out come the coated ProX pistons, so disappointed

[1976RD400C]

So, I tried these ProX pistons after using the 2 sets Wisecos for the last 10 years with no problems except a crack forming from excessive clearance, they didn't work out. I had about 150 miles on them and noticed the power was no where near the Wisecos. Anyway, I loaded my bike up along with my SV for a track day yesterday. After lunch I fired up the RD and the first run, down the straight I come, where's the power!? Not there. It was running 20mph slower compared to the Wisecos. Ran it for the one session and said I better park it. Tore it down this morning and wow. My cylinders are torn up and a another rebuild is needed. I don't get it. I scraped the coating off a little on the pistons, like the Chuck suggested, measured, set up clearance at .0019". Check cylinder taper and roundness, within .0002". Should be good to go. I don't think I did anything wrong?? I guess I'll try again. I almost looks like it was eating dirt but I have foam air filters. I never saw anything like this. It seems the rings didn't seat, maybe because of the coating? There is severe wear above the exhaust port and the piston skirt is wearing the cylinder below the intake port. The Wisecos didn't wear the cylinders anything like this severe. Contemplating what to do next. After riding the SV, I think the RD can barnstorm through the back section of the track better, it is so flickable compared to the SV that I have to plan and guide through the turns. I just want the power back like it used to have. I didn't take the kickstand off the RD and had a moment when it hit in a turn with a dip. The photographer was at that turn, maybe he got a pic.

[m in sc]

Weird, i run prox a lot, i also tend to run them at .0022-.0025 and have never had that issue. bad rings? Maybe switch over to vertex?
that does suck though.

[1976RD400C]

Alright, I figured it out. THE RINGS ARE ABSOULTLY WIPPED AFTER 150 MILES. Totally shot worse than any and rings I've seen, and it happened in 150 miles. What the hell. Are these counterfeit China pistons. Crazy. So pissed off. My brain is ok now wow oh wow.

[m in sc]

might be counterfeits. what are the markings inside the piston? the underside?

[Striker1423]

oofta

[1976RD400C]

Pic of the piston. The rings have no markings on them at all. Piston skirts are shot, cylinder will need at least .002" to clean up so they are shot. The money and time I spent to do a precise rebuild is gone. My track day ruined. I can't believe this thing didn't blow and hurt me. I have no idea how the rings couldn't take it. Wisecos did fine for many many hours.

[edgefinder]

Just my opinion but it looks like your right on the borderline minimum clearance and you got lucky. Hone it a half thousandth and put new pro x pistons in. I bet it doesn't do that again

[Striker1423]

I dunno, if it was too tight, you would more likely have a four-corner seizure first. My 90 did these soft seizes repeatedly and still ran until I had the cylinder re-bored a tad bigger. You officially joined the pissed-off oops I broke it club. At least you got 150 miles out of it. I got like 7 out of my one mistake.

[rodneya]

I have used Pro X in a few different motors and they have always been excellent quality. They are made in the same factory that makes OEM pistons for Japanese bikes. So I would not blame the pistons here.

That ring gap looks like 1/4 inch. Was that how they went in?
Skirt wear looks like grit not cleaned out after honing the bores.

Were did you buy the pistons and what was printed on the rings box?
Mine have always come with Riken rings is a red box.

[1976RD400C]

I'm still baffled. Everything was done right with the rebuild, my job included doing motor rebuilding for 40 years with all kinds of motors. Measuring, honing with proper grit stones for type of rings, scrubbing parts, etc. It looks like a lack of lubrication, almost just like a motor that was at the end of it's lifespan, everything is worn. There is no signs it had seized, no aluminum had come off the pistons or is on the cylinder walls. Now I'm thinking about this. I used to use Sunoco 110 cut 50/50 with non ethanol. Can't get it this year so I bought VP110 and cut that 50/50. Anyone know what color VP110 is, this is clear? Could the can be labeled wrong and I put something else in there? Yamalube R used to come in a different looking container. The new stuff I bought looks like the pic. Is it counterfeit? I thought at one point the texture looked different, but maybe not. I bought the pistons on Ebay with the link I listed. It plum wore out in 150 miles. I'm not sure if just the rings failing can cause this and why did they fail. The rings are pounded to holy hell, very loose in the piston grooves too. I don't remember what the box they came in looked like. I looked in the exhaust port after it was first run a bit and that coating was coming off and goopy everywhere. Thanks for any clues.





https://www.ebay.com/itm/334470837153

[m in sc]

i think you just had a shit set of rings maybe. the blowby on the pistons is excessive IMHO for the mileage.

[Dvsrd]

IIRC, the OEM Yamaha rings were hard chrome coated, since they were meant to run in a cast iron or steel liner. While TZ 750 rings were NOT hard chrome coated, as they were intended to run in a hard chrome cylinder bore.
Is it possible that somehow piston rings intended for chrome or nikasil cylinders were supplied with those pistons?

[1976RD400C]

I'm going to put forged Wossner pistons in it. I still don't get what happened. I think the rings did not seat for some reason and then the blow by, while pushing it, fried the piston skirts. It's hard to believe the rings literally cooked in such a short time. Here's a pic of me grinding the kickstand while my rings are grinding away on my cylinders. This track has a "jump" which makes things exciting and sketchy at the same time.   

[m in sc]

i mean, it may just have been a manufacturing defect. I've had that with a piston before. not pro x, but had one bad out of the box. Im pretty sure you did nothing wrong. IF i were in your position, you are in, that's where i would assume the issue was.

[IR8D8R]

Did you say that the VP 110 from that can was clear? If it's leaded with TEL it should be very pink.

Tetraethyl lead is red. I don't think there's a way to not make it red. I've heard that even pump leaded super premium back in the day had enough that it would stain your hands. I know the leaded that was sold in the early 80's at a marina in Richmond where I used to fill my cars at would stain white polypropylene plastic gas containers pink. It was only 94 octane.

The tracks I raced at in California had banned leaded so most of the race gas in their pumps was unleaded blue Trick 115 or purple Cam 2 which I think was 112? The primary octane boosters in the unleaded race fuel are xylene and toluene which you can smell. since spec fuel is common at race tracks they use the color coding to verify you're using track fuel. I honestly don't have much experience with canned race gas.

IR8D8R