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New motor started burning a lot of oil suddenly and was abnormally pressing up the crank case. Plugs showed it was running a little warm, but not crazy, no signs of detonation, but a splash of aluminum on #5. Dual onboard widebands and logs showed everything was running normal when the problem kicked off. Compression test showed low compression on #5.
Tore the engine down this weekend and discovered an issue with the off-the-shelf -32cc Wiseco boost pistons. The valve relief was machined too close to the end of the dish creating a sliver of aluminum prone to coming off. The aluminum cleared the cylinder in 6 of 8 pistons, but deposited/melted onto the top ring on cylinders 5 and 6. The small amount of aluminum material caused severe top ring binding on these 2 cylinders leading to the blow-by and oil burn.
Other than the piston issue, everything else in the motor looks great. Right now I'm in the process of swapping out the pistons, getting the cylinder honing redone, swap the crank/rod bearings while I'm in there (why not) and anything else you folks think worth doing on a brand new (2,500 mile) engine.
A friend had a similar issue about 5 years ago with a different Wiseco boost piston - so Wiseco seems to keep putting these out there. This will be my last one I ever put in - apparently their Q/A sucks.
This is the 2nd Wiseco-caused failure I have seen in the last few years. I think they have Q/A problems. Even if I was given a set for free, I'm not sure I would put them in the motor again and roll the dice.
Prep the top of the pistons with a fine hard roll and eliminate the problem.
There is aluminum garbage in the upper ring groove and melted on the ring - not sure how I get that out without creating an odd issue with the upper ring groove. Sanding the rings and the ring groove seems like something I would do on race day, but not so much on a street motor. Open to suggestions.
I think he means to prep the new pistons before assembly, could be wrong on that. The thin sliver of aluminum looks like it would be problem ( hot spot ) even in an NA application , I'm a little surprised that wiseco would desire it that way, does the valve relief need to be that large? And that close to the edge ? If you had fresh slugs you could remove the very thin section to the point where it's about 1/8th inch and round the edges. Might be able to clean up the ring and groove but you'd have to be very careful, if bottom of ring and bottom of groove are un damaged it should still seal well
I think he means to prep the new pistons before assembly, could be wrong on that. The thin sliver of aluminum looks like it would be problem ( hot spot ) even in an NA application , I'm a little surprised that wiseco would desire it that way, does the valve relief need to be that large? And that close to the edge ? If you had fresh slugs you could remove the very thin section to the point where it's about 1/8th inch and round the edges. Might be able to clean up the ring and groove but you'd have to be very careful, if bottom of ring and bottom of groove are un damaged it should still seal well
The relief doesn't need to be that big at all for what I'm doing. It is an off-the-shelf piston, so I'm guessing they just machine a giant relief so that it fits everything - and then just left the bad part on these pistons.
Looks the same as most off the shelf pistons. Engine builder needs to prep the pistons prior to install.
I wouldn’t expect wiseco to do anything beyond selling you replacements.
check your timing.
I think a little piston prep is normal (deburr, remove sharp edges, etc...). I'm not sure I would consider re-machining/grinding 1/8" of material from the relief/dish as normal engine assembly. That would seem like a poor design to be selling.
But that being said, I guess I'm the one with the blown motor.
Why check the timing? It looked okay on the strap?
Wiseco manufactures huge runs of the same pistons at a time so lots and lots of motors have the same pistons.
the strap isn’t the only indicator of detonation or preignition. Would be interesting to see pictures of your upper rod bearings
It didn't fall out when I disconnected the rod. I check the width of the upper bearing vs. the lower and it was 0.001 thicker, but I suspect that is just normal tolerances or normal compression. The small spots of liquified babbit looked a little off, but I chalked those up as a tight run-in for a new motor. Also, looks like a little crud made the rounds, but nothing notable. Looked okay to me, but maybe you'll see something I don't.
Interesting thread from Yellowbullet about a decade ago with a Wiseco rep chiming in. Some other dudes had the same failure. I guess they expect you to stone the **** out of these things when they show up.
it looks to me like you got some lower quality fuel and/or your tune was pretty close to the edge and you zapped some pistons. those bearings looks pretty beat too. id start with pulling a couple degrees across the board and then to a review of the whole tune.
while they are out you can clean up the sharp edges or get a different piston thats a better design. im not saying it isnt a problem with the piston, but they needed to be cleaned up before use. thats the cost of using pistons at the lower end of the spectrum. and i really suspect your tune highlighted the flaw.
I think a little piston prep is normal (deburr, remove sharp edges, etc...). I'm not sure I would consider re-machining/grinding 1/8" of material from the relief/dish as normal engine assembly. That would seem like a poor design to be selling.
But that being said, I guess I'm the one with the blown motor.
Why check the timing? It looked okay on the strap?
I didn't mean, take 1/8" off , just that sharp little bit at the edge of the relief ( it's going to act like a glow plug and either melt or cause pre ignition or both ) there's going to be a little material still protruding into the CC but instead of a knife edge a rounded piece say .090- .125 - would take only minutes per slug
Thanks. I understood what you meant. I was pointing out to take down the "wall" that the deep valve recession creates, I would have to cut off about 1/8" x 1/8" to 1/8 x 1/4 of material on the crown - which I don't think is a reasonable thing to do with new pistons. I think it is a poor design that probably works fine at lower power levels.
This is my first time running these pistons. Got caught in the supply chain mess with this build and made what I thought was a reasonable compromise. Historically, I have run a custom Diamond piston d-dish with just a kiss for the valve relief. I'll just go back to what works. Live and learn.
06-09-2024, 09:34 PM
Wiseco Boost Piston Issue 
