I have a question for anyone here with knowledge about wiseco pistons. My son's Sport 400 has recently been bored .060 and we installed a new Wiseco, set up with .0035 clearance. After running this in the bike for approximatly 25 hours, we started hearing piston slap (rattle). So, we pulled it down and checked our piston clearance and couldn't believe it but we had .016 clearance measuring on the intake or the exhaust side! The piston itself looked fine but there was there was considerable difference in diameter measuring the top of the piston as opposed to the skirt.

It is oiling fine, no scoring, not appearantly running hot. The cylinder looks totally normal and has no taper.

Now here's the rub. I sent the piston back to Wiseco for inspection by one of thier engineers. I just yesterday got a call from one of them and was told that on appearance everything looks totally normal. However, they did a Rockwell hardness test on it, normal and as sold they run 75 on the rockwell scale. he told me that the center of this piston registered a 30 and the lowest allowable is evidently 45. He says it can only happen from running hot, even though there are no visible signs of doing so. He said I should use water wetter in the cooling system, drop the spark plug one heat range and use octane boost in the fuel. He thinks that the MTBE in our fuel out here in Calif. is a contributing factor but also said that this machine should not be held WOT for extended periods. Basically he sounded as though we should no run it on the dunes or full throttle on trails (wonder where it would be ok to ride it).

Now my question here is, has any one had similar problems and if so have you found a cure? Does what the engineer says sound right? This bike has a Hotseat pipe and clutch kit, K&N filter, stock carb jetted with a 290.

Thanks for listening!

 

Jerry,

I too had this problem on my Sport when I had it ported. The problem solver was to get the piston coated. Swaintech did mine for $32 over the cost of the piston. The top is coated with a ceramic substance called TBC (Thermal Barrier Coating) and the sides with Polly-Molly (teflon like substance).

Your setting up the machine's skirt clearance to .0035" is slightly on the large side, but well with in specs (.0023 - .0037&quot. When I set mine up, we used two .0015" feeler gauges (front and rear) to get the "middle of the road" skirt clearance at .003".

I sure hope that Wiseco wasn't talking "C" scale Rockwell hardness on their pistons. Frankly, the idea that a machine shouldn't be held wide open for extended periods isn't going to wash in my book, unless he was running diesel fuel.

 

Mike, thanks for the info. Can you tell me how to find Swaintech. I sure don't wish to go thru this again. And I was wrong we did set the piston clearance at .003. As for the scale they (wiseco) used, I am not sure that he even told me. He was just explaining that they had certain standards and limits. Thanks again for your response!

BTW do you have the stock head or would you recommend one of the aftermarket heads?

 

Mike,

I've got a 97' Sport that is in the motor rebuild stage. I'm putting a big bore piston in my alky burning HPD race motor. This Swain Tech piston coating sounds like the ticket. Polly Molly skirt coating is .0007 thick, so I would assume that this would come into play when boring for the piston. HPD recommends .0045 piston clearance with their race porting. Do you think that I could or should go with closer tolerances with this coating?

Sorry Jerry for jumping in on your post but, Mike sounds like he might have the solution for the both of us and perhaps many others.

By the way Swain Tech's site is http://swaintech.com/index.shtml in case you are interested.

Thanks
Jay Miller

 

How much difference did you find between the top of the piston and the skirt when you checked ? And could you tell me what it measured ?

Wiseco pistons are made on a big taper and are egg shaped too .This is all by design . (I'll mike one tommorrow so I don't just toss out numbers)

I don't think the machine ran hot honestly . If it did you would have score marks . Look for the machining marks on the skirt . See if they are still there, or ,,,,,,,,,, worn off.

I have seen ones like Mike Cheros seize , and upon seizing the skirt will collapse about .010" from heat, in a case like that the machining marks will still be in place on the piston skirt . Ussually seizures like this happen within the first 4 hours .

I have seen oils that just won't mix with some fuels . It does exactly what yours did , but ussually the rings show wear , as well as the piston . The bore many times will not show as much wear .

My experience with boring 400 Polaris cylinders is this :
Stock , non ported engines .003" minimum, anything tighter siezes more times than not.
Ported engines .0035" minimum , anything tighter siezes more times than not .
I have had to learn both these lessons the hard way .

I am not drawing any conclusions yet as to what went wrong , just tossing out a few *matter of fact* things I personally have seen in my own experiences.

Just trying to help . :-)

Rick

 

O.K. Guys,

Here is the link for Swaintech.

Jerry,

I run the Hot Seat "Cool Head" on mine at 12:1. If I were going any higher in my compression ratio, I'd get the HPD. I've heard horror stories of "Cool Heads" blowing their tops without the girdle kits on them at higher compression ratios.

pudjumper,

I just bored my cylinder to the standard (.040+) size and honed .003 in for the skirt clearance. My motor's been ported and hasn't let me down yet. Granted, it's not the hottest motor on the block, but it's well over a stock one.

It's absolutely incredible how much abuse the Swaintech coated pistons will take. If you read the article on the snowmobile that they modified for drag racing, you'll see that they were getting temps on the EGT gauge of well over 1400 degrees WITHOUT piston failure. WOW! Between the TBC protecting the piston from heat and the Poly-Moly making the sides "non-stick", I wouldn't be afraid to take it closer than .003 on the skirt clearance. It's just that all we had were two .0015" feeler gauges. Besides .003" is a nice round number, right in the middle of the .0023-.0037 tollerances. It works for me!

 

Rick;
You're dead on. I was wondering if anybody caught that. The Wiseco pistons are tapered and with the 190 main jet; the piston should have been plenty cool.

 

I guess this question is for both Mike and Rick:

Rick, I've talked with you about the wiseco making rattling noises, but I'm just not sure how to tell if it is normal and needs to be addressed. My atv had probably 10 tanks of gas or less run through it on the stock piston when I changed the piston out with the wiseco standard piston(for durability reasons). I didn't mic anything......just simply installed it. For the first hour or so, it was very quiet.......but sometime after that (not sure when), I started noticing the rattling sound at idle, slightly above idle too.

Is there any way without disassembly to determine whether or not my engine is ok? I've heard wisecos "rattle" more, but mine does it cold or hot.....sounds basically the same.

Mike, how much time do you have on your swaintech coated piston?

I'm a worry wart, and believe in preventative maintenance.......I'll agree to this, but I don't want to rebuild my bike if everything is perfectly fine. Thanks guys.

 

What kind of turn around time does this Swain Tech have. Do you send them your previously purchase piston, or do they sell them already coated? Hmmmm Wiseco Hot Rod, HPD big bore, Piston coating, powder coating....gonna be a busy winter.

Ken........Jet mechanics love their thrust!!!!!!!!!!

 

walexa,

I have about two full seasons on my piston, with no knocking sound yet. The darn thing still wants to pull my arm out of its socket everytime I try to pull start it, so it's still getting great compression.

modquad,

I got my piston coated back when there was a "Great Piston Famine". Wiseco wasn't making any .040-.060" pistons for the 400 Polaris machines. This was because they had a cracked die for the two pistons and needed to make new ones. All told it took about two weeks to get the piston coated once I found one. It might take Swaintech even less time if they have one in stock.