KDXRIDER.NET

"Maybe I should see about exchanging for a Wiseco."

Na...like Ski says...or sumpthin'...Just Do It!!

Yikes. That would be a pretty big difference in height.

Lacking a suitable measuring device...perhaps setting them up beside each other will point out any obvious difference and .020 is quite visible with a background reference point for your eye.

Yes .020" is very easy to see. And the easiest way to check is to put the old and new piston on a common piston pin and slide the two pistons together. Now you can see if the top edges of the pistons line up.

Ron

What a clever (and very simple) idea!!!

Thanks Ron

I'm pretty busy, with not much time for maintenance projects, so I really need to stack the odds in my favor as far as things going together well. I think I'd rather not risk messing with a questionable piston and have the bike down for a longer period of time. I'd rather exchange it for a Wiseco before I take the bike apart if it is reputed to be a better quality and precision part. It may be a good time to invest in a micrometer as well.

Wow. With a .020" increase in height, I'd be worried about valve interference!!

Maybe I missed it...but I'd be interested in what the piston-to-cylinder clearance was, too. Feeler gauges can be used to give you a fairly close idea. If, for whatever reason, it turned out that a .002" gauge was pretty snug...I wouldn't use that piston (that figure used as an obviously too-tight situation). .004-5" is probably minimal for a forged piston?

Sure...it shouldn't be that close..but that's why (like ski said) you check those sorts of things. There's always the chance that something's not right.

If you know your head volume, you can determine the compression ratio difference between two pistons of said configuration difference. It figures to...uh...what? About 2cc difference (1.868?) That comes out to maybe .1 on the ratio?

That would be no big deal. Do your own math..mine is likely rusty at best.

I have NO idea what is considered the minimum piston-head clearance is. You can check that with a piece of solder...place it on the piston crown, bolt the head on, move through a TDC by hand, take the head off, measure the thickness the solder squished to.

I wouldn't think it would be close enough to worry about.

I'm not saying you have to do that...just that's how you could check it. If you do it..do NOT move the piston but from just before to just past TDC. You don't want any solder dropping into a transfer/intake port!

Repeated for effect: DO make some preliminary measurements. Just 'bolting it up' 'cuz it's supposed to work is not prudence in action.

Interesting note on the .020" difference!! Who'da thunk that would be the case!!??

I sure didn't....I probably would have refused it if I had known what I know now.

Comparing the 2 pistons, there are definitely some differences. The Deck height isn't quite the same but very close. The skirts are a little different as well. The oil holes in the side of the piston are quite a bit smaller as well. Does a Wiseco have the same differences?

rdsrf wrote:Comparing the 2 pistons, there are definitely some differences. The Deck height isn't quite the same but very close. The skirts are a little different as well. The oil holes in the side of the piston are quite a bit smaller as well.

If the deck height of the German piston is lower, you have nothing to worry about. If the deck height is higher, check the clearance to the head via the solder technique, then report back here. Use a micrometer to measure, a digital caliper is second best. Skirt shape and oil holes are the designer's choice, we hope they have tested their design.

M^2

The deck height was a tad lower than my stock piston. I showed the two pistons to my local shop owner and he said it would be fine. So I put it all together very carefully and it fired up on the first kick. It seemed to sound a bit different at first and didn’t seem to have the same response as it did with the stock piston. This concerned me a bit but I decided to go ahead and do a careful break-in: 10 minutes of idle then cool down, another 10 minutes of easy steady riding then cool down, then an easy 20 minute ride to the first trail where my friend’s bike experienced some mechanical difficulties allowing for yet another cool down. At that point it still didn’t seem to be running quite right but we went ahead and rode about 5 hours of tough technical trails where at some point it began running nice and crisp and responding very well. Perhaps I used a bit too much assembly grease or it needed some time to break in but it seems fine at this point. It’s nice having a properly functioning power valve again and an engine that fires up with one kick….that is, when the kick starter engages!
It used to very rarely not engage, but now it doesn’t engage very often! I had to remove the right side clutch/engine cover to repair the KIPS actuator shaft (I needed to install the shaft retainer pin that was mysteriously not present). Perhaps during the installation of the cover something went awry? The only other changes I made were to switch to Amsoil 10w-40 synthetic motorcycle oil of which I added 1000 ml instead of the 700 ml specified in the shop manual. I’ve read a few threads on here stating that adding the extra 300 ml of oil quiets the motor a bit. I don’t know if either of those things would affect the kick starting mechanism but I sure didn’t notice any decrease in noise! Any thoughts or advice on the kick starter issue is much appreciated!

Check Jeb's thread on KIPS modification. Note the washer from that assy that likes to drop off..and how he held the spring in place when he put the cover back on. That and his popped OUT of place when he took the cover off:

CLICKY!



Re: Oil volume
The noise decrease isn't huge..but it's probably there (well...or NOT there depending on your point of view).

i think the athena piston is cast. wiseco piston is forged ,stronger/more durable than cast pistons.the oem kawasaki piston is also cast.

The box my piston came in says forged, so I’d imagine that it is. I’ve heard various things, but most say it’s a high quality piston.

Thanks Canyncarvr, for leading me to Jeb’s thread. I didn’t notice a washer falling off, but I bet that spring may have popped out. I’ll pull it off and have a look.

Jeb...if you're looking at this...

Since that spring is under discussion...do you have an idea as to why it's 'popping' off? It's got a pretty good tang on it to be 'falling out' in the first place and its placement is such that as the spring would tend to come out, the tang would engage 'better', wouldn't it?

Or is it the other end of the spring that dislodges?


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Athena pistons are forged...which is to say they are not cast.

From an Athena ad:

All pistons are forged using a precision heat-treatment process that allows for production tolerances of just .005mm

(My bold emphasis)

Take note of this (from a like ad):

Forged piston kits are available in A, B and C sizing.

That sizing is .01mm..less that 1/2 of one thousandth of an inch...the same alpha groupings as the Pro-X.

More BTW from Athena:

2-stroke pistons are made from 4032 silicium. 4-stroke pistons are made from 2618 silicium - the same material used to produce Formula 1 pistons. Both include 3% copper in materials for better heat resistance. All pistons are forged using a precision heat-treatment process that allows for production tolerances of just .005mm. Forged piston tooling allows for the lightest available product. Kits include antiwear coated piston, rings, pin and circlip.
Made in Germany.

Hope it comes with TWO circlipS!

Maybe I missed it..if so, would you re-say what your piston-to-cylinder gap ended up being? And with which 'oversize' Athena? Ring gap?

Thanks.

maybe they're partially circlipsized, although I've heard many Euros aren't.

I THINK the spring tang became "unhooked" (probably a better word) from its intended spot because I bumped it while pulling off the cover for the first time (I didn't remove the brake pedal initially and tried to wrest the cover out).

I didn't notice that it had unhooked until I was ready to put the cover back on. As I tried to push the tang back into the hole it wanted to pop back out - the spring was a tad cockeyed and wanted to pull the now slightly angled tang out. Once I got it in place the first time I tried to put the cover back on I bumped it again and heard it pop back out. I got everything buttoned back together OK without too much trouble on the next try.

When I pulled the cover back off here recently I was careful with removal of the cover and it stayed put. In fact, I pushed at it a little and the tang held it's ground (no, I can't leave well enough alone). Apparently some normal use of the kickstarter sort of "seated" the spring so to speak.

So CC's suspicion is correct: the tang wants to stay put. Go messin' with it too much, though, and it's going to want to fight back!!

Moral of the story: try not to bump the spring!!

Sorry to be thoughtfully disadvantaged (happening a lot of late..) but, it IS the tang visible in the pic that comes undone? NOT the opposite end of the spring.

Looks from the pic that the spring would have to be placed before the shaft to get the angle you would need...unless you force the spring a good bit.

Anyway...I'm lookin' for rd to find his spring slipped off...put back on..and everything be 5-by-5.

. . . it IS the tang visible in the pic that comes undone?
yes . . . pic 16 of 16, where the tang fits into the hole in the case directly below the kickstarter assy.

Thanks!

You don't have that cover off YET rd?

Nope, I haven’t got the cover off yet but I’ll post up when I do. I didn’t notice anything like Jeb described when I pulled it off or when I reinstalled it, but anything is possible I suppose. In fact, I really hope it’s something simple like the spring being dislodged. I spoke to a guy with a KX250 that described the same problem. He said he wound up having the replace the spur gear and ratchet parts in the kick start mechanism to correct it and that the parts weren’t cheap. I did a search on here but didn’t find much…..It may not be a common problem.