KX125 - Just replaced piston, now has no compression

[Crasherfromwayback]

never be to tight oiling the new piston & cylinder, that the includes gudgeon pin aswell.

If the ring wasn't fitted properly on the piston and riding the locator pin there'd be heaps of compression, as well as one farked ring a scored bore & 2 people who'd have noticed the difficulty assembling it.

You can actually assemble a two stroke engine 100% dry, with absolutely NO problems. I've done so several times, and in fact a lot of old school two stroke guru's do like wise. The minute you kick it into life the premixed fuel lubes it just as well as it does when it's running, and for the milli second it moves without creates no wear issues.
If the ring has not been located properly, it can actually get jammed into the groove over the pin and then cause the bike to have little or no compression.
It sounds like the people doing this may well not have had an issue with applying too much force fitting the cyl, seeing as they're learning as they go.
I've seen this on more than one occasion.

[Coyote]

My Dad thinks he knows what the problem was. A bracket holding the head of the barrel was overtightened, so the head wasn't able to be tightened all the way allowing the pressure to escape. We're not sure if this was the problem or not but after taking the head off and putting the bike back together it runs now. And it runs very well

Also this replacement is a Wiseco piston and it felt a fair bit lighter than the 2 original Kawasaki pistons that had been in before and before that. Sounds like it's revving that much higher because of it

[Ixion]

Just be careful with that piston, some of the Wisecos have a habit of cold seizing, because they expend differently to cast pistons.

[Crasherfromwayback]

Mate....I hate to tell you this, but if you've got a std cyl (still electrofusion), Wiesco pistons are not the go.
They SHOULD be ok, but for some reason they don't get on.

[Coyote]

The bike is an '04 KX125, and the piston is designed for it. I shouldn't see why it wouldn't work

What can be done to avoid it seizing whilst cold?

[Ixion]

Just take it easy on the welly until it's good and hot. The piston expands a bit quicker than the cylinder so it gets big quicker (could be a fortune in that if y'could put it into a tablet).

[paturoa]

Sounds like it's revving that much higher because of it

So you'll be doing it again soon! New piston and rings need a little tender care for the first hour. Work you way up to full noise!

[Coyote]

Oh yeah, of course. Didn't ring it all the way, and my Dad always warms the bikes up for a damned long time. The bike came with a motominder so we'll keep an eye on it

[Titanium]

Piston rings in up side down
Pistion installed wrong way round.
No base gasket or badly seated.
no head basket or badly seated.

Wiseco Pistons need double the piston to bore clearence than OEM pistons. - In anything.

We always hone nikasil plated cylinders.

We always use Wiseco Pistons - BUT use rings that are matched for Nikasil or Steel sleeves.

Cheers


Peter

[Titanium]

Mate....I hate to tell you this, but if you've got a std cyl (still electrofusion), Wiesco pistons are not the go.
They SHOULD be ok, but for some reason they don't get on.

It be the rings that are important to match - not the pistons. Wiseco Pistons are fine with nik cylinders, just need tha correct rings to suit.

Cheers


Peter

[Crasherfromwayback]

You're a seller of Wiesco products yeah?
I've used them in many different applications, some results were good, some not so.
I don't believe they're the right thing for electrofusion bores, correct rings or not.
I know nickasil/chrome/electrofusion coated cyl's all have the same goal in mind, but maybe the slight difference in them gives Wiesco pistons grief in Kawasakis.

[Crasherfromwayback]

So you'll be doing it again soon! New piston and rings need a little tender care for the first hour. Work you way up to full noise!

With a 2004 KX 125......new piston and ring fitted..?
Start the bike.
Run it in neutral just blipping the throttle till it gets to normal running temp.
Then shut it down, and have a few beers while you let it cool down.
Repeat, but take it easy on the beers this time.
Now take it out and thrash fuck out of it.
This is the correct running in procedure for anyone that wants a fast two stroke race bike.
Trust me.

[F5 Dave]

On older Kawasakis they were renowned for that bracket causing head sealing problems when the frame flexed. Older & jumped bikes are more of an issue apparently. The Mod according to Eric Gorr’s book (find & buy it) is to enlarge that bracket hole.

[crazyxr250rider]

nothing wrong with wiesco's got one in my bike took awhile to bed in but is good now and has much more power.
using good oil at a healthy mix does help.

[Coyote]

My brother was out testing the KX today. It's running pretty damn sweet. There were no issues starting it up and it sounded great. Another days riding should be enough running in

Also I'm getting much better wheelie-ing the Montesa. I can stay at the balancing point for 30m consistently