Piston Slap?

[Brian]

I think I've narrowed the noise thing on my bike down. I'm leaning towards piston slap, but wanted to know what you guys that know what you're talking about think. When cold, my bike is much noisier than when warmed up. It knocks under decelleration when warm, but to a much worse extent when cold. The knocking also occurs when in neutral, and revved slightly, the bike will knock several times on it's way back down to idle. I don't think it's jetting, because I've toyed with that, and now have it running clean everwhere. What do you guys think? Piston slap, or something else? And, if it is piston slap, would a new top end do the trick, or might the cyclinder slightly too large from the factory?

 

[cr25096er]

i know howe it is when something like this happens but if the performence is good just ride it.

 

[Brian]

Maybe it could be a rod knock? That means I need to replace the wristpin and needle bearing, right?

 

[RM_guy]

When's the last time you replaced the piston?

If it is piston slap it is due to a worn cylinder bore or worn piston. Either one could mean big failure. The only way to know for sure is to tear it down and measure things. Loud noises coming from the engine need to be checked out as soon as possible so they don't lead to very expensive fixes down the road, even if the performance still feels good.

 

[Brian]

Still on original top end. I'll look into it. I thought Nikasil was pretty tough, and takes quite a bit to wear one down. Do you think The cylinder could be worn unevenly?

 

[kciH]

RM Guy is 100% on the right track here. If you are experiencing piston slap and it is not cured, you WILL break a skirt off the piston and it WILL get lodged between your crankshaft and the cases. On the upside a top end job is cheap compared to a complete teardown, even if you do it yourself. If you find that you need to have the crank rebuilt when you take the top end off, it will still be cheaper than having to repair/replace your case halves if you break a piston or worse yet have a rod failure. Kawasaki cylinders are known for the inferior quality of the factory cylinder lining, so you may only need to have the top end done.

Just my $.02

 

[RM_guy]

The plating is probably OK but the piston is worn. You get the same effect whether the bore or the piston wears. If you're on the original piston I'd replace it tonight :eek:

 

[evenslower]

Have someone measure the bore and inspect the plating. Kawi's are notorious for having poor plating. You will always have some degree of noise related to piston slap, even with a new top end. When it becomes excessive it becomes a problem. Let us know how it works out.

 

[JesteTac]

I hate to dredge up an old subject, but I just had this happen.

My piston skirt broke, fell into the crankcase and seized my motor. :( Fortunately I pulled the clutch in when I heard it break, so it didn't seize too hard. Top end still looks fine--it just pooped out a bunch of metal bits.

I decided to rebuild the bottom end, since I will be tearing into it anyway, but where the heck can I get a new crankshaft for less than $450. for a 2001 Suzuki RM250. This is stumping me terribly.

I have searched online, and searched this forum--no dice. Surely I can't be the only person who ever needed to change this on their Zuki. Thanks for the help guys.

 

[blackoutyz125]

You might wanna check the up/down play on the big end bearing on the rod. Sometimes that will make a sound similair to piston slap.

 

[reelrazor]

What Blackout said. I am of the (admittedly online and w/o hearing it irl) opinion that you prolly have a lower end issue.

Pull the flywheel cover off and get the piston to TDC and rock it back and forth.Try this with the plug in and with it out. Try it at 90° btdc or atdc. Try it while holding the tip of a screwdriver against the piston crown.

You can feel slop if there is any this way. Do this to enough bikes and you can pinpoint wrist pin or crankpin. You can check crank mains too by trying to move the flywheel.

 

[JesteTac]

This issue is really old. I just want to make it clear that I am dragging it out of the archives. I searched for another topic like it, and didn't find one about crankshafts.

So I am guessing this guy already solved his problem. Sorry if I generated any confusion--maybe I should have started a new thread.

 

[Uchytil]

Tear Down

Your bikes a 01, eh? No top end yet? You better take off the jug and inspect/measure it per the shop manual, same with the piston and everything else that the shop manual specifies for a top end/power valve job. While apart check the big end bearing per the manual.

JesteTac: Did you consider rebuilding that crank with a hot rod kit? Does Wiesco sell one, theirs seem, reasonable? How bout the usual internet buy sites, I got a brand new OEM crank for 1/3 the price of new. Last time I did a zuki I had the crank rebuilt. It ran me about 80 bucks for the parts (I had a press but a shop could press/true it).