Two Stroke Motocross

Two Stroke Motocross Forum => Technical => Topic started by: kxchap on April 20, 2010, 01:51:39 PM

Title: Engine pinging
Post by: kxchap on April 20, 2010, 01:51:39 PM

Hi fellow 2 smokers, I recently bought a 2001 kx144 big bore. The bike runs fine, I just felt it could have more compression, and as I was unsure how long the piston had been in I decided on a top end rebuild.  It has a Wiseco piston that is in great condition with no score marks so I just changed the piston ring, small end bearing, gudgeon pin and circlips which all came from a Wiseco dealer and every part that I replaced was identical to the previous.
when I completed the rebuild I kicked the bike over and with the engine idling I can now hear what I can only describe as a metallic pinging coming from the engine that wasn't there before the rebuild. I'm thinking maybe the piston ring could be hitting the exhaust valve, this is all I can come up with !
any advice please ? I'm stuck !   

Title: Re: Engine pinging
Post by: TMKIWI on April 20, 2010, 04:36:15 PM

Pull your exhaust off and check the ring is free. You can use a small srewdriver to push against the ring.It should be free in the groove.
Next take off your ignition cover. Put a socket on the flywheel. With the plug out slowly turn over the motor to see if there is any point the motor feels it is sticking. If it feels like the motor has a notchy feel check to see what position the piston is in. That should give you an idea whats wrong.
Let us know what you find.

It might pay to pull the reed valve out as well to check the intake side.

Title: Re: Engine pinging
Post by: graham472 on April 20, 2010, 05:26:47 PM

Check the base gasket is the same thickness as the old one or if there was more than one gasket in the first place. Piston could be hitting the head, old mate got caught out like this.

Title: Re: Engine pinging
Post by: kxchap on April 21, 2010, 12:17:28 AM

Thanks for all the advice guys, I'll be taking a look at my bike this weekend

Title: Re: Engine pinging
Post by: TMKIWI on April 21, 2010, 02:00:40 PM

Dont worry about pulling the reeds out at this stage.
I forgot they are a case reed motor.
My bad.

Did you put new o-rings on the pipe ?

Title: Re: Engine pinging
Post by: kxchap on April 21, 2010, 02:37:05 PM

I have a HGS exhaust system , which has a different type of fitting than the standard exhaust so no need for O-rings, I just use a silicon sealant instead so no problems there. I'll let you know how I get on after saturday.

Title: Re: Engine pinging
Post by: TMKIWI on April 27, 2010, 09:37:18 PM

Kxchap did you find out what was wrong ?

Title: Re: Engine pinging
Post by: wexy21 on May 02, 2010, 08:21:59 PM

I have a similar prb too.  Mine sounds good..but not the same after my rebuild.  My original had one base gasket and my new gasket kit came with two.  One green and one black one.  I only used the green one.  Should I have used both?  Maybe this is the also your prb here....

Title: Re: Engine pinging
Post by: TMKIWI on May 02, 2010, 08:39:50 PM

It sounds like you 2 may have the squish clearence wrong.
Take the head off and with the piston at TDC measure the distance from piston to top of cylinder.
Don't know what it should be on your models but would be easy to find out.
Thats why you get different thickness gaskets in the gasket sets.
This measurement MUST be done correctly.
Good luck.