Wiesco piston slap!

perfectly normal if you ask me.

davel wrote: If you had loose pistons that were making noise, I would expect them to make just as much noise as the engine heats up and the oil thins out.

No!
As the engine heats up the piston will also expand to close the clearance.
Piston/bore clearance is there to allow for piston expansion due to heat as the engine gets hotter.
The hotter it gets the more clearance you need.
Turbo's and race engines run hotter so use more clearance and will rattle when cold but quieten when at running temp.
Rattling when warm in this case means too much initial clearance for its designed running temp.

I wonder if the machinist did measure the pistons but measured them in the wrong place? I don't know if they are made like stock pistons, but if they are when they are cold they are tapered toward the top and they are elliptical rather than perfectly round. This enables them to become round and cylindrical when they come up to operating temperature. Because of this shape, at least on stock KZ650 pistons, it is important that you measure them as shown in the FSM, otherwise your measurement will be off. Ed

that is true of every piston i have ever measured ed.

leon

p.s. well maybe not those cast iron model a pistons :lol: ....

Here's an update from what come of this...

Please read the below thread and comment on what you think. :S

Hey guys, an update on the piston slap issue. The top end has been pulled down only to find the the pistons and bores measure up perfectly, thou and half clearance all the way down on all four, it has me and the engine fella stumped. The rods feel good, ok behind the alternator cover. He did suggest we use the spare stock cylinder block and pistons i purchased from the US as a spare, they measured up quiet well for used items, honed and re ringed as a last resort measure, but we are not convienced 100% this may fix it, any ideas anyone?

0Z.Z1R Mk2 wrote: Here's an update from what come of this...

Please read the below thread and comment on what you think. :S

Hey guys, an update on the piston slap issue. The top end has been pulled down only to find the the pistons and bores measure up perfectly, thou and half clearance all the way down on all four, it has me and the engine fella stumped. The rods feel good, ok behind the alternator cover. He did suggest we use the spare stock cylinder block and pistons i purchased from the US as a spare, they measured up quiet well for used items, honed and re ringed as a last resort measure, but we are not convienced 100% this may fix it, any ideas anyone?

Is this a KZ or a J motor?

1980 1000st or KZ1000st Larry.

A thou and a half clearance? Doubt it. I can't think of any machinist who would set up a big bore KZ motor to that spec. Might be time to have a second opinion on the clearance. Take it over and have it measured somewhere else, if you don't have the tools.
.0025" would be more like it. After boring the final honing will set the clearance, and it needs to be done with a precision hone so the bore is true. No flex hones or balls.
Was the bore kit the only work done at that time? Was there engine noise before the work?

Motor Head wrote: A thou and a half clearance? Doubt it. I can't think of any machinist who would set up a big bore KZ motor to that spec. Might be time to have a second opinion on the clearance. Take it over and have it measured somewhere else, if you don't have the tools.
.0025" would be more like it. After boring the final honing will set the clearance, and it needs to be done with a precision hone so the bore is true. No flex hones or balls.
Was the bore kit the only work done at that time? Was there engine noise before the work?

MH...this is his response to your question.

The initial reason for the top end rebuild was one of the cam chain idler sprockets, the top one actually was collapsing and noisy, luckily i caught it in time and no bits passed through the botom end. As the engine had travelled a lot of miles every componet in the top end, every piece and part or the cam train, valves and springs 1075, 9.1 weisco pots everything is new, it runs fantastic, just this annoying rattle at startup which cannot be found. To me it sounds more of a knock than a rattle but the the guy who did the rebuild is certain that it is slap.

0Z.Z1R Mk2 wrote:

Motor Head wrote: A thou and a half clearance? Doubt it. I can't think of any machinist who would set up a big bore KZ motor to that spec. Might be time to have a second opinion on the clearance. Take it over and have it measured somewhere else, if you don't have the tools.
.0025" would be more like it. After boring the final honing will set the clearance, and it needs to be done with a precision hone so the bore is true. No flex hones or balls.
Was the bore kit the only work done at that time? Was there engine noise before the work?

MH...this is his response to your question.

The initial reason for the top end rebuild was one of the cam chain idler sprockets, the top one actually was collapsing and noisy, luckily i caught it in time and no bits passed through the botom end. As the engine had travelled a lot of miles every componet in the top end, every piece and part or the cam train, valves and springs 1075, 9.1 weisco pots everything is new, it runs fantastic, just this annoying rattle at startup which cannot be found. To me it sounds more of a knock than a rattle but the the guy who did the rebuild is certain that it is slap.

It could be the stock automatic cam chain tensioner causing the cam chain to rattle. They were problematic. The plungers could stick. The one way locking ball mechanism is not reliable.

I've seen that many times and fixed it by using a longer bolt with a lock nut to replace the short plunger load set bolt.

Start the bike cold, Remove the 6mm bolt on the side of the tensioner body and tap the body with something while the bike is idling. Don't waste your money on an aftermarket manual cam chain tensioner. You don't need it with that motor. If it was J model...then OK.


.

With that clearance you don't have piston slap.so that leaves timing chain slap, or valve shims so loose they are rattling.
I would lean towards timing chain slap.
Larry's suggestion would be a quick easy way to eliminate the possibilty of chain slap.
While that cylinder clearance does sound tight, if it didn't scuff the skirts and proper break in was done you shouldn't have an issue there.
That's my .02

Leon

If you still think slap. If you have the screw on terminal at the top of each spark plug. You can make a small say 3" extension for your plug to wire connection with a small bolt/ screw. Then with a ground wire back to the head, and the other end attached to an insulator, block of wood or plastic, ground each plug wire one at a time to try to determine if one cylinder is at fault. You may have to slightly increase the Idle speed to do this cold, so it doesn't die.
If the chain is noisy, I'd go back to re-balance the carbs, to see if that helps.