piston weight

[k2000x]

im about to use a different bike (brand) piston in one of my bikes its weight its a little heavier than the original piston... will this make the bike vibrate or have any bad effects

[Freakshow]

is the weight above or below the pin ?
cant see it making any differance as its centre is going up and down not really round and round. 
the weight increase may change the piston speed and that may be a small timing adjustment, but go for it.

see how it goes.  nothing will blow up so long as the squish is correct.  and vibrations can even come in on the correct parts, its the sort of thing you run and see how it goes i reckon.

[IT400C]

Depends a bit on the bike capacity and use..

In the late 90's I was riding enduros on YZ125's, and tried the Wiseco Pro Lite piston.  It was appreciably lighter than the standard YZ125 piston, and lasted very well, but it changed the power delivery a lot..

The bike definitely had less vibration than with the standard piston, and it picked up revs much more quickly.  Unfortunately it also lost revs much more quickly - less reciprocating mass meant less torque (the flywheel or steel clutch plate type torque).  It fell 'off the pipe' much more quickly on hills than with the heavier standard Yamaha piston..

I loved it for MX, but hated it for Enduros... 

It was noticable on a YZ125, but may not be as noticable on a larger capacity bike as the weight difference would probably be a smaller percentage of the piston weight... 

[IT400C]

Hmmm, of course all of the above would work in reverse for a heavier piston..   

[Lozza]

Reciprocating mass has no effect on torque, that is produced by work applied on the crankpin. Heavier piston will alter crank balance factor usualy bringing it down by a few %.

[IT400C]

I didn't mean the actual ft-lbs or Nm torque produced by the motor. 

I meant the seat of the pants feel of the bike - in much the same way that a heavier flywheel effects the percieved torque of the bike, or replacing aluminium clutch plates with steel plates..  The motor produces no more actual torque, but with a heavier flywheel/heavier clutch plates/heavier piston it feels torquier because the added rotational/reciprocating mass resists changes in momentum.  It will rev up slower and lose revs slower...

And from my experience it is particularly noticable in a small bore, high revving motor.   Maybe less noticable in a larger, slower revving motor..   

[Lozza]

What your talking about is "in-cycle speed variation" of the crankshaft. Particularly over TDC and to exhaust port open.

[mainline]

What your talking about is "in-cycle speed variation" of the crankshaft. Particularly over TDC and to exhaust port open.

i was just about to say that

[pancho]

 Piston weight effects the vibration of the engine at a particular rev range, and should be calculated as a percentage of the reciprocating weight which includes the piston and the top part of the conrod.
 The old way [probably still accepted method] of finding this is to weigh the piston with rings and assembled to the rod, then lay the flywheel and all on the bench with the piston sitting on a scale.
 The balance factor was then calculated as 2 thirds [from memory] of the reciprocating weight which was then dangled from the little end and static balanced to the crank assembly.
 This figure [2/3] varied according to the usable rev range of the unit concerned to minimise power robbing vibration.
 In terms of practicality if the slight increase in piston weight has no ill effect in the case in question, don't worry about it, cheers pancho

[Freakshow]

basically all that means is............... stick it in and see if it vibrates. if it dont twist harder, if it does put a stcoky back in .

[motomaniac]

When Greg Albetyn (remember him, 3xWorld MX CHAMP) went to the US . Suzuki was trying to match the Honda's power delivery etc. It wasn't until they used a Honda piston in the Suzuki (bore and stroke was alreday the same) that they got it right and Albee was happy , finally winning the outdoors. The Honda piston was heavier than the Suzuki's.