piston rings

[bondy]

hi all im in the middel of tarting my 199A ive took the barrol off and cleaned and resprayed took piston off to just check it looks ok. theres no damage to the ring but they was easy to get off there was loads of comprestion before is it worth changing them?

[pschrauber]

hi all im in the middel of tarting my 199A ive took the barrol off and cleaned and resprayed took piston off to just check it looks ok. theres no damage to the ring but they was easy to get off there was loads of comprestion before is it worth changing them?

Don't check them too often, there is little wear on a "trials thumper" like the Bultaco.

Once you did a rebuild and just ride it on weekends they will work for years

if you don't have any breakdows caused by other reasons.

To check the pistons rings there are two things to check:

First the wear or toleance of the notches where the rings are mounted to the pistom.

The gap between the noth of the piston and the bar of the ring should be a clearence of

- around 0,05mm this is good / normal

- around 0,10mm there is some wear still useable a limited time

- around 0,15mm is the limit, then you have to replace.

Then you can check the clearance of the joint of the rings.

To check this you have to put them inside the cylinder, the ring has to sit 40mm below the upper cylinder edge, the ring has to sit absolutly parallel to the surface of the cylinder.

Now you can measure the gap between the joints, the clearance of

- around 0,20mm is OK/normal,

- around 0,30mm there is some wear but sitll useable a limited time,

- around 0,35mm or more then the ring has weared out and you have to replace.

If only one of them shows exessive wear you should replace both rings.

BTW:

Be very carefully when deassamble and assembling the rings.