Yamaha TRX850 Enthusiasts Forum

So today i honed the spare cylinder....buffed up the spare pistons...some paint on the forks...repaint of front fender with extra hard clear coat....tore my pants. And went to the gym....did laundry...food shopping....i´m fekked now!!









What a day!!

You didn't buff the piston skirts did you?

earywig wrote:You didn't buff the piston skirts did you?

Wich are those? ...remember, i´m Swedish!

The part of the piston below the oil ring.

earywig wrote:The part of the piston below the oil ring.

Yep, did it all over. Not polished now just buffed to take the crap out.
Did i do a mistake? Should i use my standard pistons instead??

yes you polished it, Some ppl say its bad, some ppl say it doesnt matter, some say its good to do.

I honestly dont know and cant comment. But the work you have done so far is nice. Should be sweet.

this honeing job is it a do it yourself sort of job or does it need to go to a pro i need more details ,, how long do you hone ? do you do it wet ,,more details !!!! please

steve speed wrote:this honeing job is it a do it yourself sort of job or does it need to go to a pro i need more details ,, how long do you hone ? do you do it wet ,,more details !!!! please

well, you see the tool i used in the pics. I use a bit of break oil to lubricate....never stop the movement.....go until you got a nice criss cross pattern.
Then do the hard "motoman" run in of rings.
....if anything goes south along the way i´ll tell ya all.....

thanks killer ,,, now how do you go on with ring gap if the bore is now a bit bigger ??? do you use over size rings and gap them ?

steve speed wrote:thanks killer ,,, now how do you go on with ring gap if the bore is now a bit bigger ??? do you use over size rings and gap them ?

The bore is not bigger....you could say it´s scratched....in a pattern....

Did i do a mistake? Should i use my standard pistons instead??

Most definitely! You were right to hone the cylinder bores, but if you look closely at the piston skirt you will find what appears to be very fine grooves in the surface, in effect it's like a very fine pitch screw thread, with a peak to valley depth of about 0.07mm.

It is designed to retain some oil on the skirt surface, rather like the honed finish does in the cylinder bores. It also has the effect of reducing the friction of the piston against the cylinder wall. By polishing the skirt you may have buggered the pistons, the effect of which will be to increase what's known as blow-by.

If it was light polishing on the skirt you may get away with it.

earywig wrote:

Did i do a mistake? Should i use my standard pistons instead??

Most definitely! You were right to hone the cylinder bores, but if you look closely at the piston skirt you will find what appears to be very fine grooves in the surface, in effect it's like a very fine pitch screw thread, with a peak to valley depth of about 0.07mm.

It is designed to retain some oil on the skirt surface, rather like the honed finish does in the cylinder bores. It also has the effect of reducing the friction of the piston against the cylinder wall. By polishing the skirt you may have buggered the pistons, the effect of which will be to increase what's known as blow-by.

If it was light polishing on the skirt you may get away with it.

So, what´s the difference with JE pistons wich are REALLY polished?? Are they smaller so friction only affects rings?

I think that what I suggested may be lost in translation - your English is better than my Swedish

The JE pistons are not polished on the skirt, it is the machining which gives the impression that they are polished. They are diamond turned on the O.D. which gives a shiny finish. The grooves on the skirt look ilke this:



Ignore the black speckles - that is corrosion as the piston has been sitting on a shelf in my damp garage. The pitch between each groove is 0.25mm

I was just concerned that you may have polished the piston skirt, which may have removed the above.

earywig wrote:I think that what I suggested may be lost in translation - your English is better than my Swedish

The JE pistons are not polished on the skirt, it is the machining which gives the impression that they are polished. They are diamond turned on the O.D. which gives a shiny finish. The grooves on the skirt look ilke this:


Ignore the black speckles - that is corrosion as the piston has been sitting on a shelf in my damp garage. The pitch between each groove is 0.25mm

I was just concerned that you may have polished the piston skirt, which may have removed the above.

I´ll check with the scope at work on monday.
Cheers for the heads up in case i went to deep!

earywig wrote:I think that what I suggested may be lost in translation - your English is better than my Swedish

The JE pistons are not polished on the skirt, it is the machining which gives the impression that they are polished. They are diamond turned on the O.D. which gives a shiny finish. The grooves on the skirt look ilke this:



Ignore the black speckles - that is corrosion as the piston has been sitting on a shelf in my damp garage. The pitch between each groove is 0.25mm

I was just concerned that you may have polished the piston skirt, which may have removed the above.

would you be able to make up some pistons earwig if you were given the correct dimentions? just a thought