a,b,c piston question ?

[britishgas]

i went to order a new piston for my 2012 300 racing , the dealer said i need to take the barrel of and look and see which piston it is , i am reluctant to do this in case the new piston does not arrive before the weekend[as i want to ride it this weekend } is there any other way of checking which piston i need ?

 

[gassergrant]

i went to order a new piston for my 2012 300 racing , the dealer said i need to take the barrel of and look and see which piston it is , i am reluctant to do this in case the new piston does not arrive before the weekend[as i want to ride it this weekend } is there any other way of checking which piston i need ?

its to do with the piston/bore size its under the rad valve on the back of the barrel stamped A OR B OR C. get it wrong and it will not be good news. clean the old piston and it should be stamped on the top

 

[cbutler]

The back side of the cylinder will have the letter on it

 

[britishgas]

found it . its an a should i just but an a piston in ,the bike only had about twenty five hours when i bought it ?

 

[Jakobi]

Yeah above the cases where the reed block attaches.

 

[britishgas]

its an a will it be ok tobuy a a piston for it ? or do i neeed to strip it down ?

 

[Jakobi]

How longs a piece of string?

The correct method is to pull it down, measure the bore with a 3 point bore gauge and the select the right piston based on tolerances.

Realistically though, if the nikasil looks good with cross hatching still visible and no nicks or gouges you shouldn't have any issues putting an A piston in there. This has been my approach, but I do intend on buying the tools down the track. Others have used B pistons with no issues as well.

 

[wa_ndro]

Just get an A it will be fine

 

[cbutler]

Just get an A it will be fine

+1

I have countless hours on mine.

 

[Moto7man]

How longs a piece of string?

The correct method is to pull it down, measure the bore with a 3 point bore gauge and the select the right piston based on tolerances.

Realistically though, if the nikasil looks good with cross hatching still visible and no nicks or gouges you shouldn't have any issues putting an A piston in there. This has been my approach, but I do intend on buying the tools down the track. Others have used B pistons with no issues as well.

Here is a video on using a dial bore gauge to measure cylinder wear. Skip to 6.22......

http://www.youtube.com/watch?v=Q1nr65rm0h0

 

[Elvis74]

The Play for the piston should be 0.05mm to 0.06mm

 

[gassergrant]

its an a will it be ok tobuy a a piston for it ? or do i neeed to strip it down ?

If it only has 25hrs I would say no, maybe rings but personaly I would just ride it

 

[Moto7man]

Btw, did you do a compression check?

 

[hannesd]

just ride the damn bike until you've done about 200hrs

 

[britishgas]

It had 25 hours on when I got it I have put quote a few more on it

 

[gassergrant]

My one has done well over 100hrs at a wild guess, book says 60hrs change the rings and 90 piston, me when it starts loosing power
If you race change it if yiu plod up lanes etc wait, but it your choise at the end of the day.
Its not a hard jod and if your around hertfordshire area I dont mind helping, its got to be worth a few cups of tea lol

 

[Moto7man]

just ride the damn bike until you've done about 200hrs

I would agree. I have about 135 to 155(I need to look at the hour meter) on my 2011 and it still runs great.
I'm going to do a compression check tomorrow and I will post the results.

 

[papa_j]

I just discovered the Jeff Slavens YouTube video on piston and cylinder clearance at http://www.youtube.com/watch?v=hdTW_RBR3Aw . Definitely worth watching.

 

[Moto7man]

I just discovered the Jeff Slavens YouTube video on piston and cylinder clearance at http://www.youtube.com/watch?v=hdTW_RBR3Aw . Definitely worth watching.

Good video with a lot of insightful information. Thanks for posting it!

 

[papa_j]

He has a bunch of videos: one on "reading" pistons, ring gap, cylinder care (spoiler alert don't hone your cylinder), jetting, and fork stuff.

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