DT125R ARCHIVE

gareth_iowc · DTR Member

flat top or domed piston?

Dingle001 · DTR Senior Member

I would recommend sticking with the DT piston as this is designed to suit the combustion chamber shape. My view, simple as it might be, is that if Yamaha could design all their 125s to run with the same piston design they would.

If the engine has sucked in water be careful that the con rod isnt bent, as this does sometimes happen when an engine tries to compress water and can't. A visual check should be ok and make sure the piston comes to the top of the cylinder.

gareth_iowc · DTR Member

Ok thanks buddy didn't think of checking the rod

NEV · Guru

Yes you can use the TZR piston, I've just recently had a 2.4mm overbore using a 2 mm oversize TZR piston, this is also a higher compression piston. The lads at Cornish Motorcycles in Plymouth did the work for me, and touch wood, no problems as yet, and it pulls like a train,

http://www.youtube.com/watch?feature=player_detailpage&v=U0IkhDmQ0eI

Energized · DTR Legend

Sounds top that does boss, loving how you've done your bike now Nev!

NEV · Guru

Energized wrote:
Sounds top that does boss, loving how you've done your bike now Nev!

Cheers mate, it's the careful running in bit thats the ball ache at the minute, when thats sorted its going on the dyno.

Energized · DTR Legend

Nice one mate! Can't wait to see the Dyno results!!

Dingle001 · DTR Senior Member

Can someone explain to me how a flat top piston is higher compression than a domed top? I must be missing something here........!

NEV · Guru

Not with ya Dingle, where it say that, but if you mean you can't get domed TZR pistons, have a butchers here

ATHENA PISTON 56MM (DOME CROWN) - DTR-TDR-TZR 125
http://www.yamahamotorcyclespares.co.uk/spares/partImage.asp?GPN=Z%5B%5F%3B56562U&model=YAMAHA TZR 125 - UK SPEC ONLY&uid=0

gareth_iowc · DTR Member

sorry also forgot to ask forged or standard?

El_Faggo · Forum idiot

Copied and pasted from another website:

Flat Top:-Advantages:

-Minimum surface area, hence lightest with shortest heat path to cylinder wall
-Faster heat transfer to cylinder wall.
-Piston crown is in tension under load
-Ports open faster, not masked at partial opening by chamfer.
-Piston shape does not interfere with the entry and exit angles set by the ports
-Combustion chamber can be a true hemisphere

Disadvantages:

-Aluminium is poor under tension when hot
-Greater possibility of ring over-heating due to more rapid heat transfer
-Nothing to prevent gas crossing piston from transfers to exhaust port. (this is not always a disadvantage with a tuned exhaust)
-Achieving an efficient squish band is not easy.

Dome Top Advantages

-Piston crown is in compression under load
-Dome pushes incoming mixture to top of cylinder and reduces "short circuiting"
-Scavenging tends to be better so less four-stroking at partial throttle.

Disadvantages:

-Additional weight
-Compression forces tend to spread the top ring land.
-Port timing is slightly fuzzy.
-Increased surface area of piston and head produce more quench effect in squish band.
-Combustion chamber tends to crescent shape, slowing flame spread.

dirtpoor · DTR Senior Member

hi nev do you live in plymouth if so give me a mesage on hear sometime and could go for a lil blitz.