YZ pistons in MX250 what year works without mods?

[cyclegod]

What year YZ250 pistons work in 74 MX250s ?

[Freakshow]

i didnt think they did unless they are later ones.  I got Dt and MX 250 ones here what size you looking for, hook you up with a few standards i could :O)

[vandy010]

whilst on the subject of these piston thingies,
and to add to the confusion of this thread perhaps,
does anyone know if the 75/76 dt250 pistons will work in the 74 model mx/dt?
yeah i know i've changed the direction a little but it's all about getting the bikes going right...

[cyclegod]

whilst on the subject of these piston thingies,
and to add to the confusion of this thread perhaps,
does anyone know if the 75/76 dt250 pistons will work in the 74 model mx/dt?
yeah i know i've changed the direction a little but it's all about getting the bikes going right...

DT250 engine didn't change much 74-76, neither did the pistons they just stopped using dyke rings on top. the YZ piston uses a cut away on the intake side instead of two round holes which allows better intake breathing (apparently). But at some point the gap between pin and crown increased, so I need to know which year that was so I don't have to modify the barrel by adding a spacer plate.

[Freakshow]

the MXb does the same thing with the curve cut away and i think 76+ Dt also,

Can you use the MXb piston ? cyclegod ?

Vandy if its Dt it will fit, all that model used the same piston A-B-C  you could also upgrade it to the MXA - single ringer :O)

Dt Part # = 438-11635-01-00
Part Description = PISTON (1ST) ( just change the 5 to 6 to 7 etc to go up in over sizes)

Also these models are said to be the same Piston =
DT2 1973 250
DT250A 1974 250
DT250B 1975 250
DT250C 1976 250
DT3 1973 250
TY250E 1978 250 Trials

[Nathan S]

Info not available in the Wiseco catalogue?

[cyclegod]

Info not available in the Wiseco catalogue?

Probably, but since I don't have one it's hard to say.

[vandy010]

freaky's answered my question.
my mx250a arrived as a non-runner with no piston so i'm in the dark from the get-go.
my bike will need a rebore so which piston for me?
thanks freaky.
i dig these kinds of convo's, very helpfull indeed...

[oldfart]

Direct from serco catalolgue   page 51  if this is any help

YZ 250  1976-79              bore 70 mm         stroke 64 mm
IT  250  1978-80                                                             
DT 250  1974-79
MX 250  1973-1975

[DJRacing]

Could it be that the YZ250C,D,E,F piston will work in the MX250A? If so Wiseco list that the DT1;DT2;DT3 and MX can run the same piston. The number is 234PS for standard all the way up to 234P8 = 2mm oversize
234P6 = 1.5mm
234P4 =1mm
234P2 = .5mm

[Freakshow]

freaky's answered my question.
my mx250a arrived as a non-runner with no piston so i'm in the dark from the get-go.
my bike will need a rebore so which piston for me?
thanks freaky.
i dig these kinds of convo's, very helpfull indeed...

what size is it on now ? piston crown should be stamped .25, .50, .75 so youll know what its on now, if ya like i can lend you a piston to get it running so at least you know where your at, then when you know its a runner you can get a new piston, which you will need to take with you anyway to the reborers so they can get the right clearances with the piston you intend to use

[vandy010]

thanks freaky but as i said it came with no piston. the rebuild is still a bit down the track as theres other things i'm wanting to do first.
it's been a while since i measured the bore but it will most likely need either 1.25 over or 1.5 over as i'm pretty sure it's 1mm over now.
cheers

[jimson]

DJ the early DT1 250 didn't have reeds so the back of the piston has no cut away so the piston is different to the reed models I think they are DT2 maybe.I have heard you can use a IT 250 piston in a DT2 reed model but have not seen this done with my own eyes. jimson

[Freakshow]

thanks freaky but as i said it came with no piston. the rebuild is still a bit down the track as theres other things i'm wanting to do first.
it's been a while since i measured the bore but it will most likely need either 1.25 over or 1.5 over as i'm pretty sure it's 1mm over now.
cheers

if the bore is over 71mm you will need to be After market,  start you wiseco hunt !