7 replies to this topic

[smelling123]

Im going to be rebuilding a 325 and wondered if anyone has an opinion on wether its worth boring to 340ccs ?? Anyone had any experience of this and was it an improvement??

What size piston do the 340s use? I guess the head will need machining to suit which is no problem - what squish clearance is prefered??

many thanks
Stu

[Nigel Dabster]

smelling123, on 22 January 2012 - 03:43 PM, said:

Im going to be rebuilding a 325 and wondered if anyone has an opinion on wether its worth boring to 340ccs ?? Anyone had any experience of this and was it an improvement??

What size piston do the 340s use? I guess the head will need machining to suit which is no problem - what squish clearance is prefered??

many thanks
Stu

Quite a few prefer a 325 so I wouldnt bother.
getting all the other bits right is much more worthwhile.

[John Collins]

In simple terms - forget it, just not worth the hassle and expense, let alone the difficulty of getting piston etc

[Woody]

As above, not worth it. In terms of performance I practically guarantee you won't feel any difference going from 325 to 340 - much the same as going from 320 to 340 on a Majesty.

If you're on the last oversize on the 325 bore then yes, it's probably a cheaper option than having a new liner and going back to standard. 340 pistons are pricey now if you can find one.

The 340 uses an 85mm piston from the 360 Pursang (which has a dfferent stroke, hence 360 not 340)

Early 325 engines from M92, 125 and 151 can't be overbored as the liners aren't thick enough, they were basically overbored 250 barrels. The M159 onwards had the thicker liner.

[Nigel Dabster]

are pistons even available ?
remember trying to get one a decade ago and size was right but it didnt have the oem holes? is that right?

[wayne_weedon]

I had one original a couple years ago. Think I traded it with DR for one of his customers.

They are scarce!

[PSchrauber]

NOS pistons are still in limited numbers available. They don't have the holes you have to take the measurements for drilling the two holes in the piston from the cylinder or the old piston, (if you trust the holes of old piston).

When I got the piston I was again astonished about the size and took a picture in combination with a piston of a 500cc KTM engine, this is really a big "bucket" for 350cc.

[smelling123]

Many thanks for all the replies guys, will have a think about it....