2 Strokes Down Under

Just looking for some guidance with 29L/1XG Barrel head interchangeability.

Coming from an air-cooled RD+LC back ground i am not overly familiar with the RZ Gear...

I have a 1983 RZ Race bike, and a spare pair of 1XG Barrels, I would like to know if the differences between the 29l and the 1XG barrels, I would like to know if 29L Pistons can be used in the 1XG barrels? Is the head drastically different? Are Power Valves interchangeable? and would the differences be drastic enough to need to re-jet the Carbs?



Any help would be great.


Regards,


Alex.

I'm no expert but my understanding is that though porting changed slightly the key dimensions didn't so any pair of barrels and presumably the head would be interchangable.
Aftermarket pistons are a "standard" design from any manufacturer and (with subtleties for earlier models like trimming the bridge tab off) are I believe backwards compatible all the way through LC's probably to air coolers.
Plenty of experts on here to pick out the details

youre right BRG. In basic terms, the only really different 250 was the 51L, and that runs the same pistons anyway. the 29L and 1XGs are pretty similar. PVs are the same AFAIK across the 250 range, Yam was very lazy with the 350 units so I doubt they did anything special with the 250s lol.

My understanding is that the 350 is in essence an over bored 250.
As such the 250 is the "natural" state.
There are (surprisingly few, and very practically for manufacturing purposes) differences between 250 and 350, but that's another conversation. Jon's website covers that comprehensively.

250 PV's should be the same across the years I would think, as far as makes any real difference.

I remember conversations on the old Alek Hayes forum and maybe read somewhere about the (350) combustion chamber dome shape being different between the early 31K and later models, would guess that might translate to the 250, don't know if that affects compression ratio - doubt it.

Also fairly sure older bits turned up on later bikes, early F2 bikes with 31K heads and so on.

about?

BRG1200 wrote:My understanding is that the 350 is in essence an over bored 250.
As such the 250 is the "natural" state.
There are (surprisingly and very practically for manufacturing purposes few) differences between 250 and 350, but that's another conversation.

250 PV's should be the same across the years, as far as makes any real difference.

I remember conversations on the old Alek Hayes forum about

yep 350 is indeed a big bore 250.

But, Yama did upgrade the later 350s with the info they learnt with the 51L 250, ie better squish and port work to get a few more bhp.

Jon I thought you were an engineer - do you moonlight as an English teacher? >;-)

haha, I see you were mid edit now! thought youd got bored and wandered off LOL And no... Im not an engineer, these days im a writer... hence i need a real job

yep, the Yam stuff is all over the place really, the 250 they seemed to tire off when the other mdoels like TZRs came out so then we just got the old 29L cyls redone as 1XGs. The shame of it is that the 84(japan only) and 85 (aus) 51L is the best of the 2fiddy RZs, but yam went backwards with the 1XG after that, who knows why, costs for the licencing of the tech perhaps?

I'm not familiar with 51L, will have to look that up

Thanks to everybody for their insight. It has been more than useful.

JonW wrote:

BRG1200 wrote:My understanding is that the 350 is in essence an over bored 250.
As such the 250 is the "natural" state.
There are (surprisingly and very practically for manufacturing purposes few) differences between 250 and 350, but that's another conversation.

250 PV's should be the same across the years, as far as makes any real difference.

I remember conversations on the old Alek Hayes forum about

yep 350 is indeed a big bore 250.

But, Yama did upgrade the later 350s with the info they learnt with the 51L 250, ie better squish and port work to get a few more bhp.

I'm confused... My RZ250 Barrels are very different to my RZ350 ones, the powervalve housings are different, and the 350 liners are about 10mm bigger O.D. than the 250. Not as simple as the 350 being "indeed a big bore 250".

LOL too funny. This cracked me up 'and the 350 liners are about 10mm bigger O.D. than the 250'. I deduce you are joking with us Jools.

To be sure no one finds this thread in the future and wonders: No body is suggesting you can over bore a 250 to make a 350, thats just silly. I was referring to what yamaha did when they made the larger cyls, ie scaled them up for a larger bore in the same outer 'case'. And, the smaller 250 PVs dont fit the 350, the intakes are different sizes too, more LC than 350RZ etc etc etc etc.

Jon jokingly pokes Yamaha a little for being a bit lazy making the 350 on the platform of what I'll call a "natural" 250. It's GREAT that they did, for their production and for us 30 years down the track.
The techies out there will mention balance factors etc being a bit "out" on the 350 compared to the 250, but you can see how Yamaha brought the 250/350 models closer and closer from the aircooled then LC then RZ. Wish my aircooled front fork and wheel had disc mounts and caliper mounts for a second disc like ghe LC series did!

(Jools what I meant was...) "Module" and sub assembly sizes and stud spacings etc are the same so barrels and heads oil pumps etc fit between capacities and variations. Totally sensible approach, minimise parts inventory, maximise our abiliy to repair and adapt.

I have a pair of 250 cylinders on the shelf next to the 350 ones. Intake tracts and intake size very different, and I'm kicking myself that my rebored 350 barrels don't have PV's or bushes, and I can't recycle any 250 parts! :-/

Absolutely boys, dead right. Sorry, I think my response was prompted by the fact that someone on here once advised me to fit 2mm oversize pistons in my 250, (That'd result in a nice liner thickness eh!?)
(Mate,I'm in the same boat with having 350 barrels but whilst I've got spare 250 PVs, I haven't got 350 ones) As you say, :-/

you can make your own bushes tho, its much harder to make PVs, but the FFTP price is keen, Ive said before we should bandy together and share the postage...

Er, you can fit 2mm bigger pistons in the RZ250 bores, thats the max tho....