350 pistons on 250 conrods???

[seezyer]

help required please!....
i have a set of seized 250 barrels, i have newish conrods bought for the 250.
does anyone know if the 350 pistons will fit on the 250 conrods? as i have a head and carbs off of a 350, and would only need to buy the barrels, pistons and gaskets.

id like to convert it to 350, but not if i have to have the crank altered......

thanks in advance...

[midlifecrisisrd]

Remember to change the oil pump and drive to a 350 one.

Steve

[seezyer]

aah, thats brilliant news then, i will buy the small end bearings for the 350, use my crank, and dig through the bucket of spares (and overhaul) the 350 pump and drive i have.

cheers fella's :-)

[marddy]

I am assuming you are talking about LCs and not YPVS.

Bottom end of both LC 250 and 350 are the same. But, that is where the similarity ends.

1] Top end bearings [on the Gudgeon Pins] are smaller in the 250s. So, use the 350's bearings that are larger in dia.
2] Oil Pump ratio is different. Either use both the Gear wheel drive and the Oil Pump from a 350 OR you will need to tune up the 250's Oil Pump...now that is a bit tedious.
3] Reed Valve stopper of a 250 is 9.2mm wide whereas in the 350s, it is 10.50mm. Try to use 350 reeds.
4] Retard the timing by about 0.2 degrees for a 350.
5] Run a 39 teeth rear sprocket
6] See if you can get a rear wheel of a 350. It has sprocket cush rubbers and runs on 3 bearings [2 for the wheel and 1 for the Sprocket]. 250's run on 2 bearings and are without cush rubbers.
5] The Muffler units especially the stinger section is smaller in the 250s.

I have a 4L3 250 and a 4L0-01 350. I studied and made the required conversions but yet, my bike does not run like a true 350. And, the bike vibrates a lot. My assessment is that Yam had a lighter Crank in their 4L3, which is a Japanese model. Any takes??

[seezyer]

great info, thanks Marddy!
i stripped the top end off last night, and have discovered its eaten the crank as well, so looks like a bit more of a wait, but i'll turn it all into 350 now whilst im at it....
i am also chasing a mate to sell me her crashed TZR250, and if that comes off i will swap all the bits over (engine/loom/controls etc).....

cheers guys.

[marddy]

TZR 250 in a LC can be done. Ensure fitment of the engine bedding well. However, the weight of a TZR engine is less than that of LC which may change the handling...for the better maybe.

Secondly, TZRs run on 17 inch wheels. If you are fitting 17 inch wheels also, it is good but that will require some mods to be done. If you are going to run LC [18 inch wheels], then ensure to get your sprocketing right.

Thirdly, TZRs lack low rpm torque. LC350s have good low end torque...something you may miss in city runs.

Take a call...just do it!! Keep us informed.

[oldelsieboy]

Nov 28, 2011 19:07:01 GMT 1 marddy said:

3] Reed Valve stopper of a 250 is 9.2mm wide whereas in the 350s, it is 10.50mm. Try to use 350 reeds.

Never come across that one before according to the official Yamaha service manual both 250 & 350 reed valve stoppers are set the same, 9mm.
One major difference between a 250 & 350 are the carbs. 250 carbs are stamped 4L1-00 & 350 4L0-00 or if they are the later factory modded ones 4L0-01. AFAIK the 250 carbs have smaller internal airways/jets that cannot be modified & reading posts from other forum members do not work well on a 350.

OEB

[marddy]

I missed mentioning about the Carbs. There are some more to my list, but thought not to mention all and demotivate.

I have a series of Yam manuals and about 6 Yam bikes. Each of these are having different part numbers for Reed Valves. Both on reading and physical verification, I have come to understand that 250s have smaller reed stopper openings when compared to 350s. It is true to AC and LC [incl YPVS] models.

I am glad we have 2 points of view here. Let us share some notes for our mutual benefit and benefit of all as well.