75' RD350 chain swap to 520..

[grcamna3]

I called Sprocket Specialists today and asked about gearing changes for my RD250B(it's going to become a 350 w/ a top-end swap later)and the man said "most people are going with the conversion to 520".
I held-off from ordering a rear sprocket,as I don't know what my final gearing ratio 'should be' with the 250 (352) primary drive,although I did order a 16 tooth front CS.
He has 520 countershaft sprockets in stock.
Can a 520 chain take the higher power of an RD350 top-end ?

[m in sc]

you can run like 100 hp thru a 520, rd isn't going to do anything to it. fwiw john at economy cycle sells the whole kit specifically for an rd

[grcamna3]

you can run like 100 hp thru a 520, rd isn't going to do anything to it. fwiw john at economy cycle sells the whole kit specifically for an rd

Thanks 

[grcamna3]

Was also wondering: What final drive gearing will work best for me when switching-over from my stock RD250 top-end up to an RD350 top-end ?
The 250 has much lower primary drive gearing than the 350 engine.
I might guess I'll need to at least change my front CS sprocket to the 16T.

[RDryan]

Sprocket Specialist...I'm surprised you got thru them. I tried years ago and it must've been a holiday as no one answered the phone. This was to replace a special rear sprocket that they made out of aluminum for my GSXR1000. I bought the bike used and it had Marvic Magnesium wheels on it which of course have their own bolt circle that's not OEM Gixxer specs. I got lucky for that bike and found a Super Sprox sprocket on Ebay for that wheel. A way better sprocket too as the carrier is aluminum but the teeth are steel, best of both worlds.

I imagine Sprocket Specialist can and will make what ever you want out of any material but I don't know why anybody would even consider Aluminum tooth sprocket for street use. Racing maybe if the weight loss really matters and you got money to burn but I dunno. I will say I got a fair bit of use out of that all Aluminum sprocket.

[RDryan]

Was also wondering: What final drive gearing will work best for me when switching-over from my stock RD250 top-end up to an RD350 top-end ?
The 250 has much lower primary drive gearing than the 350 engine.
I might guess I'll need to at least change my front CS sprocket to the 16T.

FWIW I just did this 250/350 conversion with my RD250B and I gotta tell ya...although I have never ridden a true RD350 I think the bike rides pretty nice with the original RD250 gear ratios. I have not  had the bike any faster than 75mph but that's plenty fast for me on the backroads I am riding. I can notice a bit extra power, torque over the 250 but it doesn't feel that much faster. Of course maybe it's just gearing limited. I think I read somewhere here on the forum that simply going up a tooth on the front sprocket corrects the difference? Not sure I wanna do that though, I actually have a rear sprocket that is the original tooth size for the 350 that I put on and took off as it kinda killed the pep of my 250, it's one tooth smaller I believe... I will also say that I did attempt to launch the bike hard once in first gear and you would think it would have some ballsy power wheelie action with the 250 gearing but I dunno maybe I didn't do right or my bike is a dog but I didn't lift the front wheel like I thought it would and I am cool with that.

[RDnuTZ]

you can run like 100 hp thru a 520, rd isn't going to do anything to it. fwiw john at economy cycle sells the whole kit specifically for an rd

what about 530?

[grcamna3]

you can run like 100 hp thru a 520, rd isn't going to do anything to it. fwiw john at economy cycle sells the whole kit specifically for an rd

what about 530?

The 530 is stock,but I'm not certain a 530 O-ring chain will be able to fit it's extra width w/o rubbing somewhere on the cases,etc.

[RDryan]

Well I took my 250/350 for a rip late,late last night when ordinarily I would be in bed. Decided to test my earlier comment to this thread as per the local weather forecast it is currently raining hard outside here in Gloucester,Ma. which means I probably will not be working today.

Having said that no doubt the bike has more grunt as a 350 and no doubt maybe somewhat held back by the 250 gearing.

One thing that I find more prevalent in this conversion especially if you haven't done so is addressing the clutch. My clutch is slipping bad as the revs build up to 5k/6k. Sometimes it grabs ok and if I ease into the higher rpms giving her the beans but really that old 250 clutch just can't handle the power.

In my case there is still an adj. to try, I need to address the clutch cable tension/action at the motor which I never did/understood. I did prematurely stress a clutch cable once at the lever/perch side because I wasn't getting the slack correct on the motor side,I felt like that adj. was seized and my answer was to place a lock washer in between the cable housing and where it rests on top of the chain case cover. Seemed to work. Long before that when I had the cases split to replace seals I did put in a cheap set of EBC friction plates but left the steel plates and springs alone and reinstalled those old rubber dampening rings. I searched this forum and found an old thread relating how those rubber rings can harden and not really work as intended but rather aid and abet in clutch slippage. Not sure if just throwing a set of wider YZ/FZR friction plates would solve this or if I have to spend more and get new steels and springs to make the clutch grab better. I will say if it tends to be the latter, latter then it looks like another couple hundred bucks for new friction,steels and springs.

If you factor in that $moola$...and not to thread drift but maybe money better spent. However if you need new chain and sprockets then it is what it is.

I will also say I did spend a bit more unexpectedly on the longer 350 cylinder studs plus the stud extraction tool vs. sticking with the 250 studs which are technically just long enough to bolt down the top end. Reflecting on this in my experience I will say that is money well spent. The 350 studs have more threads and I believe there fore bolt down the top end much nicer than with the existing,shorter 250 studs. You may as well factor this into your build if you decide to do it, just say'in. I've rechecked the torque on those cylinder nuts to studs a couple times upon running/riding my bike the past six times, surprising how they just need a bit of snugging up as the new parts bed in.   

[bitzz]

A decent 520 chain will have no problem with the "higher power" of your RD.
A modern 520 has more tensile strength than the stock POS 530 chain.
I run a 520 on a GS1000 racer with twice the HP and almost twice the weight of your RD
The TZ250/350's of the day ran a 520 chain and the sprockets are drop in to a RD... the RZ front sprockets fit too. IIRC the Daytona rears are different, I think you use XT/TT rear sprockets

[RDnuTZ]

you can run like 100 hp thru a 520, rd isn't going to do anything to it. fwiw john at economy cycle sells the whole kit specifically for an rd

what about 530?

The 530 is stock,but I'm not certain a 530 O-ring chain will be able to fit it's extra width w/o rubbing somewhere on the cases,etc.

I'm not building a HP monster, so stock 530 non-O-ring will be fine. I got a stock gearing kit off eBay with JT sprockets and generic chain for under $100.00 delivered as a starting set up.

[RDnuTZ]

Well I took my 250/350 for a rip late,late last night when ordinarily I would be in bed. Decided to test my earlier comment to this thread as per the local weather forecast it is currently raining hard outside here in Gloucester,Ma. which means I probably will not be working today.

Having said that no doubt the bike has more grunt as a 350 and no doubt maybe somewhat held back by the 250 gearing.

One thing that I find more prevalent in this conversion especially if you haven't done so is addressing the clutch. My clutch is slipping bad as the revs build up to 5k/6k. Sometimes it grabs ok and if I ease into the higher rpms giving her the beans but really that old 250 clutch just can't handle the power.

In my case there is still an adj. to try, I need to address the clutch cable tension/action at the motor which I never did/understood. I did prematurely stress a clutch cable once at the lever/perch side because I wasn't getting the slack correct on the motor side,I felt like that adj. was seized and my answer was to place a lock washer in between the cable housing and where it rests on top of the chain case cover. Seemed to work. Long before that when I had the cases split to replace seals I did put in a cheap set of EBC friction plates but left the steel plates and springs alone and reinstalled those old rubber dampening rings. I searched this forum and found an old thread relating how those rubber rings can harden and not really work as intended but rather aid and abet in clutch slippage. Not sure if just throwing a set of wider YZ/FZR friction plates would solve this or if I have to spend more and get new steels and springs to make the clutch grab better. I will say if it tends to be the latter, latter then it looks like another couple hundred bucks for new friction,steels and springs.

If you factor in that $moola$...and not to thread drift but maybe money better spent. However if you need new chain and sprockets then it is what it is.

I will also say I did spend a bit more unexpectedly on the longer 350 cylinder studs plus the stud extraction tool vs. sticking with the 250 studs which are technically just long enough to bolt down the top end. Reflecting on this in my experience I will say that is money well spent. The 350 studs have more threads and I believe there fore bolt down the top end much nicer than with the existing,shorter 250 studs. You may as well factor this into your build if you decide to do it, just say'in. I've rechecked the torque on those cylinder nuts to studs a couple times upon running/riding my bike the past six times, surprising how they just need a bit of snugging up as the new parts bed in. 

did you do anything about your pipes yet, like getting less restrictive baffles like Mark suggested or am I mixing you up with another poster?

[m in sc]

fwiw the rz and 400 front sprockets will not fit a 250/350 input shaft. the splines are different

[RDryan]

Well I took my 250/350 for a rip late,late last night when ordinarily I would be in bed. Decided to test my earlier comment to this thread as per the local weather forecast it is currently raining hard outside here in Gloucester,Ma. which means I probably will not be working today.

Having said that no doubt the bike has more grunt as a 350 and no doubt maybe somewhat held back by the 250 gearing.

One thing that I find more prevalent in this conversion especially if you haven't done so is addressing the clutch. My clutch is slipping bad as the revs build up to 5k/6k. Sometimes it grabs ok and if I ease into the higher rpms giving her the beans but really that old 250 clutch just can't handle the power.

In my case there is still an adj. to try, I need to address the clutch cable tension/action at the motor which I never did/understood. I did prematurely stress a clutch cable once at the lever/perch side because I wasn't getting the slack correct on the motor side,I felt like that adj. was seized and my answer was to place a lock washer in between the cable housing and where it rests on top of the chain case cover. Seemed to work. Long before that when I had the cases split to replace seals I did put in a cheap set of EBC friction plates but left the steel plates and springs alone and reinstalled those old rubber dampening rings. I searched this forum and found an old thread relating how those rubber rings can harden and not really work as intended but rather aid and abet in clutch slippage. Not sure if just throwing a set of wider YZ/FZR friction plates would solve this or if I have to spend more and get new steels and springs to make the clutch grab better. I will say if it tends to be the latter, latter then it looks like another couple hundred bucks for new friction,steels and springs.

If you factor in that $moola$...and not to thread drift but maybe money better spent. However if you need new chain and sprockets then it is what it is.

I will also say I did spend a bit more unexpectedly on the longer 350 cylinder studs plus the stud extraction tool vs. sticking with the 250 studs which are technically just long enough to bolt down the top end. Reflecting on this in my experience I will say that is money well spent. The 350 studs have more threads and I believe there fore bolt down the top end much nicer than with the existing,shorter 250 studs. You may as well factor this into your build if you decide to do it, just say'in. I've rechecked the torque on those cylinder nuts to studs a couple times upon running/riding my bike the past six times, surprising how they just need a bit of snugging up as the new parts bed in. 

did you do anything about your pipes yet, like getting less restrictive baffles like Mark suggested or am I mixing you up with another poster?

You sir are right on point, I'm the fella you're thinking of. As an  aside it's funny how there's a few of us with 250's  and kinda doing the same thing converting to 350's

So I haven't done what Mark suggested but I think I will. Thing is I already thoroughly cleaned the old baffles, chucked into my woodstove   and they came out really clean. When I posted about em I was pretty sure I was going to reinstall them but I kinda wondered if there was benefit otherwise and more specifically just not adding the muffler packing but I had that on hand as well so I did that too.

I was just messing around with the clutch cable adj. and finally figured out the adjusting screw at the engine end. For the longest time I couldn't free up the lock nut. Had to take off the stater/sprocket cover and put that opposite end of the adj. screw in a vise to hold it and very easily loosened the lock nut. Of course all the sand and grim accumulation around that front sprocked, clutch pushrod area needed a good cleaning. Well the cable is now properly lubed and adjusted. Not sure if this will help with the clutch slipping.

The baffles and the clutch...I think from a performance perspective I need both. Definitely need to do the clutch but I wanted to do the cheapest things first of course.

It's raining today so no test rides see an improvement with the clutch adj. however I am 99% between Mark's other suggestion to do the FZR friction plates and reading an old Chuck Supertune post about these old stock clutches I think I ought a spring for the whole shebang. Just seems like a hassle to get just friction plates and pull the clutch apart only to find old springs outta tolerance or steel plates that don't seem to pass a flatness test.

Obviously I wasn't patient enough to wait a week on the oil change for more parts but it's funny how the progress of one aspect of the bike kinda exposes another shortcoming. I was happy to do the gear oil change though because it gave me a better understanding of it also I replaced the main two stroke oil feed line and that rectangled rubber grommet that it passes thru to the oil pump, those parts I singed with the torch in my first attempt at trying to remove studs.

I wonder if I do the clutch rebuild can I just lean the bike on its left side and try to save some gear oil? or is that a bad idea?

[m in sc]

yes, you can . have done it. Just remove or drain fuel tank