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1971 Yamaha R5

Started by Dylan H, September 12, 2022, 04:15:09 PM

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Dylan H

Hello, I'm new to this form due to NATS forum going down or whatever happened to it. As stated in the subject I have a R5B that I'm looking to restomod a little but not heavily as I want to keep the original look but make some changes for looks and performance. I'm looking at expansion chamber pipes but don't necessarily want the upswept look or them to stand out too much. I was looking at the DG pipes or a set of Spec II. I'm also planning to bore it up some but don't know the best way to go about it. :umm: For a little background I am 18 and got this bike when I was 16 as it had sat in a barn since the late 80s. When I got it she was rough and I had done some work to it and got it running. My goal was to drive it my last day of senior year and while out test riding it and making sure everything was good to go a few days prior I was unaware that it was running lean and it burned a hole through the top of the piston on the left cylinder. :bang: Upon recently taking the bike apart since I'm planning on doing this build over winter I am led to believe it was rebuilt once before due to broken fins on the cylinders. The cylinders don't look very pretty on the outside which I assume is due to the previous owner using it essentially as a dirtbike around a campground. When I got the bike it had street tires but i was told when he got it there was a dirtbike tire on the back. Is there any companies out there that sell cylinders or were they ever reproduced? I've been searching all over but ones I'm seeing up for sale are on eBay and would probably be as much work to clean up as my own. My exhausts currently have part of the chrome gone due to I'm assuming acid spilling on them. I would like to do a 6 speed swap on them but haven't found much on doing so. I believe it was on this page I had seen someone saying you could put rd400 gears in it and I'd like to do that to mine but I'm not sure on how much would go into doing so. I have to split my case this winter so I am planning on probably changing the crankshaft out, hopefully gears and doing all new seals and see if I can fix the oil leak. I would like to bore it up but not sure what is the best size over to go to. I also was debating on putting rd350 cylinders on it but I would rather leave it piston ported. Any help or tips is greatly appreciated :cheers:

m in sc


boring it gives no power advantage, so just let that go. (yes im serious). as far as r5 cyls, no, no one has reproduced them. cheapest way to go would be to rebore yours or fit a repro rd350 topend. I mean, they can be had pretty cheaply. been mixed reviews on quality, but i've ridden a few bikes with them and honestly, not bad and faster than the r5 stock.

(i own 2 r5s fyi).

it needs to be tuned if you are running non stock airfilters (avoid k&n style or anything with flat backs if possible. will work 'ok ' at best on a piston port but not great). as far as going 6 speed, etc, depends what your budget is. 400 transmissions are gettign hard to find and therefore expensive. However, rd250/350 transmissions are 6 speed and can be swapped in, but you need to change everything,, drum, forks, etc. My 72 has a 6 speed in it, my 70 is a 5.

My suggestion would be to get the cyls bored, and then get new pistons.

Dylan H

im looking to bore mine up a little due to a broke piston and ring. just to be on the safe side since it beat the head up quite a bit. i have a y boot filter on it. If i were to pick up a 400 transmission would it fit in same as the rd250/350 one? And in your opinion do you prefer the 6 speed swap or should i leave the 5 speed. Also being with the rd top end how much work is involved with changing it over from the piston port to reed valve and is it worth doing so? I got the bike for free with a Honda mt125 Elsinore that is in worse condition engine wise so I figure I might as well just put the money into the r5 and by the time i could by a decent one i could have built a nice one with better performance. so far what i have found on my bike it has kz400 forks and front wheel. i figure if im gonna change it back to Yamaha parts i'll do a disc brake swap but being that i can get new forks relatively cheap ill probably leave the kz stuff on it.

m in sc

the 400 trans will also require all the parts (drum/forks/etc/ AND a different inner clutch basket. TBH, on an r5 that doesnt really make any serious power, not worth it. I like my 6th gear but my 72 has chambers, a digital programmable cdi and a few other things so it can pull 6th pretty well, and was originally set up way back as a track bike. I mean, is it worth it to split the cases? probably not. if you do, then you should also do crank seals, etc. it gets deep quick.

as far as swapping top ends, its a bolt on. literally. carbs work, exhaust, etc. you will need to reroute the oil injection to feed the carbs or intakes somehow, but thats it (assuming you are running the injection pump).  there will be more tuning involved as well. you will also need reedcages and intakes, but those can be had cheaply

I'll be honest, if i only had ONE bike, and i was in your position, id do the rd topend swap. I also have a few rds as well, so thats why i haven't swapped any of mine (not trying to be hypocritical, just being honest).

your bike isn't going to be a show bike anytime soon, so swapping topends isn't going to hurt anything, and the rd top-ends do make better power, even with stock r5 pipes. pistons are more readily available, etc. and as weird as it is, its probably the more cost effective option.

i would strongly recommend changing crank seals on your bike if you haven't or don't know how old they are. you do not need to split the cases on an r5 motor, so you are in luck there. 

I mean, it depends where you want to land with it and what your capabilities are. I mean, dig into it, and spend th etime and you'll be rewarded by it, greatly. i havent gotten bored of them yet, and ive had these things for 30+ years.

as far as your front end, many years ago, my original rd had a cl350 front end on it, all i could get at the time, so i get it.

Just remember: free bikes always wind up being the most expensive the longer you own them.   :dawg: (its not a bad thing) .

Dylan H

I have to split the cases on it anyway since a chunk of the piston that broke went down in there. I'm planning to redo all the seals and everything on it just for peace of mind since its so old and sat for roughly 30 years and I have no history on the bike. I ran premix in it when I did have it running because I didn't know if the injection worked(previous owner used premix). Honestly being that I can buy the whole top end for it relatively cheap ill probably go with the rd so it looks a little nicer, I'll probably end up buying a nice all original r5 down the road if I ever come across one anyway.

As you said on your 72 with the cdi, is that an upgrade worth doing?

I really appreciate the advice and information on this stuff


CDI once set you can forget and get better charging output, etc. Dependent on the CDI you choose. Worth it? Well, how much do you know about adjusting, cleaning, and fiddling with points?

m in sc

good deal on the teardown, it'll be worth it.  :cheerleader:

the cdi? it def is worth it, but the only one to really consider is the vape unit, the HPI is good, but not great for a street bike. (have one on one of my rds). I would def focus on the other stuff 1st, the cdi can come later as the motor and top-end are going to eat a lot of resources and time. the cdi can be changed later after its assembled and mechanically dialed in.  again, just some advice.

I'd put a list of what you need together, see if anyone on here has stuff you need (ad in the wanted section a good idea).

also, get familiar with 'economy cycle', he also offers a discount on orders over 250 for forum members. (2sw is the code).


Dylan H

-Striker, I don't know that much about messing with the points, my dad helped me with adjusting them the first time around and we cleaned them up some and it seemed to be running good, I'll probably change to a cdi later down the road

mark- I'm gonna start looking into everything for rebuilding it and ill check into the wanted section once i got that all figured out, I have bought just about every part I've needed off of economy cycle so far, the only exception being a seat off of another bike and front brake shoes once I realized that it wasn't the original front end.

Ill keep updating as I continue the rebuild(may come to a stop for a small amount of time due to having to rebuild the engine for my brothers truck also). I really appreciate all the advice, thank you! :cheers:


Take some pics as you go and update the build thread here as we all love to see the progress on builds and the guys here will be a TREMENDOUS resource with questions about these old bikes. I've owned my 2 smoker for over 30 years but these guys on this forum have forgotten more about 2 strokes than I've learned in 30+ years! Very much a wealth of knowledge here. I was only 19 when I went after my Daytona because I knew once I started riding it I'd never get rid of it. As the years have gone by, it's only solidified that sentiment as these babies are getting really difficult to find for less than an arm, a leg, AND your first born. Good luck with the build! Love it already even without the pics.  :taz:

Dylan H

So on my original post I had tried to add photos of my bike but it was putting up an error so assuming the photos were too big, after resizing them here is some photos of my bike from a few months ago right after it burned a hole in that piston, back at school we could paint our parking stalls so i had mine painted to match my bike but never did get to ride it there due to it blowing up, so i trailered it up there to take photos anyway.  :like:

Dylan H

sorry its been a little since my latest update on the bike, currently as it sits it is all apart. I painted the frame today and I'm picking it up tomorrow. I have yet to sandblast and paint my swingarm which will be probably the end of the month. I went through the wiring harness and replaced all bad wires and connections and taped it back up to be looking better, the red wire the whole way through the harness was melted. I was wondering if anyone on here knows what all I would need to put a rd350 top end on it or could direct me to a thread on the topic. My current cylinders and heads took some minor damage when the ring broke so I would like to switch over to rd350 ones. Another thing I'm looking for some help with is exhausts. I have the stock ones but they had what I assume is battery acid on them since the finish is gone and they have some small dents due to being used as a dirt bike in the 80s. I would like to buy a nice set of pipes for it but don't want them to stand out too much since I still wanna kind of keep the original look. Also I have no center stand and the bracket is bent a little bit, would that interfere with the mounting of the pipes? Also the foot pegs, does anyone have suggestions on them if it is more comfortable to leave them in the original place or move them back and if it would be worth doing? any tips or help is greatly appreciated

Dylan H

here's some photos of the frame, I think it will turn out nice, paint was still a little wet. Its a matte black


Great start, I have a 1970 R5 , I have a front fender in very good condition and lots of parts. Center stand .. let me know. I swapped to the rd 350 front end disk brake up grade.

m in sc

if hes not interested, pm me on the fender and if you have a stock airbox...

Dylan H

hey mark I do have the stock airbox off my bike, I swapped it for a different filter, and TPR5 thank you but I assume mine was crashed at some point or forks bent since it has a kz400 wheel and forks on it. As of right now I'm not sure on the center stand because I'm looking at swapping pipes and don't know if there's pipes that will clear it without modifying more stuff