Author Topic: RD350 Track Bike build  (Read 45774 times)

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Offline 5port

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RD350 Track Bike build
« on: May 24, 2020, 10:05:55 AM »
Hi everyone!
This is going to be a slowish saga of putting together a track-only RD350.  :)
I started off wanting a TZ350 race bike and collecting bits to build one. That was 25 years ago!  Well, over that time my knowledge about these bikes and the collection of parts has morphed a bit.  The basic limitation is cost .  I have to spend on the roadbikes so, the race/track bike project has been slow.  However, the parts have been acquired and progress made.  :)  I have found that TZ parts are now rare and very expensive. In the UK, DTR (Dennis Trollope Racing) and Greenham Racing (run By Dawn Greenham) are good suppliers of mostly OE. There is a good supply of repro TZ parts from various niche suppliers, eg Vince at Fondseca and the very good Meadspeed company run by Barry Mead. Overall, I think that most repro TZ parts are excellent but not all suppliers are as good.
So, why an RD350?  Well, it is for fun with nostalgia mixed in.  The getting it together and building it is also a big part of the fun for me.  Of course, the RD is very similar to the TZ but, very few parts are identical when you get down to the nitty gritty.  That said, as George Harrison quipped about the Ruttles "it's bloody close!"  :D   So, yes, an RD350 shares the basic bloodline as the twinshock TZ.   
I decided to use good RD and not-quite-right "TZ" parts to make a "TZ" track bike that I could actually use.  The cylinders would be 350LC and I expected about 50bhp was easy to achieve with good tuning.  However, when it came to the sorting out of the water cooling, it was looking very expensive to sort out the waterpump using TZ parts. ???  I did not want to deviate very far from the 1973 layout, not an LC engine in an aircooled frame.   So... how about aircooled 350?  Dan Peacock has built a very nice tuned R5 using similar thinking and, he gets over 50bhp.  The aircooled thinking was also a good fit with my "early" time period.  The preceeding 1972 Yamaha 350 GP production racebike was the TR3.  The TR3 was based around the YR5 road 350 and, although both the YR5 and TR3 are piston-ported, the RD350 reed valved cylinders are a good upgrade.  :)
So that was some of the basic background.   I will try to get a sort-of "episode" on here every month.  The next installment will be a talk through the engine components that are ready and it will include photo's!   :) 

Cheers

5port


             
« Last Edit: June 13, 2020, 11:06:21 AM by 5port »
5port

Offline KGR33N

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Re: RD350 Track Bike build
« Reply #1 on: May 24, 2020, 11:37:48 AM »
Well done and looking forward to reading more about it.
Yamaha RD 250 C (1976)
Yamaha RD 250 C (1976)
Kawasaki GPZ 1100 (1983)
Yamaha XJ 600 N Diversion (1995)
Ducati Hypermotard SP (2013)

Offline 5port

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Re: RD350 Track Bike build
« Reply #2 on: May 24, 2020, 02:58:00 PM »
Thanks!  Here is a pic of a great bike! :)



Cheers

5port
5port

Offline tony2stroke

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Re: RD350 Track Bike build
« Reply #3 on: May 24, 2020, 03:02:15 PM »
Looking forward to this one, I'll get some popcorn in ready  ;D

Offline 5port

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Re: RD350 Track Bike build
« Reply #4 on: May 24, 2020, 04:22:24 PM »
1972 was probably the most formative year for the Yamaha 250 and 350 parallel twin 2 strokes.  The engine layout of the roadbike DS7 and YR5 had been re-defined with the horizontally split cases,  54mm stroke crank and "5port" piston porting.  :)  The TD3 and TR3 production race bikes were designed to use the same layout but incorporating a new 6-speed "328" gearbox, 328 being the TR3 model code.  The new engine layout consolidated the varied layouts that had been seen on previous middleweight Yamaha twins, getting rid of vertical split cases and maximising common components.
  Chassis wise, the DS7 and YR5 had a good double cradle frame and drum brakes.  The TD3 and TR3 had very similar layout, but differed from the roadbikes in all details, not least the brakes, huge Double twin-leading drum on the front!  The TD3/TR3 introduced CDI ignition to improve reliability over the previous points systems at 10,500 rpm.
The 328 type gearbox was very successful and, was copied forward onto the RD250/350, with different clutch and gear ratio's, for 1973 model year onwards.... In fact, the 328 gearbox on the racebikes went through right until 1980!  You can see 328 parts in your aircooled RD gearbox! 
So, that was the time of maximum similarity for the road and race bikes.  When the TZ came along in 1973, it got watercooling and, the road RD got the reed valves and the front disc brake!  :D

Cheers

5port
   
« Last Edit: June 09, 2020, 10:01:02 AM by 5port »
5port

Offline tony2stroke

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Re: RD350 Track Bike build
« Reply #5 on: May 24, 2020, 04:50:37 PM »
Hang on, I haven't got my popcorn in yet  :D

Offline 5port

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Re: RD350 Track Bike build
« Reply #6 on: May 25, 2020, 11:37:15 AM »
Hang on, I haven't got my popcorn in yet  :D

Sorry Tony, I forgot how long those Harrods deliveries take!  :)

Cheers

5port


5port

Online magbuster

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Re: RD350 Track Bike build
« Reply #7 on: May 29, 2020, 09:05:53 AM »
Had that picture on my toolbox at work


Amongst others ??? ???

Offline 5port

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Re: RD350 Track Bike build
« Reply #8 on: June 08, 2020, 12:43:19 PM »
Hope you have the popcorn!   :)



Hows that for size?

5port
5port

Offline 5port

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Re: RD350 Track Bike build
« Reply #9 on: June 08, 2020, 02:02:54 PM »
So, onwards with the engine!  As I said before, the bike is based on an aircooled RD,  :)  the frame and engine cases 1A2, I think '77 250D.  The build is a complete mixture of what I have available, with some tasty bits added.  I am not trying to make a perfect replica in any way and neither am I trying to make a competitive race bike, it is an attempt to make something that will work and be fun.
RD based track/race bikes have done very well.  There are many highly tuned and successful aircooled RD's out there.  That said, there are certain parts of the different RD engines that are, maybe, more suitable for the track.  The gearbox was always great.  The RD250/350 gbox was designed from the TD/TR3 328/329 '72 GP racebike and incorporated 6 speeds with the "positive stop" shifting mechanism.  In fact, the shifter parts are the same in the RD and the TD/TR3 and TZ250/350, just the ratio's were completely different for the roadbike.  The '75 UK/Eu 250/350B got much better closer ratio's and that was continued into the '76 onwards RD250/400. The gbox that I am using on this is a 250/400E, it has the same ratio's as the earlier 521/522, 1A1, 1A2 and 1A3 gbox.  Likewise, the clutch had various changes that improved it.  The RD gbox is used in many tuned bikes, Ed Erlenbach uses an RD gbox in his LSR engine-I think he has had the gear engagement dogs undercut in that, standard RD are not undercut.
So, back to the basic engine.

   


The cases are 250D I think. They are well used but, not too bad.  I decided to go with the original TD/TR3/TZ250/350 front rubber mounts and so, the mounting points were machined out and the race bike rubber bushes and spacer tubes fitted. It has been found that the fixed upper rear mount can crack the top of the case in this configuration so, the rear top mount will not be used.



The left side of the case is fairly standard, just some chain damage.
So, what is inside and, what else can anyone spot so far?  :)

5port





     
« Last Edit: July 05, 2020, 10:54:24 AM by 5port »
5port

Offline tony2stroke

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Re: RD350 Track Bike build
« Reply #10 on: June 08, 2020, 03:05:24 PM »
So, onwards with the engine!  As I said before, the bike is based on an aircooled RD,  :)  the frame and engine cases 1A2, I think '77 250D.  The build is a complete mixture of what I have available, with some tasty bits added.  I am not trying to make a perfect replica in any way and neither am I trying to make a competitive race bike, it is an attempt to make something that will work and be fun.
RD based track/race bikes have done very well.  There many highly tuned and successful aircooled RD's out there.  That said, there are certain parts of the engine that are, maybe, more suitable for the track.  The gearbox was always great.  The RD250/350 gbox was designed from the TD/TR3 328/329 '72 GP racebike and incorporated 6 speeds with the "positive stop" shifting mechanism.  In fact, the shifter parts are the same, just the ratio's were completely different for the roadbike.  The '75 UK/Eu 250/350B got much better closer ratio's and that was continued into the '76 onwards RD250/400. Likewise, the clutch had various changes that improved it.  The RD gbox is used in many tuned bikes, Ed Erlenbach uses an RD gbox in his LSR engine-I think he has had the gear engagement dogs undercut in that, standard RD are not undercut.
So, back to the basic engine.

(Attachment Link)    


The cases are 250D I think. They are well used but, not too bad.  I decided to go with the original TD/TR3/TZ250/350 front rubber mounts and so, the mounting points were machined out and the race bike rubber bushes and spacer tubes fitted. It has been found that the fixed upper rear mount can crack the top of the case in this configuration so, the rear top mount will not be used.

(Attachment Link)

The left side of the case is fairly standard, just some chain damage.
So, what is inside and, what else can anyone spot so far?  :)

5port





     

Straight cut gears.

Do I get any prizes.

O damn I just got butterscotch sticky stuff on my computer  :D

Offline 5port

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Re: RD350 Track Bike build
« Reply #11 on: June 08, 2020, 05:55:22 PM »
Point for TONY!  :D
Yes, straight cut TZ350 primaries.  Now, normally, that would be a tad expensive, but I was fortunate that I found a guy with a damaged primary 1H4 (TZ350C) gear and... well we can come to that in a mo.   :)
A couple of other things though, the 520 conversion sprocket and the TZ gear lever, although I will probably use rearsets that keep the normal UP for UP gearchange.  ???
So, what next.....



Yes, opened up.  I think the crank can come into the picture...



Yes, the crank.  The RD (until the 2R8/9) uses the crank with lead balance weights.  The weights do have a habit of becoming loose at high mileages. Also, adding weight to balance makes the assembly a little heavier.  Yamaha had introduced a new crank for the TD/TR3 bikes that used large lightening holes either side of the crankpin to get the balance without lead weights.  Yamaha copied that onto the 2R8/9 range 5 years later.  So, 42 years later  :D I am using a 2R8 crank.  This is nothing new on RD track bikes and provides a good crank at low cost.  Yamaha also used slotted b/ends on the TD/TR3 rods for extra oiling so, I have got slotted rods.  In fact, this crank came with the slotted rods from a previous rebuild.  The outer bearings were tired but everything else is reasonable so, I have fitted new outer main bearings and we will go and see how she runs.  :)  Overall, I think the crank is good for my shakedown stage. All the deflections and play values have been checked.  That said, you can never be sure about the internals so, my policy here is that I don't mind If I have to redo it later. Things will go wrong!  ::)
One thing that you can also easily check on a "previously loved" crank is the small end eye where the needle roller goes.  Check for any sign of wear or rust/pitting.  If there is any, it needs a rebuild.

 

So, back to the clutch.  There I was with a bargain TZ350C straight cut Primary, damaged! Well that is why it was a bargain, the splined centre drive extension was shagged (and I am not certain how, except, it may well have been due to failure in a race). I decided that I could design a way to mount an RD clutch outer basket onto the TZ gear.  Now, the standard RD basket has four alloy drive posts that stick into an rd gear and have rubbers either side for cush.  The TZ drives through the centre drive extension but, that had gone. ???  I decided to use 6 of the 9 holes in the gear to fit circular alloy driving pucks and rubber cush rings.  My thinking is that 6 steel-riveted drive pucks will be strong enough, the RD just drives through the four alloy pegs.  So, an OK 250D basket assembly was used. I drilled off the four rivet heads and punched out the rivets to leave me with the rear steel plate and the alloy basket.  The old drive pegs were machined off the back of the basket and the bare basket was then set up and "clocked" on a special milling machine that could be set to give the very accurate placing of the 6 holes being used from the 9 in the TZ 350C gear.  The steel plate was done similar, although one hole was welded up first.  The configuration is nicely balanced, with the 3 pairs of drive pucks separated each by a single blind hole in the gear.  You should be able to see the pairs of rivets and the edges of the pucks behind the outer steel ring.  Now, I cannot claim the skill of the machining as that was done by my friend Mal!

     

Cheers

5port

   
   
« Last Edit: June 10, 2020, 12:35:37 PM by 5port »
5port

Offline tony2stroke

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Re: RD350 Track Bike build
« Reply #12 on: June 08, 2020, 06:04:53 PM »
Some good progress there  8) 8) 8) 8) 8)

Offline 5port

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Re: RD350 Track Bike build
« Reply #13 on: June 09, 2020, 07:35:09 AM »
The clutch itself is a later RD type.  It should be fine for the 50 horsepower or so that I expect to have.  :).  The TR3 came with a wet clutch but changed over to a dry one later in production. There are advantages in the dry clutch, less likely to slip and no drag when clutch pulled in in gear.  The lack of drag makes it easier to push-start in gear and, was a major benefit in those push start races.  I would like a full dry clutch on this but, the full set-up is very expensive.  The RD clutch with the straight cut primaries should be a good compromise, esp as I am able to use that bargain damaged gear!
The next instalment should cover the top end!  Cheers

5port
5port

Offline tony2stroke

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Re: RD350 Track Bike build
« Reply #14 on: June 09, 2020, 07:47:14 AM »
Personally I think adding a dry clutch would just be a massive waist of money really, you won't be doing any push starting anyway, or will you ?