R45 Racer Project

[Voltaire]

Hello, I'm new to this forum. I am a longtime airhead owner but only the last year dabbled in R65s.
I ran a 1981 R65 last year as a work bike and its nimble handling and pep got me thinking...
Currently I run a R90/6 racebike in the local NZ classic series and have been looking at building a 500 cc bike for another class.
Over the last year I collected a couple of dead R65 motors and a R45 top end.
Last week I picked up an R65 racer.
The local cam shop converted an R65 cam to the 336 grind and planning to go with lighter valves and raise the compression.
I did a lot of searching and on the German forums( using Bing) found one guy 'Michael" who has built an R45 racer with 50 hp.
If anyone has done similar I'd be keen to hear from them.
Cheers
John

[Barry]

Welcome Voltaire,

I'm guessing you will already know as much or more than we do about R45 tuning.  Sounds like you have the cam sorted. The 336 was never available for The R45/65's was it. I have heard that replacing the 28mm carbs with 32mm makes a difference but never tried it. Making 50Hp from an R45 has got to mean higher revs so maybe together with the cam they would help it breath better.  

Sorry I can't be of much help.

[Voltaire]

Hi Barry, mostly I find when anyone asks about R45 tuning is sell it and buy xyz.
I have only got as far a engine parts on the bench but both the R65 and R45 heads are similar castings with the R65 having larger valves and 60cc chamber instead of 40cc.
Yes a 336 style cam ( its not a direct swap) may well be new ground.
Plan is to machine the base of the cylinders, raise the deck height and improve the squish band.
Cheers on the 32 mm carbs as thats what I was planning as stage 1.

[steve hawkins]

Voltaire,

I for one would love to hear about your progress.

As you say, most people would 'just add cubes' or recommend a different airhead.

Weight reduction will be high on your list.  They certainly aren't light.  What sort of things are you up to in this regard?

Tony and I are currently hacking off great lumps off his frame (centre stand and side stand mounts, plus any other unused bracket).  Bosch starters are heavy beasts also.  What about the flywheel, is your R65 post 81? i.e. clutch carrier, nicasil bores, lighter starter - if you are carrying one, etc

Cheers

Rev. Light

[Voltaire]

Hi Steve, I built a 900 a couple of years ago out of bits I bought on the net, its had pretty much any extra bits removed. So I'm looking at doing the same to the R65/45.
Its an 82 so has the later flywheel, looks like a smaller starter and I'll just run a Shorai battery.
Gearbox and FD are heavy but not much you can do about that.
Going to go with spoked wheels, Toaster tank and modified SS seat.
hmmm having trouble with pics...

[Luca]

You can even take things a little further.  Grind off the reflector tabs on the forks, ditch the steering head lock, take off the engine covers, go to a small, digital tach, one big front disc, lighter and snappier slide carbs.  I've also heard of people sealing spoked wheels so they can run tubeless.

Balancing and lightening the crank rods and pistons will improve throttle response.

I think the R45 might have a taller final drive ratio?

[nhmaf]

Hey - that bike has LS wheels on it!
New spoked ones might be even lighter, but at least those LS alloy wheels are already 1-2 pounds lighter than the snowflakes of the same period.

Interesting customization of the LS seat&tail piece too!

This should be quite a project  - hot-rodding an R45 is something you don't see often.   I'll second/third the moving to 32 mm Bings for more breathing.

The R45 came stock with a 35/9 final drive ratio if I recall correctly, and it needed that short ratio to accelerate.  But, if you can get the 50 horsepower out of your modified engine in a usable area of the RPM range, the 32/9 final drive of the R65 will get you some more top end if your going to be running on a fast track.

[Voltaire]

Yes it was an LS, the PO had it as a road bike then made it into a track bike, back wheel is cracked hence him selling it.
I intend to put spoked wheels on it.
I'm taking the spare R65 motor I have and R45 top end down to my ex engine reconditioner mate this weekend to formulate a plan.
He's already looking into SS valves and lighter springs/retainers.
Common comments I read about the r45/56 series is that they are fragile.
Interesting as the crank is almost identical just with a 10mm shorter stroke and the rods are shorter.
I'm guessing it comes from dropped valves which are 7mm and 2 piece.
cheers
John

[nhmaf]

The BMw 2-piece valves are actually pretty good, and the short stroke 248 engine's are 7mm diameter instead of 8mm on the 247 engine.  But, I think the issue with the valves was largely due to the valve seat issue which afflicted all the airheads in the early 80s, that resulted in valve overheating and deformation&breakage.   If you'll have new headwork done and good valveseats installed and cut properly, I'd expect it to be as reliable in the top end as any other airhead.

The tough part with fitting spoked wheels on these is getting the proper hub for the front - if you want to retain the stock disk carriers, etc.  It needs a narrow, 2-rib hub like on the R80ST bikes, and not the wider hubs from the /6  and early /7 spoked wheels.

[Voltaire]

Here is a pic of the 900 racer I built from parts, the R45 one will  be much the same to look at.
Lots of oil from running oil at max and doing 7500 rpm...opps....

[nhmaf]

I bet that is one of the fastest "toasters" around!

[Rob Valdez 79 R65]

If you are not using a starter motor, you should consider removing the top 1/3 (1/4?) of the engine block/timing cover/front cover, and relocate the diode board.
Have you seen this done?  Looks great.  Then you can get by with a MUCH smaller battery.

[bruce_launceston]

I saw that bike come up on TradeMe, that's the 5th LS rear wheel I know of that has cracked including the 2 that have cracked for me. Is the crack through the spoke, about 10mm away from the rim?
BMW Australia will sell you a new rear rim for AUD$2250. I told them they were joking of course but as they only built about 6500 LS's second hand wheels are getting hard to find.

I'm working and living in Christchurch at the moment.

[Voltaire]

Yes the one on TM, I wasn't going to bother but its a cheap test bench to see if I can tweek up a 450 motor.
I'm converting it to spoked wheels, I made a template up and it looks to clear the Brembos.
ChCh...? part of the rebuild there?
Good base for a bit of NZ touring.
I think a mate of mine has a set of the LS wheels in his shed.

[bruce_launceston]

Yes, I'm a draftsman doing rebuild repair documentation.
 
I would be interested in finding a spare LS wheel after my experiences with my old rear alloys.
I have been lucky, both replacements have had good splines, brake drum and wheel bearings and have bolted straight on after cleaning and repainting.

I have bought a Honda GB400TT for racing riding around the hills over here.