Hi everyone, as my mate Stuart pointed me in the direction of this site maybe someone can answer this question,
I,m about to buy a 1936 Bsa R4 350cc. can anyone tell me if there is any similarity between it and a M20 ?.
Certainly the engine is different as its ohv and has an exposed exhaust valve.

Vaughan.

Hi Vaughan..An interesting bike..half a V twin, as it used one barrel and head from the Y13. The box looks like the M20 type, but the rest is of lighter construction I think. Leon will know more I'm sure...Ian

email (option): ian@wright52.plus.com

It seems that lots of nuts and bolts are the same and these are often still available from Russell motors. Leon will know more but I guess that the similarity stops at the nuts and bolts.

Very pretty motorcycle.

Henk

email (option): ahum@quicknet.nl

Get a copy of the parts book .
The pre WWII usually showed all models with individual parts on one page and a table of numbers & models on the other so it is a really easy ( if slightly tedious ) job to run the ruler over the page.
Where there is one illustration but several numbers then at least the original blank of that part was common to the listed models but some may be machined a bit differently so at least you know you can modify the wrong part to fit.

email (option): wariron@tpg.com.au

Thanks for the tip can I download one off here ?.


Vaughan

Nearly all parts lists are available on one DVD, not as a down load at the moment.

http://wdbsa.nl/for_sale.htm

Henk

email (option): ahum@quicknet.nl

Hi Vaughan,

I have an R19 which is the competition version of the R4. The R4 is very different from an M20. The gearbox internals are nore or less the same as those of an M20 execept for the selector forks shaft and the forks.
Very few other parts are interchangeable and if any of the rare bits are missing you will be looking for those for a long time.

The R4 is a high camshaft model where the camshaft sits directly above the crankshaft pinion thus reducing the length of the pushrods and lessening the flexing fo the push rods, at least in theory.

To be able to rebuild that bike you need at least the parts books but preferably also some other books like Pitman's Book of the BSA 9th up until the 11th editon. These books show up regularly on Ebay. Next would be BMS of Motor Cycling BSA Motorcycles 1935-1940. This book is very nice to have as it has some tolerances of bushes and bearings in it so you can determine what to replace and what the tolerances on the new parts should be. Nad then there is D.W. Munro a practical guide on BSA motorcycles from 1931 up to 1950. These last two books also show up on Ebay regurlarly.

I also have the instruction manual and this shows the tappet and ignition settings which is nice when you are in the finishing stages.

I have a website on 1930's BSA motorcyles: BSA motorcycles 1930-1940

Regards,
Leon

PS I also looking for an R4

email (option): leonhop3@planet.nl

A guy i know bought one last year & still haven't got round to looking at it.
Ive always been curious & maybe Leon could answer this... as Ian says, that model shares top end parts with the Y13 but although the barrels share the same part number, the head doesn't share its number with the Y13 front head as you woud think.
Somewhere in there it loses around 25cc which may be rod length, Small end position on the piston, crank pin position ETC.
But I'm wondering if the head is the same but maybe only difference is smaller exhaust pipe. Any chance of exhaust size at head ?

Leon, thanks for the info, the bike is complete and was restored over 20 years ago. It was purchased about 15 years ago by a friend who promptly covered it up with a tarp and left it, fortunately he had the sense to smother it in oil, persistent badgering resulted in a surprise offer to sell .
If I knew how to upload pics I,d do so

Vaughan

Fred, when I get it I,ll let you know, presumably you want the ID dims across the threaded part ???.

Vaughan

Ohh, you are that ! Leon.
Thanks for your site I have probably directed 1000 people to it over the years.

I got my parts books on a 3 CD set from Bavid Brailey who used to run a flat tank web site before he retired.
They used to be available from a few retailers.
If you can find one they are brilliant as he formatted them in html so you can search through them with a web browser.
This feature is really useful particularly if you are tracking parts over years.

As a legacy of it's gun making heritage BSA had a backwards compatability rule that drove the designers & engineers mad but made life really good for us.
While latter model parts are not correct & give the rivet counters nightmares a lot of them either fit latter models or can with minimal machining be made to fit parts that they were not designed for which is really good for those of us for who a ride is more important than a trophy.

email (option): wariron@tpg.com.au

Hi. Vaughan .. just the OD of the pipe where it enters the head ..
And like others on here, I would love to see some pics of the machine : )

Just to follow up on this off topic thread. I am trying to collect all 18 models in the 1936 catalogue. I have 9 models already but still looking for the following models:
X0 150cc OHV
B3 250cc OHV (250cc model same frame as the R4)
R4 350cc OHV
R17 350cc OHV
R20 350cc OHV New Blue Star
Q21 500cc OHV New Blue star
W6 500cc SV
Q7 500cc OHV
Y13 750cc OHV V twin

Preferably in as found condition but complete but I also would consider restored bikes. If you know or have any of these bikes for sale please drop me a line. The engine and frame numbers should have the D prefix in order to "qualify" for my collection.

Regards,
Leon

email (option): leonhop3@planet.nl

I,ve sent some pics to Stuart and hopefully when he,s finished tinkering he will post them tonight

Finished 'tinkering' with the WM20 so here are the pics Not sure why the right hand edge of the images has been cropped?










Stuart

email (option): stu.gibbins@btinternet.com

very nice !
I would love to own that.

Me too!!

email (option): leonhop3@planet.nl

I like it to, when my friend went to see the bike I said to him if you dont buy it I will, so I,ve watched it slowly deteriate in his back garden, anyway it will soon be in my garage
The observant amongst you might have noted its the wrong tank, this one is for a hand change, the original was lost at the chromers !!!
Also there is no wiring on it ????????, so it will be a good clean but not over done and the wiring sorted and out on the road.
How does it compare power and performance wise against a M20 ????.

Vaughan

Hi Vaughan

I can see a run with the M20 midland section comming up soon, well there is 3 of us!

Pete

email (option): cruaser@aol.com

Dont ask me to paint it green though Pete

Vaughan,

I have never ridden an R4 but the R19 accelerates much faster than the M20 but it's also much lighter. According to a (secret) BSA data book form 1936 the hore power rating of the R4 and the R19 shows a remarkable difference. I am at work (but obviously not working right now) but if my memory serves me right it is 13BHP (R4) versus 19BHP (R19). I like the handling very much because it's a very nimble bike although a little small for my length (6' 4").

I didn't notice the petrol tank. I did see the cut away for the rocker box which should be there on the R4 tank. But I failed to notice the attachments for the gear lever gate. So someone did some clever conversion work on the petrol tank (like BSA did when they found out the rockerbox wouldnt fit under the petrol tank).

Regards,
Leon

email (option): leonhop3@planet.nl

I also missed those tank mounting lugs for hand change.
So that tank is off something else then... but as long as it fits, I would repaint the sides to original spec as it hides the holes which can be carefully filled but with care to preserve them.

No Fred, after the original tank was lost my mate found this tank at an autojumble, it is for a R4 but a hand change, I,ll put some mushroom head screws in the unwanted holes before its painted, this tank has been chromed

Vaughan

Yes they were chromed, I noticed the chrome looked good enough to just paint the panels & have a reasonably good looking tank.
Ive had to get a tank made & chromed on a 30's BSA & its is not a cheap process :D

I will mention something if you dont mind. I know most people slacken valve gear off before removing rocker boxes but ...its very easy for a certain part to snap on those rocker boxes so its very important to losen tappet adjusters fully on disassembly on those.
Its the "fingers" on the left (Drive side) that ive seen snapped & need to be slackened first & tightened last.

also even with valve gear slackened when undoing those left side bolts if you dont hold the cylinder head bolt underneath. . that can suddenly undo (instead of the rockerbox bolt) & it jacks up that "alloy finger" & puts dangerous strain on it.

Its not happened to me but I was warned. it would be horrible to have to buy a replacement.
the 4th pic of your bike shows its the exhaust one mainly at risk. on early versions of that design on the Vee Twin that didnt have the added casting to enclose the inlet valve, there's four of those fairly weak alloy fingers to care for.

Message for cycle Fred,

Fred, the O.D. of the exhaust on the R4 is 1 and 5/8" ths .

Vaughan.

Thanks for that, well that's same size as "J" & "Y" VTwins then, so still a mystery why the heads part number isn't the same, maybe its the inlet port where they differ.

I,ve been working away steadily on this and other projects, (Laverda SF) and this weekend I hope to fit the rebuilt mag.
I thought hang the expence I,ll fit a new plug but I cant find what sort it should be, can anyone help me out with this please ?. The one I,ve taken out is a Motocraft BF32 18mm, I seem to recall fitting these to 2 litre Ford engines years ago.
Vaughan.

Re: "Somewhere in there it loses around 25cc which may be rod length, Small end position on the piston, crank pin position ETC."

Of those factors, only the crankpin position in the flywheel affects displacement.

19 HP from 350cc is huge!!

email (option): sales@victorylibrary.com

According to Roy Bacon (British Motorcycles of the 1930’s) the bore & stroke measurements are
71 x 94.5 for Y13
71 x 88 for R4/R19
Hence the “missing” 25 c.c.

19bhp from a 1930’s 350 is indeed impressive.

ChrisJ

How does the R17 compare to the W35-17 twin port, I am trying to restore.
It's hard to find any data, I have the parts list. I was informed there was only 190 produced.
Darren

email (option): Darrenacartwright@yahoo.com.au

I am sorry you felt I hi-jacked your post, it was not my intention.
I will not post anymore

email (option): Darrenacartwright@yahoo.com.au

Chris J's reply shows they shortened the stroke. as we know they used the same barrel it is very likely they also changed wrist pin position or rod length as i suggested.
i wasn't just looking how to get less capacity, i was looking to see how they got less capacity on this particular machine whist using the same barrel.
Its better to read the entire thread, to avoid correcting perfectly legitimate comments. ; )

Hi,
I am looking for 2 rockers of this type. Anything is welcome.
Anybody ?

Michael

Quote Reply
Re: Bsa R4

Surely most forum users are only looking for their own subject interests and/or technical answers where ever they may be on the forum....most of my posts are taken off on a tangent with another question.....no problem, just post another :-) We all have the same interest here don't we?

Vaughan now has his R4 up and running and a very nice bike it has turned out to be. He's asked me to post a couple of photo's of the finished article:

email (option): stu.gibbins@btinternet.com

Very nice indeed !