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Sov's 1940 BSA WM20 Project


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Hey all, this was my intro thread: http://hmvf.co.uk/forumvb/showthread.php?54071-Me-and-my-new-bike-say-hi


I'm going to catalog my work here, getting this old creature running again, and any restoration or work I do on her.





She ran with the previous owner, which only put a few miles on her and is a military vehicle restoration dude. He sold this to me with the trust I would take care of her and give her good attention, love and a restoration of at least some capacity. He's working on a jeep now too, so has a project in progress that looks great. He took off the fuel tank and petcocks as they were in very bad shape and not a good idea to run this bike as it was.


In reality I am not certain how many civilian miles this bike has, as most of it looks straight out of the army. The tires are War Department tires still! Still has it's army registration plates on it as well. It served until 1970 according to records. The only thing newer looking is a larger aftermarket tail light that is wired up (poorly) and it's original tail light is disconnected. Aside from that it's all antique (vintage?). It's missing very little in parts, but some parts were certainly interchanged during it's rebuild and maintenance in the British army. I'd say it's 98% complete although some of those parts will be replaced due to severe wear. I'm saving as much as I can in it's rebuild, keeping it original, or tracking down NOS parts when forced to replace anything. I'm preserving anything removed from the bike and keeping it. Lucky, it seems there are still plenty of good quality original English made parts around.


For now, I'm focused on getting it running and driving well; Hopefully in time for a yearly Vintage English bike show here in CT, USA.

Edited by SovereignZuul
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Going to do some catch-up posting, because I have already started working on it and accomplished a bit since my introduction post.


First, I knew the petrol tank was a big problem and started here.


Here it is before I touched anything. Inside is coated in either a red color sealer or red oxide paint or something.




I planned on using course sand and bb's with water to agitate the loose paint off to begin with. Then switching to a weak acid, the infamous vinegar bath to remove the remaining paint and rust.


I temporarily sealed the petcock holes with bolts using plumbers tape and some caulk.




Vinegar is soaking in, left it for days checking frequently and it didn't do a very good job... You can see how rusty it is in there still.




I had some Evapo-Rust sitting around and gave that a try. Using some more bb's to agitate the rust and a soft brush to knock it off. This worked much better than the vinegar! It only took a few hours of work to completely clean the inside of the tank. I dried the tank as fast as I could with a hot air gun and some alcohol to disperse the water I used to wash out the evapo-rust (evaporust seems to gum up when it dries and is water soluble).




Finally, the sealing phase. I put the petcocks back in, covered in plastic wrap, plumbers tape, and heavy tape to keep them protected from the sealant. I used por-15 tank sealer for this, a nice silvery color, to make it easy to see in the tank to check fuel levels, etc.




Very happy with the result, it looks great!


Now onto the next vital section of restoration... Rebuilding the carburetor.

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This is the last three days of labors for me (after work hours). "Finished" this last night.


I decided the carb might as well get a fresh rebuild and I have plenty of time to wait with all the parts shipping so was a good time to tackle it. Of course nothing is so simple, and being the very first part I've rebuilt on this bike I have now learned the meaning of military surplus that my father warned me every time I told him I want a military vehicle to rebuild one day.


The carb is a disgusting mess here, covered in rust, grease, dirt and all sorts of a mess. (much like the rest of the bike)




And the discoveries made during the disassembly are what I mean by learning about military surplus...


The carb's air filter didn't fit well. There is a collar that screws onto the car and the air filter screws into that. It wasn't fully screwed in there there was an open gap in the intake at the bottom of the carb that went unnoticed, which pretty much defeated the purpose of putting the filter on anyway.


Someone tried to secure the filter collar ring onto the carb by using a punch to deform the aluminum and "pinch" the ring on. Didn't work so well aside from causing minor damage to the carb body. You can see the next broken piece in this pic as well.




Another discovery! Seems like someone in the army who rebuilt this carb in the past broke the needle jet off in the carb sleeve (maybe 1960 according to the rebuild tag on the bike). It's all brass, shouldn't have been stuck in the first place so I wonder what happened here back then. Rather than replace it, someone just threaded it back in with the small fraction of thread left on the needle jet. I admit, I did laugh a bit at this pure laziness (cost saving???), haha.




Finally, the throttle stop screw looks like it was hit with a center punch as well, as the head was all deformed and caused the hole it was in to suffer minor thread damage. I'll have to fix this when my whitworth tap & die set arrives via shipping. God knows why this was done at all, seems like another pointless "fix" by army mechanics.




I was able to (with incredible ease mind you) remove the broken needle jet from the base. I brought out a bitty wrench but I ended up just twisting it out with two fingers in a matter of a second. Amal is still around so I ordered a replacement main and needle jet for just a few dollars.




I gave all the parts a good wash in soapy water to get rid of as much grease and dirt as reasonable before they went in my rust remover bath. They look a mess still. The aluminum parts have so much rust on them... Looking better, but still everything looks bad.




I used Evapo-Rust after doing some research about rust dissolvers. People said it had no effect on brass or aluminum but I saw otherwise. This, plus using appropriate plastic, brass and steel brushes and hours of work got everything looking grand. It's amazing the difference! Some parts that were 100% rusty are clean and shiny now. I can't recommend this product enough. About half the parts came out great in just a few hours of soaking and brushing while they soaked, the rest I left overnight and they came out great in a single short brushing afterwards. I tried to set up the parts in the same way between shots to make comparison easy.




I did a mock assembly with my new gaskets, not even finger tight, just to get a look at the carb. I still need the parts to arrive before it's finished and I need to work on the slide more, clean & polish. Either way, super impressed on how good it came out! Happy with my work so far.




Next step is to give the whole bike a good degrease and pressure wash.


I have new tires, tubes and wheel bands, a new seat, new cables, new petcocks, and battery/box planned before I consider this roadworthy (or until I discover another problem). Pretty much all that has either arrived or is on order. Hope I can get it all done asap.

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You're doing a grand job of cleaning up. But a few observations if I may. Firstly you don't mention where you are, but your $ reference would indicate USA or Australia?


I'm sure there has been some civilian tinkering to this bike. I don't think there would be any need to bodge/break things in a military/REME workshop. Parts for these Amal carbs were and still are easy to obtain.


The Air filter is non standard. For normal use the carb would have just had a standard open bell mouth. Later in the war or for extreme conditions, a tank top Vokes filter could have been fitted.


Personally I would also have fitted a new slide, to at least eradicate some of the wear that might have taken place in the carb body.

I would also rub the flange flat on emery paper taped to a surface plate or piece of plate glass as they are more often than not warped.


If you intend to re-tap the idle screw thread, you will need a 3/16 x 28tpi tap. Ron

M20 246.jpg

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I've never seen a monkey-metal (mazac) jet block with a brass insert like that one. I can only assume that it is a late-war economy measure. I'd be inclined to fit a new brass jet block and check the slide for wear carefully too.


I think that you're being a little unfair to the British Army. They certainly never fitted Del'Orto air filters and the broken needle jet could well have been done by a previous private owner too. There would be no reason for a REME fitter with a huge stock of Ordnance stores to re-fit a broken part like that.


The expanded end to the throttle-stop screw seems to have been a factory aspect as I've seen it on NOS carbs - presumably to ensure that the screw couldn't fall out if it loosened. Isn't the thread 2BA rather than Whitworth ?

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Isn't the thread 2BA rather than Whitworth ?


No Rik! (I think we were typing together). It's one of those 3/16" sizes. I made it 28tpi and the only reference i found to that size is UNS. Ron

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Sorry, don't mean to be unfair to the British Army.


I'm over here in USA, East Coast, Connecticut.


American surplus equipment has a bad reputation, with people I know, for being abused to the point of when they sell it everything needs to be replaced and is broken, I was sterotyping, my bad. My father had a lot to say about how messed up his surplus WLA was when he got it 40+ years ago.


Also, I guess I can say I am younger guy, 31 years old (but more like 15 year old mind).


Not done with this carb, I know the slide is in really bad shape, I had to give it a sanding to remove some raised edges from deep gouges! I'm going to polish it as smooth as I can and pray it functions, not done with it yet. A new replacement slide was mighty expensive and trying to cut cost a bit. At some point I'm sure I'll replace it.


Air filter says something in Italian, certainly not English.


After exploring the bike and having it's written history of civilian ownership it just seems that not many civilian hands touched this machine. It has very little use after being sold at BAOR. Probably spent most of it's time in a shed or garage somewhere. I first assumed it was all civilian work, the more I learn the more I realize it's mostly military. I even thought it was a bad civilian paint job until I learned that brush stroke paint job was military.


I felt inclined to use the bell mouth intake flange but decided to buy a new gauze air filter from Amal as well. It's not correct for the bike, but I want to preserve the engine and run an air filter. I may switch it to the open version later down the line but want to stick with a filter for now. Perhaps a Vokes type filter later on at some point too, we'll see what happens.


I did some light sanding on the carb in general. Flattened the punch marks in the intake, I did sand the flange to the engine flatter/smooth as it was warped. I'm going to polish these parts a bit with some very high grit emery paper.


Maybe this carb isn't military at all? The shiny brass looks out of place and doesn't match most pictures I see, and the big brass nut at the bottom of the main carb bottom is a slightly different shape than some WD carbs I've seen.

Edited by SovereignZuul
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The engine will probably run ok with that slide. But when they are worn and sucking in too much air past the sides, you will never get a decent tick over. Bear in mind that the body is also worn as well. Ron

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No Rik! (I think we were typing together). It's one of those 3/16" sizes. I made it 28tpi and the only reference i found to that size is UNS. Ron


Cheers Ron,


With my preference for NOS mixing chambers, I've never had to do it....simply an idea in the back of my head that the screws were BA.


What do you make of the jet block, Ron ? Ever seen one ? I've had late carbs with chromed slides and stainless steel needle jets but never seen a block other than the three-piece soldered brass types.

Edited by 79x100
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Rik. I can't recall ever seeing one of those monkey jet blocks. But as long as it doesn't distort like the oil pump bodies, I can't see why it wouldn't work as well as a brass one. My concern would be the worn slide. Ron

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That's funny, I didn't know most jet blocks were brass. This is the first Amal carb I've ever dealt with. This jet block is in poor shape as well, pitted in places, etc.


I'm sure a brand new 276 would be great, hope this one can get me puttering around for a bit at least. Gearhead friends of mine were equally as concerned with the air slipping past the slide too. Crossing my fingers this is okay for now but not counting on it.



Edited by SovereignZuul
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Well at least you can buy all new Amal parts for these including a complete carb (around £270 I think). My preference however for Amal parts is to use Hitchcocks Motorcycles. http://www.hitchcocksmotorcycles.com/home They sell genuine Amal parts at the same price as Amal and are a much nicer and easier firm to deal with. Order on line for a next day delivery (UK).



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Wish I could get next day parts, any shipping to the US is expensive and slow.


Here's some more pics of that slide and block. I did polish it up a bit with 3000 grit cloth. You can see some deep gouges and the other wear.







I worked on the gas cap and other tank parts that were rusty as well. Just the cleanup, going to make gaskets today maybe, and put it back together. After rust dissolving and brushing I washed them in distilled water and then in gasoline. When dry, I sprayed WD40 onto a rag and wiped down the steel parts with the light oil.








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Got my new carb parts, looking pretty. Waiting on my tap & die set to re-thread that stripped hole before I reassemble it.





Made new tank gaskets and put on the cap. New cotter pins.





Removed wheels for upcoming tire replacement. I have some new 350x19 Dunlop K70's to go on with new tubes and wheel bands.


I've got to say removing the rear wheel was mind blowing simple. Genius in it's simplicity. The three bolts that hold the hub to the wheel had holes opposite to them for a socket extension. When torquing them off the wheel would spin backwards but someone cleverly designed a notch in the frame for the socket extension to lock into and hold the wheel still while unbolting it. So clever! Amazing machine that someone had the foresight for this and it really changed my mind from being a crude machine to being perhaps even better engineered than some modern bikes. This makes swapping the rear wheel a very fast easy task, and can be done anywhere with limited tools. Kind of blew me away, very eye opening.






A look at the brakes and some of the bike's original paint. I was originally concerned that I may have to replace the shoes or material but these look in excellent shape and plenty of meat left on them. This is the front drum.



Edited by SovereignZuul
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Personally I never remove those 3 QD bolts. They have a habit of coming lose, so I loctite mine in place and from then on I remove the whole lot.


Seemed easier than having to deal with the chain and other assembly. I'll keep my eye on those bolts in case they start to back out though, thanks for the tip! :)


I put the new tires on the wheels with help from my old biker father yesterday; Caught him working on his 64' Panhead when I got to his place.


The tubes that were in there were certainly replaced not that long ago, they were some "modern" ones made in Taiwan.


Got home with them and rushed with joy to remount everything on the BSA, really love the way it looks!


At this rate I'll get the bike ready for it's first attempt at starting within the week.






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Just looking at your filler cap gasket, if that is NBR bonded cork and you have any ethanol in the fuel where you are, it will turn into a wrinkled mess quite quickly. Plain cork would work or viton-bonded if you can find it.


The originals seem to have been some sort of paper / card gasket layered gasket material - although tougher than just card...whatever you do, itll never be completely fuel tight if the tank is brim-full.

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Been a little while since my last update, considering how often I was working on the bike. I kind of just plowed through and finished everything on my list asap. Restored petcock with new cork, assembled carb fully and mounted, fuel lines, tank, seat cover.


Long story short, got it running, took it for a ride, had a blast!


Needs many more tweaks and work of course but it moves and pretty well I've gotta say. What a unique ride and such character, vibration, suspension, handling, shifting like I've never experienced in a bike. I haven't had to kick start a bike in 15 years.


Pic of the new seat cover, high quality and comfy. (and battery box)








I've been getting some goodies to decorate the bike with long term. Keeping it all originals where possible, avoiding reproduction stuff. I scored a water bottle in mint un-issued condition dated 1940, a Pyrene vehicle fire extinguisher and an entrenching tool from WW2.







Future immediate plans are to get the pannier bags, supports and frames, check into getting more proper NOS parts to replace anything that many be incorrect for this bike. Example: The horn is chrome under the paint, can't be WD.

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  • 3 weeks later...

Took the bike to it's first show. CT Brit Jam 2016. Hundreds of bikes, mostly English but from everywhere and every age.


Wasn't expecting anything but a fun day of hanging out but ended up winning the People's Choice trophy for most votes by attendees. This was the big final trophy at the end of the show!


I'll upload the whole album later today perhaps, and share it. Lots of bikes, but only one military bike in the whole show....


IMG_20160821_124136 - Copy.jpg

IMG_20160821_155728 - Copy.jpg

IMG_20160821_124136 - Copy.jpg

IMG_20160821_155728 - Copy.jpg

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  • 1 month later...

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