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Model 49 rebuild project

Ian T

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1 hour ago, Hydramatic said:

Pic of my M49 as purchased. Why oh why did I go to the pub that night. 


Would going to the pub account for the seat unit being on backwards.... :)

Your frame is confusing, it has the twin tubes under the engine from the last series 49 but has the top shock mount position of the first series 49. Also has the timing cover from the earlier model. Any evidence that the top shock mounts have been altered?  Doesn't matter obviously, just curious. Frame number would be interesting but I understand if you don't want to put that out

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Having never ridden trials ( I used to Grasstrack many years ago ) the seat being backwards might help my technique ?the bottom tubes caused much confusion initially, eventually ‘Twinnshock’ came to the conclusion that it had been modified for extra clearance. I’ve got it back to standard early M49 layout now as I want to restore it to as near standard as I can. It’s silver now too. I used to work for a Rolls Royce dealer, and there’s a Rolls colour that’s very similar to the Bultaco one, amazing how overspray from a Phantom repair could get all over a Bultaco frame ?I’d love to see any pics of a standard early M49 as things like mudguard brackets need to be sourced or fabricated. The biggest problem I have is the fuel tank, it’s in very poor condition and ideally needs replacing. 

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Yes it's possible someone has grafted in the bottom section from a later model, also moved the rear brake pedal to inside the frame.  In Motion sell a new seat base unit and seat. This place in Spain do lots of parts for Bultaco including the mudguard stays, mudguards and fuel tank


Picture of M49 here, the colour picture is of the last version, the black and white pictures are the first version


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Here is another early M49. I took these photos in the 1990s when it was for sale but I didn't buy it. I've posted these because it looks fairly original and also looks like it hasn't been ridden since the early 1970s. The seller had been fairly serious about trials competition in his youth. He even had a spare set of crank seal carriers and told me he would have the spare seal carriers ready fitted with new seals to make for a quick turnaround in his workshop between trials (crank seals didn't last as long back then as they do now)

Location was Woorim (Bribie Island) Queensland








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On 4/18/2020 at 3:32 PM, lorenzo said:

r.h. inner/ outer - 18 off   length 189/195mm ?  )

l.h. inner           -  9 off        "      165/167mm ?  )        depending on which parts book you are looking at

l.h. outer           - 9 off         "      162/165mm ?  )

The stumbling block for obtaining replacements is that l.h. outer - I couldn't get any for years until I found a seller in the US with NOS. (I don't think spoke suppliers are very keen on replicating the double bend in stainless, a pretty unforgiving material). The double bend is to allow sufficient offset of the rim/tyre to clear the chain line and chainguard. Ultimately, these are the first spokes to suffer damage, or breakage if the chain derails...............

The alternative would be a set in single gauge galvanised, similar (but not identical, unfortunately) to Pursang fitting.

Let us know how you fare.

In my book they are 192, 165 and 167. Also it says M3.5 x diameter 4 (rather than the other way around). For the nipple it says M3.6, but maybe this is a typo.

Central Wheel have asked me to provide measurements, so I'm not sure what to ask for. They give guidance on how to measure spokes, but who's to say Bultaco used the same method!

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Further thinking... I am going to do a trial run at putting a second bend in one of the spokes I have. Possibly I could mill a jig and use the press, to get them nice and even.

I have just been digging in the scrap bin and found some bits of spoke. The rear ones are not stainless, and I don't know if they're original, but I have found a few that look a little like the ones in Lorenzo's photo. I can measure the bend in them anyway, unless anyone has some genuine Bultaco ones they can measure.

I am also sending the photo to Central Wheel to see if they've ever come across this before.

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On 4/11/2020 at 5:11 PM, Ian T said:

Hi Andy, I was wondering the same thing re the seat. Not sure yet, need to work that out, but it's some way down the list of priorities. I will get there though - the fibreglass definitely needs some work.

Unfortunately I don't know much (yet) about Bultacos.

I've been cleaning a few bits up, and also disassembled the engine...





The engine took a bit of work, and didn't quite come apart as expected. The layshaft was stuck in the right-hand case and all the gears came loose instead of staying in the lefthand case. Then when I came to remove the crankshaft it practically fell out of the bearing (which remained in the LH case). There's some evidence that the crankshaft had slipped inside the bearing - the bearing being completely worn-out.

Talking of worn out, just about every bearing in there is knackered. The old man must've got some use out of this thing. I have a few questions at this point:

- The bearings that are pressed into blind recesses in the case - how to get them out? Presumably heat plus a special tool to hook them out?
- Are there any tricks for removing the two main bearings from the RH side of the crankshaft?
- I don't think the LH side of the crankshaft is necessarily toast (I tried a new 6205 bearing on it and there's interference) but if it turns out a rebuild is needed, does anyone here do that as a service?
- The 'detent' in the LH case seems seized in there - does it have to come out, or could I just leave it there? I'm wary of going too mad with the blowtorch.

The frame also needs some attention shortly. I want to switch to a tapered headstock bearing arrangement as sold by inmotion. Does this first require the old ball race cups in the headstock to be tapped out? As I am about to prep the frame for painting it would make sense to do this beforehand.

Thanks in advance for any help, it'll be greatly appreciated!

When I removed the bearings from my Mk2 Pursang (similar engine) I put the cases open side down in my mother's oven and they came out by gravity with a resounding clang when the cases were hot enough. Mother was not too happy with the smell of Roast 'Gunk'.

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On 4/18/2020 at 9:25 AM, Ian T said:

I have two other engines I could use bits from but both have a different (later) type of shaft. One even has needle bearing races for the sleeve gear, so presumably Bultaco did learn.

I do have a complete M49 engine which I could strip down, but something tells me the main shaft will be equally worn.


Hi Ian,

To your mainshaft issue... I'd bet good money that any used motor from the same design period that you pull apart will have evidence of wear.  I'd highly recommend that you not mix/match parts if, for no other reason, than loose parts can and do often find a way of becoming lost.  That's been my experience anyway (more on that in a moment). 

As to the needle bearing gear shafts - yes, Bultaco did eventually learn that the bronze bearings needed regular replacing.  My 199a is on it's original shaft bearings and are still nice and tight after many, many years of use.  Converting to the later shaft would be nice upgrade but would also require the later year clutch components as well, as the later shaft is splined vs. the earlier key.  But if you do decide to go this route, do let us know if anything further needs to be done to complete the mod.  Seems like it'd be a direct replacement that could drop right in, but I've been fooled by this assumption more times than I can count!

Which brings me back around to the loose parts issue I ran into that I mentioned above...

My m49 resto was made all the harder by my simultaneous work on a m80 that I picked up at the same time.  I immediately fell prey to the misconception that the two motors were basically identical - as my m49 was a late production model and the m80 an early production version (first couple hundred made) - and so I began the mistake of picking and choosing the best parts to keep vs those to part with. (I'm likely going to move along the 49 at some point and will be keeping the m80.)  After a teardown of both motors and often doing so in a sleep-deprived state (gotta get the garage time whenever I can!), I started mis-labeling, mis-placing, and mis-expletiving my way into a MUCH longer rebuild process than I can even describe.  Trust me... it is SOOOOO much better to have one motor apart at a time (if rebuilding both) than robbing Peter to pay Paul and finding out the hard way that Peter's parts and Paul's parts should never be mixed... (or something like that.) 

Anyway... keep the thread rolling and let us know how things are progressing.  I'm particularly interested in your views on the replacement tubes once you get them. I need a set myself (for the m80) as it would happen. I did see In Motion is unfortunately down at present...  hopefully they'll be back on line soon as I do have a few additional odds and ends I do need to order shortly.

Good luck and enjoy!



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In addendum...

I purchased my replacement NOS shaft from Lynn Mobley (mentioned earlier in this thread)... for $80.00.  So worth it.  I did see a NOS shaft on a still-popular auction site for the same price but went with Lynn's replacement mostly due to an intense desire to have to split my motor only once during this rebuild and buying from him provided that peace of mind.  An earlier build required a couple of attempts thanks to a gearbox that only produced three gears during its test ride (see the above reference regarding sleep deprivation and, in this case, the proper loading of shift forks).

So, in sum, definitely get yourself a new shaft.  You'll love it!

Cheers -


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59 minutes ago, vintagenut said:

Trust me... it is SOOOOO much better to have one motor apart at a time (if rebuilding both) than robbing Peter to pay Paul and finding out the hard way that Peter's parts and Paul's parts should never be mixed... (or something like that.) 

I totally hear you on that, not least because I've been trying to identify bits of other bikes my dad had in bits and it's difficult to tell, unless he happened to write on them with a marker pen what they were.

I noted your advice about asking Lynn and I phoned him earlier this week and I'm pleased to say that as we speak a brand new mainshaft is en route to me. Thanks again for mentioning him. Unfortunately he didn't have any spokes, so I'm just going to go with the quoted lengths from the parts book and get Central Wheel to make some (and hope they fit!).

There'll be more to report at the weekend - I've been doing other stuff for a week or so, but I'm going to have another crack at the paint. Also I have about 30 things coming from inmotion. I got my order in just before the website went offline - if you phone them (01784 440033) then they will most likely take your order over the phone, which is what they did for me.

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  • 2 weeks later...

A couple of minor updates. First all that gearbox detent. After soaking in penetrating oil and with a little heat from the heatgun it finally agreed to vacate the crankcase...



Next I went back to the sleeve gear. Last time I tried to make the bushes I wasn't careful enough with my measurements and turned the bronze down too small. I worked out that it needed to be 18.05mm on the outside, and decided that it would be best to drill the inside of each bush out to only 12mm, and then drill and ream it to match the new mainshaft when it arrives from the US. I will do this with it clamped in the lathe chuck on the sleeve gear's bearing journal to ensure concentricity.







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