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Ian T

Model 49 rebuild project

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This story begins sometime in 1971, or maybe it was 1972, when dad bought a nearly new model 49 Bultaco. This was to replace the 4-speed model he'd ridden briefly, worn-out heap that it was. I never knew that much about that bike as a kid growing up, although I learnt plenty about the other few in the garage. After digging out some boxes of photos from my parents loft I have found that when dad left home in the late 70s to move in with my mum, he left the Bultaco behind in his own mum's garage. A set of photos from 1985 show a very young version of me looking at the bike on the trailer outside her house, and then the early stages of it being dismantled.

1961282971_DadChairmansTrialKent1972BultacoGPB5J.thumb.jpg.a6e4067a886821b67361be1cf896f50e.jpg

(Dad in the 1972 Chairman's Trial, Kent)

A year or two ago dad said he was going to get it back together, and got as far as stripping the paint off the frame. His plan was - I think - to rebuild it and ride the Manx classic 2-day in 2022, 50 years after riding in the 2-day on the same bike back in 1972. Unfortunately though dad left us unexpectedly two months ago, claimed by a heart attack. Whilst he knew practically nothing of this turn of events, and was gone practically in an instant, now of course the opportunity to learn from him has gone. Each time I feel myself teetering on the edge of that nasty rabbit hole called regret (at not asking more, listening more), I remember that he gave me a sound basis in engineering, that we did do a fair bit together. The principles of mechanics were firmly instilled. Everything mechanical responds to reason. Stop, look, think. Use the right tool. Don't rush. And so it goes on.

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(Largely forgotten about, and as retrieved in 1985)

But what of the model 49? I found the bits in plastic tubs in the shed. Maybe he hadn't realised but the felt at the back was leaking, and those plastic tubs were now half full of water. The engine, top-end missing but with duck tape covering the hole, had enjoyed some shelter under a wooden shelf.

Here's most of what I found (I do have the missing bits):

DSCF6956P.thumb.jpg.29bc10c2dc0b8c71e2bfe8238dbc11ba.jpg

 

It saddens me that dad will never have the opportunity to see it run again, but run again it must. I'll share my progress here, but I confess I have many questions to ask!
 

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Using my very limited knowledge of things M49 and info given to me by my dearly missed friend ‘Twinnshock’ it would appear to be a mk2 judging by the rear damper mounts. A question, how does the seat fix to the fibreglass unit ? Looks like gravity holds it in place to me, can’t see any fixings at all. 
I’ll be following this build with interest. 
Take care everyone, Andy. 

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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...

DSCF7110P.thumb.jpg.e133959bf6d34ba59607447b63b61d5f.jpg

DSCF7117P.thumb.jpg.9643a567353213f0a3bad42ce447b5fa.jpg

DSCF7176P.thumb.jpg.f9e200a2665aec9708b025997d66ed5b.jpg

 

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!

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The blind bearings in the crankcase, heat the casing and try tapping the housings with a hide or rubber mallet or such like, as this might drop them out, if not use a blind bearing puller

The two main bearings usually stay in the crankcase, I'm guessing they didn't as the bush that sits on the crank behind the clutch weight is still in situ ? It looks to be from the picture but not sure. If it is it will hold the bearings onto the crank. These bushes can be very tight sometimes so you may need a normal bearing puller to get them off and pull the bush with them. Without the bush they would normally prise off quite easily

Not sure about repairing crankshaft surfaces as that's specialist and I've never had it done. Someone will know. Make sure you use 6205 C3 bearings on the crank, not plain 6205

The detent needs to come out really otherwise reassembling the gearbox can be awkward as it means trying to get the selctor drum in whilst holding the plunger back and out of the way against the spring. They can be tight but it should undo without too much trouble

Yes the old race cups need to come out of the headstock as the taper rollers have their own

The seat is a push fit into a slot at the front of the fibreglass side panel unit and then held at the rear by two springs from the seat to the frame, there should be two spring hooks on the inside of the frame by the top shock mount

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Thanks woody, all good info, cheers for taking the time to explain all that.

There was a bush on the crank that took some persuasion to get off. The two main bearings are now the only things left. The Haynes manual - which I'm not fully trusting - did say the main bearings should stay on the crank as it comes out.

Noted on the C3 rating - I saw this on inmotion and will make sure I buy the correct ones.

The seat does have the bracket at the front, and at the back it has two pegs which I am assuming the springs located on.

Tomorrow I'll have a go at those bearings and see how I get on.

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The remaining two bearings on the drive end of the crankshaft can be removed like this.

Ease the outer one away from the inner one using wedges between them, then when there is enough gap, use a bearing puller.

Ease the inner bearing away from the crankwheel using wedges between it and the crankwheel.then when the gap is big enough, use a bearing puller.

For both of them, heat up the bearing to make it move easier.

As for the magneto side bearing having been moving relative to the shaft, that is commonly seen with these motors. Even with the C3 bearings there is not enough side freedom for the crankshaft expansion during heating/cooling cycles of the motor and whichever bearing fit is the loosest will see movement which gradually further loosens the fit. As long as that bearing remains free-spinning and there is at least enough interference to spin the bearing, the tightness of that fit is not a problem. On some of these motors the outer race is the fit that moves which can cause enough wear to require that the casing hole be sleeved back to size.

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Ah, that makes sense re-the seat. I wondered what those two little hooks were for. Thanks. 
andy

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18 hours ago, woody said:

The blind bearings in the crankcase, heat the casing and try tapping the housings with a hide or rubber mallet or such like, as this might drop them out, if not use a blind bearing puller

 

The detent needs to come out really otherwise reassembling the gearbox can be awkward as it means trying to get the selctor drum in whilst holding the plunger back and out of the way against the spring. They can be tight but it should undo without too much trouble

One of the blind bearings tapped out like that, the other didn't. I think I will wait until I have a puller.

As for the detent, applied a fair bit of heat and it won't budge. I could try getting an impact gun on it.

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I will share a couple of field tricks for removing blind bearings, first is a through bolt or anchor bolt to get grip on the bearing bore a bit of heat and some visegrips or even better a slide hammer 'Et Voila!'

You mentioned a blow torch I very rarely resort to an open flame on ally cases usually finding a good electric hot air gun is enough.

The second is much more fun and has amazed me in its efficiency in the past freeing the most stubborn of bearings! Pump some grease into the bearing shaft hole. Find a piece of shaft that will fits well inside the bore and hold it against the grease (a piece of wooden dowel will work metal is obviously favourite). Cover the shaft and grease with a rag and tap (don't hit)  it into the bore with a hammer you will force the grease behind the bearing and the hydraulic force transmitted by the grease will drive the bearing out of the hole Jobs a gooden!

 image.thumb.png.a0061c0300fdfca76cc7cf4e04076ddd.png

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21 hours ago, Cemoto said:

I will share a couple of field tricks for removing blind bearings, first is a through bolt or anchor bolt to get grip on the bearing bore a bit of heat and some visegrips or even better a slide hammer 'Et Voila!'

You mentioned a blow torch I very rarely resort to an open flame on ally cases usually finding a good electric hot air gun is enough.

The second is much more fun and has amazed me in its efficiency in the past freeing the most stubborn of bearings! Pump some grease into the bearing shaft hole. Find a piece of shaft that will fits well inside the bore and hold it against the grease (a piece of wooden dowel will work metal is obviously favourite). Cover the shaft and grease with a rag and tap (don't hit)  it into the bore with a hammer you will force the grease behind the bearing and the hydraulic force transmitted by the grease will drive the bearing out of the hole Jobs a gooden!

 

Thanks, useful tricks there.

I also need to get the bearing race of the bottom yoke, as I'm switching to tapered bearings. Seems none of these things want to play nicely!

Also I was looking at the nuts and bolts in the parts book. It uses 'MA' and 'MB' - do these denote different thread pitches? So far it seems to me that 6MA is M6 x 1mm, and 8MA is M8 x 1.25mm. Is that right?

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Ok so I decided to at least try to act like an engineer and broke out the thread gauge. Seems the MB reference is a fine pitch, 8MB being M8 x 1.00mm.

Lorenzo - I found a bearing separator like you linked to, worked a treat.

I'm now preparing the frame for some paint, and noticed something that looks non-standard...

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There's a little tap mounted there, and at the top between the headstock and the petrol tank mount there's a drilled and threaded hole. I can't imagine - on a two stroke - why you'd want to store oil in the frame, assuming that's what it is. The only possible idea I had was that it might be convenient to keep oil somewhere for when refuelling on long distance trials.

I also found this in the box of parts, same idea perhaps:

IMG_7812.thumb.jpg.dc3a3f277b98b5f8ef8d44a4307d0760.jpg

 

The Sammy Miller sticker may or may not be original!

Another interesting thing to note is that the (presumably genuine) Sammy Miller top yoke has 5/16 BSF bolts for the handlebar clamps. I am guessing they weren't specifically aimed at Bultaco owners?

And lastly, the swinging arm spindle appears to be half inch, with a 1/2 BSF thread on each end. I thought standard was 12mm. Maybe dad had some play so he reamed it out to half inch and fitted a bigger spindle?

 

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As far as I know the only different threads on a Sherpa T are on the early ones the nuts which hold the carby on are 8 x 1.0 thread and on the later one the 8mm screw which holds the top of the kickstart on is a 8 x 1.0 thread.

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1 hour ago, bullylover said:

As far as I know the only different threads on a Sherpa T are on the early ones the nuts which hold the carby on are 8 x 1.0 thread and on the later one the 8mm screw which holds the top of the kickstart on is a 8 x 1.0 thread.

Also the cylinder head nuts on the M49

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Ian - 

As you have already found,  cylinder head nuts and carb. fixing are 8MB = m8 x 1.00, although the other end of the relevant studs are 8MA = m8 x 1.25 where they thread into the crankcase and carb. stub, respectively. (Also applies to the two cylinder head studs in the barrel)

6MA = m6 x 1.00 pitch

Re the tap in the frame top tube : how does the oil/liquid get in there ?. The mind boggles..........

The frame-mounted tank is a chain oiler :-

1539946802_SMchainoilerBSM2-SherpaT.jpg.4367182d06a690789cb6dbe5db9327ae.jpg

(extract from 1973 SM catalogue)

Later Sherpa models incorporated a chain oiler in the swing-arm tube, from the factory..

Hope this helps.

 

Edited by lorenzo
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