feetupfun

I've got a little story about a Bultaco M49 I bought from a distance having only seen photos. The bike was advertised as a "1976 Bultaco" and it was in the classified section of a magazine with no photos but even if there had been photos I doubt I would have recognised it as a M49. I phoned with the thought that it could possibly be a Sherpa T of some sort and when the photos turned up showing engine number M49-00100 I had to have a very hard look to recognise it. Someone had "converted" it to a dual seat trail bike. A 7kg (approx 16 lb) home-made steel-based double seat had been fitted, including bending the rear frame loop down flat to get the seat to fit better. Front and rear footpeg sets were supported by 32mm x 6mm flat steel strips running along the bike and attached to the original bolt-on footpeg locations. The shockies were gas konis with springs suitable for MX with a heavy rider and the leaking fibreglass tank had been coated with about 5mm of green spray putty and covered with a blue paint scheme reminiscent of a late 1970s Pursang. The frame and swingarm were horribly twisted and yes someone had respoked the rear wheel with the rim way off where it should be. Things that surprised me were that the front wheel still had an early 1970s Firestone Vee pattern trials tyre and the original aluminium mudguard and stays were there and relatively undamaged, with original riveted brake shoes, wheel bearings and spokes. Unusual spares that turned up with it included a cylinder head (not sure why they needed a spare head) and go-kart sprockets! Lots of hours went into the fibreglass and the frame. Its not meant to be a show bike, just to be recognisable as a M49 and able to be confidently ridden in competition.

Its the TY250 monos that need the piston skirt trimmed depending on what piston is used. The twinshock TY250 can use the DT250 piston of the same era without modification. Yamaha and Wiseco DT/MX250 (and probably other brands too but I haven't tried them) pistons work fine in TY250 twinshocks.

You next step is to work out why you can't turn the crankshaft. As Andy.T said, drain the gearbox oil and take off the primary drive/clutch cover so you can take the gear off the end of the crankshaft and see if the problem is with the crankshaft bearings or with something else.

So you don't have to carry a socket set in your backpack to get the cover off if you need to while out riding

The white is either mould or aluminium corrosion product and both are quite normal for a bike that has been stored damp. The white stuff is the least of your problems. Can you clarify what you mean by "I can turn it though, not a bit"?

I couldn't find an open-face helmet small enough for my kid (boy on right) so we got an MX type. Competition insurance requirements here mean the helmet has to be either road legal or approved for use in motorcycle trials to an international standard. That MX helmet is road legal. The other kid (girl on left) has a Shiro trials helmet on but they only go down to a certain size and my kid's head is still too small for them.

Theres no crankcase drain on a TY175. Turn the whole bike over and catch it in a pan. If youve taken the handlebars off it might be easier to remove the primary gear and the spacer behind and tip the bike on its right hand side. Don't take the motor out of the frame till you have loosened all the shaft nuts and engine inner casing screws as it is a good way to hold the motor still.

Exhaust shops sell perforated steel plate in sheets too so you can roll your own to whatever diameter you want.

Breaking a ring is relatively common in YZ and IT Yamahas but that's the first I have heard in a TY250A. I am interested in the failure mechanism in your bike. Here are some things to check that might help work out what happened: Was there much gum in the ring grooves? Which ring land failed? What side of the ring groove broke away? What port did it catch in? Was it the original piston and rings? Is there evidence on the rings of uneven ring wear? (uneven radial thickness) Does the port that broke the ring have chamfers around the edges? Is there evidence of ring blowby on the bore (uneven ring sealing?) How rattly is the piston in the bore without any rings? Is there a lip near the top of the bore? (if the little end develops play, the rings can hit a previously generated lip)

Here in the most nannified country in the world, competition rules require not just self-returning- folding footpegs, but they must use a spring to return them not just gravity. Here is what I did on my TY175 with Miller pegs. There is a spring loaded pin that will lock the peg in the up position, and it releases by just bumping the peg after the motor starts.

No Yes If the main bearings or big end bearing has suffered any corrosion at all, they will self-destruct soon after you start the motor the first time, sending metal particles everywhere, meaning that you will need to rebore the barrel yet again. It is the bearing surfaces that usually rust - the balls and rollers etc, it doesn't creep in from elsewhere. By the look of the piston pin, I would say that there has probably been corrosion happening within the crankcase. When you work out why the crank will not turn, you will be in a better position to know what needs fixing. The bottom end may not be siezed via corrosion in the bearings. It could have something jammed in the meshing region of the primary gears. I have seen that in a TY175 motor with a loose piece of clutch casing floating around until it jammed up the primary gears, bending the gearbox shaft and wrecking the primary gears in the process. Until you can see what is really happening, it is all just conjecture.

Do you mean XC TING riding gear?

Dave your M49 page using the link in this topic wont load properly for me - there seems to be multiple pages of text and photos all on top of each other. I'm using MS Internet Explorer. Regards David

Here are the best photos I have showing the engine cradle area of early M49s.

Dave, Bultaco didn't identify different series within a model designation and neither did Montesa, but since then people have created series designations as a way of making communication about them easier. Bultaco made the M49 for about three years with lots of changes along the way and they are all just M49 as far as Bultaco was concerned. Montesa made the Cota 247 for about seven years and changed lots of things along the way but they are all Montesa 21M. Woody is just referring to the production records showing that the frame tube arrangement under the engine changed at frame number x. The frame number record for the change to the top shockie mount location was probably just not considered imporant enough to record or has been lost over time, but is probably a worthy goal to find out or work out if we can somehow.

Thats right Wayne and I'm sure it was pretty frenetic in the factory and they had the philosophy of making improvements to a bike as soon as it was possible rather than holding off changes till the next years production run. It shouldn't be a surprise that the M49 frame looks like a M80 frame. The only differences I can think of are the mounting points for the seat/sidecovers and mufflers.

Wayne I just looked in Historia de la Sherpa T and the text there says "A new chassis comes into production from bike number 4902426 onwards. Previously, the mudguards and the engine's outer cases had been modified"

Wayne the numbers on that bike matched but there is no guarantee the magneto cover hadn't been replaced. I do think though that the magneto covers changed to the M80 type at some time during the M49 model run as I have seen plenty of other M49s with the M80 type magneto cover. My series 1 M49 has the older mag cover with the multi-start thread clutch release mechanism but the clutch has a surprisingly nice action. When I first got the bike I was worried it would be inferior to the later, cam type clutch actuator with the arm on top. David

Here is a photo of a Series 1 M49 for reference purposes showing the more upright shockie positioning. Serial number M4900100

Here are the M49 Series 3 photos. Serial number is M4902517. I put the handlebar clamp photo in because I wanted to show why many people replaced the top steering yoke on their M49 for one with a better clamp.

I visited a bike boneyard to look at two M49s and luckily they were examples of a series 2 and a series 3 bike. This posting has the photos of the series 2 M49 serial number M4902195 and the next posting shows the other bike. What got me motivated to go looking was a post by Woody: "The serial numbers are from Bultaco's own figures so they should be right. However, they only list the model 49 as having one frame change during its production run but there were two. Series 1 with single tube under engine, upright shocks. Series 2, single frame tube under engine, angled shocks with seat unit altered to accomodate relocated top shock mounts. Series 3, twin frame tubes under the engine, like the M80 and which was the basis for the Kit Campeon."

Way less than 33 BHP. I would estimate about 15 BHP.

There are no hard and fast rules for this. One of my friends only ever uses first gear for absolutely everything (250 Majesty) and another only ever uses third gear for absolutely everything (240 Fantic). If you can develop good enough technique with the clutch, you can use a higher gear than if you are a bit gumby with the clutch. That way you can use second or third even in tight stuff and still have great speed potential for big ups. Another thing is that if you get your bike running so it revs out cleanly, you can get high ground speed even in first gear. This is one of the technical advantages of a well set up four stroke - they generally have a greater range of useful RPM than a two stroke.

Many years ago when petrol could be stored for weeks and seemed to work well, it was drummed into me that it was important to leave the addition of the oil till the last minute for the best results from the brew. With the pump petrol we get here, it goes to crap so fast that it is now quite irrelevant when you mix in the oil. If straight modern petrol or premix is more than 2 weeks old, it goes into my car fuel tank.

I've found you can keep things under control better during the straightening if you leave the axle in place - this reduces the risk of the arms being bent sideways. Another thing is that to do the bending you can usually use a bar positioned under one arm and over the other rather than a bar on each arm. Some bikes you can get the bar in position with the wheel still in place but for some others you will need to make a spacer up to replace the wheel so the axle can be left in place tight. Depending on how difficult it is to clamp the bike down, it may be easier overall to make a fixture to hold the swingarm and swingarm axle while you straighten the swingarm. Last one I did the frame and the swingarm were both twisted so I made a fixture that clamped the bike via the swingarm axle ends so I could straighten both the frame and swingarm at the same time.