feetupfun

On your bike, the gusseting at the headstock looks standard but there is a doubler/patch on your front downtube that is not standard. I have two Bultaco frames (both Alpina M115/116) that use that same arrangement for the headstock gusseting and one of them has cracks in the gussets at the bottom ends of the main gussets. To me your frame looks like it has been either repaired or strengthened at that same point on the front down tube. If no-one else has photos of a Model 125 frame, I will post photos of my M115/116 frame showing the cracking. I looked at a few of my Bultacos and they have five digits after the model number. Cracking of the frame downtube below the steering head gusseting is a common frame failure mode on dirt bikes and is usually attributed to spirited riding (repeated overloading). Frontal impact as in front wheel hitting a tree/car/wall etc with a frame design like your Sherpa T usually causes the top and front main frame tubes to deform into a curve, rather than to crack.

Hey Belldane that makes me wonder what tool I use on my 348. You've got me thinking now. I know I usually undo the nut with a rattle gun but what do I do it up with??? hmmm....

Yes it is standard practice on some bikes to have the head sealing against the sleeve without a gasket. The sleeve usually sits proud of the top of the barrell on such bikes and there is usually a recess in the head that locates on the sleeve. The head being aluminium and the sleeve being cast iron or steel makes for an effective joint.

Gearbox oil and pre-mix oil will migrate downwards through the foam over time leaving the top sections short of oil and the bottom sections sloppy. If you only use the bike the same day as oiling the foam, it probably doesn't matter if you use filter oil or premix oil in the filter because it won't have time to migrate. Before air filter oils were developed, it was common practice to oil filters with either two stroke premix oil, or 4 stroke engine oil. Another thing some people do for events where the air filter needs to be replaced more than once during each day of an event, is to wash the filter that comes out in a strong premix ie petrol and oil mixed at say 10:1. This means they only have to own two filters per bike. You wouldn't want to have any sparks nearby while you are doing the washing and drying though.

Using a strap spanner is doing it the hard way. The easy way is to use an adjustable two-pin spanner to hold the flywheel still. I haven't found a flywheel yet that doesn't have at least two holes in the face. Available at any tool shop.

If you intend to get it welded eventually, don't use plastic metal filler, epoxy or silicone sealant on the hole or your weld repair will take more labour to complete due to having to get rid of all the gunk before the welding can start.

Mike I didn't say that extending by 50mm was right. I said that other people had extended theirs by about 50mm. I've also seen someone make a TY175 swingarm up that was about 100mm longer than standard. I've been considering extending the swingarm on one of my TY175s and was thinking that I would add about 25mm but haven't decided yet. When you fitted you mono TY forks, did you use the mono TY clamps or bored-out TY twinshock clamps? If you used the mono TY clamps it will have made very little change to the wheelbase or steering geometry.

There is no "best" way but most I've seen have extended the axle plates to move the wheel about 50mm further back. Others have made a complete swingarm.

Be careful there are three different types of M49 frame. The last type (after about M49- 02800 from memory) is the one that is very similar to the M80. The earlier M49 frames are nothing like M80 - they are very similar to the M27 frame. Another thing before you buy another frame - make sure it has a legit frame number or you will be no better off

I think it might be a bit dicey to grease the taper surface. I remember that warning being drummed into me when I was an apprentice machinist. I don't remember why though!

Not too sure about that statement

Headstock angle looks standard in your photos. Some stampings are quite poor. Here is what you are looking for (photo of a M49 frame headstock)

You have not said if the erratic running is throttle-position dependent or not. Because you have said that first and second gears are OK but not the higher gears, I suspect the problem is that the fuel level in the float bowl is not being sustained under conditions of high demand. This is because when accellerating through the gears, the throttle is usually held open for longer in the higher gears, yet while the bike is idling before you start to ride away, the fuel level is more likely to be able to recover). To check for this you will need to check the flow rate through the whole fuel path ie from tank though tap, hose, in-line filter if fitted, banjo fitting filter and float needle/seat and with the fuel tank cap in place all at the same time. The original fuel taps on Bultacos are notorious for being restrictive but your problem may be anywhere in the system. It would help with the diagnosis if you could work out if your problem is throttle-position dependent. It is possible for an ignition problem to be RPM dependent, but if it was that, you would probably have the problem in all gears.

Yes, YZ125 and IT175 clutch covers from C to F model at least and maybe later fit perfectly on TY175 bottom ends Sorry I don't know if there are any 250 or open class MX, YZ or IT (premix type) clutch covers that fit the TY250 bottom end. I suspect the TY250 bottom end is most similar to the trail/MX motors made from 1968 to 1973 and the production motors of that era had oil pumps.

The triple clamp geometry and steering head axis angle relative to the front downtubes are identical on all twinshock TY250 models. If one of your bikes has the wheel closer to the frame tubes than another bike, there is something non-standard about at least one of the bikes. My first thoughts were that: Are the fork tubes set to the same height in the clamps? Are you measuring with both sets of forks extended the same amount?

I must say I've not heard that sentiment before. Most people I know who have bought Fantic twinshocks have done it because they are one of the easiest bike to win twinshock trials on. I expect next someone will say that it isn't fair to fit Fantic twinshock/Marzocchi forks to a Yamaha twinshock.

If you ask your question here: http://ozvmx.com/community/index.php?board=11.0 you stand a good chance of getting a well-informed answer from Doc

Yes you are right. You are in the wrong forum and probably website as well Yes the sideport exhaust motor will have exhaust pipe issues in the twin-downtube frame - that is why Suzuki changed the frame when they changed the motor design

It would have originally had 428 chain but sprockets are available for either chain size. How accurate do you want the fork travel measurement? They should have something like 7" fork travel

No matter how well set-up a clutch is, the rear wheel will turn if the bike is in gear and the wheel is off the ground. Your not being able to stop the wheel with your hand is not unusual at all as far as clutch drag goes. You will find that the rear brake is very effective at stopping the wheel turning while you are stationary balancing.

I welded a small piece of steel on the upper side of the brake pedal arm so that the lug on the clutch cover continues to be the up-stop. If you are also wanting a neat way to hold the footrest up for starting while retaining the footpeg spring, there is a forum thread showing how. I'll see if I can find it. David Here it is http://www.trials.com.au/content/index.php...r&Itemid=42

I'll have a go Honda plan to reduce production costs. One change will be the reduction in size of operations in Spain Honda will continue to market the 4RT as a Montesa The 4RT will be assembled at a Honda plant in Italy instead of in Spain The Spanish Honda (montesa) plant will cotinue to make plastics and do painting

When new, linings are 3 to 5mm, depending on brand. Depending on how worn the drum is, the cam may go over centre with 2-3mm still left on the linings. I suggest you inspect and measure the drum diameter and measure the OD of the linings with them installed on the backing plate. Also compare the radius of curvature of your linings against the ID of the drum. To work properly ie to touch over the whole surface, the radii should be very close to the same. Many old bikes need the drum resleeved or machined and oversized linings fitted to restore the radii to be the same again.

I had to do that little filing job too but on my 348.

If you are using it for trials competition a BP5ES is ideal. I use BP5ES in my OSSA, Bultaco and Montesa twinshock trials bikes with no issues. If you are doing road riding or energetic trail riding, then go for a cooler plug.