Frame and Suspension for our MK10 Bultaco Pursang 125 DoctorDanger.com

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>Project Pursang: Frame and Suspension...

When you pay £100 for a bike you just know that the suspension will need looking at. The Pursang has fairly basic suspension which we think we can rebuild, well at least the forks anyway.

With the shocks it is often a question of whether a rebuild is cost effective - if they are Ohlins shocks then the answer is probably yes, if they are unidentifiable springs like ours then replacement is probably in order.

Suspenders

	Stripping the forks is straightforward. Simply undo the drain screw and the allen key at the base of the fork and then unscrew the fork tops - which came out fairly easily. The picture on the left shows the springs and the damper rod. When refurbishing forks make sure that they are thoroughly cleaned, as you can see from the picture water has got in to one of the fork legs and the damper rod is beginning to corrode - this can cause problems with the fork action. The actual fork legs (not shown) were not corroded but, as we discovered when we tried to disassemble them, they were bent. To check whether the forks are bent, roll the two fork legs together - if you see any light between them they are bent. We had ours straightened by Dynasurf in Sandbach (01270 793032) for £20. Another tell tale sign is that the forks don't move up and down in the stanchions when you are trying to remove them, in fact ours got well and truly stuck.
	To fully disassemble the forks you need to remove the circlip in the bottom of the fork leg to remove the damper rod.
	The damping control valve sits within the large metal barrel on the damper rod, the picture shows one rod as it comes out of the leg and the other shows it with the barrel moved down to show the damping valve.
	This is the end of the damper rod that bolts to the fork slider at the bottom of the assembly, note the O-ring, one leg had one, the other didn't - this helps to seal the fork, we also noticed some distortion in the hole on one leg, probably from hitting a rut...
	The distortion in the damper rod corresponds to damage to the wheel clamps on the slider, in fact one leg had the clamp snapped off (the one on the left). We rebuilt this using a combination of washers and chemical metal - not sure it will hold, but cheaper than £60 for a new slider.
	To finish off the refurb, we fitted new fork seals - a good investment at £10 each and hopefully with the legs straightened the fork action should be plush...
	The tops of the forks feature an air valve and a small cap that fits over the spring. Note that the caps can't be fitted until the legs are in the fork yokes as the fork top is wider than the hole in the yokes.
	Rebuilding the forks is simply the reverse of the dismantling procedure
	And here are the new, straightened forks, they don't seem to be to plush, but hopefully they will bed in...
	The rear suspension units look like Girling shocks or a copy of that type of unit. They should be Betor remote reservoir jobs - either we locate a pair of these (unlikely) or source a new pair - any suggestions or recommendations would be welcome.
	Refurbishing the forks won't count for much if the wheel bearings are knackered and when we fitted the forks and front wheel we noticed a large amount of lateral wheel movement, so we decided to replace the bearings.
	Wheel bearings for the Pursang were £5 each, and relatively simple to fit, although removing the outer seal was a little tricky without destroying them (remember we are trying to economise).

The costs so far...

New seals cost £10 per leg, straightening cost £20, some fork oil £5, wheel bearing £5 each and we haven't bought the shocks (still looking for some cheap ones)

and here's the plan...

1	Get a Bike...
4	Paint it
5	Seat
6	Engine
7	Frame and Suspension
9	Race it

Parts list & Costs

What we learnt this time...

Top calibre racers such as ourselves require the best suspension. OK, so more accurately - the better the suspension the less likely you are to end up on your arse. Vintage MX suspension is never going to be as good as modern stuff, but putting it back into working condition at least gives you half a chance.

the next installment is Race it>