Friday, May 28, 2004

Rear drum clean up

The chainguide, chainguard and rear hub have all been cleaned over the last week. A messy and not very exciting job but the rearend looks better for it. Annoyingly the shock had to be removed to gain access to the bolt holding the chain slipper in place.

There was plenty of lining left on the shoes so there were reused as there was no evidence of oil leaks.

Note that the brake torque arm is held with 10mm fine bolt and a half nut with 17mm WAF heads. These are hard to find replacements for, not that I needed to.

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Wednesday, May 26, 2004

Rebuild front brake
Now I can work again I've replaced the seals in the front master cylinder and reassembled it after a thorough cleaning. Once the lever is removed the piston can be withdrawn from the cylinder. I was surprised how much slime there was in the bottom of the reservoir, together with rust on the steel parts. As the fluid is hygroscopic I shouldn't have been surprised.

The brake pipe was looking rough at each connector and I'd damaged one of them whilst undoing it. A new pipe was needed. The pipe has a rubber boot for the master cylinder and a piece of protective pipe on it, and these would need to be included on the new pipe. The companies I contacted weren't keen on me sending the old pipe as a pattern and then fitting my old bits so I decided to make the pipe up myself.

I'd been warned that this was unsafe and I can see that argument. However as I have stripped and rebuilt the master cylinder and I would be joining all the bits together, the pipe itself doesn't seem like the weakest link.

Assembly was straightforward but slow and fiddly. The hardest part was neatly splaying the braid to allow the olive to fit between it and the plastic pipe.

At the caliper end I've fitted a 120degree banjo instead of the OE male fitting. There were two reasons for this. Firstly I thought it would allow the pipe to fit more neatly without needing 2 bends. Secondly this means the pipe can be removed without removing the caliper.

I've reassembled the system, bled the air out and so far it hasn't leaked at any joint. It was a tough job getting the air out even though I had the caliper above the master cylinder.

Rebuilding Master cylinder seal kit

Concertina for 'bullet'
Be careful not to scratch the cylider bore or the piston parts when stripping. Easy to refit with a spot of fresh brake fluid on them.
Brake pipe 1050mm of braided hose

10x1.25 male connector

10x1.25 banjo bolt with 120 degree banjo connector

with appropriate washers and olives
Build with a lot of care!

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Thursday, May 13, 2004

Sub ungual haematoma
Ouch! I've trapped my finger. Not badly and it didn't hurt at the time. But overnight it was really throbbing. Today I've learnt a lot about the condition and recieved a lot of 'advice'. As this isn't a First Aid site I'm not going into it here.

The major problem is that my finger is now badly swollen and a little tingly at the end. I've had radiographs and nothing is broken - I just have to wait for an improvement...

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Front brake caliper overhaul
I'd noticed that only one piston seemed to be moving when the front brake was applied and as the bike is 20 years old it seemed wise to strip the caliper and replace the seals. A pair of odd pads suggested that the PO had noticed the uneven braking force but not dealt with it. A seal kit contains two types of seal for each piston plus an O-ring for the joint between the two halves of the caliper.
The caliper is held together by two 8mm Allen bolts which are tightened quite firmly. It might be possible to access the pistons via the disc slot but it is a lot easier if the caliper is split...or so I thought.
One bolt came undone readily, the other turned a little. So I added penetrating oil and turned a bit more. Gave up for a day and soaked it in engine oil. It turned some more and then head chewed up due to the high torque being used. So I drilled it off and welded metal onto the remaining stud and it turned some more. Great, that's got it. Not quite, it got stiff and then sheared.
I'll bet you saw that coming!
OK so now it could be drilled out and helicoiled, spark-eroded and retapped etc etc. Now I know that helicoils are 'stronger than the original thread' but do I trust it to hold together? If it's not square will the fluid leak one day? Don't know, but I'm not going to risk it especially when one of the pistons is rusted and would need a light emery paper rub to get to metal.
For £60 I'm getting a new caliper with fresh pads and seals!

There are several morals to this perhaps:
1. If it ain't broke, don't fix it. Well it was broke, but it's more broke now!
2. If in doubt don't force it. - If I'd stopped at the beginning it could have been possible to rebuild it via the slot (except for the halfway O-ring).
3. How do you value your time and safety compared to a new part? OK so nobody rebuilds a bike to save money but maybe it would be wise to assess every part of a job and decide whether to leave, rebuild or replace.

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Monday, May 10, 2004

Front end back together
In an attempt to reduce the fork clunking, NP removed 0.004" of play from the damper piston assembly.

These parts must move on each other but it seemed that in this case they actually wobbled.
On reassembly it became apparent that the noisy fork was far better, but the quieter one still had its noise. After all this work I've been forced to admit that these forks aren't silent due to the loose parts within - such as the pump, the top-out spring and the little valve assembly.

Fork oil230ml of 5wtNLM suggest 5wt for off-road use and 10wt for the road. The higher viscosity oil reduces noise too, by damping the rattle of the parts. If you overfill the forks the noise will be greater.

Tacho drive
I had hoped to remove the tacho drive from the camshaft and fit an old-style flat cover. My thinking was that a dirt bike doesn't really need a tacho and that the cable was one more thing to get hooked onto a branch. Well it can't be done easily as the 'black' ignition pick up needs the space. Oh well. The domed cover looks better for having the relics of paint removed.

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Tuesday, May 04, 2004

Fork Seals

I'm still struggling with the clunking forks. It's been suggested to me that an element of the sudden movement might be due to excess stiction caused by old fork seals.

With the sliders off it is an easy matter to remove the dust covers. Then there is a spring steel clip which can be gently tweaked out with a screwdriver. Move round in a circle so it spirals out. The seals themselves are a different matter. Mine were stuck firm - even after heating the slider. I couldn't get my bearing puller to catch the rim of the seal so resorted to the Dremel to slice the body of the seal. This enabled me to fold the seal into itself and then it came out easily. After cleaning all parts were reassembled with a slight smear of coppaslip. The seals were seated with a hammer and a big socket worked around the seal. A proper seal driver would make it a doddle...

Seals 2 off 35 x 47 x 10/10.5(I'm told that fork seals are subtly different to ordinary oil seals as the latter are intended for rotary rather than reciprocal movement)

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