The centre stand and crankcase mounting repair

The centre stand on this bike was wobbly which I had attributed this to the fact that the mounting bolts were loose. In fact I found that these were damaged and wouldn't screw up any tighter. The bolts themselves are 30mm M10 bolts with a 5mm M12 shoulder. The shoulder fits into the centre stand and the M10 section fits through lugs moulded into the bottom of the crankcase. Each bolt has two washers and is retained by an M10 nut.

I found the threads were damaged so I recut them using an M10 1.0 tap and die.

I cleaned up and examined the stand and crankcase lugs and found that both were damaged. (Wouldn't it be nice if I took something on this bike apart and found it was in good condition!) The LHS in particular was badly worn and the holes were distorted. One side of the stand was worn very thin.

LHS crankcase lug-hole worn oval

LHS stand lug- hole distorted and worn close to the side of the stand- I think I got this one just in time.

RHS crankcase lug

RHS centre stand lug- enlarged but still almost circular and there is a lot of metal remaining all round.

The stand is steel and so could be welded. I decided to fix this with repair washers fitted inside the metal and to the outside of the stand. I couldn't fit anything on the inside as this would obstruct the fit with the crankcase. On the RHS I  enlarged the bolt hole to 18mm with drill and reamer. At this size its a good fit for an M10 washer so I fitted two into the thickness in the metal and fixed them with spot welds on both sides.

Hole drilled and reamed to 18mm

This fits two stainless steel 10mm washers perfectly

Washers secured on both sides with weld.

On the LHS the hole was already, so distorted and the edges worn so thin that I didn't want to drill or ream here. In fact owing to the wear there wasn't really anything to drill into and the hole was already too large for my repair washer! I used a 10mm drill as a line marker, passing it through both lugs to position a 10mm washer on the outside of the RHS mount. I did this by eye, holding the drill such that the washers were at the same height and the drill passed horizontally between the two legs of the stand.  I could then clamp  the washer in position and secure it with weld. However the wear was so bad that the washer didn't cover all the damage. I filled in  below and behind the washer with extra weld to replace the missing metal.

All that was necessary now was to drill and ream the holes on both sides to accept the 12mm bolt shoulder. I had used stainless steel A2 washers for the infill. These are very hard and probably harder than actually required. This meant I had a difficult job to drill and ream them to 12mm but after many drill sharpenings I eventually succeeded. 

Centre stand lug, reamed out to 12mm and welds ground down.

Welded washers now accept the 12mm shoulder

I ground the weld down in both sides of the stand before degreasing and painting in blue Hammerite; this isn't quite a colour match but I wanted a durable finish.

Inside surface ground smooth

Painted in Hammerite.

The Motor Lugs

The motor lugs were distorted and would need lining. I ordered some 1/2" (12.75mm) brass tube specified as 10m id. This is thinner in the  wall than I would like, but its a bit of a compromise as I don't want to remove too much metal from the lugs themselves.  I enlarged the M10 holes (probably rather larger already!) using a drill bit passed through the narrowest first to line drill both holes.

Once the hole was enlarged close to 12.75mm I was able to pass an adjustable reamer through and line ream them both to accept the tubing as a tight fit.

In the meantime I cut two inserts from the tubing. The lugs are not actually the same thickness and I needed inserts of different lengths so I cut one 13.4mm and one 14.8mm. I cut these on the lathe partly to ensure the ends were square but also to chamfer the leading side for insertion. I suspect cutting them with a hacksaw would be perfectly adequate.

I pressed both linings into the lugs with hand pressure and secured them with Loctite bearing fit.
The linings had closed up a little in the insertion so I cleaned them with an M10 drill and checked that the bolts would fit.

The repaired stand could then be attached and jobs done.

Refitted to frame. 

Saddle

I was aware that the saddle would need a new cover and foam underlay, but I'd not expected to do much more. However when I removed it for cleaning I saw that a spring was broken and one of the spring pressure plates was loose and detached. This meant I had to take it apart to repair and so could treat rust and repaint the components.  I took some general views before starting. The saddle is remarkably complex. It consists of two top sections and a pivoting base. The top sections comprise a "V" shaped yoke and a crescent strip which joins the free ends of the "V". A small fan piece slips into a slot at the front of the yoke and bears holes for 10 springs which span between this piece and the crescent at the rear. This fan  of springs forms the base for the saddle itself. This seat assembly is attached at the front to a pivotting base which is sprung against the yoke by means of an adjustable (double) spring. At its far end the base section carries the attachment bracket to fix the saddle to the seat tube on the bike. This is sandwiched against the base with two sectored plates that provide a stable tilt adjustment to the bracket.

The top of the spring sits in two end plates; a rectangular spring seat and a 90 degree "guide" plate which bears on an adjuster screw mounted in the apex of the "V" section. This allows the spring pre-load to be adjusted for rider weight.  

View from from left, note the front nut on the shouldered bolt securing the pivoting section underneath and the main bolt on the seat post which passes through the attachment bracket and  attaches the saddle to the bike.

Rear view of seat post and attachment bracket.

Layout of springs between the crescent rear section and the detachable fan at the front/ Note two are fixed in each outside mounting point. In my case, one is missing (3rd from right).

Remove the saddle by unscrewing the seat bolt attachment. This bolt is a complex design with a ridged square section in the centre. Each side is secured by a nut and washer. Once released the saddle will lift off the post.

Seat Bracket attachment bolt

Seat bracket attachment bolt, seat bracket and the two sectored plates for tilt adjustment.

I removed the crescent section by unscrewing the two nuts beneath. These are attached to short dome-headed shouldered bolts.

Dome headed bolts securing crescent section (actually photo'd during reassembly)

Crescent section attachment bolts, dome heads and square shoulders.

Once released the  crescent lifts off. The seat post bracket and square sectored plates can then be pulled out of the pivot section.

Seat post bracket and square sectored washers.

At this point it became clear that all was not well with the pivot/yoke sections remaining. As I tilted this I could hear something sliding inside. Checking below showed that one of the two top  spring plates had become detached and was sliding up and down beside the spring.

Lower end of spring, no plates here, spring retained by folded detent on the pivot bar. Note this tongue doesn't engage properly with the spring at this stage.

I had to separate yoke and pivot to retrieve this plate and refit it. This meant releasing the pivot shoulder bolt. Sadly I couldn't turn the nut and was forced to cut it off with a Dremmel.

Cutting through the pivot bolt nut.

The pivot bolt was then tapped out and the loose plate retrieved. The pivot bolt itself also appeared to have grooves machined to fit into the pivoting section. It was quite hard to release.

Pivot folded down releasing spring tension, the loose plate is shown together with the shouldered pivot bolt.

However closer inspection showed that the grooves in the bolt were actually wear ridges so I ordered a new one.

Wear marks in seat pivot bolt.

The pivot section now pulls out of the yoke revealing the tensioning screw on the front underside of the yoke. Here the spring is seen end on and you can see that in fact its a double spring.

View of tensioning screw upper left. Note also the pivot bolt upper right, and the grooves in it that made it so hard to release.  

View showing yoke spring, pivot bolt and both end plates, note the 90 deg guide plate (bottom centre) and the rectangular spring seat (middle left)

Close up of adjustment screw.

I didn't remove the adjustment screw but cleaned and treated the rust on all parts before repainting in black Hammerite.

Reassembly was relatively straightforward, I reattached the crescent 

... and positioned the guide plate in the front of the "V". The slots in this plate slip over the end of the adjustment screw behind the washer so that the screw can drive the plate forwards and backwards for spring adjustment.

The spring seat then fits onto the guide plate

followed by the spring.

I assembled the seat attachment bracket and its two side plates

Before slipping the assembly between the sides of the pivotting base.

and reinserting the rectangular retaining bolt.

I could then insert the front end of the pivoting base. I held this temporarily with an M8 bolt whilst I await my new pivot bolt's arrival. With the spring now seated correctly, the tongue on the pivot section now docks into the top of the spring.

Turning the seat over, I slipped the fan section into its mounting.

and replaced the ( springs that I do have. I don't want to have to buy a complete set simply because one has broken so I'm casting around for a source of a single suitable spring.

In the meantime my new saddle was delivered. It came with 4 rivets, 2 long and 2 short and I also ordered the foam underlay.

Comparing the new to the old showed firstly that hevrear fastenings looked pretty easy, just swivel the metal strips up and bend around the rear saddle frame. The front however required the fixing bracket to be transferred from the old saddle to the new.

I just bent up the old rivets and pulled them out. These were the shorter of the two sizes.

The front bracket curvature didn't match the new saddle so I tapped it to flatten it out a bit and conform better to the saddle.

I marked he holes by pushing a needle point through before drilling the and inserting the rivets. These were then flattened from the rear to fix the bracket.

I had sourced an extn spring although this turned out not to be coiled it's whole length. I covered it in a spilt tube to stop the single wire section from cutting into the foam.

Fit the foam

• Hook the front bracket in and push down, it's tricky because the saddle probably needs to stretch a bit, but I could drill and fit the two rear rivets. I'm not sure why these are longer than the front rivets, there seems no reason for it and they don't fit well. When I next place an order I'll change them for the shorter type which should give a better fit.

Finally fit to bike!