Friday, 23 May 2014

21 - Thoughts on bearing choice

On the rare occasion I changed the gearbox oil I noted that it was a little dirty.  It was as if mucky water was getting in somehow.
 I was giving this some thought and looking at the drawings in the Bultaco books. All of the bearings I took out of this engine were of the plain open type and this I think is where the problem lies.

 The area around the front sprocket (35) is always dirty, muck, grass, twigs and water gets dragged around it by the chain and there is really nothing to protect the oil seal (39) on the output shaft. Even if you where to place a felt washer in front of it, it wouldn't last long. All of this debris running past the oil seal in time damages the seal and lets water creep in under the lip of the seal. Because the bearing (36) behind this seal is of the open type the water gets through the bearing itself into the gearbox.

 My solution is to use a 2RS bearing on the output shaft but to remove the bearing seal on the gearbox side of the bearing. You can do this easily with a penknife, just lever it in below the edge of the seal and pop it out. The inside face of the bearing is now still open and lubricated by oil in the gearbox, but the outer side is sealed.

 With this setup if the oil seal on the output shaft gets damaged and water creeps in underneath, there is a secondary seal on the bearing itself to stop it getting any further into the gearbox. That's the theory anyway !!

 By the same theory I used a 2RS bearing on the clutch side (37) to lessen the chance of gearbox and primary chaincase oils mixing. Again I popped the bearing seal off the inside face to leave this side open to the gearbox oil lubrication.

 For the crankshaft bearings (44) I used a class 3 type. Class 3 bearings are made with a greater clearance in the races and are often specified for this application. The greater clearance allows for expansion when the engine is up to running temperature. 

20 - Engine Casings

 I got one half of the engine casings back from John at Anvil Engineering. He was welding over a small hole in the gearbox for me. The damage looked to have been caused by someone trying to tighten up a screw that was too long for the hole. It had burst through into the gearbox and had been repaired with araldite. The repair was good and would probably have lasted another 40 years but I wanted it welded. 

 We looked over the cracks on the frame and discussed repairing, and came to the agreement that if I did all the fitting work he would do the welding. This suits me fine as my welding is nothing special, John however has years of experience welding tube. 

 With the casing back I tried cleaning the interiors a bit more by soda blasting. I saw some videos on You Tube of guys making their own set up so I gave it a try. Pretty simple really. Just an air line inserted into the top of another pipe to create a venturi effect that lifts powder from a bag of ordinary baking soda, £2 for a kilo in the supermarket.

It worked ok but it's messy. Definately don't do this inside your shed. Everything gets covered including yourself. It does however clean things, a little slowly, but for me it was enough. I washed off the baking soda with the garden hose and left them to dry in the sun.

 Later I ran a tap down all the threaded holes and put the casings in the oven while I got the bearings ready.

About 20 minutes at 170c and all the bearings just dropped into the engine without even a tap.  

Saturday, 17 May 2014

19 - Putting things right.

This week was the North West 200 races, since it was such a nice night I went up on Thursday to watch a bit of the racing. Here's a little clip coming into the Magherabouy chicane.

 Back at the beginning I noticed that the shock absorber mounts where not at the same height. It might have been ok to leave it and just compress the springs a bit when installing the shocks, but I decided to make it right. I cut out the bolt and slotted the hole but I could not get a decent high tensile bolt anywhere in Larne, just the BZP 8.8 type, so I need to source one this week.

I've also reworked the straightening jig in order to press the frame a bit more. There's a section on the right hand side which is still a bit high.

 And there's a big crack running around the bottom tube. I'm considering cutting this section out completely and making a new piece. I need to make a new side stand bracket anyway. So this could be the next job to tackle.

Monday, 12 May 2014

18 - Back Brake Shoes

 This week has went in quickly. I gave one of the crankcase halves to a friend to weld a small hole in the gearbox. I'll pick it up at the end of the week.

 To keep things moving I decided to replace the two pivot pins from the back brake plate. The cir-clip grooves were badly worn. They are in the parts book as pt. no. 107-017 but I thought I would make my own in stainless steel, that way they would last forever. 

They just pressed out quite easily

And here are the new ones fitted

Also I've been making new pins for the clutch. For some odd reason mine are all bent and the threads are broken. I've only just begun this job. 

Saturday, 3 May 2014

17 - A few new parts arrive

 Last week I emailed Jeff at in the USA. They have available a few parts which I couldn't find anywhere in the UK. I first enquired about the engine filler plugs, and after a couple of friendly emails back and forth I bought these plus a couple of small rubber items that I thought might be good to fit during the rebuild.

Above :
rubber tank rests for the frame gusset and the stud on the top tube. Ignition cable grommet and the primary and gearbox filler plugs.

 The filler plugs are very good quality. Here it is again beside the original and one that I had made myself from aluminium.

 Also this week a new Pirelli back tyre arrived in the post as well as bearings for the crankshaft, and I got a message from the chrome platers to say the spoke carrier from the back wheel was ready, so that should arrive soon. Hopefully by next weekend I'll have the back wheel assembled again. Work wise I didn't get much done other than more washing and cleaning of the gearbox internals.