Brake caliper rebuild

This seemed like such an easy task before I started it.  I wanted to go through the front brake caliper and make sure that everything inside was good to go. Well I split the caliper into halves and took a look under the brake pads which looked nearly new.  Underneath was a different story, RUST, so much rust.  See brake fluid is hygroscopic, meaning that when exposed to the moisture in air it pics up water and the water then causes the system to rust from the inside out.  Couple this with sitting for several years and you get brake pistons that look like this.

To get to this stage, I had to free the pistons from the caliper body which took reattaching the master cylinder to the caliper and refilling the system with brake fluid and putting pressure on the pistons which helped me get them unfrozen but not all the way out.  For that I had to stick an air hose in each side and blow compressed air in while trying to keep from blowing the piston into my face.  This was not easy.  Once I got the pistons out I inspected the rubber seals and the pistons and found that there was no way I was going to be able to reuse these again.  I was lucky to find a company that manufactures stainless steel pistons for the caliper at $80 a pair, which isn't great, but helps me feel better about the stopping on the bike (when I first test rode the bike the front brake wasn't working at all, which was interesting to say the least).

After getting all of the parts in I cleaned all of the rust out of the caliper body and bore and worked on changing the rubber seals.

Then the final challenge was getting the pistons back in with the new seals.  The tolerance is so small on these that this was no small order.  I manged to get both of then partially in, but had to use a c clamp to get them the rest of the way seated.  Then fully assembled final product:

I didn't paint this part like all of the others for a few reason, first there wasn't a lot of rust on the outside and for the most part it looks pretty good.  That plus the fact that brake calipers need special paint due to the high temperatures and corrosive brake fluid, I thought it best to leave it and see how it looks on the finished bike before bothering to refinish it.

Finishing the engine

Alright, it has been two months and I have been plugging away at the engine that whole time when I got a chance.  It was a long process that was really helped by a great step by step procedure someone in the UK had documented (link).

We left off after having redone the jugs and heads, after this it was on to the main case and separating and cleaning it up.

Undoing all of the very rusted case bolts, I had to smack it good a few times with a mallet to separate it.

Inside you can see the crank up front and the two transmission shafts in the back.  I pulled out my caliper and measured the crank play and everything was in spec.  I pulled everything from the two case halves and tagged and bagged it.  Now it was time to get down to cleaning the cases.

Now case cleaning was a pain...in...the...ass.  The top half was pretty straight forward, some degreaser and scotchbrite pads got me a pretty good looking result.  The bottom half was heavily oxidized and super dinged up.  The front portion of the lower half is covered in aluminum cooling fins and my grandfather really only rode his bike around on the dirt roads near our farm.  This means that rocks that were run over by the front tires were picked up and thrown at the underside of the engine.  I cleaned and cleaned with degreaser and scotchbrite, hit it with the soda blaster, and event resorted to using a small screwdriver and mineral spirits on a rag trying to scrape and dissolve the worst of it.  Here are my results, not concours quality, but pretty damn good.

So having gone through the struggle of cleaning up all of the parts it was time to start reassembly of the engine.  Through this process I learned pretty much how everything on the motorcycle worked including the gearbox, which was the most interesting part and where the rebuild begins.

First thing we do is install the selector drum and the selector forks.

Then we install the inter meshing transmission gears.

Now we install the crankshaft.  Throughout this process I am replacing all of the rubber seals in the engine.  With a two stroke engine the portion of the case around the crank must be air tight since the fuel oil mix move both above and below the pistons to assure the lubrication, if you have an air leak the fuel mix will lean out and then you will start melting holes in pistons or seize the engine.  This is why I tore apart a working engine, this way I know everything is up to spec.  The next step is applying special RTV sealant to the bottom half of the case everywhere it meets the top case and dropping the top half on the bottom half and tightening the bolts.

Tada!  Now I reinstalled the array of gears, the rebuilt clutch, and the rest of the inner workings that mount to each side of the sealed up case.  Then we get to add our shiny restored covers.

Then we install the cleaned up jugs and heads.

I need to hit the sides of those heads with some more aluminum polish and a buffing wheel, but lets remind ourselves how far we have come.

Now the last step is to make sure all of those new seals and the case sealer I used sealed up our crankcase.  Now they sell a special leak down tester for two stroke engines, it costs, wait for it, $250!  Now this tester just comes with two things to plug up the two exhaust ports and two other things that plug the intake and allows you to pump it up and measure the pressure.  I decided to do this for under $20, with some PVC ends that I RTV sealed a tire valve and a pressure gauge from a farm sprayer, to plug the exhaust I bought some freeze plugs from the auto parts store and I pressurized the engine with 5 psi from a bicycle pump.

I had some air leaks around the rubber intake boots (where it meets the reed cage), I applied some left over engine sealer from the cases and let it harden and the pressure gauge above shows my results.  A near perfect seal, I held 5 psi with almost no fluctuation for 6 minutes!

I did rebuild the clutch while I was at it and found the first thing that needed wear based replacment, clutch springs.  I will order a set with my next bulk order from Economy Cycle.  I did end up replacing the clutch friction discs since one was cracked when I opened it up (I might have broke it trying to get it out).

Next up will either be the front brake or the frame.

  

Breaking the engine open

It could be put off no longer, it was time to dig into the engine.  I am using the factory service manual to disassemble the engine in the best order.  First up comes the heads and cylinders which are the last remaining engine components that need painting, the main case is supposed to be bare aluminum.  The state of the head and cylinders was rather poor, most of the paint was gone and there were old mud wasp nests between half of the cooling fins.

The first step was scrubbing 30 years of dirt and wasp nest off of everything.  I washed them with warm water and a stiff brush, which cleaned up everything and then took heavy cleaner/degreaser and q-tips and cleaned all of the dirt and oil out of all of the small crevices in the cooling fins.  Once that was done I used the soda blaster to strip the remaining paint and oxidation and went through the same hand cleaning process again to make sure everything was clean.  I then carefully masked off all of the opening and hit everything with 3 coats of high temperature engine paint.  Now as you can see below the edges of all of the fins are bare metal and semi polished, this proved to be a bit of a headache as there is no good way to mask that edge as the edge is no longer square.  I ended up painting it and the scraping and using a scotch pad to polish the edges.  Now scotch pads release small particles of aluminum abrasive, small enough to hide in engines and large enough to ruin bearings, so I had to make sure the masking was still good and wash everything a third time to get rid of the sanding dust, but they turned out pretty good in the end.

Next up is Clutch and engine gear disassembly and inspection.

Slow, but steady progress...

Well it has been a while since I updated, but I have been plugging away at the project.  I have been taking components off individually and bringing them inside all winter and cleaning them up and painting or zinc plating them as I go.  I now have the engine out now and all that is left to strip from the frame is the front suspension and a few other little bits.  I have decided to go with painting all of the components including the frame rather than powder coating.  I have been impressed with the chassis paint I bought in the spray can and it has done a really good job, so i think I will save some cash and do the painting myself.

For this update, I am going to go through the cleaning and refurbishing of one of the key little components that make this two stroke street bike a little more civilized, the oil injection pump.

Above you can see the side cover, which I also redid as part of this task, the pump is housed under the front of that cover.

What this little pump does is take oil from a tank and inject the correct amount depending on throttle position into the carburetors to lubricate the engine.  Before these pumps were created you had to premix the oil with the gas when you fill up which is a hassle and has the problem of starving the engine of oil at idle, so coasting down a hill could seize your engine!  So, this component is really vital to prevent engine damage.

Yamaha never meat this pump to be user serviced, in the service manual that simple say to get another pump from your dealer if yours fails.  Fortunately, these little pumps are near indestructible.  The problem is oil leaks getting oil all over my nice clean engine.  I found a few places that sell seal kits for about $35 that come with the 4 oil seals you need and new screws for the body and gaskets.  So I carefully took the pump apart and I see why they aren't user serviceable, it is full of some very, very tiny parts.  There are two gear retaining pins that are literally 2mm long and .75mm thick!  I managed to get everything replaced and back together and turned the pump by hand and it works, it was like watch repair.

Above is the finished product out of the housing, all new seals in place and the shiny new screws all tightened and cleaned up. Below is the pump installed back in the cleaned up, repainted and polished engine cover.

                                        

Below is everything back in place like I found it, I plan on getting new screws to replace those rusted 3 screws holding the pump cover on, but other than that it isa ready to go on the engine.

Next up is the rear swing arm assembly and followed by that soon by the engine inspection.  I have another bike in pieces right now in the garage, plus it has been super cold in Minnesota this winter which cuts down on my initiative to get out to the shop.