It’s Alive

My friend Doug, had quadruple bypass surgery and then hernia surgery this summer. As a result, he made slow, intermittent progress on the BSA over the summer. His health is finally improving and he’s spent the better part of two full days time sorting out several niggling problems.

  • The carburetor needed to be cleaned again. The fuel filters I’d installed were dirty (as was the inside of the carburetor). The float and needle settings were way off.
  • New points and condenser were installed using the updated setup where the backing plate from a twin is used and the condenser is relocated under the gas tank.
  • The valve clearances were off enough that the one of the valves was not closing all the way.
  • Several almost stripped case screws were heli-coiled. This fixed the worst of the oil leaks.

With these work, the bike is almost ready for the street. It starts easily, runs well and is ridable. To be street safe it needs a bit more attention:

  • The tires are very old.
  • The front brakes are dangerously weak.
  • Brake light switch doesn’t work.
  • Needs a mirror.
  • Needs new swingarm bushings.
  • And?…


Finished putting the TY175 back together a couple of weeks ago. Rode it at the Exeter, RI trials on September, 27th. The bike runs great and is a much better trials machine than my TLR200 Honda. The TY175 is lighter, handles better and easier to start.

Smashed the rear brake lever into a rock and jammed it into the kick start lever. Fortunately, I was able to bend it back into place well enough to finish the trials.


The photo shows everything that was replaced on the TY175 in rebuilding it.

Most of the Yamaha parts came from Ron Ayers. Their prices are competetive with other OEM mail order sellers and the parts are typically delivered in about a week. Free shipping on orders over $99.00.

I purchase most of my general parts (Parts Unlimited stuff) and consumables through my friendly local dealer, Route 3A Motorsports.

Trials specific and some general parts came from Speed & Sport. Helpful friendly service, but on the wrong side of the country for quick delivery.

  • Trials handlebars
  • Sprockets & chain
  • Muffler
  • Front fender & above fender fork brace
  • Cable making supplies
  • Foot pegs
  • Amal throttle

Several items were purchased via eBay. The decals came from Anglia Vinyl Art.  A spoke set came from Vintage Avenue Shop. A used brake rod, chain guard and oil pump were purchased from individuals selling items.

The rear fender is from DG Plastics, purchased at the Mid-Ohio swap meet for $20.00. It’s supposedly a replica of the original OEM fender. It’s the same shape but the dimensions are off.  The DG fender narrower and the radius seems slightly less. I was able to get it to fit with a minor bit of heat gun shaping.

New IRC trials tires came from Dennis Kirk.

The Wossner piston, rings and wrist pin were ordered from Racer’s Edge.

Wheel, headset and swingarm bearings came from Moto Part Hub. I discovered these ship from Maine and therefore arrive in a couple of days.

I replaced the 1.40×21 rim with a slightly wider 1.60×21 rim that I had on hand. My thinking was the wider rim would allow the front tire to make a little better contact with the ground. The front tube seems happier with the wider rim, with the 1.40 rim and the low tire pressure used in trials the valve stem barely poked through the rim.


The cables appeared to be original. Both the clutch and brake cable had broken strands. The housings on all of the cables were stiff and with the vinyl cracked or missing in sections. They all needed to be replaced.

I decided to make cables for several reasons:

  • The OEM cables appeared to be a bit too long for the stock bars.
  • I installed new handlebars with about 1″ less rise than the original bars so the new cables needed to be even shorter.
  • One of the cable sections is no longer available.
  • I like making stuff.

After reading about them, I made a simple solder pot from a short 1.25″ diameter piece of steel rod with a short handle welded to it.  The pot is heated with a MAPP torch. The mass of the pot keeps the solder liquid for several minutes. It took some experimentation to find the right flux. But with the right flux the pot makes soldering fittings onto cables an easy task.

I also made both 6mm & 7mm ferrule compression fixtures. A ferrule is compressed via the fixture with a vise. These fixtures were made from two pieces 1/4″ thick steel plate and a couple of short sections of 1/4″ diameter steel rod.

Oil Injector Pump

The injector pump was leaking oil. I ordered a seal kit from HVCcycle. After installing the kit, I discovered seals were not the primary cause of the leak. The pump shaft had rusted and was pitted enough to let oil seal by the seal.

Turns out the TY175 and RT180 share the same oil pump. Pumps for the RT180 are common and cheap. A “eBay” pump cost less than the rebuild kit and stopped the leak. The newer injector pumps lack the manual pumping wheel, so that cannot be primed by hand. I made a quart of pre-mix and started the bike with it before switching over to straight gas.


I removed the head and cylinder to measure the piston clearance because there was a lot of top end noise. Things were worse than I expected, both the piston and cylinder were scored. The bike was probably run without oil at some point. Possibly, the injector tank ran empty or the injector hose was left off the carburetor.

Fortunately, 0.5mm oversize piston cleared up the cylinder. TY175 uses the same piston as a 1974-76 DT175.  Pistons are no longer available from Yamaha, but they are available from several piston manufacturers.  I used a piston from Wossner. Wiseco also still makes pistons that fit.

While the cylinder was being rebored, I decided to take the bike and engine the rest of the way apart and do the restoration I’d been planning for the winter.