TS250 Joy, Then Sadness

[Weldangrind]

I finally sourced the parts I needed to make our Suzuki TS250 run properly (or so I thought). The original carb was missing the idle screw, and the float pin hinge bosses were completely worn out, which allowed the float to sit crooked. I put the carb aside and bought a China copy on eBay, but Son of Weldangrind and I could never make it run without the choke, despite trying different jet sizes. I imagine that we could have beat it eventually, but it had a goofy choke mechanism, and it lacked the necessary oil injector tuning hole. The stock carb has a plug that conceals a dimple in the slider; once the dimple comes into view, the timing marks on the oil injector should line up. For the uninitiated, the Suzuki TS bikes are two stroke machines.

All that said, I decided to resurrect the stock carb. I read a tip about using JB weld to rebuild the float hinge pin bosses. I used Permatex Cold Weld, because it actually claims to be compatible with gasoline, whereas JB Weld does not. I cleaned the bosses, applied the Cold Weld, filed it square and drilled the pin hole. It worked! I installed the new idle screw, spring and o-ring that I bought from Bike Bandit, and a new air screw and float valve from www.jerryscycles.com. I was disappointed to find that neither the float bowl gasket from Bike Bandit nor Jerry's Cycles was a match. the carb is from a late year model, so the carb on the fiche for the '79 is wrong. The carb on the '80 looks to be correct, but not the float bowl. Undaunted, I coated both sides of the original gasket with grease and installed it.

I didn't want to perform a complete restoration at this time, because it's insured until August. We wanted to ride! Instead, I cooked the nasty old oil out of the expansion chamber and muffler, then painted it with VHT semi-gloss high heat paint. Here are the bits:



I bought a NOS side cover on eBay and painted it with Krylon Fusion red Pepper. It looks good enough for now. I'll paint the rest of the plastics and tins eventually.







I bought some bulk Uni foam from Bike Bandit, and cut it to fit the stock filter cage.





I have a new seat cover for it, but I'll install it later. Gorilla tape will do for now. Here's the assembled bike:







After a couple of kicks, it fired right up! I took it for a couple of victory laps that day, and then Son of Weldangrind and I went for a ride after work the next day. With the tuned oil pump, factory airbox and cooked exhaust, it smoked much less that before. It also ran beautifully without the choke. It had a slight off-idle bog, but I'm sure that's just an air screw adjustment.

With Son of Weldangrind on my tail through the twisties up a neighbourhood mountain road, the joy suddenly stopped. The engine came to an abrupt halt at 6000rpm, followed by a long black stripe from the back tire. Crap. Son of Weldangrind took my bike home and returned with his Ranger and a ramp. Once I got it home, I began the post-mortem. Here's what I found:



Any guesses as to the cause?

[pete]

lets see the rest of the piston bits "crown"

[cheesy]

Ouch.

[MICRider]

Wow, that's nasty! Is it possible that the old oil pump cratered and stopped lubing? Deep down, I've never really trusted the oil injection systems...

Though on hindsight, I would think that if it was a loss of oiling it would be more prone to slowing and then seizing vs outright destruction and lock up. Guess it would depend on RPM's? My other guess would be a casting flaw maybe?

[Weldangrind]

Originally Posted by pete

lets see the rest of the piston bits "crown"

Here's the only shot I had handy. The top of the piston was oily, with only light carbon on it. it wire brushed nicely to reveal the exhaust port arrow.



A fellow on the TS forum suggested that an exhaust leak at the head caused it to lean out. I know it was leaking, because it was puffing smoke out at that point. The only difference between the two rides I took and the ride that Son of Weldangrind took was the fuel. I was burning some old premium fuel, whereas he had a fresh tank of regular. The higher octane in the premium fuel likely thwarted detonation in the lean condition, but the regular grade allowed it to ping itself to death. I'm gonna order new exhaust gaskets and I'm gonna install a fatter main jet to see how it behaves.

[pete]

No..a lot of 2 stroke pipes were held on by springs... always leaked...

Yer never realy going to know for sure...
How much oil is in the motor.. the piston didn't
fail before it seized ?
To me from how/where the piston has broke it looks
as if it started to crack from a square corner from
the pin boss..
was it a 30 year old piston ?

[Weldangrind]

The motor has the required 800ml of oil, but it is segregated from the crank. Only the CCI oil pump feeds the left crank bearing and mixes with the fuel.

The piston never seized. It simply came apart and the broken bits lodged against the connecting rod, preventing the crank from turning.

It is likely a 30 year old piston, and there is considerable rust on the frame, shocks, etc. I figure that it was stored out in the rain for several years, so maybe the piston was compromised due to corrosion.

I'm seeing what looks like melting where the wristpin bosses broke away, which is what makes me think that detonation was the cause.

Thanks for all of your comments! I'm looking to learn from this process, so I don't repeat it.

[gloud]

Weld have you replaced the crank seals yet? they are almost 100% guaranteed to be bad if the bike has been sitting. I would look at the coil side and see if there is gas in it. don't just toss another piston in and hope for the best.

[Weldangrind]

You gotta split the case to replace the coil side. I can replace the clutch side easily enough, but I don't think it's pulling trans oil in.

No plans of splitting the case at this time. My thinking is that with the exhaust properly sealed up, a tank of premium fuel and a fatter jet, we should be fine. I will probably remove the coil side to see if there's residue, though.

[FastDoc]

That sucks.

You put a lot of effort in and did a great job. :wink:

I'm no expert but to me it seems obvious. The piston siezed, likely due to lack of oil. On an ancient bike I also don't trust the oil injector pump.

The crank pulled the piston pin out with the skirt in the process. This relieved the 'stiction' and when the motor cooled it no longer appeared siezed. :idea:

Have it bored to the next size, run premix, get a new piston and rings and if there's no lower end damage (should be fine) you're good to go.

[FastDoc]

Again I'm no 2-stroke expert but I doubt an exhaust leak could have caused this.

[pete]

If you were to run it on pre-mix...
with the old Suzuki CCI injection you
have to pull the motor down & drill
a hole from the left transfur port
resecces in the crank case down to
the main bearing for the oil to get
to the main bearing..
CCI = Crank Case Injection..

[FastDoc]

It could also have been an adjustment issue. Here is some useful (I think) information:

http://www.dansmc.com/2_stroke_oilpump.htm

[FastDoc]

More:

http://www.dansmc.com/kaw_a7_oil.JPG

http://www.dansmc.com/2_stroke_pump_views.htm

[Weldangrind]

Originally Posted by FastDoc

That sucks.

You put a lot of effort in and did a great job. :wink:

I'm no expert but to me it seems obvious. The piston siezed, likely due to lack of oil. On an ancient bike I also don't trust the oil injector pump.

The crank pulled the piston pin out with the skirt in the process. This relieved the 'stiction' and when the motor cooled it no longer appeared siezed. :idea:

Have it bored to the next size, run premix, get a new piston and rings and if there's no lower end damage (should be fine) you're good to go.

Thanks for your thoughts, Doc.

I don't believe that the piston seized, because there are no witness marks of any kind. When the motor locked up, it remained that way until I removed the cylinder and the chunks of piston that prevented the crank from moving.

I'm convinced that the CCI injector is functioning properly, and the camp over at the TS forum agrees. It's a very reliable system, even at over 30 years old.

As Pete says, you need to modify the transfer port, and I'm not ready to do that yet.