The continuing saga of the 66 Yamaha YDS 3

Well, last night I closed out my previous threads because the Yami was finally running like it should. Today I took it to the store for another project and while running down the freeway at freeway speed (60 mph+) the rear wheel suddenly locked up on me. I gave the folks in the car next to me a demonstration of riding I didn't know I could still do. Finally got control and pulled to the side of the road. She was still running but just bearly. Called my son to bring his trailer and got her home. First thing I did was pull the plugs. One looked fine but the other was fouled with aluminum. Not a good sign. Put a piece of wire in the sparkplug hole and found the piston was still going up and down. Pulled that head and could look clear into the crankcase. Had a hole the size of a 50 cent piece burned right in the middle of the piston. Shoved a drain pan underneath and drained the oil. Lots of shiny metal in the oil. Took off the cylinder and it didn't look too bad. Took off the piston and called it several names not allowed on this site. Looks like I will spend the winter getting to know the people at NWVMCP pretty well.

Started by washing out the inside of the damaged cylinder real well and then looking at it. Didn't seem to be scorched and no deep scratches. Took a cylinder hone and ran it up and down a half dozen times and then looked in with a strong light. the scratches are nearly gone and the cross hatch covers the entire surface. Checked the piston skirt clearance at the bottom of the sleeve and had about .0018. At the top was about .0014. Still haven't measured the bore to see if I might have to go oversize. Think I will hone the cylinder a few more passes and see of the scratches disappear, then mic it for size.

Is it possible to wash out the crankcase with ATF or diesel to get the metal out or is it better to split the case and pressure wash it?

Think I will clean it real well while waiting for parts and refinish the paint. Need to put on a standard front fender and get rid of the off road fender. Will probably repaint the tank, fork covers, oil tank and tool cover while I'm at it. More to come I'm sure and will post some pix as things progress.

 

OH MAN. I thought we HAD this sweet old crate fixed. Since it's a two-stroke, and since you've gotta pull it down as far as you do, if it were me I would go ahead, split the cases, and replace anything else along the way that might need it. Better that than do it twice if you miss a shard. Sorry to hear about the meltdown; probably running way to lean on that side for some reason. I wonder if/how well a colortune works with 2-strokes?

 

Talked to a former bike builder and racer who now sells parts. He took one look at the hole in the piston and asked if I had recently changed plugs and bought non Yamaha parts. In fact I had just purchased plugs at my local Yamaha shop but they were Champion replacements, not OEM. He feels the non OEM plugs were unable to disipate the heat and this caused the melting of the piston.

I had run a hone through the offending cylinder and when he tried a standard piston in the hole it was well within tolerances. Got a OEM piston with rings and necessary gaskets for $20.00. Think I may have dodged the bullet on the failure. Used a wire wheel to decarbonize the intake and exhaust ports on the cylinders

With the cylinders off I can see a lot of cleaning that needs to be done. Have been scraping mud and grime and getting back to the original paint. While I'm at it, think I will repaint the frame and colored parts. Is anyone aware of the Yamaha paint code for the blue and white used on the 66 YDS 3 scrambler? Is the lower end of the 250 anodized or is mine oxidized. When hit with a wire wheel it looks like polished aluminum under the gray coating. Was thinking of buffing the case if it is possible to remove the coating.

Spent the last two nights cleaning the chrome on the original rims. Shined up pretty good. One good thing about having the cylinders off, I was able to find TDC easily and set the timing indicator.

 

COOL! Really glad to hear this minor setback hasn't swayed you from the task at hand. Unless the plugs were a VASTLY different heat range, or mismatched horribly, I don't think that was the cause. I think that whatever was causing your high-speed "sputtering" was a lean condition that ate the piston. I would use the proper plugs from here on out though. The guys at NWVCP or Speed n' Sport (the other NOS place I told you about) should be able to help on the paint codes. Speed n' Sport was/is an actual Yamaha dealer, dunno about NWVCP in that respect. And be sure you save that piston.

 

Polished it up and put it on my desk at work to be a daily reminder of how fast things can go bad and how close I came to being a statistic.

 

Well I have spent the greater part of the past week trying to polish the point cover housing. Seemed like such a good idea at the time and how much work could it take? Seems like I should have taken more time to read some of the posts on this site. What I thought was oxidation was probably the clear coat I have been reading about. I grabbed my trusty cordless drill and a wire wheel and attacked the case. Got the coating off and then spent the next week working out the scratches I left.
For those of you thinking of polishing a case, remember every scratch you put on that case will have to be sanded out. Save yourself a lot of time and NEVER use anything heavier than 600 grit paper. Once I got past the 600 grit stage I went to 1000, 1200, 1500 and 2000 grit. At times it was necessary to back up a couple of stages to take out a scratch or two. After the 2000 I went to Mothers Polish on a felt buffing wheel and then to Fabuluster and a muslin buff.
Next I tried to pound out the dents and polish the point cover. Thought I had done a good job of smothing the metal until I started sanding out the scratches. The metal was so lumpy that I sanded right through the chrome in places and exposed the copper coat and even the base metal. Didn't let that stop me so finished the polishing and will have the cover rechromed. Actually looks kind of neat with the swirls of copper mixed with the silver.
Now I am faced with doing the clutch case to match. So much for the original good idea.

 

Wow Bob! Wow. For the color, did you contact Speed-n-Sport? They might be able to help. I was poking on the web somewhere recently and ran across color codes for old bikes, I'll start sifting thru my "history" and try to find it. For chrome plating work, I found these folks http://www.justchromeit.com/ to be quite reasonable, price-wise (you would not BELIEVE some of the quotes I got!?!) and easy to deal with.

 

Finally started to put the old beast back together and noticed I was missing the exhaust gasket from the cylinder to the header on the failed side. Could this have contributed to the melt down and failure of the piston?

 

Yes it certainly could, at highway speed you might have been sucking some (cold) air in there I know on a 4-stroke it can cause you to destroy a valve (raw experience of youth.)

 

PICTURE HEAVY While I have been waiting for the weather to clear, I have finished polishing the side covers and hubs. Sanded the colored parts and refinished with a matching metalic blue. Haven't been able to find a replacement front fender this side of the Pacific. While repainting the tank I notices the tank badges were both broken so looked for replacements.

There aren't many of the old parts around so tried to repair the originals.
Here are some pix of the process. Final outcome is a pair of badges that look like dodoo but will have to work until I can find replacements.

 

Wow, takes me back , I had a '66 DS3 street bike in 1969-70.
From what I remember, plugs were critical, a slight change
in the heat range meant fouling or holing if you were wrong.
Any change to the exhaust meant rejetting and plug changes.
I seem to recall the Autolube was driven off the transmission
and the clutch was on the end of the crankshaft, pulling in the
clutch shut down the Autolube. The throttle cable used to stick
and I dumped several times because of it. Thanks for the
memories.

---

 

How mad ya gonna get if I find you some NOS badges? I JUST saw a set of those on eBay about a week ago "buried" in a store somewhere I think the guy wanted like $27 for the pair. Now I gotta find them again.

Nice save on the broken one though. Bike's looking good too. BTW, just got some "unobtainium" from Mr. Groom myself.

 

WOW Reminds me of my 305. Nice to see an old girl come back to life. Good Luck

 

On a two stroke, especially one of that vintage, spark plug heat range is very important and CAN cause you to hole a piston. I don't know that there's much difference between the two plugs you mentioned. I would definitely stick to the recommended plugs, but I think the missing exhaust gasket on the failed side is more likely the culprit, or that in combination with the carburetor issues you had been experiencing and the sustained high-speed running. That old bird is certainly capable of running all day at highway speeds, but only once it's in a healthy state of tune.

 

Hey Fitz,
That bike is oil injected, Not sure but I would look at the oil lines and the pump and make sure that is all clean and working properly. If I remember right you can adjust the oil 'shot" by adding or removing shims on the pump. I'm sure the gasket missing didn't help much either.

 

a lot of old MX bikes held the expansion chamber to the cylinder with springs
without a gasket, they always showed signs of leakage
on "enduro" bikes with oil injection, that was the first thing to come off
we just used premix and never had a problem
use good oil, none of that Lawn Boy crap

 

Most old motocross bikes (and modern ones as well I suspect) don't spend more than a few tenths of a second at a time WOT and almost no time extended running at mid-high RPMs. The missing exhaust gasket could have contributed.

 

WOW i don't believe you said that

 

Maybe I phrased it wrong, I'm talking about the fact that motocrossers don't have extended periods of "steady-state" throttle, 5, 10, 20 minutes at a time holding one RPM like you do running on the highway. Bob was doing a bit of extended highway running when it blew up.