Forum > Engine

Need Help: 1969 RS200 MkII, Melting Hole In Piston & Crank Seal Leak

(1/9) > >>

robinkwmack:
Alright, reaching out to the knowledgeable folks here on the forum to try and figure out a reoccurring issue with my 1969 RS200 MkII.

First off some info on how I am running it.
87 oct fuel
40:1 yamalube premix in tank
cleaned points but haven't checked timing. Seems to be either fine or close to what it should be.

I got the bike from the grandson of the original owner who parked it in 1971 at just under 3k miles. I tore the cylinders apart and was able to figure out exactly why he had parked it. (Broken engine stud that then caused a head gasket leak.) I fixed the stud, put in a new gasket and the bike fired right up. I road it for maybe 300-500 miles with a gas leak on the left side. So I brought it to the local vintage motorcycle mechanic just to have them go through the carbs since I couldn't find why the leak was happening, had them make sure everything was set to "stock" so I could then tune it myself. They found the left float had a hole in it causing the leak and replaced it fixing that problem. with some carb cleaner I was able to find out there was a slight base gasket leak as well on the right cylinder. But about 50-100 miles after getting it back from them I lost compression on the right cylinder and found out that I had melted a hole in the center of the piston. Thinking that it was the base gasket issue I put a new piston on, new gaskets and it fired right up and ran like a top, but like an idiot, I did not check the carb seeing as it just came back from the shop, but then 50-100 miles later, same problem. Hole in the piston on the exact same road as when it happened before. I had noticed that the right fuel line was not filling up all the way and almost seemed "empty" only allowing a trickle at throttle, so I think the issue with the right cylinder is the right carb needs to be gone through again and readjusted and cleaned. But while I was in there I noticed some transmission oil was getting onto the crank when I turned it by hand (brown oil), very slight, but enough for me to realize I should do the crank seals as well.

So here are my questions:

Could my ignition coil be causing the spark plug to fire "hot" resulting in the melted piston?

Could it be an ignition timing issue?

Could the crank shaft seal leak be causing it to run lean as well?

What part number is that seal anyways? and what other parts will I need to do, or should do, while I have it open? I have had a hard time tracking it down in the parts catalogue and don't want to waste time and money trying to track it down seeing as I am 26 and basically broke and have already basically thrown away a few hundred bucks in a few hundred miles.

This time I will be sure to go through both carbs, all the cylinder gaskets again as well as that new right piston. I just can't afford to keep replacing that expensive piece.

Any insight would be a huge help and much appreciated.

Thank you.
-Robin

OldSwartout:
The right side crankshaft seal you need is 09090-109, 28 oil seal.  The seal could cause a lean condition that would melt the piston, but a leak big enough to cause  melted piston would let a lot of transmission oil past and cause a lot of smoke while riding.  My best guess is it is the ignition timing advanced  too much on the right side. I don't think the coil itself will cause an early spark.  Of course, some of the other items you've considered are still possibilities. The carburetor might still be suspect - if you're certain there isn't a blocked jet, check the main jet size. It should be a 90 or 95. Compare to what the left side has. Check is to see if fuel will flow through the float valve freely. With the carburetor still connected to the fuel line, just leave the bowl off, hold over a container and turn on the gas. It should flow a steady stream. If that's good, check the float height per the service manual. I had a Suzuki that had the float set too low in the bowl, it would starve at high rpm, yet everything looked good otherwise.

Maybe others on here have more suggestions or experiences that will help.

OldSwartout:
An outside chance is that the fuel cap isn't vented properly. Usually, an unvented cap will just cause the bike to slowly die of fuel starvation on both cylinders as fuel flow slows; however, I know from experience that the right cylinder on these bikes will start to miss first when running out of gas.

BRT-GTR:
          If the fuel cap vent is ok (just blow through it), take the fuel tap off and clean it thoroughly, tubes, filters etc.

Old BS Guy:
Yes, of course, start from the top down and validate the tank cap, but it should affect both sides equally, not selectively. Still, good cause for checking. The only thing not mentioned here, unless I missed it, is the bowl vent for the carb, and under the circumstances seems most likely given the other carb is doing fine. I do agree, however, that validating each part from the cap down is required. Slim chance it's ignition, but ignition must always be vetted before carburetion in any diagnostic to prevent mistakes with fuel.

Navigation

[0] Message Index

[#] Next page