skawbo_dk

Hi,

I've just accuired a second hand YS 63 FZ which looks ok (although I think that the bearings are a bit worn). I've adjusted valves and I'm now trying to adjust the engine starting with settings as per manual using an APC 12x7 prop and Cool Power 25 % fuel (which works nicely on my YS 91 AC). I've noticed that top end rmp is somewhat unstable. It will initially reach 10500 but then after a few seconds drop to approximately 9800 rpm. Is this normal and - if not - what could be the cause?

petec

My Feedback: (58)

That could be caused by a few different things, bearings (since you mentioned it), ring, glow plug. What makes you think the bearings are worn?

skawbo_dk

I think the bearings are worn because when I push/pull at the tip of the prop I feel a slight play (not visible but I feel it). The plug is a new OS F plug so it should be OK.

petec

My Feedback: (58)

Lateral play would certainly be a good inidicator. If you can do the work yourself a ring and bearings would be a good start otherwise you might want to contact the YS agent for your country.

skawbo_dk

Before ordering ring and bearings I decided to take the engine apart to see if there are any other surprises. First of all I noted a significant play at the con rod copper bushings. I can also see some wear on the wrist pin but I don't know how much wear there is on the cranckshaft where it connects with the con rod as I have nothing to compare with. As can be seen from the pictures there are also a lot of carbon deposits on top of the piston (which has been gas ported) and - not least - around the valves. When I look at the liner there is a lot of TINY lines/scratches, but the surface feels very smooth. I'm very much in doubt if the engine is worth a rebuild - any comments much appreciated.

3d-aholic

My Feedback: (7)

I have my YS63 currently completely apart and its about to go back together. So if you want a picture of something let me know. That piston is very dirty on top. When I pulled mine after about 6 years and at least 30 gallons of fuel mine was still sparkling chrome with only the slightest yellowing....so I'm surprised to see yours looking the way it does...especially with the valves looking so clean. On my motor that area was pretty dirty. I would suspect some amount of castor at first glance but the valves sort of defeat that.

Is it possible the valves were recently replaced? They don't even match the the top of the engine.

I would not expect play on the rod...mine does not have any and it has seen heavy use. In addition, I can tell you there should be NO play whatsoever in the crank. Mine has zero even with all the use I am describing. My bearings in fact look to be still fine with no play whatsoever that I can feel. When I spin them, they sound clean just hear ball noise. The crank and bearings from what I can see are very high quality...a lot better than what I see in most engines.

I can't tell from the picture its too small but does your wrist pin still have the teflon pieces on the sides.... You should not have scratches in the liner.

If you really take care of these engines, you would be really surprised at how little the wear is inside. I was shocked when I cracked mine open for the amount of run time and fuel put through it. They are really high quality with tight tolerances.

I would still suspect the bearings. Besides the play does it sound and feel gritty when you turn the motor over. Now that the head is off the motor, you should be able to see the rear bearings peaking through the crank. Rub you finger across and make sure no brown stuff comes off on your finger.

I would also check your ring and make sure its not worn. You can call YS and ask them the tolerance. Mine actually was only about 1/3-1/2 worn after all that fuel...but I replaced it anyway.

skawbo_dk

Hi 3d-aholic,

Thanks for your input. I don't know what fuel that has been used on this engine but I don't think it is Coolpower I think the description of your engine confirms that my engine is generally pretty worn out. The teflon pieces on the wrist pin are not on the picture but they were OK. How do you measure the wear on the ring - by its thickness? I'm considering just buying a complete new engine. I think this engine will require at least a new ring, bearings, con rod and wrist pin - as a minimum.

3d-aholic

My Feedback: (7)

The thickness or how big the snip is.
A new ring is $19.50, a bearings set is probably $20 ish, the other parts are probably much cheaper. Those are going to be the "high wear" parts.

Its a lot of work but a new one is over $230

petec

My Feedback: (58)

The pin on the crankshaft is steel so it should not be showing ill effects from the connecting rod bushing wearing out, that is the reason for the brass bushing in the rod.

As for the ring, you would need to check the actual end gap on it as opposed to when it was new....too much math, just put a new one in as they are cheap insurance. The parts you need to put in this engine are still going to MUCH less expensive than a new engine. You're looking at a ring, rod, bearings, gaskets and a bit of your time thus far unless you found some other items that need replaced.

3d-aholic

My Feedback: (7)

My engine had no compression and now with the new ring, it has a massive amount of compression. Its actually truely amazing as over time you forget. I think the rings on these little motors can wear much quicker as they are turning a lot of revs and the ring is serving double duty up stroke and down stroke.

I think the ring and the bearings will almost be a given on just about any used YS motor unless you are very lucky....everytime I buy a used motor the bearings are like a 90% guaranteed replacement. Most folks have let the motors sit in their garages for a minimum of 2.5 years before they finally motivated themselves to sell it.

I'd hate to see you get another used motor and find yourself needing to do the exact same thing minus one minor $10 part here or there.

skawbo_dk

Thanks for your input. I have decided to go for a rebuild. The tiny lines/scratches in the liner are actually in the lower part. The upper half - where the ring moves back and forth actually has a mirror-like surface with only one tiny scratch which can only be seen at a certain angle of light. The valves should be OK - they are air tight (I placed a balloon around the bottom of the cylinder and inflated it by blowing air into the exhaust while pressing on the exhaust valve. When I released the pressure on the exhaust valve the balloon stayed inflated[8D]).