Hi Guys,

I was out flying my YS170 (converted CDI) with no problems. When I came to run the engine dry, as it may be more than a week before I get to fly again, I noticed there was a bit of play in the bearings. How much play, I'd guess at a bit more than 1/64th of an inch. My 63, and 110 don't have this much play. If I held a prop blade in each hand and pushed and pulled the prop to the tail, I could feel a tiny, tiny knock front and back bearing. This isn't knock front and back, only side to side.

It doesn't feel 'gritty ' ie as if it has broken particles floating about. I replaced the bearings last year, it's only run 12 times since new bearings, although it's had a lengthy layup over winter, layed-up with oil.

I'd be amazed if the need replacing so soon, having had a YS110 go with a rear bearing fail inflight and cause so much damage, I'd hate the 170 to go through the same.

Your help is appreciated.

Mike

The 170 has some play, but I have never measured it, I will if I can remember to do it. The play becomes greater if I remember correctly when the engine is warm after run.

Yamada told me we should change the bearings every 300 flights as a rule of thumb.

Best regards

Thanks Apereira, you put my mind at rest. 300 flights would sound more like it.

Best Regards,

Mike.

I have experienced a premature rear bearing failure after storing the engine through the winter months, although only once. What I did was just prime the engine and start it. After about 6 flights I noticed that something was wrong, as you describe “some metal particles floating around”. Once I disassembled the engine I found the retainer ring of the bearing had failed, except for that the bearing looked fine no rust, races shiny,,,,My personal theory is that during the storage the oil viscosity increases, the engine is harder to turn. Being dormant for some months and suddenly spin at high rpm with this high viscosity oil may be too much for the retainer ring, or may be I just got a bad bearing? Your case sounds very similar to what I experienced. I agree with apereira that under normal circumstances that the rear bearing last 300 flights at least. Even though it is some work I would check it out so you do not damage your engine further, just my 2c worth.Arnstein

Hi Arnstein,

Storage, oil thickning would make sense. I had another look at the 170. There seems less play while it was cool. It doesn't feel gritty, turns over smoothly.

I ran it up a few days ago, as there was a bit of mis firing from slow to full throttle. Also it cut in a spin. I fitted a new spark plug & gapped it to 0.4mm, checked tappet clearance was okay.

It wouldn't hold less than 2200 rpm on the ground. In increments of 1/8th turn c/cw I leaned the pump from brass pump screw flush, to 1 1/8th turns out. Seems alot, but now it holds 1450-1400 rpm on a APC 18.1x11.

Does it matter if you make adjustments with the CDI fitted as appose to glow ? Somewhere I read set it up as a glow, then switch to CDI.

Thanks,
Mike.

Mike,Sorry, I missed your "doesn't", just go and fly!I use a fuel with less oil (10%) with the CDI, hence I cannot comment. My experience is that the position of the pump is also depended on type of diaphragm used. I have good experience with the white ones.Arnstein

Thanks Arnstein, I understand theres no comparison, all settings are different to everyone elses engines. Indeed flying is the only way to tell.

Regards,

Mike.

Mike,

Do not concern yourself with CDI vs Glow set up as they are the same but different....like apples and pears...both fruit but not the same.

To address your first question, 12 flights on new bearings and then laid up for the winter without a gritty feeling would make me think about congealed oil form sitting. It should get better after a couple tanks, I have the same issue every Spring since I put a little castor in my fuel. Since you say the idle is getting better I would ask what your oil package in your fuel is, full synthetic, synthetic/castor or castor only?

Pete