In a perfect world probably not, but runing 100% synthetic I still get a little carbon buildup on the back of the exhast valve which I clean off every rebuild. IF I were to run castor and IF it built up to the point where the exhaust valve didn't close properly then I'd expect the valve and seat to begin to burn out, but there're a few if's in there.

With 20/20 hindsight, I also suspect my bearing failure and CDI sensor failure was due to engine tuning issues (even though the temp rating on the hall sensor they used in my particular assembly was the lower rating). I had what I though was a too rich condition which I tried to tune out via leaning the engine, when the reality (?) was it was a oil fouling issue. By dropping the oil content I was able to richen it up, although some swear by running 20% oil but my DZ170cdi doesn't like it.

I understand it's a bit like describing something as an electrical fault because the conrod broke and hit the alternator but I run 50/50 castor/synthetic in some motors and 100% synthetic in my YS. As long as engines run well then I'm happy to keep feeding it to them.

I'm not opposed to synthetic and I didn't say what I said to fault it. I don't care to use much of it. I use a 50/50
cas/syn blend in my car fuel and Jett fuel. The rest of my aero engines get all castor, even my 4-strokes. My engines are mostly used in wet environments (airboats) so castor is better suited to prevent rust.

I agree that the damage claim is a bit exaggerated. The shellac effect is the result of damaging lean runs.

Leaving the lubricating properties aside, it's worth keeping an open mind to secondary effects. I had an engine that I had no lubrication concerns at all running either full caster, 50/50 or full synthetic, BUT that one one motor was difficult/impossible to tune on the lower viscosity full synthetic fuel. 22% castor and it was fine, nose up nose down full tank empty tank, but with full synthetic nose up lean, nose level rich, nose down four-stroking and no needle tweaking can fix that

Would I recomend a YS to a friend?

Here's my rear bearing, it failed 3 flights after I placed first in our State Championships with it. It was only about 3 months old, no corrosion and bits floating in oil, probably just a bad bearing or may have cooked it 10-15 flights earlier? Water under the bridge now.

I also had a rear bearing failure in my 175cdi on the 118th flight. After this i stripped down my other 175cdi which had done 184 flights. The rear bearing was very worn so i replaced it.
For the cost of a few dollars for a bearing, I will now replace bearings after 100 flights.

There are a couple of things that may be contributing to the reduced rear bearing life in the cdi engines. Firstly, the low oil content. I know these engines have been fitted with some different parts that are designed to run on low oil, but the rear bearing is the same as on the 140.
My cdi's run perfectly on 10% oil, but if i need to replace bearings every 100 flights, that's a price i am more than happy to pay.

Also, i suspect that the large diameter props are affecting the rear bearing life as well. Same bearing which was running a 15.5" inch prop, is now running a 20.5". That has got to be a substantial increase in load.

Nice pictures. I just got my rebuild spares from RC Japan today and may do a rebuild over Christmas but it's been a really slow season and I've only clocked up 135 flights.

My 2012 rebuild had a few more flights under it's belt and while the rear bearing was fine (and always is) from a corrosion perspective, I did notice very small regular "smear" spots on the outer race. Very minor but visible in the right light but you could feeel the difference between it and the new bearing. I tached the engine not long after the rebuild and again a couple of times since and it's pulling identical RPM today (allowing for fuel and weather differences) so I might put the rebuild off till the ~200 flight mark.

I bent the crank on my 175 from the crash I had mentioned in an earlier post. Normally I would straighten it, but in this case it is bent on the bearing journal not at the shoulder.
I have a new one coming from RC Japan. Should be here this week.

Are you going to the nats?

Honestly, I never understood why it happened, nor the chemistry involved, but having disassembled several almost-new YS FS's in my day that had been run with castor fuel, they present themselves as very tight, almost seized, with sticky valves, etc. I think back to my 2-stroke days, and having engines that wouldn't develop compression until after being run in extensively and looking at the sleeve and piston sides to see dark zones or shellac build-up that, I guessed, was beneficial.
The YS engines, are so tight tolerance on machining that even a few thousandths on the sleeve, piston, rings, valves makes all the difference, it seems.

Not preaching against castor, just describing what I have seen.

When my son and I sit at the field and someone with a new YS fires up and we smell the unmistakable aroma of castor, we say "here we go again..."

AP

A customer gave me a YS .91 that for whatever reason he didn't like. The engine had great compression and looked really good except for some burned oil on it. When I cleaned it up, it looked mint.

I put it on my test stand, started it up and then per every safety protocol ever, stepped behind the engine before revving it up.

I've never seen an engine backfire so violently. It send the prop clear across the yard - at least 40 feet where it hit a fence. To this day I count my blessings on that one and no other incident in my lifetime, including putting my own fingers into props, has instilled in me the danger of these things.

Anyway, I downloaded the manual for the engine so that I could set it back to factory settings. The pump was way out of adjustment. If I recall correctly it was set to pump as much as it could.

Once reset the engine has run like a jewel. No problems at all.

If there are dark spots in the liner anywhere below the very top, the liner and/or ring is out of round. Castor does varnish up if it starts to burn, and obviously carbon build-up too. Synthetics have an uncanny ability to keep metal clean, thus why so many people use a castor/synthetic blend. If I have an engine that I'm not going to run for a long period of time I will oil the engine with a mixture of mineral ATF and Seafoam motor treatment. The engines don't get stuck when I do this, nor do they rust.

I think if an engine gets ruined that was run with castor in the fuel, I'd say it was run too lean or it had a mechanical defect. IMO that is.

It would have been the regulator you adjusted. The sports series of YS's don't have a pump.
If it threw a prop it would have been lean.

Those bearings that went bad are they YS bearings? I have had the best luck with genuine YS bearings.

Yeah mine was the original bearing and i'm pretty sure bjr_93tz's was as well.

That is the first bearing failure i've had in 14 years. Like i said previously, i think the rear bearing is getting a much harder life in the 170-175cdi and it's starting to show. The 185 will be worse again, especially once they bring out a larger prop than the APC 20.5 x 10 to suit the 185.

I had the main bearing fail on my 1.20. Yes, it was the bearing as fitted by the manufacturer.

The failure was fairly catastrophic in that the bearing cage tore itself to shreds, stopping the engine dead. Internal damage was limited to gouges on the inner wall of the crankcase. Sigh of relief.

That's the only bearing failure I've experienced in 29 years of model flying. Buuuut, the engine was producing a great deal of power.

I wouldn't run castor in a YS either. I was saying the same thing about metal wear and castor. I think Omega is 3% castor and I add a couple of oz myself to bring it up some. Some people take the chance with a small amount in their YS's.

That seems to be a bit contradictory.

Bearing failures in alcohol/nitro burners is a constant ill.

I am turning the same prop as you on my OS GT33 and have for the past 3 seasons. Have about 120 hours (about 55 gallons) of operating time on my #1 and bearings are still like new. Recently took the engine apart just to see the inside and it showed no wear at all. Very nice.....

The 33 is slightly stronger than the 175 on the top (which doesn't matter one bit) with pretty similar mid range. Low throttle is a bit faster tho so downlines are a bit quicker. Can't beat gas for reliability and no maintenance. And someone said something about low oil of CDI YS versus bearing failures....well, the 33 burns gas-oil at 50:1 ratio.

It wasn't a problem with the needle.

I don't own a YS. But, there have been members who say they take the risk and use some small percentage of castor in theirs. I'm not in a position to comment on doing that, and leave it to the users who know best.

With pure synthetic blends today , castor really isnt needed except for making the plug easier to read after a flight when you are trying for that best setting. I do not run castor in any of my fules any more, but i have learned to read the plugs and what to look for. I get it set, by ear ( thats right - no tach), and I keep it a bit rich, then I fly it. After landing, I pull the plug and the color determines which way I go until I get it just right. From that point I observe the "position" and it is good to go at that point for the rest of the event, unless the plug tells me a different story.
The reliability of these engines is awesome. And remember I run 60% nitro. I race about 5 events a year with about 10 glights at each event incl practices. That is 50 flights, wide open on extremely high nitro. Never have lost an engine, and in one of my planes I am on year 3 with the same engine.

I don't call 1 bearing failure in 18 years a constant ill.

As for comparing the 175 to the 33, you have to remember the 33 is specifically designed to run on 50:1. The YS cdi's are using bearings that are from designs originally using 20% oil. The low oil may not be the problem. It is just my observation.

What size rear bearing is in the 33. I wouldn't be surprised if it is bigger.

Even though the 33 may spin the same size prop and is cheaper to run, I feel overall the YS is still a better pattern engine.

Cost isn't everything.

Yes, genuine YS bearings with NTN on the front one and KOYO on the rear one. I didn't know those two bearing companies outsourced their manufacturing to YS :D

Seriously though, I've had one bearing go bad in another engine and lose a bit of a ball ruining a piston and liner, and In my Hanno they start to get a bit rumbly first usually fatigue spalling on the inner race. The YS is the first engine I've had with a cage failure. Google will tell me what causes cage failures because it certainly can't be RPM.

The ball-bearings in our model engines ... are they really up to the loading ... or, are they operating outside their design limitations?

bogbeagle, I tend to agree with that theory. The bearing has been ok on engines up the the DZ160, but imo the bearing is being overloaded on the 170/175.

Bearings take stresses from a lot of places. Incorrect and crooked installations. (using an arbor press or drill press can fix that) Inner race size mismatch either over sized or under sized to the crankshaft after normal engine heating is a top cause. Dirt and engine debris are hard on bearings.

A lot of metal passes through engines (and bearings) during its lifetime from wear.