The Cessna 120-140 Association Forum

Hello,'
Anyone have any real world experience with the STC that permits using the 0-200 cylinders, pistons, and connecting rods vs the stock 85 and power output? I've "heard" the STC owners "say" they got 9X HP out of the engine. An airplane I'm looking at has it, and I'm wondering if it brings real value to an airplane that has it vs one that doesn't, apples to apples the rest of the way?

Down the road for rebuild on an 85, would I eventually have to do it anyway do the scarcity of 85 cranks?

Thanks for anyone's insight.

Scott

I was going to say "I think we just covered that in another thread" but then I realized, that was your thread... viewtopic.php?f=7&t=1303

Not sure what else there is to say.

I think it brings value because as you say serviceable C-85 cranks are tough to come by.
But one has to wonder if the higher HP may not cause case problems.
I believe I know who could answer that question though, and that’s Browns seaplane base, pretty sure they have been running the STC for a long time,and could probably weigh in on any perceived power increase too.

Is it “better” than an O-200 ? depends on how much you value authenticity, the higher RPM O-200 with its shorter prop is less appealing to me, I like how my C-85 with straight pipes sounds like an old farm tractor, it’s just a relaxed sound to me and fits the aircraft well.

But if you have a recently overhauled low-time C-85, it’s unlikely you will ever overhaul it, most think they will fly a lot, but most do good to fly 100 hours a year once the new wears off, and that means a good motor will last 20 years.
But in truth I think most don’t get 100 hours a year.

I thought you kept C-85 cylinders?

a64pilot wrote: ↑Sat Jan 02, 2021 8:08 pmI thought you kept C-85 cylinders?

Yes, it uses O200 crank, rods and pistons. Everything else stays the same.

6643 wrote: ↑Sat Jan 02, 2021 7:50 pm I was going to say "I think we just covered that in another thread" but then I realized, that was your thread... viewtopic.php?f=7&t=1303

Not sure what else there is to say.

John,
Oops, you are correct. My own thread. Sheesh.

We did the mod you spoke of, along with the Precision carb, millennium cylinders, and after break-in found we needed a prop re pitch to 71X48. Performance is much better than the old C85. No one will say how much the HP improvement is, but we are very pleased. 105 indicated in cruise (2400 rpm) with full fuel and 2 adults and std to about +10 ISA where it will drop off a little. We also did the VG mod to the wing which we are also very pleased with. For my money we researched this engine thoroughly before purchase (about $7000) year 1999. 1000 hrs later, it's still a strong engine.Yes, it's worth it because of scarcity of C85 cranks. Tom

1125 wrote: ↑Tue Jan 05, 2021 6:50 pm after break-in found we needed a prop re pitch to 71X48.

What necessitated the change? What pitch did you start with? 7148 is standard for the C85.

It was pitched to 71X46 originally. After the modification it was still in limits for ground run rpm but would overspeed soon after liftoff at 70 IAS (full throttle). Maxwell prop shop in Minneapolis said they had dealt with a number of these, knew exactly what to do, and 71X48 cures the overspeed issue. If I remember correctly, the original C-85 on the 120/140 could be pitched from 71X46 up to 71X52 (Information in the TC data sheet), thus the 'climb' vs. 'cruise' prop we've heard discussed while hangar flying. Tom

There are no pitch specifications in the Aircraft Specification, only length and minimum and maximum static limits.

The McCauley on a C85 is usually spec'ed as 46, 48 and 50 for climb, normal and cruise. On the C90 those numbers are 50, 52 and 54. The STC'd C85 would logically fall between the two as it sports a higher RPM limit than the C90. (2575 vs. 2475.)

Whatever pitch you choose, it has to meet the applicable static RPM limits.

If it overspeeds in normal climb then you're leaving some climb performance on the table. (Likewise, if it overspeeds in cruise you're leaving some cruise performance on the table.)

My prop is a 71x46, or at least that’s what is stamped on it, the 6 looks a little odd so I suppose it may have been re-pitched.
I can just barely hit or come real close to redline RPM in level unaccelerated flight, so I think it’s pitched correctly.
I’m also if memory serves running over 110 indicated, 2400 cruise gives me somewhere between 105 and 110 indicated and ground speed on an average day real close or sea level, closer to 105 than 110.

For those that will tell me that I have a weak engine, I don’t think so, the Millenium cylinders have I think about 200 hours on them.

I believe my speeds are about average, but as my wings are metallized, that alone may slow me down some, or may not I don’t have the experience to say.

I have not checked the accuracy of my tachometer, but likely will soon.

Ever seen one of these? it’s a strobe light tachometer that was used back in the day to see how fast anything was turning, this one was used by North American Rockwell to calibrate the aircraft tachometers of any aircraft made in the Albany Ga plant.

Yeah, I know I bet there is a smartphone app that does the same thing, but I like the old tools.