Underperforming Continental 0-200
 

I wonder if I could pick the brains of the board about a C150 that I bought a few months ago. It's a nice little bird, and on the whole I like it a lot. But the engine does seem a little "odd" in two respects:-

1. It is really lacking in oomph. According to the book, I should be able to run it up on the ground to a minimum of 2,510 rpm. In fact I'm getting a max of 2,300 rpm, with correspondingly anaemic takeoff and climb performance, even by the less-than-exciting standards of C150s generally. I'd suspect it of having a cruise prop, but inasmuch as a 2,500 rpm cruise (it will eventually turn at that rate once in flight) only corresponds to around 82 kt TAS in still air, I don't think it can be that. Compressions are good -- mid-70s on all four cylinders, and oil burn within tolerances. I'm at something of a loss to explain this.

2. While in the air it vibrates like an East German tractor. One can see the pitot head and compass ball thrumming back and forth several hundred times a minute. Again, this seems much worse than in any of the many other C150s I've flown. According to the log, though, the prop was removed and balanced only eleven months ago. Hence I'd have thought it unlikely that that's the cause (not impossible, of course).

What do you think? Is this simply the consequence of having a fairly high-time engine (1,400 hours since the last major overhaul) and I should live with it? Or does either condition -- or both -- warrant a mechanic's investigation?

Have it checked out for sure. Could be a stuck valve,a rotted out muffler, or any number of other things.

I'm assuming that your mag drops are within limits. First thing I'd check would be the magneto to engine timing. Then the fuel and air filters. Then that the prop is fitted in the correct position in the crankshaft. Then the engine rubber mounts and firewall attachments.
You're only talking about a morning's work for an engineer to do this.

Underperforming Continental 0-200
 

I would recommend it is time for an overhaul. It could possibly the camshaft is worn. We have had this previously on a 150 aerobat, it's a common problem with the RR O-200 engines

though i'm NOT an aero-engine mechanic, i'd suspect a worn camshaft.

surely a worn crank would give a noticeable mains grumble/oil-seal leakage or a pronounced big-end knock.

It is, of course possible that a big-end has "nipped" and bent the rod....that would give you vibration, but you'd expect the shells to knock out in short order.

In the absence of any report of unusual noise, starting difficulty or a severely over-advanced mag (that would "fight" the upcoming piston, would also cause vibration!) which would give a dramatic rev-drop when switched ON.

I go for poor breathing at high revs....cam lobes worn= inadequate valve opening = poor gas-flow = low power output....


Now tell me i'm totally misguided....and why! :8

Isn't the Continental in the 150's of RR origin? If so, isn't there a different mag timing for these engines?

I think before you go tearing into the engine you can do a few basic things first. Remove the prop, make sure it's sitting on the crankshaft boss ok. The spinner and back plate are ok. While the props off check the part number against the type data sheet and make sure the prop is correct for the engine/airframe. You will also be able to find out if it a climb or cruise prop. Refitt it using a calibrated torque wrench with the correct cylinder on TDC. Measure the blades and make sure the are the same length. Once it's all back together check the tracking. I had a 150 with o-200, had vibration at cruise. Removed the prop reseated it and retorqued it and it was fine.
Another couple of things you can do. A compression check. Makes sure you cyclinders have got good compression. Also measure the prop RPM with a prop strobe. This will tell you if your tacho is giving you a correct reading. If your engine has 1400 hrs on it then it shouldn't be that bad. If I remember rightly TBO is 1800 hrs on an O-200

Check that each valve spring depresses the same amount. This will tell you if you have worn cams.

It might be worth contacting Harry Fenton or at least looking at his website:

Harry Fenton on Continental Engines

I asked him some questions some years ago and he answered very promptly.

Always a good idea to tighten the induction rubbers every periodic, for some reason they are always a problem on a O 200

Many thanks for all the excellent suggestions
 

From what you all say, there's certainly something there. I'll have it investigated, and report back with any results.

That's good to hear. ;)
A lot of OPs never give any feedback that might be useful to others having the same problem.

Hello... any news on your O-200 engine? Thanks...

The answer
 

Dear all,

Many thanks for your very helpful suggestions, and apologies for the delay in providing the denouement. 146fixer more or less hit the nail on the head. On mechanical inspection, it transpired that:-

1. The prop was NOT in fact one approved for use on a Cessna 150, but rather was intended for the Bolkow 208 Junior only. As if that were not enough...

2. One blade was an eighth of an inch shorter than the other, and both blades were out of alignment by as much as 4 degrees from one station to the next. On top of that...

3. Both spinner back plates were cracked, and had to be junked.

The cost of fixing all this? Around $5,000, including labour. None of it picked up by the expensive (and well-regarded) independent maintenance shop that I brought in from a neighbouring airfield to conduct a pre-purchase inspection. Nor is there any indication in the aircraft log-books as to why the non-approved prop was put on the aircraft in the first place (I wonder, I wonder...just why does one replace a prop??), or why its grotesquely non-airworthy condition was not noticed by the specialist outfit that, according to those same log-books, inspected and rebalanced it less than a year before I became the owner of the aircraft to which it was attached.

This matter is now the subject of an investigation by the proper authorities.

I saw a Rallye with the wrong prop fitted. Reason, they bought the wrong one, couldn't return it, so they made it fit by counter boring the rear of the boss to fit on to the dowels on the crankshaft. Scrap!!!!!!

Nothing ever surprises me as to what happens in the world of light G.A.

Blind Squirrel - you don't say whether the $5000 has fixed your problem. Are you now getting the performance you anticipated?

jxk -- So far as the vibration and low static RPM problems are concerned, yes. There were many other unpleasant surprises with the aircraft, almost as reprehensible (and even more expensive), that surfaced only when I instructed my mechanic not to believe a word the log-books said but to verify everything with his own eyes. The authorities are looking into some of those too. Suffice it to say that the pre-purchase inspection I commissioned was a complete waste of time and money.

Of which you should be able to try to get back. So many people seem to believe the logbook is the see and be it all that sadly is often not the case, anyone can be creative on paper, however a wrong prop cannot be hidden.
I did one inspection and noted the prop had been replaced, querying it the owner and the company where totally honest and said it had been dinged sufficiently to have a new prop fitted some 5 years and about 150 hours before, asking did they shock load inspect the engine I got blank stares... Pointing out that if the damage was sufficient to scrap a prop and bearing in mind simply taxying through water or long grass that slows an engine requires it being shock loaded I was left with no option to tell the potential owner to walk away, which he did.
The engine might have been fine, but the worry of it letting go or the shock of an expensive overhaul bill later just wasn't worth the risk with his money.


..

Many years ago a UK company imported an overhauled Hiller from the states as they believed they could get a cheaper aircraft there.

To get a UK Cof A it had to undergo main gearbox inspection to comply with a UK AD brought in following an fatal accident to a UK aircraft.

The results of the said inspection were not pretty especially as the aircraft was "overhauled" and the CAA became involved.

They then asked the question who overhauled all the other components fitted including the engine.

Sadly the answer was the same company and the result was that the whole drive train had to be inspected and recertified at enormous expense relative to the value of the aircraft.

Caveat Emptor

blindsquirrel how long since the magnetos were serviced?

the magnetos have a set of points inside them. if the little points cam is worn it will gradually send the magneto timing out.
magnetos have an internal E setting which synchronises the points to the magnetic exciting as well as the magneto setup on the back of the engine.

if your maggies have been on for 500 hours get them serviced.
you will be amazed at the difference a set of magnetos in good fettle make.

my engine went from anaemic to book values immediately.

W8 -- to the best of my knowledge the mags are currently performing as they should, but many thanks for the reminder. Something to bear in mind at annual inspection time, certainly.