Cotton Waiex 191 - N191YX

[Bryan Cotton]

No photos. I was going to do my flight review in the Waiex today. Did the ground portion and then on startup the airplane ran like crap. Right aft EGT was low. So I have some troubleshooting to do. The good news is it seems to be a hard failure and I know what cylinder. The last few flights we had a slight miss in some conditions, like climb on the primary only. But we could only feel it, not really see it on the gauges. It did smooth out above 1400 RPM today but that's not good enough.

Was going to switch to the C140 but the winds came up over the flight school limits for the airplane.

[daleandee]

No photos. I was going to do my flight review in the Waiex today. Did the ground portion and then on startup the airplane ran like crap. Right aft EGT was low. So I have some troubleshooting to do. The good news is it seems to be a hard failure and I know what cylinder. The last few flights we had a slight miss in some conditions, like climb on the primary only. But we could only feel it, not really see it on the gauges. It did smooth out above 1400 RPM today but that's not good enough.

Was going to switch to the C140 but the winds came up over the flight school limits for the airplane.

Good call on not flying a (possibly) broken airplane. As for the engine ... you and your son have been working it pretty steady from day one so it likely is just wanting you to show it some love and attention ... 8~)

Dale
3.0 Corvair/Tailwheel

[Bryan Cotton]

Cylinder #3 measured 80/12 on the leakdown tester. The others ranged from 72-80. On the suspect cylinder, I found these things:
1) Secondary plug was heavily lead fouled
2) Lots of lead fouling in the combustion chamber
3) We were out of adjustment on the exhaust valve, in the loose direction.
4) When I took the rocker arms off, I got the compression up to 80/40 or so.

I'm thinking I have a valve seat recessing. We are going to pull the head and investigate. Also I've proactively ordered a new head.
We will likely be driving to Oshkosh this year.

[Area 51%]

If the seat were receding, I would think the adjustment would get tighter and not looser. And a "tight" valve is an unhappy valve. .

[Kai]

Nope,

When the seat loses its grip in the head, one would think that the fairly hefty valve spring(s) would pull both valve and seat back into the head recess, reducing the clearance. Alas- no such luck!

On the contrary: owing among other things to carbon deposits and heat deformation, the seat will slowly start to work its way out of the head recession, taking the valve with it and thus increasing tappet clearance. Until the day comes of course that you will have far more serious issues to worry about.

Sorry.

[Bryan Cotton]

If the seat were receding, I would think the adjustment would get tighter and not looser. And a "tight" valve is an unhappy valve. .

The adjusting screw is turned all the way out. The valve to rocker clearance is tighter. In the current state I need a shorter pushrod.

[Kai]

Interesting

Are you sure an overheated valve stem has not increased a few fractions in length? We´ll see!

[Bryan Cotton]

Interesting

Are you sure an overheated valve stem has not increased a few fractions in length? We´ll see!

That is absolutely a possibility. But what gets hotter - the valve stem or the edge of the valve? I would think the edge. Yes we will see and I'll report what we find.

[Area 51%]

The adjusting screw is turned all the way out. The valve to rocker clearance is tighter. In the current state I need a shorter pushrod.

How long are your pushrods? I have a set that are 10 31/32in tip-to-tip if you think they might work. WARNING...WARNING...WARNING..They have aluminum shafts.

[Kai]

[/quote]
That is absolutely a possibility. But what gets hotter - the valve stem or the edge of the valve? I would think the edge. Yes we will see and I'll report what we find.[/quote]


Since the stem is the longer part I would speculate that the elongation would be in this part of the valve. Anyhow, fixing this is just fixing the symptom. The root cause is what matters: getting to grips with head overheating.