Significant loss of power?!?!? Timing? Cam?

[GEM930]

I'm having an issue with my recent engine swap from an o-320 with a fixed pitch to an o-360 with a constant speed. Initially the increase in performance was what I'd expected (better rate of climb ...1600+ , better top speed ...almost 180 kts at 5000'), but recently I've noticed a substantial decrease in performance .... Only seeing 800-1000 ft/min and top speed of 144 knots true). I initially thought I was having some instrumentation problems, until I noticed I was only getting 2490 rpm on climb. I adjusted the stops to get 2700 and took off next to a friend with the same engine/prop combo in an RV4. Now I know a similarity equipped 4 will always out perform a 6A, but this was embarrassing! He said that to stay with me at take off he was at less then half throttle. Our indicated speeds were within 2 knots once level at around 3000'. He was at 19" manifold pressure I was at 27" (wot indicating 144kts). I had to leave town immediately after this run (possibly too embarrassed to show my face at the airport ) , so I had no chance to pull the cowl and check things out. I have been unable to get it out of my mind. I can come up with two possibilities... Timing has slipped and is way retarded or the lobes on the cam on my new rebuild have gone the way of the dinosaur. A few things about the engine.... It was rebuilt by an a&p and sat pickled in a dry climate for 9 years before I got it. I did find some very mild corrosion in the engine upon pulling the valve covers and a few small spots on the timing gears, hence my concern that the cam may be grinding itself flat. As far as the timing goes, the engine is equipped with an electronic ignition and fuel injection system. The timing is picked up using a unit made by Electroair (MTH) that mounts to one of the mag locations. It is adjusted the same as any regular mag. I'm thinking (hoping) it's lose and has slipped. I'm sure some of you are thinking fuel after I mentioned the efi. I have a wide band O2 meter (yes I know the life span is shortened running 100ll) and it was indicating 10-10.5 to 1 on climb and 12.5-13 to 1 during the 144 kts run. Additionally my fuel flow was indication 17 gal/hr on climb and 14 gal/hr on the 144kts run. The computer uses manifold pressure to meter the fuel, so I'm thinking with these numbers timing is likely the culprit. Have I missed another possibility? I know I should just check the timing and then the filter for metal, but I will not be able to get to the hangar for a couple more days and this is driving me crazy! Any ideas????

[Mike S]

Check the prop, throttle and mixture cables, and the lever arms too, to be sure you are getting full travel in both directions.

[GEM930]

That's a good call.... I did check the prop cable when I adjusted the stops, but the throttle would certainly be worth looking at. The fuel flow, however, would tend to indicate that it is getting all its travel, but I will check... Thx!

[rv6ejguy]

If the timing was that far retarded for this level of power loss, your EGTs would likely be really high.

I am thinking the cam has gone south. Put a dial indicator on the rockers and check lift against the specs.

[GEM930]

Oh man.... I hope your wrong. Ill check my data, but I do remember seeing higher Egts. 1600 I think. I did not pay much attention as I thought the actual numbers were not important on non turbo engines. What you are saying makes sense if the valve is starting to open before combustion is complete. Even if my cam is ok now I might have to deal with burnt valves. 😳

[GEM930]

Another thing I forgot to mention is that noticed a larger than normal rpm reduction when doing the mag check. Normally, I remember only seeing about 50 rpm on either set of plugs, but on last couple flights it seems like it was around 100rpm drop. Not sure what that could mean???

Thx for the responses!

[turbo]

check the oil filter for metal?

[DanBaier]

Originally Posted by GEM930

... noticed a larger than normal rpm reduction when doing the mag check...

You don't say over how many hours the problem has developed - a cam wearing out can take hundreds of hours before you see the results you're citing. The quote suggests an ignition issue. There's enough going on with your setup (EI & FI) that you need to go through it completely to be sure in spec.

The conventional compression test can tell you if the jugs are leaking but says nothing about the cam. To get an idea of the ability of the engine to breath (including the condition of the cam), you could use an automotive compression tester (taken with engine turning - disconnect all plugs and remove the top only for testing cylinders). You can do some offline math to get an approximate comparison of the readings on one to the other. If they line up, and there is no steel in the oil filter, the cam is not likely an issue.

I'd also check the tach for accuracy - you mention adjusting the stops (on a fixed pitch Lyc - that doesn't seem like it should be necessary).

Dan

[GEM930]

The new propeller is a constant speed. The engine only has 30 hours on it and problem occurred over last 5 hours... Just did compression all jugs 79/80. Home early gonna go to hangar now!

[rv6ejguy]

Only 5 hours since you had a big performance drop is unlikely to be the cam. Would normally take 50+ hours to see this kind of performance loss and it would be very gradual.

With the serious loss in speed and climb performance and the high fuel flows (assuming they are accurate), despite proper AFRs, clearly you are way down on power. Would be hard to flow this much fuel if the cam lobes were seriously trashed. The engine just wouldn't make enough power to have that kind of fuel burn.

If EGTs were that high with good AFRs in the 10s and 12s, timing would appear to be way retarded. This would cause most of the symptoms you describe. Check for something that has slipped with regards to the pickups. This is a reason why I prefer crank triggered ignition systems- as long as the crank/flywheel is attached to the engine, timing can't move.