Lando143

Lando143

I'm New Here
Gentlemen,

I am looking for advice on how to proceed with a rough running O-320 (400SMOH) on my RV-6. Here are the symptoms:
1. During engine warm-up in the hold-short RPM=800
2. After oil was coming up to temp (80 degrees), engine started running rough
3. I assumed foul plugs and waited til oil temp hit 100 degrees to accomplish mag check and clear plug at high RPM/lean mixture.
4. As I pushed throttle up past 1200 RPM it was obvious to me I had bigger problems than a fouled plug because of the significant vibrations associated with the additional power.
5. CHT's were as follows: #1-260, #2-280, #3-275, #4-135. yes 135 degrees.
6. Compression check on #4 revealed 76/80 with a hissing sound of air escape.
7. Air was escaping out of the oil breather line I have clamped to Left Stack for burn off.
8. I plugged the breather line with my thumb and all hissing stopped.

My conclusion thus far is that I have ring issues. No sign of metal upon magnetic sweep of cylinder.

What advise would you guys (that are clearly smarter than me) have regarding pulling the cylinder vs more inspection/testing? Borescope worth the trouble?

I eagerly await response form the engine gurus!

Thanks All,

Hank
 
First don’t plug the breather for fear you could blow a seal! It sounds like your engine is fine; it’s going to hiss a little, preferably from the breather, there never 100% sealed, 76 is fine, it would probably run ok in the 40s. The problem is more then likely both plugs on your cold cylinder, clean and check them and try again, always taxi with the mix as lean as possible to avoid plug fouling.
 
Check #4 intake tube for leaks...... 2 hose clamps. Condition of rubber connector hose. And good seal at the head.
 
I agree with Russ on the compression - 76/80 is not indicative of ring "issues", it shows very healthy rings! Induction leaks are good to check for, and you might think about sticking valves - this could be Lycoming "morning sickness". I'd pull the rocker shaft on #4, take off the springs and see how the valves feel in the guides to see if they are smooth and free.

Paul
 
Ironflight said:
- this could be Lycoming "morning sickness".
Click to expand...

My first thought as well, and the time SMOH puts you right at the target when these things start showing up. 135CHT is not an induction leak - that rascal is simply not firing and you're seeing the warm air from the #2 cylinder in front for the CHT reading. You've either got a stuck valve or two completely fouled plugs.
 
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...Thank you all for your input. I will work off each of your recommendations and report back.

Thanks much,

Hank
 
Fouled plugs

I experienced two fouled plugs in the same cylinder once. Mechanic couldn't get them to fire at all on the bench. Replaced both plugs; problem solved. Hope it's that easy for you.

T.
 
Valves

If you perform the valve guide cleaning procedure recommended by Lycoming things might improve. With the number of hours on the engine it looks and sounds like a possibility to me. What type of oil are you using and how often are you changing it?
 
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