CHT

[Carl Froehlich]

Colin,

This just does not add up.

Based on your data, I would suspect timing but you ruled that out. Here you may want to check the timing setting with a light - just to make sure.

A local RV-7 guy was flying around for a long time with CHTs like yours and he did a boatload of cooling mods to try to fix it. His timing was verified several times by more than one person, but never with a light. The light check showed timing at 40 degrees (bad electronic ignitions, both sides). Ignitions fixed and his CHTs are now in the 360-380 range.

Carl

[scottmillhouse]

Originally Posted by 49clipper

There is also an AD out on that if the drift occurs within 5 hours of timing. Just for you reference.
Jim

Actually I believe it is Service Letter L264A. Lycoming confirmed the mag was set correctly at the test cell run. When told about the timing drift in only 10 hours, Lycoming did not recommend flight with the mag and approved a warranty claim for a new mag. They felt the drift would continue. So far their distributor has been unresponsive on how to do a warranty swap so I'm flying and will check timing ever 5 hours.

For my installation I have noted that if I had the boost pump off during take off the CHT will climb faster and higher. I assume the engine pump alone can not pull the maximum fuel flow needed during a full power climb.

[WingsOnWheels]

Carl,

I verified TDC on #1 and it aligned with the TDC timing mark. I have check the mag-to-engine timing at least 3 times so far. The engine starts and idles fine, no kickback. Hard to imagine the timing could be that far off. However, it doesnt hurt to check.

If I had the harness timing order wrong I think the engine would have a lot of other issues. The mag harness is modified and running auto plugs. Everything else is stock. I do however have a hesitation around 1400rpm, which is on my list of things to solve.

I have calibrated my fuel flow sender. At last check it was within 0.1 gallon over 20, so I think the fuel flow is accurate. Since all 4 are similar temps, I think that rules out a sensor problem.

One thing to note, surface OATs here are 90-100 degrees right now. However, I have been flying early and high to stay out of the heat.

[Bavafa]

I was going to suggest what Dan has suggested. Look at your baffles at the bottom portion of your cylinder and make sure air can not scape easily on the sides and it is force to travel thru the fins all the way to the very end.

[Carl Froehlich]

Colin,

While I have no issue with the recommendations on engine cooling checks, your numbers are still way out of line for an engine with the right timing and right fuel flow, regardless of potential problems on the engine cooling air side.

I suggest:
- Verify timing with a light.
- If good, do a couple of test flights with standard aviation plugs. Perhaps something weird is in play and the cylinders are lighting off early.

Carl

[Bavafa]

Originally Posted by Carl Froehlich

Colin,

While I have no issue with the recommendations on engine cooling checks, your numbers are still way out of line for an engine with the right timing and right fuel flow, regardless of potential problems on the engine cooling air side.

I suggest:
- Verify timing with a light.
- If good, do a couple of test flights with standard aviation plugs. Perhaps something weird is in play and the cylinders are lighting off early.

Carl

Colin,
How does one check timing with a light? Is this the same process as with a car? I have never done it with a plane and if it is as with a car, it will scare the *&%$ out of me to be so close to the turning prop.

I know many people do it, just never seen the process.

[Ted RV8]

Mehrdad, Correct you do it like a car and it is very scary!

Helped a guy installing an electronic ignition and needed to verify timing at a higher rpm. Very,very scary and doubtful that I would ever do it again.

[Carl Froehlich]

Originally Posted by Bavafa

Colin,
How does one check timing with a light? Is this the same process as with a car? I have never done it with a plane and if it is as with a car, it will scare the *&%$ out of me to be so close to the turning prop.

I know many people do it, just never seen the process.

Look at the back of your flywheel the next time you have the top cowl off. The back has timing marks just like the front, just clocked in a different place. The reference line is the engine case joint. Easy to line up via timing light from behind the prop. DO NOT DO THIS USING THE FORWARD TIMING MARKS!

But - still a little scary. We take an extra precaution to put a strap around the guy doing this so that if he slipped he would not fall forward.

Amazing that this check has found more than one timing problem.

Carl

[Bavafa]

Originally Posted by Carl Froehlich

But - still a little scary. We take an extra precaution to put a strap around the guy doing this so that if he slipped he would not fall forward.


Carl

Thanks but no thanks

[WingsOnWheels]

Have to make sure you have a very reliable helper. I have adjusted the carb on a running engine many times. Just dont end up in the sausage maker.

There is no way for me to test with standard plugs, but I will try a different heat range.