Low compression on one cylinder of my Lycoming IO-540-C4D5D engine..anything to worry about?

Continental has done extensive Tests of this matter, and they found out that even engines with compression as low as 20/80 did not suffer from ANY loss of rated power. The static leakage is test is something completely different than a running and hot engine – and cannot be compared 1:1.

OK guys, please educate me. Why low compression does not effect power? I know that after O/H my engine I have gained 5kts for the same fuel flow, T/O run was shorter and climb became much better/steeper for the same airspeed.

Thanks

Personally I would always worry about excessive cylinder leakage. It might, just might be a precursor to something serious.

I was going to say just what vic did: it’s quite quick and requires no special tools (eg borescope) to determine where the air is going, just your ears.

Finding out the reason for compression leaks should be quite easy to do: Set the suspect cylinder under pressure then listen at the exhaust pipe: No hissing – no exhaust valve leak. Listen at the carb intake: No hissing – no inlet valve leak. Then listen at the oil filler inlet: Hissing means leaking piston rings into the crank case. So this is no real mystery to do. Vic

@Achim … that “minusculus” change is on my agenda …

nobbi wrote:

My CHT probe cable is running to the old factory CHT instrument. The EDM700 is connected by some backpack type to that probe. As a result the EDM 700 shows a 70°F lower value than the other cylinders.

Even if that might be the correct approach from a certification standpoint, it doesn’t make much sense to get a precision temperature sensor device and then introduce a huge error with that piggyback probe. Just remove the factory probe, tie it up safely in the engine room and insert a new EDM probe. That’s safe and sensible and your A&P/IA will agree. Guess what I have done myself…

My CHT probe cable is running to the old factory CHT instrument. The EDM700 is connected by some backpack type to that probe. As a result the EDM 700 shows a 70°F lower value. This is also described in the EDM700 pilot’s guide.

AFAIK, that is not the correct way. Contrary to what has been posted the other day on the Socata owner group, I was told by Socata that they certified the EDM700 as “primary” for CHT so there is no longer any other CHT instrument (not so on the TB21 which is why that retains the factory CHT+EGT). So the original CHT+EGT gauge should not be present (and measuring a single cylinder is rather useless anyway). That is how my aircraft came from the factory.

What I don’t know is whether the above applies to all TB20 airframe serial numbers…

The EDM700 is not STCd by JPI as “primary” but it is within the power of a Type Certificate holder to certify anything as “primary”.

If Howard still has the original CHT gauge, that could however the explanation for the lower EDM #1 reading…

What kind of CHTprobe connection does the EDM700 use on your no. 1 cylinder? My CHT probe cable is running to the old factory CHT instrument. The EDM700 is connected by some backpack type to that probe. As a result the EDM 700 shows a 70°F lower value than the other cylinders. This is also described in the EDM700 pilot’s guide.