A little over a month ago I decided to do the Conditional on the SQ-2 a month early as I planned to take her to the Idaho backcountry last week. The compression was 60, 78, 78, 78. I could hear hissing in the exhaust pipe.
I bought a bore scope and took a look at the exhaust valve. I was pleased to find a symmetrical burn pattern with no hot spots indicated. I also saw some carbon buildup at one location on the valve and valve seat.
I had some TCP laying around and even though it's a lead scavenging agent I decided to give it a try. I doubled the recommended dosage and flew two tank fulls through the plane. Checked the compression again and got the same results. Borescoped the cylinder and saw exactly the same thing as previously.
I jumped on the Interweb to find the best carbon cleaning additive and found Chevron Techron to be recommended by BMW. That was all I needed. I bought a case from the nearest Autozone and doubled the recommended dosage. After two tank fulls I again checked the compression and it was up to 64, but I could still hear air hissing in the exhaust. I borescoped the valve and seat and the carbon buildup was gone.
I still didn't feel comfortable in taking her to the Idaho backcountry so changed my plans to take the 185 to Taos and fly-fish for four days. In the meantime I decided to first try staking the valve and if that didn't work then pulling the cylinder and lapping the valve.
Ran another couple of tanks of fuel laced with Techron and then pulled the rocker cover, removed the rocker arms, and staked the valve. Compression was now 68. Decided the best thing to do was to pull the cylinder and lap the valve. Ordered the appropriate parts and ran a couple of more tankfuls of fuel with Techron added.
Off to New Mexico I went, caught lots of rainbows and browns, and back home Friday. Went out to the hangar today to pull the cylinder and lap the valve. But first one more compression test. 75! Checked it again, 75! Woohoo! No open heart surgery required.
Techron is amazing! Oh, and I despise running ROP. When the SQ-2 needs a new engine she is getting fuel injection so I can run her LOP, which greatly diminishes carbon deposits.
If I had added Techron to the 185's fuel, which I didn't of course because she is a certificated aircraft and Techron is not approved for certificated aircraft, I would have seen the fuel gauges loose their minds and have all kinds of erratic readings. Of course if that had happened I would just revert to a calibrated fuel stick I use to visually check fuel levels. Had this happened, after a couple of tanks of just Avgas, the fuel gauges would have returned to normal. But of course none of this happened, it's all hypothetical.
From now on every time I change the oil in the SQ-2 her fuel tanks will get a dose of Techron. Awesome stuff.
