The International Cessna^® 170 Association

I was just playing around during a spark plug rotate. How do I check compression correctly? This is how I did it. I removed all leads removed the plug of the cylinder I was checking rotated to TDC inserted the adapter, held the prop (stood out of the arc). Then I adjusted the pressure on the left on my gauge to 80 then it would drop a little then I would bump it up and finally it would stabilze. Is it correct to keep bumping up the regulator pressure on the left side once the adapter is connected. I got no reading below 76. Which is funny because the aircraft has been sitting a while and its higher then it was at last annual.

Thanks

If I understand your discription it sounds about right. The regulated air should be adjusted to maintain 80lbs. Swinging the prop carefully a little one way or the other might have revealed even higher compressions.

Most of the time I find it more conveniant to have one plug out from all the cylinders while doing the test.

It's not unusual for compressions to float up and down depending on a lot of things such as carbon on the valve seat and ring gap alignment. This is why low compression one time on a cylinder doesn't mean the cylinder necessarily needs to be repaired.

cfiatzph,
As Bruce said it sounds like you are doing every thing right! When you say the A/C has been down for some time, How long? a week? a month? ect. It sounds like your valves and guides are in good shape! Aparently you have no broken rings or scared cyls. The reason for higher comp's can be varied, from technique, to residual oil in the cyls. In any case it isn't any thing to worry about. After all the test is just to find a real problem, and to monitor abroupt changes in a certin cyl. from year to year, or 100 hr to 100 hr.
brad

IAW Continental you must do the master oriface thing.

see the service buliten, and or the newest maintenance manual.

but you now must subscribe to the service to get their bullentins.

to quote.

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Tom,
Do you now need to do the master orfice thing with small bore engines? The last I read it was just for the large bore.
brad

TCMs compession check is too fancy for me. I just pull the top plugs, put my thumb on the plug hole, and have my buddy crank the engine over with the starter. If it blows my thumb off the hole, it must be good enough to fly for another year.

bradbrady wrote:Tom,
Do you now need to do the master orfice thing with small bore engines? The last I read it was just for the large bore.
brad

As I read it its all TCM engines.

but it is not required for part 91

blueldr wrote:TCMs compession check is too fancy for me. I just pull the top plugs, put my thumb on the plug hole, and have my buddy crank the engine over with the starter. If it blows my thumb off the hole, it must be good enough to fly for another year.

Thats a good one! Still laughing. Actually, just pulling the prop through I bet I can guess within a few pounds what the differential pressure is.

Joe

mit wrote:but it is not required for part 91

READ

§43.13 Performance rules (general).

(a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator, except as noted in §43.16. He shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices. If special equipment or test apparatus is recommended by the manufacturer involved, he must use that equipment or apparatus or its equivalent acceptable to the Administrator

I wish you were right.

I knew you where going to post that! That Does not mean you have to do service bulletins. We will have to beat it up when I meet you. And the compression test in particular.

In sum, the fact that "TCM requires a cylinder borescope inspection....." does NOT MAKE borescope inspection mandatory from a regulatory perspective.

Signed FAA big wig.

I can't figure out haw to cut and paste that darn thing!

Even though Continental is looking for subscribers a number of bulletins
are available without.
http://www.tcmlink.com/serviceBulletins/index.cfm

DIFFERENTIAL PRESSURE TEST AND BORESCOPE INSPECTION
http://www.tcmlink.com/pdf2/SB03-3.pdf

mit wrote:I knew you where going to post that! That Does not mean you have to do service bulletins. We will have to beat it up when I meet you. And the compression test in particular.

Next weekend, 6-7 Jan, we hve our FAA IA siminar I'll bring this up to the Continental rep, and the FAA GA supervisor.

I will ask you what you use as a list required by.

(c) Annual and 100-hour inspections.

(1) Each person performing an annual or 100-hour inspection shall use a checklist while performing the inspection. The checklist may be of the person's own design, one provided by the manufacturer of the equipment being inspected or one obtained from another source. This checklist must include the scope and detail of the items contained in Appendix D to this part and paragraph (b) of this section.


plus 43.D says

(3) Internal engine-for cylinder compression and for metal particles or foreign matter on screens and sump drain plugs. If there is weak cylinder compression, for improper internal condition and improper internal tolerances.

I think the FAA could make a pretty good case for doing a compression check, and if you are going to do the check, you are reqired to do it in the way that the manufacturer wants you to.

Just MHO