Thorp Air Command - T18.net

Does the engine need to be run to normal op temp to do a diff. compression test ? EAA site indicates it is not required as I viewed the video . Other links say a "warm" engine/rings is best ?

RB

You can do it either way... you may find that everything seals up a little better, with warm parts at the proper clearances & a fresh coat of oil on everything if you do it after a run, with a warm engine. You'll probably get a little better/higher reading that way. I think that the most important thing is to do it the same way each time, so that you're comparing apples to apples.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

I agree with John. I do mine cold as it reduces the tendency to drop a spark plug (hot!) when done warm. If a cylinder comes up short, I will run the engine and try again. Remember, a compression test is only a screening test; not decisive. Several articles by Mike Busch in Sport Aviation have addressed the meanings of the results of compression tests.

Lastly, NEVER try to do a compression test alone. We have a fellow on the field who nearly bled to death when he was struck in the shoulder by a blade as he tried to check a C-150 alone. He has limited use of that arm to this day.

_________________
Bob Highley
N711SH
SN 835
KLAL

Good points from Bob - I check comps at conditional only by and large. I checked at oil change once just to get a comparison. When I change oil, I always fly the plane to get the oil viscosity as low as possible before draining it, and after I check mags off and can see the keys on my dashboard, I pull the prop through (as though it were hot) while the oil is draining - you can tell if there is an abnormally low compression in a cylinder that might need an additional check.

Since I always check and rotate my plugs at oil change, I handle them hot. A piece of carpet under the drop zone is a smart move. In case anyone is not aware, dropping a heavy REM 38/40 plug on a concrete floor pretty much assures a cracked ceramic resistor.....and hence a now useless plug.

I consider Mike Busch one of the greatest resources of the aviation community, other than Bob of course....

_________________
Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)

All good points guys ! I was either told or read somewhere if you drop a plug on the deck , you might as well throw it away . Carpet might work ?

RB

My mechanic tells me you can drop a plug twice but the second time has to be in the trash can.

Does he drop the plug or you ? If I drop the plug and new one goes in ! How do you know if the mech drops the plug twice ? I guess the old saying still stands true..."Just do the right thing if no one is looking !"

RB