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
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| Author: | Rich Brazell [ Mon Feb 17, 2014 12:18 am ] |
| Post subject: | Compression test |
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
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| Author: | jrevens [ Mon Feb 17, 2014 12:34 am ] |
| Post subject: | Re: Compression test |
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. |
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| Author: | fytrplt [ Mon Feb 17, 2014 7:20 am ] |
| Post subject: | Re: Compression test |
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. |
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| Author: | Fraser MacPhee [ Mon Feb 17, 2014 4:01 pm ] |
| Post subject: | Re: Compression test |
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.... |
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| Author: | Rich Brazell [ Mon Feb 17, 2014 5:39 pm ] |
| Post subject: | Re: Compression test |
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
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| Author: | david read [ Mon Feb 17, 2014 9:26 pm ] |
| Post subject: | Re: Compression test |
My mechanic tells me you can drop a plug twice but the second time has to be in the trash can. |
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| Author: | Rich Brazell [ Mon Feb 17, 2014 11:04 pm ] |
| Post subject: | Re: Compression test |
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
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