Compression Test

[mike.smith]

One of the DAR checklists I have says to have engine compression test information available. I don't recall seeing any suggestion from Sonex about doing a compression check except at the annual condition inspection. I also don't own, nor know anyone who does, the equipment to do so. Is this something that others have had to do for inspection?

Mike Smith
#439

[MichaelFarley56]

To be honest Mike, nothing was ever said about a compression check during my inspection. I didn't use a DAR though; around my home, the FSDO staff does most of the airworthiness inspections. Unfortunately, one of the challenges I think we face on these inspections is the variation on inspectors, as well as the day, the airplane, etc.

Just as an example, I had the same FSDO inspector look at my Waiex that my father had several years before when his Wheeler Express was inspected. Same guy...one airplane took 30 minutes, while the other took 90. The same things were checked, but to different levels of detail. No big deal but it is somewhat frustrating...

Again, I've never worked with a DAR so your experience may vary...

[daleandee]

It wasn't a requirement for me. I did find what you are referring to. An example of the ASI/DAR "Amateur-Built Airplane Certification Inspection Guide" is found here:

http://members.eaa.org/home/govt/issues ... rplane.asp

and it says,

Ask for a record of the differential compression/cylinder pressure test to determine if it meets specifications of the engine manufacturer. If any cylinders are below specifications, then don’t issue the A/W certificate until repairs are made.

This is not regulatory but is a guideline for them to use. Still, if you balk at his request he will no doubt stand firm so either you will have to do a differential cylinder compression test, or find another DAR to do your A/W inspection.

Here are a couple of Cylinder Compression Testers to consider:

http://www.skygeek.com/eastern-e2a-comp ... ester.html

http://www.amazon.com/OTC-5609-Cylinder ... ure+tester

You might as well buy the tester as you will need it next year and you will know how to use it by then ...

Dale
N319WF

[Sonerai13]

Typically the inspector will only ask for a compression test if the aircraft incorporates a used engine, especially if the engine has many hours on it. If the engine is brand new the compression test isn't going to tell us a lot, so why worry about it. I have never seen an inspector request a compression test on a new engine, and I never requested one when I was doing DAR inspections.

Having said all that, the point was made that these things vary from inspector to inspector, and that's very true. So the old "your mileage may vary" applies here. If your inspector tries to insist on a compression test on a brand new engine, try to reason with him/her that it's not going to be very valid until the engine is well seated in and has some time on it.

Good luck!

[kmacht]

Mike,

Talk to Joe. I'm pretty sure he is just looking for a normal compression test not a leak down test if I remember correctly. The point of it is just to set a relative baseline for your particular engine so you can see how it is doing during each annual. It isn't in the checklist to meet a certain manufacturers spec. Most autozone and advance autos will loan you a compression tool that screws right into the spark plug hole. You can also buy them pretty cheap from harbor freight. If all else fails let me know and you can borrow one of mine. Finally. You might want to do two tests. One with the engine cold and one with it warmed up. You will get different readings for both


Keith
#554

[radfordc]

Mike,

I'm pretty sure he is just looking for a normal compression test not a leak down test if I remember correctly.

The quote above says "differential compression/cylinder pressure test"....that's a leak down test.

[radfordc]

Here is a great article that talks about the myths and facts of compression testing: http://www.avweb.com/news/savvyaviator/ ... directed=1

[radfordc]

Here is one for $60 that will work just fine for a VW engine: http://www.ebay.com/itm/Engine-Cylinder ... 35d1585c5b

You have to do a test at every annual inspection so you will need it anyway.

[mike.smith]

Mike,

Talk to Joe. I'm pretty sure he is just looking for a normal compression test not a leak down test if I remember correctly. The point of it is just to set a relative baseline for your particular engine so you can see how it is doing during each annual. It isn't in the checklist to meet a certain manufacturers spec. Most autozone and advance autos will loan you a compression tool that screws right into the spark plug hole. You can also buy them pretty cheap from harbor freight. If all else fails let me know and you can borrow one of mine. Finally. You might want to do two tests. One with the engine cold and one with it warmed up. You will get different readings for both


Keith
#554

I already emailed him. I just wanted to know the experience of others.

Thanks,
Mike
#439

[mike.smith]

Here is a great article that talks about the myths and facts of compression testing: http://www.avweb.com/news/savvyaviator/ ... directed=1

Yes, I read that recently. I really like his approach to facts, data and common sense. Some call him a heretic for it ;) For now I'm just concerned about passing an inspection without any surprises.

Mike