Annual Compression Tests

[nwawingman]

Just wondering what brand compression tester other builders have used to do compression tests at annual on an AeroVee. Is anyone using any of the models they sell at Harbor Freight and if so what model? Also any other hints and suggestion you can offer around doing a compression test would be greatly appreciated.

Thanks!

[wlarson861]

Don't bother with the Harbor Freight model. You want one that is designed for aircraft. you want to be able to charge the cylinder to 80 psi and gauge the leak down. Usually expressed as ##/80 . HF model works at about 15 psi which is probably ok for cars.

[Major4567]

I recently purchased the ATS leak down tester from Aircraft Spruce. It seems to be a well made piece of testing equipment. You will probably have to purchase a set of spark plug adapters. I purchased mine from Amazon. When you do the leak down test make sure you hold onto the prop because if it is not at TDC, the prop will want to spin.

Steve Stahl
Jab 3300

[Rynoth]

I use the following from Aircraft Tool Supply. Works great. The adapter fits in the Aerovee plugs.

2E DIFFERENTIAL CYLINDER PRESSURE TESTER (18MM) 1 $69.95 $69.95
12MM ADAPTER, 2E PRESSURE TESTER 1 $8.95 $8.95

[SonexN76ET]

Have any of you had to lap your valves to improve your compression?

If so, how difficult was it? Did lapping the valves help?

Thanks,

Jake

[Bruce593SX]

Also, remember a proper leakdown test is done with the engine HOT, testing a cold engine can result in lower then actual numbers.

[Sonerai13]

Also, remember a proper leakdown test is done with the engine HOT, testing a cold engine can result in lower then actual numbers.

Keep in mind that pulling spark plugs out of a hot VW head can result in thread damage. Food for thought.

[Rynoth]

Also, remember a proper leakdown test is done with the engine HOT, testing a cold engine can result in lower then actual numbers.

Keep in mind that pulling spark plugs out of a hot VW head can result in thread damage. Food for thought.

How does aeroconversions suggest that we do compression testing on an Aerovee?

[nwawingman]

I think I pulled my heads off of a well running AeroVee without really needing too.

The manual says to perform a leak-down test at Every annual and you should see between 60 and 80. I forgot that Bruce said to do this on a hot engine. :( Anyway. this is what I was seeing using an ATS Differential pressure tester on a cold engine after I set valves and torqued the heads. I had the intake manifolds off also. 1 -65lb. 2-4 ranged from 25-30 lb. I could hear noticeable air in both the intake and exhaust. Again this was on a cold engine and the spark plugs all looked good with know signs of issues on a well running AeroVee. It too bad that I forgot Bruce's comments before doing the test and called Bob and Charlie after I already pulled the heads off. I keep reminding myself, this why I like working on my own plane. I am always learning more about my aircraft and If something is done wrong, there is know one to blame but myself. From some more research I have done along with advice from Bob and Charlie, I will do my test like this next time.

This is just my thought going forward based on this experience, as I am clearly not an expert in this area. For now my heads are in the shop getting the valve cleaned and re-lapped. Now I can say II know what the insides of my heads and pistons look like with a 100 hrs on them anyway. :)

Step 1 - With a cold engine remove and check plug condition of all bottom spark plugs.

Step 2 Put anti-seize compound on plug treads and install with a snug fit. Not fully torqued.

Step 3 Run engine enough to get heads and cylinder to operating temp. Then let it cool enough that I can do test without burning myself.

Step 4 Remove bottom spark plugs and screw on standard single gauge compression testers for each spark plug opening and run the starter for 5 sec or so to get a good pressure reading. I read that all of your cylinders should be within 25% of each other. So take your highest pressure reading and multiply by .75 to see the low end pressure limit. (Example 125 X .75 = 94) for this example all cylinders should be within the 125 - 94 range and the closer they are together the better.

Step 5 if needed use my ATS Differential pressure tester to help locate where the issue may be.

Step 6 sleep on it and call Sonex or a few Sonex builder builders for ideas and thoughts before you take anything apart.

[Bruce593SX]

My comments of doing the leakdown on a hot engine are from the Lyc/Continental world.... I am a bit wary of the process on VW from the other comment about removing spark plugs from a hot VW damaging the head.... Perhaps remove the planned spark plug cold, give a nice fresh small dab of anti seize then torque to the new (now lower) setting of 12lbs before starting the process?

YMMV... Mine's not running yet but will soon-ish .... Having a 172 and a camper down on the beach within 2 miles of the airport has severely curtailed my weekend Sonex progress....