I need compression chart

[helihead01]

Hi all.
I order me a compression gauge, and want to monitor compression on my engines.
I have OS32 and OS50 helicopter engines.
Where can I find compression chart for all OS engines.

thanks

[DavidH]

I have tried using a compression gauge on these 2 stroke engines. Your readings are going to be all over the place nothing will be consistent. On a brand new engine , the readings will be different each time checked.
As for doing a leak by test, same thing. Some times it will hold pressure, sometimes it won't.

David

[helihead01]

SO the $35 gauge is a scam :) ??? :cheers
Anyone else???


Thanks David

[DavidH]

Which gauge did you buy?

David

[helihead01]

http://www.roguerc.com/product.php?productid=15555 << this one

[DavidH]

Yeah that is the one I thought you had. Was the same one I used when I was working in a hobby shop. The nitro car and truck racers find it useful since most of there motors are ABC. ( Alnuminun Piston in Brass Chromed plated sleeve). As opposed to most of the engines used in helis that are ringed.
It can be used as a gauge to see if the engine is wearing out the ring to cylinder fit. But as for a chart stating the pressure should be this much or that much. Don't think you will fine one. Like I mentioned in the other post. The readings will be different on two of the same engines new out of the box. Had some time when bored in the hobby shop. So we would do things like check compression on NIB engines to pass the time. LOL

David

[helihead01]

Sounds good.
SO if I test my engines, what pressure should it be?? Good pressure???
Give me something :)

[DavidH]

Well just for an example only.

Lets say when you check it. You need to take several readings at the same time. Write them all down. Add them up, then divide by the number of checks you made. That will be your average.
Lets say for example your average is 30PSI.

Now 1 month later you do the same thing and your average reading is 10PSI.
Then I would think need to check the piston ring for wear and see if it scoring the linerr.

The above is just examples. You will know the actual average readings after you do the test.

But in my opinion. IT is a useless tool for our application. At least from my experience with it. Others may not have the same results and thoughts. When I was in the Hobby shop. We did not reccomend to anyone they needed the gauge. We had one hanging on the wall for sale for over 2 years.<G>

David

[helihead01]

thanks.

[JimLerch]

I would also think that the conditions prior to the compression test would be important.

For instance, perhaps this might be a reasonable approach


Beginning with a room temp engine
Start the engine and allow to warm up
Shut down the engine the same way every time

Pinch fuel line?



Move throttle to closed?

Install compression gauge
Crank the engine with wide open throttle (either fuel crimped off or not, your call, but do it the same way every time)
Take three sets of measurements, find average.
For excessively anal retentive folks, perhaps repeating steps 1-5 three times, then finding the average of the average results, and for the "off the chart" anal retentive folks (like me), calculate the standard deviation.

Keep in mind, altering any of the steps will most likely change your results. So, finding numbers to make comparisons against is going to be hard, unless you make the measurements yourself, against yours or others hardware.

BTW, now I'm curious enough to consider getting one to play with :-)

[helihead01]

I did about 5 runs on room temp engine with throttle closed.
it jumped around min 85 to max 102.
Is this good numbers at all?????

thanks

[forjer]

Just in case you didn't know, compression tests and leakdown tests are to be performed with the engine at operating temperature so the proper clearances are achieved.