fisher1648

Can you use a compression tester like the ones used for Auto and motorcycle engines with reliable results ? What ballpark compression should I see for a typical 50CC aircraft engine - specifically a near new Brison 3.2.

Thanks, Eric

pe reivers

Is there a need to use devices, when the best sensory equipment is available with every hand start?
I rather trust my feeling of an engine than mere compression readings, though they may well correlate on compression values only. The feel of an engine however tells a lot more than that.

fisher1648

I understand your comment but, for me, gradual degradation is somewhat hard to detect and I dont fly it every weekend so I forget the "feel" sometimes. I'm not good at "it seemed easier before "....I can talk myself into anything []. I'm sure I'd notice a sharp decline but I feel more comfortable using a tester if possible. Plus, I'm no engine guru (it's my first gasser) so it's an easy diagnostic aid, if it's applicable.

If I notice a lack of power or hard starting it would be nice to be able to correlate that to poor (or lesser than before) compression measurements. Nothing necessarily absolute but just comparitive.

pe reivers

In that case, Yes, you can use a compression gauge to test the condition of your engine, though I do not know anyone who does it on two stroke engines.
You can take your plane to a garage and have them test compression.
The engine must make several revolutions, so you will also need an electrical starter that is up to the job at hand.

tripp3d

Not familiar with Brison but the Stihl 2 strokes I sell generally have in the neighborhood of 90psi or better, but will run on anything over 70

WRK

My Feedback: (2)

yes you can use a compression tester, you should also turn over the engine several times if you are just flipping by hand, it will usually take several flips before the gauge stops climbing. Choke engine to get the cylinders a bit wet before you sftart taking readings, this will give a more accurate indication.

The numbers you see will vary from engine type to engine type, some types will show as low at 70-80 pounds and some will show 120 or more pounds, the most important thing is that if you have another engine of the same kind that runs well to compare the readings with. A variation of 10 pounds between similar engines is not unusual, a hot engine will usually show lower numbers than a cold engine.

You may find that if you flip the engine backwards compression readings will be higher, this is not unusual with ringed engines. If you notice higher readings flipping backwards then compare both engines this way.

excaliber

120 lbs is a very good value and is used by some mfg's as a new engine standard. one way to tell if your not getting the compression is if you have to use an electric starter to spin the engine faster. loss of compresion=look for cyl.head gasket leaks.loose spark plug.front seal leak or any gasgit that is used on the crankcase.

Steve Sanford

The compression readings will vary with rpm changes, ie: battery condition with electric starter. STeve

rmh

I have a "model aircraft engine compression gauge"
Probably the least used tool in the box.
It works -but readings vs engine performance seem to have nothing in common.
The oil quantity in the cyl wil l slew the readings all over the place .
The engines will never feel like a glow ABC setup
I got my gauge as a gift - that's why I still have it .

Steve Sanford

Has anyone ever used a leak down tester on their 2 cycle engines? A friend of mine bought her husband a chainsaw from the pawn shop the other day and asked me to check it out for her. Pulled the cover off, no air filter, pulled the plug, cyl is scratched up bad, saw will run, but very hard to start. Checked compression, highest reading was a surprising 120lbs. My koritz, echo chainsaw conversion engine has 160lbs. Leakdown test on the Koritz showed 8 percent leakage, leakdown on the poulan 42 chainsaw was 60 percent. I checked my wifes chain saw, puolan, 6 percent leakage, 155 lbs comp, and my ryobi 31, 5 percent leakage.
If you check it with a leakdown tester, take note of this, if you turn loose the prop it will spin like its got a starter motor on it!!! Best thing is to take the prop off. Steve

dirtybird

My Feedback: (5)

I got a tester with a 1/4x32 connector from Tower hobbies. I had to specify I wanted the higher test range for gas engines.

fisher1648

I used the standard Sears automotive comp tester and just fliped the prop as hard and fast as I could until the reading stopped increasing.....It maxxed out at 110 PSI....not bad for hand flipping.

As long as I repeat the same technique using the same tester I think it should provide comparitive readings over time.....we'll see.