With any luck this one will be answered by TKG, RCIGN, PEreivers, RCBugman, Dave Wallace, and D. Hansen. You guys ARE the specialists!

I'm looking for a very good compression gauge that can be easily adapted for use on gassers ranging in size from 28cc to 150cc. The inlet must be adaptable to fit a wide range of plug openings. Currently the method we are using to gauge an engine's health is a max rpm comparison from one day to the next, but I believe an additional test comparing engine compression from one flight to the next would provide additional baseline data to detemine if an engine is up for another long flight or not.

Any ideas as to where a good gauge can be found? It doesn't have to be accurate to the fifteenth decimal point or anything like that, but should be accurate enough to provided consistent pressure readings and somewhat reasonable in price. Under $75.00 should put it in a range that I would want to deal with.

Thanks,
Pat

One was marketed to the model community. complete with adapters worked very vell
I gave mine away two days ago as I had not used it in years -
I will find out the specifics on it as the friend I gave it to got it with all the instructions - .

Hey Pat, try this link: http://www.lislecorp.com/tool_detail.cfm?detail=195 very good gauge. I have and older one I adapted to my needs. Also as I am sure you know you can look at the plug too to get real close on tuning etc. The guage will be more efficient detecting issues though IMHO.

I4C products has one and micro troque wrench.

Compression testers are kind of crude for what you want to do. If you want to determine the health of the piston/ring/cylinder, you should get a hold of a leakdown tester. It can also be used to determine if you have a crankcase leak, and the health of the bearing seals.

Thanks, guys. I'll look into all of them. Where I'm at we're kind of limited on what will make it from there to here, and what may be available locally.

Diablo, if yo could expand a bit more on the leakdown unit that could adapt to CM-6 sized openings I'd be appreciative.

Thanks again,
Pat

I'm with Tim, a leakdown tester is going to be the most useful tool for determining an engines condition. You'll have to establish a standard for the percentage of loss associated with your engines. Piston-ring seal on new engines will improve as the ring package takes a set so learned documentation is in order.

Hey Pat,

A leak down tester is used on GA piston engine stuff during inspections. We also used to use one on a buddies NHRA car for tracking purposes. On full scale piston aircraft engines used in General Aviation, an input pressure of 80 psi. through a metered orifice is supplied to the cylinder with the piston at TDC and the residual pressure is measured on the second gauge. Generally a loss of 20% is considered as the maximum allowable before finding and repairing the cause of the leak, usually exhaust valves on GA stuff.

They use a standard air chuck fitting screwed into a sparkplug adapter, so the difficulty would be in obtaining or building those adapters for the sizes you need.

Anyone have any part numbers, manufacturers, and points of origin? Sorry to ask for so much but you can't stay long on the internet out here and doing a search usually results in timing out. Oders alone are difficult in completing a transaction.

Thanks again to all of you.

Pat

Pat
www.i4c Products.com for compression gauge with 1/4x32, 10mm an 14mm adapters. A leakdown gauge is a standard hot rod supplie thing. SO try Summitracing. com ... pn PRO-66839

Other than multiple cylinder model engine - I don't see a real application for compression tester or leakdown on our little gassers
Unless every test is with same oil film, the results are all over the place.
power is NOT related to cold compresion.

Consider the Dykes ring -
My 160J ZDZ is almost impossible to move thru compression -just holding the hub
My 50's are pretty easy to turn and leak a fair bit but are real power houses
as long as the rings seal on the downstroke -you get full power.
On our hot rod engines - we used the gauges to se RELATIVE cylinder performance

It was never a secret when I broke a piston land or ring on a run-

one quick cycle of the starter motor and all was revealed .

Dick,

With all due respect, the application of the engines that I'm using and the ability to determine a rough condition from new has tremendous financila impacts on the mission. Enough that success or failure could possibly be determined. By itself, this would not be a reliable indication of anything, but comparartive rpm values between the last and the next flight, along with ground and in-flight telemetry in multiple areas, can possibly provide a go or no go decision when it comes to anticipated engine relibility/condition for the next flight. This IS NOT for modeling purposes.

Terry,

Thanks a bunch for the part numbers, I'll be going there later today to place an order.

Pat

If a number of engines are involved-so that some sort of comparative data can be developed - sure- knowing compression numbers, could be of value.
For most modelers tho - the device is simply something to putter with.
Not really necessary.

A gauge by it self for a one time use is about usless.... But keep a log and then there is value. If the data starts to show trends then its real valuable in making decsions.

When you are using a base of a hundred or more engines, each running for long periods of time, with an anticipated lifespan measured in the hundreds of hours, all with exactly the same gas/oil mix, you can see where a data base developed over a relative period of time could be useful to provide an indication of anticipated failure prior to an upcoming flight. That was about as much background as I'm both inclined and able to provide. Needless to say, this is not for "model" type engines but for those more "industrialized types. I'm still looking for the difference between the two, but I've been told that there is one

there is a big difference - but it is not "which is better " -It is which is more applicable to the task.
If I were dragging a insect net or trying for 1000 hours of full throttle operation I would not consider any of the popular aerobatic application engines.
Conversely----

One of the many valuable tasks a leak-down tester will allow one to perform and or determine is the condition of the bore in various locations revealing damaged areas that are not evident from wet or dry compression stroke tests/comaprisons. Conversely these tasks are accurate even with a “cold� engine. Remember with a leak-down tester we introduce outside pressurized air verses requiring the engine to mimic a pump with all its inherent shortcomings. The bore condition is revealed by introducing a regualted and maintained air resource; lets say 100psi while noting the percentage of losses. subsequently we slowly rotate the engine through its stroke, notable increases in losses indicates damage in the specific area (perhaps the bore is galled, Nikasil or chrome plating is damaged or there is an imperfection in the bore i.e., pits-gouges, maybe out of round or who knows what?

Other problematic areas become obvious too, such as gaskets, oil seals and crankcase leaks. None of the above for the most part is notable with a compression tester.

Thanks for you input Dick. I'll inform the engineers that the engine we've been using reliably for the last 25,000 hours is clearly not up to the task....... I send them to you for a greater knowledge base and ideas as to what would work better.

Your comment is completely unwarranted

Boys be nice to one another, or RCPILOT will wrap your knuckles.

The moderator may do as he wishes
The response I got for noting there were differences in engines - was completely unwarranted .
This business of 25000 hours etc.. is really a bit over the top.

We all have bad days. If I were there, every day would be bad[]

Is that one engine with 25,000 hours on it, or 250 engines with 1,000 hours on each, or 25,000 engines with one hour each? And how many hours do they go before a rebuild? I hope I don't need Robert Gates to declassify this info.

Me has a sneaky suspician that our guys lost a rather expensive aircraft due to engine failure and had to go "fetch" it out in the sand. [:'(]

I'd be looking for a compression tester or leak down device too. The only way to predict future performance is to keep records of PAST performance.

I'm out of this one because I couldn't tell you where to get either of those devices or how to accurately use them. Try and play nice guys. [8D]

Pat,

Rather than use a compression tester or a leak tester which would give variable results based on the amount of oil in the engine to seal the ring and/or the speed you spin the engine for compression, how about using a "calculated load" and log the performance of the engines over time?

For example, you have a good feeling for the engine performance from your standard prop that you fly with. But what you need to know is whether the engine is capable of performing under an increased load. Pick a prop which has 15-25% more load and measure the max rpms on a "new" engine as a relative reference. Then test the engines on the uavs with the same prop. From the initial test and the subsequent measures, you should be able to estimate the condition of the engine relative to the "reference engine" and chart the declining performance over time. The critical "rebuild or replace" decision point would have to be developed over time.

Testing under load would be a more consistent measure than a compression test.

Elson