The Stovebolt Site Forums The Shop Area Engine Shop Compression/Leakdown testing

Anyone bother with a leak-down test on the old bolts or are you
satisfied with just a compression test?
Denny Graham
Sandwich, IL

Only if one has access to the tool. You can get a rubber tipped blow gun and shoot some air into a cylinder to verify whether you have a valve, ring or head gasket problem by listening for the air noise. Becareful of the engine rolling over when you apply the air,
Scott

A leak-down tester will tell you much more about an engine than a compression tester ever will. You can get good ones on eBay cheap.

I have one I made to use for the annual inspections on my Lycoming. I was just wondering if anyone ever went to that much trouble with these old timers. My engine sounds good and I can’t see doing a major on it if it is basically sound. Think I’ll give her a good physical before I put her to bed for the winter. That would be one less thing I need to do when I do the frame up next year. It only has 50k on it and there is a good chance the the old gal’s engine still has a lot of life left in her. More than I can say for myself!
Denny Graham
Sandwich, IL

Denny, the leakdown test will indeed show a lot more that just a compression tester, but, the 235 is not a sophisticated engine such as the Lycoming aircraft engine and that much information is not necessary on the 'bolt engine. If it has enough compression to run and doesn't smoke a lot, it will be fine. The old 'bolts are pretty bulletproof so don't worry.

Yep 32, that's probably pretty true of the inline Chevy six. Anyway, this was just a thought that popped into my head while going through the toolbox. After all you don’t really need a dwell meter, timing light or even a feeler gauge to tune up one of these basic engines, you can do it by eye and ear. I kept many a jeep running that way while in the service.
But it’s a misconception about the Lycoming light aircraft engines. After spending 5000 man hours building the plane and then flying and maintaining it for a few years, I soon found out that the light aircraft engines are just like any other engine, in fact they are pretty basic and use rather antiquated technology, more like a tractor engine than anything else. Even the mag looks like it belongs on an old Farmall, The newer auto engines are decades ahead of the light aircraft engine.
The Leak Down test can show up several other problems that a simple compression tests can’t. Such as, leaks into the coolant system, worn ring lands, and of course ring/cylinder ware and it can differentiate between intake or exhaust valve leakage.
Denny Graham
Sandwich, IL

Right on Denny, Lycoming, Continental, Franklin light aircraft engines are very old unimproved technology. They typically turn slow (Cont. O-200cid, 100hp@ 2700 rpm) with comparitively large displacement ( Lycoming O-320cid 140, 150,160hp). I can't recall any small airplane engine that turns more than 3000rpm. By the way what kind of airplane is your Lycoming installed in? Weeds

Pitts S1D, 160hp, IO320. Been locked up in the heated/dehumidified hanger for 18years, I can't afford to fly it anymore and I’m ready to put it on the auction block and move on to restoring an old truck, more my speed now days. The RPM of the AC engines is really limited by the prop’s tip speed. To much more than that and the tips go supersonic and loose efficiency. The buckets in a 360ci 4 cylinder are pretty big so that is another factor in the low revs. They make lots of torque though and I say again, a lot like a tractor. Being air-cooled they are real gas hogs also, they have stayed away from water cooling to keep things simple, cooling is just one more system to give ya a problem.
Denny Graham
Sandwich, IL

that much trouble? I´m totaly gauge nut.

I have a vintage sun motor tester, several syncro testers, 2 oxygen sensors in the dual exhaust (and a Lambdatool LM1), advance timing light, infrared thermometer, compression and leakdown testers, vacuum gauge and what not - plus an air/fuel gauge, fuel pressure gauge and a vacuum gauge permanent hooked up in the cab.

The vacuum gauge at the dashboard is for milage (makes a light foot).

I hate guesswork when working on engines.

There may be some old time wizzards that can tune a carb by ear (then they run rich most the time) but I rather trust my oxygen sensors that realy tell you what goes on. I change carbs offten yust to try them out. Tuning and jetting them with the LM1 is a snap.

It is not "that much trouble" it is fun for me to tune an engine and you will be surprised how much potential is left in all those "good running" engines.

my ct2 Frank

Whatd'd ya do Frank, close down the local High School auto shop?
Ya don't need a vacuum gauge, just turn on the wipers!
Yes, it's nice knowing exactly what's goin on inside the cooker. The new cars are so bullet proof, that we've gotten used to driving them 100K without opening the head. At the family gatherings the twenty year olds listen in amassment when I tell them about, new tires at 15k and tune-ups every 10K, a grease job at a 1,000 and oil every 2000. Just finished lubin’ the 3604 and If I counted right, I had 21 grease fittings, then distributor cup and felt, starter and generator and all the linkage. Yep, there's a lot goin on with an old bolt, nice to take the guesswork out of it.
The PO had the truck for a little over two years, said it was a daily driver. It looked like it hadn't been lubed in 20 years, all the fittings were totally covered with red clay/grease and when I pulled the fittings to clean things out the old grease was like dry pie crust.
Fine tuning does pay off, like you say, run them rich and your just washin’ down the cylinders, makes for a short life span. Get the timing off a couple of degrees and it makes a goodly difference on the dyno. That said, the inliners will do their job pretty good without all that much tuning.
Denny G

48bigtruck has it. WHen you have a leak down tester it tells you the percentage of leaking, but after that you have to listen where the air is leaking from. A compression tester will compare cylinder to cylinder differences. Compressed air can tell you where the leak is occuring.

You've been around too, huh Denny?

Denny, your'e correct, flying is getting too expensive. My Rearwin will be for sale come spring. Restoring old trucks is cheap compared to restoring an airplane. Weeds

You betcha Weeds, Flyin now is for the Doctors, Lawyers and that Indian chief that owns Hochunk! I even gave up my room of 17 years at the Motel, across the street from Whittman field. For what it cost me just to attend the week of activities at the EAA convention I could buy a rebuilt 235 for the bolt.
In the beginning, back in the early 80’s, I was sharing a hanger and palling hanging round with a Sr. Captain with Delta airlines. He also had a Pitts, but he didn’t build his like I did, he wrote a check out for $100k and flew a new one back from California. We were competing in the IAC contests, he flew Intermediate and I was flying Sportsman. Every couple of weekends we were flying to a different competition, it was costing me between $200 and $300 for the weekend. That was just spending money to him but for a guy like me who was grossing $400 a week it didn’t take long to figure out I was hanging round with the wrong crowd. I scrounged my way through 2years of flying competition and a few small air shows and finally parked it in the barn I built out back for it. It’s still sittin there, waiting for some young buck to bring her back to life.
As soon as I find that young buck I can put the Chevy in it’s place and start the frame up resurrection.
Hell, these old buckets are a lot more fun to play with than the bird ever was and the peoples are a lot nicer to boot! Now back to the creeper, I got a lot more grease to scrape today!
Denny Graham
Sandwich, IL