The Hodaka Club Forum

Is there a simple way to make a leak down test for an ace 100 engine? Without spending hundreds of dollars on a kit? Looking to check the crank seals, but have never tackled such a task. I'm seeing some whitish colored smoke and making me worry that the right crank seal is going out. But want to test and make sure before a complete tear down and rebuild. Engine seems to be running rich too. Wet spark plug. 130 psi compression. Jetting maybe? I'm full of questions. Things always running through my mind.

Thanks,
Ryan

First you need to block off the intake and exhaust. With a thread on exhaust you could find an expanding plug at the hardware store that will fit or cut a disc the correct diameter out of a piece of rubber, maybe a 1/4" thick or so and sandwich that in place with the exhaust nut/pipe.
Intake side you can cut a similar piece of rubber large enough to cover the hole but just small enough to slide between the intake mounting studs. Then install the intake to sandwich it in place.
Next you need a spark plug adapter; I use the adapter from my compression tester with the valve core removed. If you don't have one of these you can fab an old spark plug, bust out the center and weld on some sort of tube that will accept a small diameter piece of tubing.
And lastly you need some sort of pump that will push air into the cylinder and that has a gauge so you can observe the leakage. I modified an old blood pressure pump with a low pressure fuel gauge; all old stuff I had hanging around. I've seen others use a cooling system tester, (think car rads) again modified to work.
Here's mine in use on my Suzuki Hustler which recently blew an inner crank seal. Sucked a liter of gear box oil through the right cylinder in ten miles. No tail gaters on that commute
You can see the rubber between the intake and the cylinder if you look closely.
Ken

Use some dish soap in water and spray it around your tester and the sealed intake and exhaust to make certain you have no leaks in your test apparatus.

About as simple as it gets. Shouldn't cost very much even if you have to buy a couple of items.

Ryan, certainly a good question. Nothing wrong with an occasional pressure test. One Sunday Winter afternoon when my team wasn't winning and the bike wasn't running well, I rummaged through all my stuff and proceeded to built a crankcase pressure tester. Here's a picture of it. Kinda basic, OK crude, but worked. The big problem was not engine leaks but apparatus leaks. Soapy water showed be the way. Bubbles everywhere. The head gasket was the problem it turned out. I have an airbrush to paint models and an adjustable regulator for low pressures which worked well for this application. Anyway, my story. It can be done.

Maxie

Mine is simple, like Max'es and Ryan's. Expanding rubber plug for the exhaust. Used as as an auto freeze plug repair, 1-3/8" I think. Aluminum plate with gaskets and a tire valve stem for the intake. Tire pump for pressure. Adapted a compression tester sparkplug adaptet to take the gauge. Pressure gauge is an old carburetor fuel pump/manifold vscuum gauge, measures something like 10-15 psi, max. You'll.run the pressure test at 5-6 psi. Used spray Windex to spritz on the joints. Found I had a leaky head gasket and a couple of cylinder studs leaking. I understand that a vacuum test is useful, too, but I'm not sure how I'd pinpoint leak locations.

I'm re-doing my pressure tester since it is useful for routine tests on any 2-stroke.

I was thinking all that's needed is a couple of steel plates to cover the intake & exhaust manifolds with maybe a rubber seal on the mating surfaces. And then a valve stem to which you could attach a compressor line or bicycle pump. Something like a basic tubeless tire valve stem. And can't you just use an old spark plug for the spark plug hole? Was just going to paint one red to mark it as the pressure test spark plug.

My big question would be how much pressure should be used so as not to be too much air pressure? 10 psi? 20? How much is too much for new seals? How much is too much for older but still functioning seals? And if a seal is bad, at what psi would a leak start showing up? Or do you just put the air in and see if it leaks out?

I plan on making some steel plates with holes drilled to match the existing bolts on the exhaust & intake manifolds, and drill a hole in the intake plate to mate a tubeless tire air valve to it same size as the ones on a tubeless tire rim. Victor

The leak down test target is 6psi and there is no useful purpose to using pressure higher than that. Leaking down from 6 psi to 5 psi in less than one minute is a "fail". Most "good" engines will show very little leakage in 1 minute (like zero, or less than 1/4 psi).

I currently have a test system with parts from a commercial unit mfgd in the 1970's. It has the pressure input through a spark plug hole fitting with O-ring seal. I find it to be kind of a pain to thread in tight enough to seal properly what with space limitations under the tank and the gauge flopping about too. So my "someday" list calls for building a plate or plug to provide for pressure input at the exhaust or intake locations. In either case, the gauge will be between the engine and the tire valve used for pressure input(same as it is now with the spark plug input). There is even good reason to use a "real" spark plug during the test (one you will use to run the engine), to test the seal of your general use spark plug at the same time everything else gets tested.

Ed

OK. So I can make plates to cover the intake & exhaust with an air input as described. But where should I have the guage which reads the pressure inside? Victor

Take a peek at the first photo in this thread. The pressure gauge is mounted to a "T" fitting, which is between the air pressure source and the engine.

Ed

OK. Got it. Hmmm. The sphigmomanometer thing looks like a good idea. I wonder if I can get an old one from the Dr.? They are all going to automated ones now, it seems. Adding a guage in between shouldn't me hard. Too bad the compression testor isn't going or at 5-6 psi. Victor

Diagnostic tool commonly used back when was a combo carburetor fuel pressure and manifold vacuum gauge. 15 psi on the pressure side, 28" on tbe vacuum side.
I think they are still available.