WHY??? An engine that has an air leak is an engine that can suck air when running, sucking air usually = burn down. Other symptoms of air leak, hard to hold a steady idle. Also and maybe more importantly this test can tell you if your inner crank seals are leaking. If your inner crank seals leak the ISOFLEX(info) grease that lubes the bearings can be lost into the engine which will lead to bearing failure. See potential $$$$ expensive mid-season repair.
You can make this leak down kit from parts at the hardware store. see pic. We (fossil99ca) got everything at Canadian Tire here in Canada.
Drill small holes in the cap to insert rubber tire stem and pressure gauge fitting. Carb boot plugs pictured are 2 pieces that thread together, use silicone on threads and tighten down hard. They fit snug into V-Force boots.
Edit: Guage we used does both vacuum and pressure, maybe this will help locating one. See pic. This Equus 3620 Vacuum Gauge will work.
Note: you can doo this test with engine in machine..these pics were taken before I put my engine back in, wanted to make sure 100% my redone crank was good before putting it in.
Simple steps
1. Plug the y-pipe
2. Plug both carbs
3. Pinch impulse line.
4. PTO elbow cap on at first to find other leaks, remove cap if able to hold 5psi.
5. If powertek engine plug extra case line..see pic
6. Spark plugs should be installed
Using a bicycle pump try to and pressurize to 5 psi...don't over do it, you don't want to blow out any seals. Most likely your first attempt you will not be able to hold any pressure. Here are all the areas we found most common to leak. Use a spray bottle with soapy water, leaking air will cause bubbles. Seal all problem areas and re-test. I had to get my y-pipe welded this year.
Common leaks
y-pipe is split at seam.
y-pipe gasket seal leaking...see pic to seal
rave valve gaskets leaking...a little grey gasket maker if tighter doesn't work.
Impulse line is not pinched off perfectly.
Carb boots are rotten and leaking. Very common.
Carb boot plugs are not tight enough.
Base gasket is leaking...sucks when this happens. I don't know of a way to temporarily seal it without a tear down.
Test #1. If you can hold 5 psi for 10 mins with the PTO elbow cap off your inner PTO & MAG bearing seals are good.
If air passes through the PTO elbow your inner PTO seal is leaking. There are varying degrees of inner seal leaking, slow leak means it hasn't failed completely but you are on borrowed time. Holding no pressure at all and the seal has completely failed.
Note: If you can't hold pressure but there is no air leaking from the PTO elbow your MAG inner or outer seals are leaking.
Test #2. If inner seal is leaking you can put the cap back on and test again, this will test the outer seals ability to hold pressure. If you can hold pressure with cap on at least you know you won't lean out a piston if you decide to run knowing your inner seal is leaking. How long until all of your ISOFLEX is gone is anybodies guess.
Ok so now you have determined your crank is doomed and you want to yank it before it leaves you dead on the trail? Sleddude5's DIY teardown threads are HERE. Goodluck.
