Wednesday, February 11, 2015

Workshop Wednesday-Leaky Boots part 2

 Last week I talked about the importance of a tightly sealed crankcase and no intake air leaks in a two cycle engine. The saw I was working on had badly damaged intake boots. Imagine my dismay when I replaced the boots and the saw still ran like it had an air leak.
 Actually, I was pissed off. This happens sometimes. You find a problem that matches the complaint then you fix the problem only to find another problem. Some would say that further tested should have been done before starting the repair. Well here's the deal. Labor rates are high. "Further testing" can add a whole lot to a bill. In order to provide a reasonably priced service to our customers, we sometimes have to "go with our gut" on some of these repairs. I gambled and lost on this one. Sort of like playing poker with Frank and John.
 So now I had to take the time I was hoping to save and pressure test the engine. To do the test I need to seal the intake and exhaust. This meant making a block off plate and seal for the exhaust port. It also meant bolting a piece of rubber between the intake boot and carb. I also had to expose the crank seals. This means removing the flywheel and associated parts on one side and the clutch and cutting parts on the other side.
 So now the ports are all sealed. I removed the spark plug and installed a special adapter that allows me to pump air into the engine. The goal is to pressurized the engine to 7 psi and have it hold that pressure for 1 minute. Spraying a soapy mix around seals and ports will reveal any leaks.

 In this picture you can see bubbles forming between the crankcase halves. The bubbles don't look like much but I couldn't even get one pound of pressure to show on my gauge. This is the worst place to have a leak because it means splitting the cases to repair. In most instances this would make the equipment non-repairable because of cost. In this case it may be worth fixing because a new saw retails for $1100. The customer was quoted $400 for the repair which includes all new gaskets and seals, new crank bearings and the new intake boots previously installed. He's thinking about it.

Lets take a closer look at a Husky 562xp that needs to be pressure tested to satisfy a warranty claim.

We need to remove the starter, flywheel, muffler, bar/chain, clutch, oil pump on some models and the carb.
Muffler removed and plate installed.

Carb removed and plugs/plate installed.

 An adapter is threaded into the spark plug hole. The adapter allows us to hook up a pump with gauge. I pumped this up to 7 psi when I suddenly had an urge to drop a deuce. When I got back several minutes later I took this pic. The engine is sealed tight and didn't lose any pressure (unlike what just happened in the bathroom). If it was leaking I would have used a soapy mix sprayed on all sealing areas and looked for bubbles. Our gauge lets us apply a vacuum to the engine also. This test is mainly for the crank seals which can sometimes only leak in one direction. I pumped the gauge to 5 in Hg vacuum and let it sit for 4 minutes with no drop of the needle. There are no sealing issues with this engine.
 So there you have it. If this looks like something you want to do on your own then I recommend buying the Mity Vac mv8500 like I've used here. It comes in a hard case along with some plugs and adapters. This tool also works great for bleeding motorcycle clutch and brake systems and that has earned it the Greasy Shop Rag stamp of approval.

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