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Old 03-12-2021, 08:19 AM   #11
slonomo
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Default Re: G1 lack of crankcase pressure

I think the OP bailed
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Old 03-21-2021, 10:36 PM   #12
Daniel.smith6
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Default Re: G1 lack of crankcase pressure

we are taught in the program to do some basic diagnostics on all equipment that comes in. Compression, leakdown test to see if the valves are seating properly, spark test to see if we have spark and a crankcase pressure and vacuum test to test on 2 strokes to test the crankcase seals. The crankcase has to seal. When the piston in a two-stroke comes down it compresses the air/fuel charge in the crankcase and pushes it, through the ports in the sides of the cylinder, into the combustion chamber. As the piston rises a vacuum is created under the piston. That vacuum sucks the air/fuel mixture through the carburetor and into the crankcase. We will usually use about 6-15 lbs of pressure and 5-7 inches of Mercury vacuum. I usually stay about 5-8 lbs of pressure to avoid blowing out the seals. It happened once and now I am a little wary of to much pressure. Any leaks of pressure or vacuum then it will effect the starting or running of the motor. We find the leaks by spraying areas with soap and water to see if it bubbles. We perform the test to see if the motor is even worth fixing or at least to help trouble shoot problems.
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Old 03-22-2021, 02:18 PM   #13
slonomo
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Default Re: G1 lack of crankcase pressure

Quote:
Originally Posted by Daniel.smith6 View Post
we are taught in the program to do some basic diagnostics on all equipment that comes in. Compression, leakdown test to see if the valves are seating properly, spark test to see if we have spark and a crankcase pressure and vacuum test to test on 2 strokes to test the crankcase seals. The crankcase has to seal. When the piston in a two-stroke comes down it compresses the air/fuel charge in the crankcase and pushes it, through the ports in the sides of the cylinder, into the combustion chamber. As the piston rises a vacuum is created under the piston. That vacuum sucks the air/fuel mixture through the carburetor and into the crankcase. We will usually use about 6-15 lbs of pressure and 5-7 inches of Mercury vacuum. I usually stay about 5-8 lbs of pressure to avoid blowing out the seals. It happened once and now I am a little wary of to much pressure. Any leaks of pressure or vacuum then it will effect the starting or running of the motor. We find the leaks by spraying areas with soap and water to see if it bubbles. We perform the test to see if the motor is even worth fixing or at least to help trouble shoot problems.
Thank you for the explanation. Some of us already know the procedure as we've done many rebuilds on this exact engine. I usually refer to the factory Yamaha service manual when I work on these engines.

Now the questions (as stated in other replies):

If you already know all that, why do you not have any pressure in the crankcase?

Did you check the seals yet?

If the engine runs good, how can it not have any pressure?

I still say this. Either your error is in your method or your equipment. Something is missing here.

And I'm still trying to figure out why you are coming to a golf cart forum to figure out your issue, when you don't have an issue (engine is running good), and you have a mechanic/instructor at your disposal.

Here is my reply from weeks ago 3/25/21 that you never responded to:
Quote:
Originally Posted by slonomo View Post
I was thinking along the same lines. I'm no professional mechanic, but I know 2 strokes operate a little differently than a typical 4 stroke, and crankcase pressure is likely a much different thing. I also know there are guys like Don Plowman that have been working on 2 strokes for 30-40 years or more that understand the air flow cycle on this engine far better than anyone here, and probably better than any small engine instructor. You could always call him. Look in the site sponsors page for Plowman's Carts.

Not saying your instructor doesn't know what he's doing, but can I ask....

"Why is your instructor looking to measure crankcase pressure on a 2 stroke golf cart that runs good?"

If the engine is running good, there absolutely has to be vacuum/pressure. The engine relies on this vacuum/pressure to function properly.

I'm thinking you are missing something when you are plugging all the holes up. When you did the leakdown test, you had good results? What % was the loss of pressure? What pressure were you using to test?

I'm thinking the error is in the method of testing the crankcase pressure/vacuum.
Not sure why you are here posting but you aren't answering the questions of the people who are trying to help you. We take time to "try" to give help but it seems you just want a debate. That's ok, but you get what you put into your search for answers. I'm guessing you haven't figured out the problem yet.

Good luck with your project. I hope you get it figured out.
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Old 06-18-2021, 05:20 AM   #14
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Default Re: G1 lack of crankcase pressure

Ccp is net zero

+ pressure = - pressure while running
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Old 06-29-2021, 05:56 AM   #15
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Default Re: G1 lack of crankcase pressure

ccp is about 1.2-1.4/1 or 1.2-1.4 x inlet pressure(about 1.2-1.4x ambient pressure) i.e.14.7x1.2=17.6psi

ccvac is about 80% of that
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