This is for anyone who has ever wondered if their bike is worth fixing. This can be something that came into your possession or simply something that has been sitting way too long. It's called a leak down test. Now be forewarned this is not for 2 stroke motors, while it can be done and yield quality results, it is more of a pain in the butt compared to other diagnostic methods. What it basically does is puts air into the cylinder while it is at top dead center and gives you a reading of how much of that air is escaping. You can even determine where the air is released allowing you to assess the general condition of the top end of an engine. Armed with this information you will be able to decide if you are willing to put your money into the bike or not. Any shop should be able to do this for you within an hour and if you have them just note down anything that sticks out at them while they are performing the test. This in my opinion, would be the best option for that “I wonder if it’s worth it?” situation. If you have a leak down tester and are brave enough I have outlined the procedure starting from the point where you have the spark plugs out and the appropriate timing covers removed.
1. Start by aligning the timing marks on the crankshaft so that the number one cylinder is at top dead center.
2. If an engine lock is available, install it now, alternatively you can use a long breaker bar with a socket on the mag side crankshaft bolt and a friend to hold it. A trick for this is to have the breaker bar rest on the floor or the foot peg because it can jerk fairly aggressively when you first hook up the gauge, especially big cylinder engines.
3. Insert the spark plug threaded adapter into the spark plug hole on cylinder number one.
4. Reduce the line pressure on your air compressor to 60psi.
5. Connect the leak down tester to your airline.
6. Turn the knob on tester until the needle is at 0psi.
7. Connect the tester to the adapter in cylinder number one.
8. Observe the gauge on your tester and check if the leak down is within spec for your bike.
If you hear air hissing in the air box, intake valves are to issue.
If you hear air hissing out the exhaust pipe, exhaust valves issue.
Take off the oil filler cap, if you hear air hissing in there, that's the rings.
To prevent damage to the tester, make sure you turn the knob so it reads 100psi before removing.