Compression test

This is so elementary that I hope you can still help me once you get over the question. What do a need to do to turn over the motor for the compression test, and what is the best way to go about getting/renting the compression test set? Looked in both my manuals and there isn't much on the subject. My bike doesn't have a kickstarter.

Thanks!

No problems.
You'll need to push your starter button to get the motor to crank, just like you're trying to start it.
BUT...
You don't want the motor to start, just crank. Since your doing a compression test, you can just remove all of the spark plugs. Label the plug wires BEFORE you pull them off the plugs, so you can put them back on correctly.
When your plugs are out, and your cylinders are exposed to the rest of the world thru the plug hole, be very careful that nothing accidently drops into the holes.
You check compression with a Compression Test Gage. It looks like a dial gage with a needle. The stem of the gage has a rubber cover to fit over the plug hole, and makes a good seal.
So, holding the plug gage in the hole with one hand, roll the throttle open, and hit the starter button. Let it crank for 3 or 4 seconds. Release the starter button, pull the gage off the hole and look at the measured pressure. The gage is made to 'stick' at the highest measured pressure so you can read it. It has a button to release the needle for the next test.
For a 900 or 1000 cc bike, the cylinder pressure should build to 115 - 145 psi. The service limit (minimum) is 100 psi. Also, the pressure should not vary by more than 15 or 20 psi from cylinder to cylinder.
If you have a helper, it's easier. One person holds the gage in the hole, and the other works the starter.
If you get a low pressure reading, try again to make sure you had a good seal during the test.

I also have seen compression test guagues that actually screw in, I'm sure there are several varieties.

For a quick easy test to see if a bike won't run because of compression you can pull the plugs as normal and put your thumb really tightly over the plug hole, if you can keep your thumb on the hole as you turn over the engine then compression is your problem.

Any auto parts store will have a variety of compression gages. The simple ones aren't expensive, and it's worth having one in your tool box.

Harbor Freight has one for under 20 bucks

Thanks guys,
I'll have to get a new battery and a gauge before I can do the test. The fella a got the bike from said it ran though it was hard to start. I'm keeping my fingers crossed that everything is ok, but I'm sure the carbs will need some (maybe a lot) of work. He said the carbs leaked from the bottom when the bike was sitting.(?)

floridamba wrote:

Harbor Freight has one for under 20 bucks

...which I picked up on sale for $6.99.

It is the screw-in type, and seems to work well.

I think ths link by this guy Dan may be helpful. It will answer some other questions you will undoubtedly run into just getting your bike fired up. One step at a time.
www.dansmc.com/MC_repaircourse.htm

Thanks! I got bookmarked.

mountain wrote:

I think ths link by this guy Dan may be helpful. It will answer some other questions you will undoubtedly run into just getting your bike fired up. One step at a time.
www.dansmc.com/MC_repaircourse.htm

Great link. Definitely one to be added to the favourites list. Thanks mountain

Yah, Dan's motorcycle repair course is pretty slick. It reinforces alot of what we've all learned on our own the hard way. I have poured through his whole site several times. I really dig it, but not any single mechanic should be trusted with all the answers. That is why this forum we are using now is really great. I have learned a ton just reading random posts.
1977 KZ 650 B(1) 002337 got for free in Bozeman, MT Dec. 1st, 2006. It sat outside for nine years. After dilligent attention, major intake cleaning, I got the bike on the road Jan. 9th. It needs work, but has promise. I've stripped the bike down to the bare frame and am rebuilding everything, sans the bottom end. Quite a project, but what a blast! Mountain Ben (I'm in Louisville, CO.)

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