• Required reading for all forum users!!!

    Welcome!
    Register to access the full functionality of the GSResources forum. Until you register and activate your account you will not have full forum access, nor will you be able to post or reply to messages.

    A note to new registrants...
    All new forum registrations must be activated via email before you have full access to the forum.

    A Special Note about Email accounts!
    DO NOT SIGN UP USING hotmail, outlook, gmx, sbcglobal, att, bellsouth or email.com. They delete our forum signup emails.

    A note to old forum members...
    I receive numerous requests from people who can no longer log in because their accounts were deleted. As mentioned in the forum FAQ, user accounts are deleted if you haven't logged in for the past 6 months. If you can't log in, then create a new forum account. If you don't get an error message, then check your email account for an activation message. If you get a message stating that the email address is already in use, then your account still exists so follow the instructions in the forum FAQ for resetting your password.

    Have you forgotten your password or have a new email address? Then read the forum FAQ for details on how to reset it.

    Any email requests for "can't log in anymore" problems or "lost my password" problems will be deleted. Read the forum FAQ and follow the instructions there - that's what we have one for...

  • Returning Visitors

    If you are a returning visitor who never received your confirmation email, then odds are your email provider is blockinig emails from our server. The only thing that can be done to get around this is you will have to try creating another forum account using an email address from another domain.

    If you are a returning visitor to the forum and can't log in using your old forum name and password but used to be able to then chances are your account is deleted. Purges of the databases are done regularly. You will have to create a new forum account and you should be all set.

how to perform a compression test? this may be the big one!

  • Thread starter Thread starter snowbeard
  • Start date Start date
S

snowbeard

Guest
so I think I did some serious damage to my #1 cylinder,,,

the bike started running rough on a thursday, surging and sputtering some on the way to work. (that morning I had jumped it from a running car to see if my hard starts on cold days were the battery. that was another thread and I don't know if that had anything to do with currrent issues.) friday on the way home it was even worse, but it had sat out in the rain all night which she never likes.

I thought it might be the plugs shorting from the water, so I reseated the caps on #1 and #2, taking a quarter inch off each to clean it up. good spark after that, but the issue continued

checked the plugs and #1 was very lean, suggesting a carb problem. #2 was black, but now I know the petcock is leaking into the vacuum hose, will deal with that later.

so I pulled the carbs and cleaned #1 very well, short of dipping it, because the problems seem centered around it. the jet next to the main needle jet seemed clogged at the end hole, but clean on the sides.

put it all back tegether, and when I finally got it started, it blew white to grey smoke consistently with every rev, and still has very weak power, surging, uneven running. this smoke is common to some degree, but this was much worse, and didn't stop for a long time, if ever.

also, when I pull the plug wire off #1 it makes no difference in the RPMs, nor does it on #2, but #3 or 4 will kill the engine completely. they all have good spark so that's not it. #2 is running rich because the petcock diaphram has spouted a leak, but I think that's a different issue as well.

the bike has been knocking slightly of late, and I suspected it may have needed the valves adjusted, but haven't gotten around to it.

also, just reading thru a search, smoke on startup (which I've had for years from the #1 side exhaust) from one cylinder could be the inlet valve seeping oil into the cylinder. I wouldn't be suprised.

SO! to the real question :roll:


what do I need to do for a compression test? what cover do I have to remove to spin the engine, and does it require draining the oil? I have an old compression testing guage, I'd have to do some work to get it to reach the inner cylinders, but #1 is easy.

what are all the tests to try in this case? I suspect the valves of being out of whack, can you tell that from compression?

maybe I'm up the wrong tree entirely, but I've done what I know so far and it hasn't done anything to help, I'm at a loss :? what could I have done to the poor girl?
 
Thats easy, just remove the gas tank, remove all 4 sparkplugs, remove the power wire to the coils, screw the compression tester in #1 cylinder, hold the throttle wide open, hit the start button and count to 5, write the reading down, then do the rest of the cylinder's until your done. Then post your results and go have a beer.
 
that easier than I thought, but I'll have to see about my guage.

hmmm, maybe I don't have a compression tester... it has a dial guage and a rubber end to press into the spark plug hole...

thanks!
 
RacingJake hit the essentials pretty well, but I'll add a few details jes cause I like to hear myself talk...

Do remove the tank, pull all the plugs and disconnect the inlet power to the coils. You may or may not have a compression tester that screws in. Some of them simply have a tapered rubber tip on the end. You have to firmly hold that tapered rubber tip on the hole where the plug was while cranking the engine over at full throttle.

With all the plugs out, the engine will spin over with very little resistance except for each time it comes up top dead center on the cylinder you're testing. DO crank the engine over for the exact same amount of time for each cylinder, 5 seconds is fine. Record it for study and comparison.

You can get more information from a compression check... You probably will see a 125 to 150 psi indication on a 5 second crank. There is no exact reading that is required, but you do want as high a reading as possible, and all cylinders should be within a close range of each other. If one cylinder is more than 20 psi off from the others I'd say you have the beginnings of a problem. Additionally you can in most cases actually pinpoint the cause of the low compression with an extra test. If you do have a low cylinder, remove the tester and squirt a tablespoon or so of engine oil into the plug hole and give it a few minutes to flow around and begin to seep down through the rings. Then redo the compression check on that cylinder. IF the problem is in the ring-cylinder wall seal... you should see an immediate improvement in the compression. The oil is simply providing a better seal for a few seconds. This will not cure any problem, it will simply tell you where it may be. IF the compression does not improve at all, the problem is probably in the valve-valve seat area. Either the valve or valve seat is burned, or maybe the valve stem is bent. In any valve related case a little bit of oil will do absolutely nothing to improve the low compression. This will cause no problem with running the engine afterwards either. You may get a few seconds of additional smoke when you first crank up, but it goes away quickly.
 
You must log in or register to reply here.
Back
Top