• 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.

850 low compression

  • Thread starter Thread starter Steve C
  • Start date Start date
S

Steve C

Guest
My new to me 79 GS850, I just checked the valves, 7 out of eight had no clearance ,reshimed, bike started and idle fine after warming up after running for a few minutes I started getting some smoke right side so I decided to check the compression and I got 30 30 30 30 more or less which as far as i know is to low for a motor to run. I put some oil in and the readings went up to around 60.
So I guess the head has to come off but first I'll have a friend do a leak down.
Bike looks great though.
 
Something is wrong with the way you did the test !! Did you open the throttle ??? A must or you will get very low readings
 
How long has it been since the engine was run regularly?

If it has been sitting for quite a while, the rings might be stuck in their grooves. There are a few ways to try to free them up, ranging from covering the piston with Marvel Mystery Oil or ATF, using some sort of solvent to cut through the grime, or simply running it for a few (hundred) miles.

.
 
Lynn's right. The compression test numbers can't be right. The engine wouldn't even run.

Soak the rings for a day or so, then take the bike out for a good hard ride - 100 miles or more. After the engine cools off double check the valve clearances.

A proper compression test must be done on a hot engine, with the throttle held wide open. If the bike has sat, some good hard miles will help free up the rings and reseat them on the cylinder wall.
 
I'm think my gage most be off since my numbers are to close. And yes wot on a warm engine.
 
Also I rode the bike home about 45 minutes on the highway doing 75 to 80. The smoke is what got my attention plus the leaky head gasket between #2 and #3.
 
On a side note - When testing compression on bike with CV carbs (not sure if the '79 had them), won't the slides have a similar effect to a closed throttle even if you hold the plates open?
 
CV carbs were released with the 80 models, so his bike should have VMs.

The slides on CV carbs don't ever close completely. In their most downward position they're still far more open than throttle butterflies at idle. But your point is noted: half-open or so would probably be fine. What is often neglected by the uninitiated is to open them at all!

Tom R said:
On a side note - When testing compression on bike with CV carbs (not sure if the '79 had them), won't the slides have a similar effect to a closed throttle even if you hold the plates open?
Click to expand...
 
I did a new check with my friends snap-on gage, and got 125 ,125, 128 ,125, so thats a lot better.
Though the head gasket is now really leaking between 3 and 4, the blub of rtv I guess isn't holding.
I need to get my other project (75 Moto Guzzi) a little more together to free up some bench space
 
You must log in or register to reply here.
Back
Top