Well now I have really done it...

Ok so a little update. Looks like I have about 60psi in each cylinder. also drained the oil. Most of it is oil I added to the bike but some of it is left over dirty goodness...it may be actual dinosaur dna in there as you can see inside the oil pan interior. Comments and accolades welcome. I am not so sure about a full rebuild now, as the downstairs looks pretty dang clean.
 

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When you checked compression you had either the carbs off or the throttle wide open right? that can make a huge difference. Also add some oil to the cylinders kick it over a bunch and let it sit for a while then test it again. The inside doesn't look that bad and the water that got in the stator cover may not have gotten in anywhere else. But you need a minimum of 100 psi for the motor to run at all and 130-140 cold psi to run well. And like sonic said, need to make sure valves are set properly and cam timing is right or it will never read correctly. My CX tested at 80-90 PSI on one side and all that was wrong was a slightly tight intake valve, once set to spec went to 150.
 
+1 to what Maritime said, Wide open throttle, choke off, pull all the plugs, put a small bit of oil in cylinder and crank or kick it over several revolutions until the pressure stops increasing. You want the maximum amount of air in each cylinder to get the highest reading.
 
Adding oil to the cylinder before compression testing can give a false reading. It's one of the ways to check if a low compression reading is valves or rings -- if adding oil brings up the psi, it's rings. At least that's what I was told... correct me if I'm wrong.
 
you are correct, but in a motor that sat dry for a while it is a good idea to get some oil in the cylinders, letting it sit for a few hours then testing again will tell you if the numbers change. dry rings won't seal right and if the motor can't run to splash the oil up and around the pistons to oil the bore you get unrealistic numbers. But you are correct, you usually test, add a little oil, test again to see if the numbers go up to know if it is rings or valves causing a low compression situation.
 
Just an aside- I was always taught to remove the plugs and drop a little Marvel Mystery Oil into an engine that's sat awhile whether you're checking compression or just trying to get it started. Always a good idea, no matter what.
 
that was kind of what I was getting at. make sure it is lubed to prevent damage before you go moving pistons up and down LOL
 
Maritime said:
you are correct, but in a motor that sat dry for a while it is a good idea to get some oil in the cylinders, letting it sit for a few hours then testing again will tell you if the numbers change. dry rings won't seal right and if the motor can't run to splash the oil up and around the pistons to oil the bore you get unrealistic numbers. But you are correct, you usually test, add a little oil, test again to see if the numbers go up to know if it is rings or valves causing a low compression situation.
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oh yeah, right you are, forgot that this one sat. I'd add oil, crank it, and then come back to do a compression test a while later...
 
Ok. Just so I am clear I am prepared for a top end rebuild. I will add some oil to the cyls but please note it sat for a week with the standard marvel oil in each cylinder. Followed by a bit of pb blaster mid week.


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if you have done the marvel etc. I would just set valves, check timing and do a compression test. If low, put a teaspoon of engine oil in each cylinder and retest right away, if it goes up a lot like 30-40 PSI it is likely rings and you need a top end job, If it does not go up it is a valve train issue and you should do a leak down test to see if it is intake or exhaust or both. each cylinder needs to be within +- 10 PSI as well. Consistant pressure accross all 4 is more important then high numbers. 4 at 120 121 120 122 is better than 130 150 160 140
 
OK been reading all of this great info and wanted to clarify the compression test scenario.

1. pull all the plugs and leave them out?

2. Remove the carbs (throttle is stuck and I was planning to rebuild these anyway)

3. Add a little oil to the cylinders

4. kick it over 5 times or until the needle no langer moves up on the tester.

thanks all of you awesome people.
 
Yes, but check your valve adjustment first.
If your valve lash is out of spec the valves may not close completely, may not open soon enough or may close too early. All of these affect how much air is pumped into the cylinder on the intake stroke.
How much air directly corresponds to how much compression can be achieved by the piston moving to top dead center on the compression stroke.
(less air = less pressure)


So your valve train has a HUGE affect on compression.


If you get them into the correct spec, then your compression test can actually tell you a lot about the motor, and roughly how much it will cost you to get it back to right.


Try to visualize the when th evalves open and close in relation to the piston moving and it may help the words make sense...
 
+ 1 to bozz, don't even bother until valves are set and timing is checked or your numbers mean nothing.
 
...and if as you said, your throttle plates are stuck closed, your numbers in the first round don't sound too awefull. You had intake air shut off.
 
Hoosier Daddy said:
...and if as you said, your throttle plates are stuck closed, your numbers in the first round don't sound too awefull. You had intake air shut off.
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Yep, this is very true if air can't get in, it can't be compressed. and like I said I lost 60 PSI due to 1 intake valve being too tight. So proper valve adjustment is critical.
 
OK so I got the carbs removed and the valve-train sorted. all the little tappet-ee bastards were within very close range of spec (less than a 1/16th of a turn) and were loose if out of spec. This whole experience is reminding me of my first car a VW transporter circa 1973, but this is waaaaay easier to manage.
 

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Then I did the compression test )with the plugs removed and the carbs off and a bit of oil down in there yonder.

1=60ish
2=90ish
3=60ish
4=60ish

So that points to a compression problem in general. any thoughts on options? also need to know who recommends what exhaust. I want to go back with a 4into1 but I am not sure which one. again all thoughts are welcome. Links to top end kits would be fabulous as well.

thanks again,
SZ
 

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Before we all panic, where did the compression tester come from? If it was Harbor Freight, just throw it away and beg, borrow or steal a good one. HF tester are notorious for sticking at 60PSI
 
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