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Low compression numbers, is this a killer...

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Well I just checked the compression on my "project" 1100E. Bought it cheap & haven't a clue as to its history. Doesn't look that beat up, but I guess there's no real way to know...

Anyway, bike has been sitting for several years. Turns over a little slow with the starter, but enough to perform the test.

I shot maybe 2-3 tablespoons of oil down each plug hole, no carbs attached, all plugs removed, and an absolutely stone cold engine.

Here's the numbers:

1 - 35 psi
2 - 70 psi
3 - 90 psi
4 - 120 psi

I know the engine's supposed to be at operating temp, & I haven't checked the valve clearances yet, but that 30 psi reading on #1 is making me wonder if I have big issues...

Thoughts??

Thanks - Mike
 
Last edited:
Yeah, the 35 psi IS disturbing. Check your valve clearances; my numbers were at the low end of the range cold, with one at 105. After setting the valve clearances, all cylinders were better than 185 cold, so this can have a big effect. But with a 35, a bore and ring job might be in your future. How many miles on the engine?
 
jknappsax said:
Yeah, the 35 psi IS disturbing. Check your valve clearances; my numbers were at the low end of the range cold, with one at 105. After setting the valve clearances, all cylinders were better than 185 cold, so this can have a big effect. But with a 35, a bore and ring job might be in your future. How many miles on the engine?
Click to expand...

39K is on the clock, but who really knows??
 
Yes who knows, but you must adjust the valves first,run it 1K miles and check them again....
 
hikermikem said:
Well I just checked the compression on my "project" 1100E.
Here's the numbers:

1 - 35 psi
2 - 70 psi
3 - 90 psi
4 - 120 psi

As the bike has been sitting for several years, the valve train / cylinders will be suffering from lack of lubrication, and movement could be "sticky" until properly lubricated and warmed up. Those numbers increasing all the way from 1 to 4 appear to be a function of increasing time the motor has turned over and lubrication getting better as you performed the test (presumably cylinder 1 first and so on to cylinder 4 last), rather than any "real" big issues. First try and get it running, and then check valve clearances etc.
Click to expand...
 
Clean the carbs, adjust valves and go ride the heck out of it. If the numbers don't come up then do the oil trick in the cylinders to see if it's rings or valves.
 
hikermikem said:
Well I just checked the compression on my "project" 1100E. Bought it cheap & haven't a clue as to its history. Doesn't look that beat up, but I guess there's no real way to know...

Anyway, bike has been sitting for several years. Turns over a little slow with the starter, but enough to perform the test.

I shot maybe 2-3 tablespoons of oil down each plug hole, no carbs attached, all plugs removed, and an absolutely stone cold engine.

Here's the numbers:

1 - 35 psi
2 - 70 psi
3 - 90 psi
4 - 120 psi

I know the engine's supposed to be at operating temp, & I haven't checked the valve clearances yet, but that 30 psi reading on #1 is making me wonder if I have big issues...

Thoughts??

Thanks - Mike
Click to expand...

Did you test the compression before you added the oil, and then after to see if there was any increase?

To check leakdown just put the cyl to be tested at TDCC and fill with air and listen for leaks. If you want to get more precise you will need a regulator and gauge, just make sure you have the bike in gear and have your buddy hold the rear brake as the air pressure in the cyl will push the piston down in its not held. Im sure there is some directions on the site somewhere.

Either way, 35psi sounds like it could be obtained without any rings at all!! I would focus on the valve adjustment/cam chain adjustment, one better might be to take off the head and make sure the valves are not bent as well.
 
When you did your compression test did you hold the throttle wide open? if not all you numbers are irrelevent. Go back with a charged battery and test again with the throttle held open and let us know what you get.
 
76FJ55 said:
When you did your compression test did you hold the throttle wide open? if not all you numbers are irrelevent. Go back with a charged battery and test again with the throttle held open and let us know what you get.
Click to expand...

As mentioned in his first post, there are no carbs attatched so WOT is not an issue.
 
Sorry, I some how managed to overlook that there where no carbs in the initial post.
 
Pop the top end off. Quit jacking around.

Want to know for sure. Just do it. lol



Really, if the compression test was done on the first attempts to turn the engine over?

Keep turning it over and check the compression again and again until the numbers become consistent.

If they rise, attempt to get it running, like Chef and others say, just trying may free up things, been sitting for a while like 2BRacing says.

If you have not adjusted the valves, do it, need to anyway, add oil to the top end/cams, turn it over a few times, and retest the compression before you put it back together.



If the numbers are still low, after many revolutions of the engine.....

You have done the oil test, valves are in check.

IMHO, hey, it turns over.

Just pull the top end, it's not that hard, and check it out.
 
tejasmud said:
Pop the top end off. Quit jacking around.

Want to know for sure. Just do it. lol



Really, if the compression test was done on the first attempts to turn the engine over?

Keep turning it over and check the compression again and again until the numbers become consistent.

If they rise, attempt to get it running, like Chef and others say, just trying may free up things, been sitting for a while like 2BRacing says.

If you have not adjusted the valves, do it, need to anyway, add oil to the top end/cams, turn it over a few times, and retest the compression before you put it back together.



If the numbers are still low, after many revolutions of the engine.....

You have done the oil test, valves are in check.

IMHO, hey, it turns over.

Just pull the top end, it's not that hard, and check it out.
Click to expand...

OK thanks, I'll be getting to this project slowly, don't have the time or space at the moment to do a proper teardown.

I'll keep posting my progress as I make some :o
 
Personally I would check the valves, clean the carbs & try to get it running. If it will run, run it & worry about checking compression in 1000 miles or so....

My Skunk got faster (presumably due to compression gains although I never checked) over a period of 1,000 miles or more when I put it back on the road.

Dan :)
 
Hey Mike,

While you are working on other things, put some Marvel Mystery Oil in the cylinders and let them soak. MMO works wonders to free up stuck rings. Can't hurt, other than make a cloud of smoke when you first fire up the bike.:)
 
Nessism said:
Hey Mike,

While you are working on other things, put some Marvel Mystery Oil in the cylinders and let them soak. MMO works wonders to free up stuck rings. Can't hurt, other than make a cloud of smoke when you first fire up the bike.:)
Click to expand...

Hi Ed,

Sounds good, I'll do that... How much ya figure?? A couple of ounces in each cylinder?
 
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