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Old August 11th, 2016, 09:30 PM   #1
2weelz
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Compression test: What size hole?

I was trying to do a compression test on my '07 and discovered that the threaded end of my compression gauge was too big. What size are those spark plug holes? I have done every search I can think of. Actually, if anyone reading this has the right tool and lives in or near Seattle, I would like to borrow one. I suspect this is a keep-or-not test, and may only use the tool once. Unfortunately I do not have the room/equipment/time/money/skills to do major engine work, or to hire it done.

Backstory:
Engine suddenly quit while merging into freeway traffic. I don't remember feeling any engine braking; it just lost power and the red light went on. It cranked but would not start again. I want to check the compression first to see if there is major engine damage--the lack of engine braking makes me suspicious. If it has decent compression, then I check for spark and gas.

thanks

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Old August 11th, 2016, 11:09 PM   #2
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10 mm x 1.0 size.
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Old August 12th, 2016, 08:37 PM   #3
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Originally Posted by 2weelz View Post
..........
Engine suddenly quit while merging into freeway traffic. I don't remember feeling any engine braking; it just lost power and the red light went on. It cranked but would not start again. I want to check the compression first to see if there is major engine damage--the lack of engine braking makes me suspicious. If it has decent compression, then I check for spark and gas.........
The causes of the problem can be much more than sudden lack of compression, which in this case can only be due to:
* Open/leaky valve during compression stroke.
* Perforated piston crown (due to incorrect spark plug grade).

Please Paul, see:
http://www.dansmc.com/leakdown.htm

http://www.dansmc.com/compression_test.htm

http://faq.ninja250.org/wiki/Troubleshooting

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Old August 12th, 2016, 09:06 PM   #4
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Don't forget valves out of adjustment, or something went wrong with the valve train.
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Old August 12th, 2016, 11:05 PM   #5
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Going by your notes: I'd check spark & gas first. There'd likley be a whole lot of ugly noise cranking it if you'd had a failure the way you've described it.
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Old August 27th, 2016, 10:21 PM   #6
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Spark is visible. Gas does not seem to be coming out of the petcock, though it looks like enough gas is in the tank to feed it. I will try putting a half gallon more in to make sure. Maybe the petcock is clogged? Can you be "out of gas" with an inch or two of gas sloshing around? Compression read only 60 lbs on left cylinder, though I am not confident of this reading. I did it with the tank on, and couldn't really tell if it was getting a good seal. I was getting ready to remove the tank when I discovered the lack of flow.
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Old August 28th, 2016, 06:35 AM   #7
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The petcock needs vacuum (provided by the running engine) to open. With the engine off or the vac line disconnected, no fuel should flow out.
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Old August 28th, 2016, 09:00 AM   #8
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D'oh!
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Old September 2nd, 2016, 06:50 PM   #9
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Update:
Compression about 60 lb each cylinder. Spark in both plugs. No unusual noise when cranking. Evidence of water/rust in fuel tank: reddish fluid from vent; smelled of gas but weaker than straight gas. Mileage just past 18K.

Could it be just the water? I read somewhere that compression of less than 100 meant "better to rebuild the engine". Is this correct, or is there a chance that no major engine work is needed?
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Old September 2nd, 2016, 08:06 PM   #10
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60 psi compression is too low for an engine to run. Did you hold the throttle wide open and crank it until it quit rising?
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Old September 2nd, 2016, 08:32 PM   #11
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Hi Paul
Again; from your notes: my money is on you having a dirty fuel system. You in all probability must clean the tank, lines and a thorough carb clean.

As your motor was running; 60psi in both cylinders suggests to me you may not be doing something right in the setup or the testing procedure. Perhaps check everything and run the test again? If you're still getting only 60 then try a leak down test and see where things are leaking
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Old September 3rd, 2016, 10:12 AM   #12
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Guess I tested wrong; I did not hold the throttle open. I'vs never seen that mentioned. Makes sense: can't build pressure if the air can't get in. Seems obvious now.

I am learning stuff, anyway. Should I test with and without adding oil to the cylinders? One of my company's fleet maintenance people said so.

If it's the fuel system, which looks more and more probable, I guess it's worth hauling it off to the dealer to have them clean the fuel system when they do the 18K mile service. I don't think I could tackle it myself.
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Old September 3rd, 2016, 10:48 AM   #13
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No harm in adding a squirt of oil for the test but do it without the added oil first. Compare figures. If there's a huge difference; your rings are worn. But a leak down test will tell you where the compression is being lost: out the exhaust if the exhaust valves have a problem, out the carburator if the intake valves have a problem and out the oil filler if the rings have a problem. Keep in mind though: the valves need to be closed on the cylinder you are testing or they will leak and give you a false reading. I'm lousy at search but @Motofool probably has all the links at his fingertips on how to do compression tests etc.

As for cleaning the fuel system: if you can do compression tests and reassemble the bike properly; you should have enough skill to clean the gas tank & lines! You may want to send out your carbs to a reputable service shop like @ducatiman as there are lots of places that say they cleaned the carbs but don't really do a complete and proper job of it which will drive you nuts if you still end up with an issue!
Personally; I'd take a stab at cleaning them myself. There are a ton of videos on how to. If it doesn't work: you could then send them out for pro cleaning.
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Old September 3rd, 2016, 11:29 AM   #14
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Quote:
Originally Posted by SLOWn60 View Post
.......... I'm lousy at search but @Motofool probably has all the links at his fingertips on how to do compression tests etc.......
Links with how-to's have been in post #3 above.

The new information suggests a plumbing or contamination problem that prevents the proper fuel feeding of the carbs.

These threads may help:
https://www.ninjette.org/forums/showthread.php?t=137770

https://www.ninjette.org/forums/showthread.php?t=235430

https://www.ninjette.org/forums/showthread.php?t=115464

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Old September 3rd, 2016, 11:42 AM   #15
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Quote:
Originally Posted by Motofool View Post
Links with how-to's have been in post #3 above.

The new information suggests a plumbing or contamination problem that prevents the proper fuel feeding of the carbs.

This thread may help:
https://www.ninjette.org/forums/showthread.php?t=137770
Just because I implied Paul should read the instructions more carefully doesn't mean I will!
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Old September 5th, 2016, 06:52 PM   #16
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I ran a compression check again holding the throttle open. Reading is the same open or closed. Somehow the left cylinder is down another 10 psi or so.

I read all those threads and was hopeful that I would just clean and dry some things out, but it looks like there is something bad in the engine internals.
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Old September 5th, 2016, 06:58 PM   #17
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Quote:
Originally Posted by 2weelz View Post
I ran a compression check again holding the throttle open. Reading is the same open or closed. Somehow the left cylinder is down another 10 psi or so.

I read all those threads and was hopeful that I would just clean and dry some things out, but it looks like there is something bad in the engine internals.
Eh, add a tablespoon of oil to the cylinder and try again.
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Old September 8th, 2016, 06:01 PM   #18
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Quote:
Originally Posted by RacinNinja View Post
Eh, add a tablespoon of oil to the cylinder and try again.
My understanding is that test will tell me whether valves or rings are the problem. Since I have already decided not to tear into the engine, I do not see the point of it. If either the rings or valves need work, it is time to pass the bike along to someone with a secure, dry place to work on it, as well as the time and inclination. Does anyone still think I'm looking at dirty/wet fuel or something else external to the engine? If the cam chain snapped, would it produce these symptoms? It was knocking around for a bit before I cleaned the cam chain tensioner last year.
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Old September 9th, 2016, 07:37 PM   #19
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Quote:
Originally Posted by 2weelz View Post
My understanding is that test will tell me whether valves or rings are the problem. Since I have already decided not to tear into the engine, I do not see the point of it. If either the rings or valves need work, it is time to pass the bike along to someone with a secure, dry place to work on it, as well as the time and inclination. Does anyone still think I'm looking at dirty/wet fuel or something else external to the engine? If the cam chain snapped, would it produce these symptoms? It was knocking around for a bit before I cleaned the cam chain tensioner last year.
A cam chain that is too loose could jump one or both sprockets of the cams.
That would deteriorate the proper timing of opening and closing of the valves and the optimum compression.
The piston could hit such out of time valve, bending its stem, which would prevent the valve from freely sliding up to a fully closed position: gases leak and low compression.

Both conditions could easily be seen by removing the valve's cover and turning the engine manually; but, we understand that you don't have the conditions to perform that exploratory surgery.

The history of fuel contamination and the sudden dying of the engine (without previous noise), however, made, and still makes me think of a problem of fuel supply, rather than more serious and costly to resolve valve/timing problem.
If that is true, your low lecture of compression may be due to other than mechanical reasons, like bad calibrated manometer, leaky connector, etc.
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