Help me not concede defeat...please!

[Rjm1973]

First time poster, but I have used a lot of resources on this site with my recently acquired 2006 250. The tech articles discussions have been great, so thanks to all for that!

Here is my issue in a nutshell...I have very little compression in either cylinder despite having replaced the rings and honed the cylinders. I checked the end gap of the top piston ring and it is within spec according to the manual. I have a leak down tester and with the head back on the engine and no rockers/cams (therefore all the valves are always closed)... I have about 80% leakage on both cylinders at tdc. If I run the pressure up a little, I can here the air escaping into the crankcase past the rings (at least that is my assumption--I can't imagine how else it's finding its way out of the cylinders with all the valves closed).

The Pistons do not have holes...and the rings are installed per the manual. Letter side up in correct order, and the gaps are 180 degree apart.

At this point, I am contemplating that either the cylinders are out of round, or the piston ring grooves are worn preventing the new rings from sealing against the cylinder walls. Could it be anything else I haven't thought of?

The bike only has 8000 miles...but it's clear that it has not had an easy life. I'm certain it's been down at LEAST once.

Any help or insight you can provide would be much appreciated! I'd love to officially become a ninja250 rider...vs just a ninja250 mechanic

[Motofool]

Welcome, Rich !!!

Put a few drops of oil into the chambers to seal the rings and repeat the leak test.
New rings always leak for a while until they get the shape of the cylinder.

The valves can be worn or burned and leak even when closed.
Same for the guides of the valves.

[Rjm1973]

A little oil makes it just a little better but it is still pretty terrible. I actually had tried that earlier as well...think I read it elsewhere on here. I actually have the motor off the bike with valve cover off. I'm pretty confident it's not leaking through the valves as I can hear the air going into the crankcase.

Having said that though...I,also have a compression tester (in addition to the leak down) and before I replaced the rings, I had low compression dry and improved with about a tsp of oil added, but still below spec...so low I couldn't get it started. A few backfires and sputters but never sustained running.

With the leakdown loss I have right now I doubt I'll ever get it started for the rings to seat.

[Motofool]

Closed exhaust valves can leak into the pipes if burned due to improper gap.
If that is your case, compression will reach low pressure even with oil sealed rings.

If leak is higher when piston is half way the stroke, the cylinder is worn (took a barrel shape).
If so, a good machine shop could measure it accurately for you to verify that.

Why were rings replaced in this young engine?
Mine is over 30k miles and compression of original rings/cylinders is excellent.

[accumack]

What was your end gap on the rings and did you measure the bore to make sure it hadn't been bored out? Have you checked your valves to make sur they are not leaking? Did you check for cracks in the cylinder wall? That's all I can think of for now.

[Rjm1973]

The ring end gap for the top ring was .279 to .305 which is still in spec according to the manual. I replaced the rings because when I did the original leak down test, it was pretty clear the air was leaking into the crankcase. I actually rotated the engine with a little pressure manually, and could hear the air go through the exhaust and carb during the appropriate prt of the cycle and then close. I'm pretty confident it's not coming through the valves. Right
Now it doesn't even have cams or rockers in it, so the the valves are always closed and even through a rotation nothing comes out the exhaust or intake that I can tell. I can however hear it in the crankcase.


I started this process because of very low compression in both cylinders that got a little better when wetted with oil. I diagnosed that as worn rings...and I'm open to that was incorrect. The compression was under 100 lbs in both cylinders. So low I couldn't even get it to start. I am thinking now that the cylinders is out of round or the piston grooves are somehow worn and are preventing the rings from sealing...if that is even possible. Unfortunately I don't have a dial bore gauge so I prob need to find a machine shop per your suggestion. Thanks for the comments!

[accumack]

Valves can be burned or have some deposits that keep them from sealing. I would check the cylinder walls closely for a crack. Has the bike ever been overheated? With no valve opening how is the air getting into the cylinder probably sucking from the crankcase. Do the compression test with the valves opening and closing.

[Motofool]

If original rings were OK, the cause may not be rings at all.

There is some play in the notches of the piston respect to the thickness of the rings because they seal (up and down) with the help of the vacuum and the pressure of combustion.

If the cylinders are so out of shape, you may be able to see light beteen the wall and ring; but the engine is too new for that.

[quarterliter]

Are you sure your gauge is accurate? Try another compression tester.

[choneofakind]

I didn't see it in your other posts, but did you thoroughly clean all carbon build up off the head/valves and lap the valves? By clean I mean shiny. Like new-shiny.

[jkv45]

I don't know that you have a problem. If the engine hasn't run, I wouldn't expect the rings to be seated. That takes high cylinder pressure.

On an engine dyno, they will measure blowby to determine if the rings are seated. It may take a while of running under load to seat them. Run a conventional oil like Rotella T, and load the engine hard and often without bogging. Keep the revs down somewhat, and vary them, at least for a while.

[Rjm1973]

So I did clean the head and valves. I did not disassemble the heads from the valves and lap them though.

To answer an earlier question, I'm not running a standard compression gauge in the engine as it sits right now because of course no valves are opening and closing and hence no air can really get into the chamber. I am using a leak down gauge currently that injects air from my compressor into the cylinder through the spark plug hole.

I think I understand about the rings seating, but with as low of compression as it has right now, I can't get it started. I actually replaced he rings and put it all back together and it had maybe 85-90 lbs of pressure and would not start at all. It has fuel and spark...I can tell by occasional backfire as well as verification of both. When I realized after the ring replacement that the cylinder pressure was still super low... I took the motor off the bike again and pulled the cyl off to double check the ring assembly etc. everything "looks" pretty good, but if I put the head back on, and pressurize the cylinder it goes right past the rings into the crankcase.

The cylinder looks ok, so I will prob take the Pistons off the connecting rods at this point and clean the ring grooves well and measure them. The Pistons were very carbines when I originally took it apart and I cleaned the tops only...wondering if the rings are "sticking" in the grooves somehow.

Someone asked if its ever been overheated...and unfortunately I can't say. I bought for cheap and it wasn't running when I got it. I wouldn't be surprised if it had...as I stated before, I think it's had a hard life.

[Motofool]

Originally Posted by Rjm1973

........ The cylinder looks ok, so I will prob take the Pistons off the connecting rods at this point and clean the ring grooves well and measure them. The Pistons were very carbines when I originally took it apart and I cleaned the tops only...wondering if the rings are "sticking" in the grooves somehow........

Be careful not to increase the size of the grooves by using sharp steel tools; a broken ring and WD-40 are safe.

Please, take a look at these:
http://www.dansmc.com/pistons.htm

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

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

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

[choneofakind]

Pull the valves out of the head and clean all carbon build up off. I bet that's more the issue than your rings. You said you could hear leaking when you did a pressured leak down test. That's all valves I bet. The valve and valve seats have to be super clean and make solid contact with each other in order to seal

[Racer x]

I am leaning toward the valves.

I have had a lot of these engine apart. I have found the rings are not that sensitive. If they look good and are new and you put some oil in there then I would say you are "probably " OK.

The valves are a it more sensitive. If the seats or valves are cupped at all or there is carbon build up then the compression will go away quick. Pull the head and just pour thin oil like mineral spirits or something into the ports. If they leak then you need to fix that.
Best is to buy new valves and cut the seats.

[Rjm1973]

RacerX--great suggestion on the mineral spirits. I tried it on both intake and exhaust ports and while it is minimal, all four valves in both cylinders are leaking a tiny bit, but under only the pressure of gravity...so I clearly need to get that fixed. Let me give that a try this week and we'll see what happens. Upon further inspection, it is clear that I apparently "cleaned" these in the dark because what is showing in the jpg is definitely not clean. Thanks everyone for the help! I'll update hopefully that it is fixed soon!!!

[MAZ 80]

RJM, sounds like you're doing all the right things.
After doing the oil thing on your valves it's obvious they need attention.

BUT

I can't believe your problem is all in the valves. 80% leakdown is massive.
If the oil is just seeping through the valves that should only account for around 5% leakdown. Even if it's running through it shouldn't be more than 30 or 40%.
You should hear air rushing out of the exhaust and/or intake if the problem was entirely in the valves.

Instead you're hearing the air out of the crank which indicates rings or piston.
Since you're sure you haven't holed a piston that leaves rings.
Even brand new rings in a good cylinder shouldn't leak more than 10%.
Anything more than that and it's going to be a long break-in.

Do you have a bore gauge? If not, see if you can borrow one and check your cylinder for round and parallel.

Try closing off the outlets to the crankcase, intake and exhaust with your hands while you're doing your leakdown. That should give you a good idea where the majority of the air is coming from.

[Rjm1973]

While cleaning the and lapping the valves, I decided to soak and clean the Pistons as well and clean the ring grooves. When I pulled the Pistons from the berrymans, I noticed the damage on the skirt in image 1. Image 2 is the other piston and the light scratches there look like the other sides of both Pistons. Any thoughts as to what caused this, and should I be concerned about their use ability?

[Rjm1973]

2nd image

[Racer x]

Those are just scuffs on the side skirts. Not tragic. Usually from revving a cold engine. Make sure the ring groves are clean. The valves must be sealing or it won't start. It's surprising but I can believe 80% but that is a sort of made up number. But it is a lot more than you want.

[Rjm1973]

Ok guys... Perhaps I am just doing something completely wrong. Perhaps my leak down gauge is junk...

I cleaned all the valves and lapped them. They now seal and I've validated
By seeing if they leak mineral spirits...and they don't.

I bolted the head to the cylinder in my workbench and put a piston in to see if I could run a leak down. There may be a reason why this won't work, but I thought it worth a try. So take a look at the attached video. I actually inverted the whole assembly and put mineral sports in the bottom of the cylinder covering the piston to see if I could identify where the air is escaping. Interesting to me anyway, is that the air seems to be coming through a couple very tiny oil passages in the piston vs between the piston and cylinder wall as I expected.

Is what I'm seeing here abnormal? Does it imply the oiling ring isn't sealing correctly? Any experience you can share would be much appreciated.

Thanks!

[MAZ 80]

The oiling ring oils, it's not supposed to hold any compression. That's for the compression ring(s). The holes you are seeing the air come out of is where the oil gets into the oiling ring to oil your cylinder walls. So the air is getting past your compression rings and past the first half of your oiling ring then escapes through the easiest path, the oiling holes. So what you are seeing is not unexpected.

A leakdown test is usually done with the piston at TDC. I always liked to check it at midpoint and bottom, as well. Your setup looks like the piston is near the bottom of the stroke. Also, what is holding it in the bore? It looks like the pressure can just shoot it out of there.

Before doing this test and after cleaning the valves properly, did you repeat your original test to see if you get the same results? Why did you originally think the pressure was being lost through the bottom end rather than the intake or exhaust?

If you are sure it's coming out through the rings, your cylinder isn't round or your rings aren't round. You said you replaced the rings. Did you hone the cylinders? Was it a rigid hone or a flexible hone? If you square up a ring in the bore, you can hold it up to the light and see a gap if it's really bad. It's pretty easy to see .0005 inches with a good light behind it.

A leakdown tester is a pretty simple instrument, they don't usually go bad. It is, however, very easy to misinterpret where the pressure is escaping. Personally, I think you should go back to your first test and see what your results are now that the valves are done.

One last thing, you are sure your head gasket is good aren't you?

[Rjm1973]

I believed that the compression was escaping past the rings because I could hear it in the crankcase...likely blowing through those oil passages. At this point I think the video pretty conclusively says air is is escaping past the rings when the cylinder is pressurized. To answer your question though, nothing but friction is holding the piston in the cylinder. I'm pressurizing the cylinder with my air compressor through the spark plug hole very slowly.

I guess my question is that based on the ring and piston design, it is not air tight. Even with alternating ring gaps, and everything perfect there is still a gap for the compressed air inside the cylinder to escape through. Right? I am pretty confident the head gasket is ok. No oil in coolant or vice versa...no bubbles in coolant from leak down, and no air coming out of opposing cylinder.

I did hone the cylinders with a flexible shaft hone. To your point though, I prob need to reassemble everything and do the tests then. Unfortumatley I lost a valve collet and can't get another until thurs this week.

[Linkin]

You didn't line up all the gaps on the rings to the same spot, did you?

The end gaps need to be 120 deg away from each other and must not face the exhaust port.

[Motofool]

Update?

[Rjm1973]

Anybody need parts? I seriously can't get anything even remotely resembling sustained combustion. It has now had 2 separate sets of Pistons, 3 sets of rings if you count the ones originally in it, and 2 cylinder blocks. The valves are sealed and seating great and will hold mineral spirits when poured in the ports. At this point I have invested so much time in it...not sure I want to invest any more. I honestly have never had this much trouble with any engine.

[Rjm1973]

Alright...a little progress. I did manage to get about a 20 second run today by shooting some carb cleaner into the spark plug holes, reinstalling the plugs and hitting start. I am inclined to believe based on that experiment that I have managed to get the engine reassembled correctly and that it now has sufficient compression to run (my comp gauge and leak down verified the same). I therefore now believe that the hopefully final issue lies in the carbs and is fuel related. Anybody think the same or differently? Thanks for all the help guys...I seriously have never been this frustrated with such a seemingly simple engine!!!

[Motofool]

Two things are your friends regarding through rings leaks:
- High rpm's: Less volume can escape per stroke.
- Heat of combustion: Higher pressure sneaking behind the rings and pushing against the cylinder.

Both combined will make the rings adopt the shape of the cylinder as miles pile up.