LEAKDOWN TEST RESULTS

[KB]

I did a compression test on the Hawk last night.

Both cylinders done at wide open throttle 150 psi
Then again with a teaspoonfull of oil in each cylinder 150 psi

Then I did a leakdown test.

With each cylinder at TDC I hooked it up to the compressor. At about 40psi I could hear air coming out of the crank case. Where the oil filler cap is.

Now I have a few questions for those that can answer.

Given the results of the leakdown and air coming out of the crankscase, one would say that the rings are bad.

With that being said, if that were the case then with the oil added to the cylinder and the test done again the results would read a higher psi CORRECT????? Or not???

I am not sure where to go wiht this. If it's bad rings then why does it only smoke when I come to a stop after banging down throught he gears. It doesn't smoke while riding only when coming to a stop. The plugs were really dark and full of carbon buildup.

Somone also said that I need a Valve adjustment and that the was the cause of the smoking. Doesn't make sense either.

Someone anyone HELP. I don't want to pull the motor out.

Anyone know any GOOD QUALIFIED motorcycle mechanics. I will do most of the work but I'll need a mechanic to do the heads.

I think what I am going to do is pull the engine. Send the heads out to be rebuilt. Send the cylinders out for measurement, bored if necessary, then throw new pistons and rings in the old girl and call it good.

If I send the heads out to be rebuilt will they adjust the valves at the same time so I can just bolt shit up and run it.

Sorry for the book

KB

[SSearchVT]

Check the compression specs on the bike to make sure you are in spec at 150 PSI. Was there a significant difference between the cylinders? If you are within spec and there was no change between the compression tests with and without oil I would rule out rings, pistons, and valves.

When is the oil smoke coming out, on acceleration, or constant?

Constant = rings or cylinder
Acceleration after coasting = Valve seals, guides

I hope this helps. Good Luck...

[Honclfibr]

Originally posted by rmbbikes
If it's bad rings then why does it only smoke when I come to a stop after banging down throught he gears. It doesn't smoke while riding only when coming to a stop.

Yeah, in my mind this seems to point more to bad valve guides than piston rings. Seems to me burning oil only on deceleration would be caused because on deceleration, the vacuum caused by the piston travelling downwards is acting on a closed throttle plate. All that pressure has to go somewhere, so it would exert more force on the area between your valve stems and valve guides, which could pull some of the oil out of the head and into your combustion chamber if the valve seats are worn.

Seems to make sense that if your valve clearances are off too, that you might hear air rushing through the crankcase at TDC, since you'll get air through the open valves, through the valve guides, into the head and from there into the crankcase through the holes that lubricate the valve train. Though if this were the case you should be able to WOT the throttle during leakdown and get air rushing out the intake instead, since it'll be a much lower resistance path.

Can't explain why you're getting good compression though, as the scenario above would require a pretty sick engine, right?

[SSearchVT]

Worn valve guides and bad valve seals mixed with good seats and closing valves would cause the oil on deceleration with good compression. Valve clearance rarely if ever decreases (which in extreme cases would cause the valve to remain open). Usually valve lash has to be decreased because the valve top and rocker arm or shim have worn.

Valve seals and guides usually require only the head to come off the bike. Hope this helps. Good Luck...

[stoinkythepig]

Originally posted by SSearchVT
Valve clearance rarely if ever decreases (which in extreme cases would cause the valve to remain open). Usually valve lash has to be decreased because the valve top and rocker arm or shim have worn.

I agree that his problem is the valve seals but disagree with the statement above. Valve clearances decrease over time due to the valve edges receding into the head from all the pounding they take when the valve springs slam them shut every other revolution. There is very little wear on the valve top, rocker arm (which is a pretty rare item on a modern bike engine anyway...) and shim.

I would start by replacing the valve seals which may be possible without pulling the heads. Use the leakdown tester and compressed air to hold the valves in place when you remove the , keepers, retainers, and valve springs. With luck, you can pop the seals off without a hassle. The guides are hopefully not worn out... They've been getting plenty of oil which helps.

I have a small valve spring compressor that you may borrow and it may allow you to get the springs off with the engine in place.

Valve seals are very cheap. Head gaskets and guides(installation) are a bit pricier. Replacing the seals may be a just a bit more work than a standard valve adjust.

[SSearchVT]

Stoinky - Sorry, but I dis-agree with your dis-agree. Here is my logic...

In a properly functioning engine the valves don't actually slam shut. They are closed at a rate determined by the cam profile. In older engines with basic ignition and fuel systems it was possible to float the valves if you over revved the engine ( i.e. the valve springs did not have enough tension to close the valves fully before the cam lobe came back around to open them). In extreme cases the valve was open so far the piston could actually make contact. Real ugly, real fast. But with electronic ignition with rev limiters this problem is all but extinct.

If the valve lash is allowed to go past recomended maximum the valve does not open as far, and the top of the valve (or shim/bucket combo) is smacked harder by the cam lobe as it comes around to open the valve again. The closure rate is still the same though. Also, the materials and geometries chosen for the valves and seats are such that they are the last to wear out. In a shim/bucket engine the shim is actually the softest part of the system because it is the cheapest and easiest to replace.

Either way, to get the post back on track, my experience tells me that valve lash has nothing to do with oil consumption.

By the way RMBbikes, how much oil are you burning, and did it start right after an oil change? If too thin of an oil was put in or one not rated for the temp range of your engine, the parts could be fine, the oil could just be getting thin enough to slip past the seals. A long shot, but worth considering before you tear apart what might be a perfectly good engine. I hope this helps. Good Luck...

[stoinkythepig]

Originally posted by SSearchVT
Stoinky - Sorry, but I dis-agree with your dis-agree. Here is my logic...

In a properly functioning engine the valves don't actually slam shut. They are closed at a rate determined by the cam profile. In older engines with basic ignition and fuel systems it was possible to float the valves if you over revved the engine ( i.e. the valve springs did not have enough tension to close the valves fully before the cam lobe came back around to open them). In extreme cases the valve was open so far the piston could actually make contact. Real ugly, real fast. But with electronic ignition with rev limiters this problem is all but extinct.

If the valve lash is allowed to go past recomended maximum the valve does not open as far, and the top of the valve (or shim/bucket combo) is smacked harder by the cam lobe as it comes around to open the valve again. The closure rate is still the same though. Also, the materials and geometries chosen for the valves and seats are such that they are the last to wear out. In a shim/bucket engine the shim is actually the softest part of the system because it is the cheapest and easiest to replace.

I can show you valves that are worn out enough that the screw and locknut lash adjusters ran out of adjustment. The heads of the valves are "tuliped" which allowed them to sink into the valve seats.

I have never replaced a shim with a thicker shim either. It's always been necessary to insert a thinner shim and my local dealer takes my old shims in trade (and gives me perfect used replacements) because they are still perfect. I tried grinding one once and did not find them at all soft, quite the contrary actually.

[KB]

Thanks for all the replies. I have found the compression ratio in the book. It should be at 164psi at 350 rpm. I've got 150. I'm going to look into a valve adjustment and replacing the valve seals. Put her back together and see what I come up with. That's the quickest and easiest option at this point. No need to tear down the heads or any of that crap. I have the manual and I am ready to go. Just don't want the bike to be down for a week or two. I got the bike with about 14,000 miles on it and the guy swore up and down that he had a valve adjustment done. But I think he's full of cah-cah!!!

So if the bike has never had a valve adjustment, and the tolerances got tighter, this causing the valve to never close all the way, would in turn cause poor compression. But what is causing the smoking? Is this where the bad valve seals come in?

Should I do another leakdown test?

KB

[SSearchVT]

Stoinky - You're right, valves can burrow into the seat. It has been my experience that it was the exhaust valves and the engine was run lean. The intakes have the incoming fuel air mixture to help cool them, but eventually they too will destroy themselves. Does this match with what you have seen?

RMBbikes - getting matching readings on all cylinders of 150 psi on a 14000 mile engine with a new spec of 164 psi is normal (variences can be caused by the gauge, tach, etc, and also some has to be attributed to wear). When the seals are replaced you have to take the valve train apart anyway, so it would be a perfect time to check and adjust valve lash. Again, just to rule out the obvious, did the smoking start after an oil change or any other service?

[KB]

The bike now has 40,000 on it.

I can't exactly pinpiont whent he smoking started.

KB

[stoinkythepig]

Originally posted by rmbbikes
Thanks for all the replies. I have found the compression ratio in the book. It should be at 164psi at 350 rpm. I've got 150. I'm going to look into a valve adjustment and replacing the valve seals. Put her back together and see what I come up with. That's the quickest and easiest option at this point. No need to tear down the heads or any of that crap. I have the manual and I am ready to go. Just don't want the bike to be down for a week or two. I got the bike with about 14,000 miles on it and the guy swore up and down that he had a valve adjustment done. But I think he's full of cah-cah!!!

So if the bike has never had a valve adjustment, and the tolerances got tighter, this causing the valve to never close all the way, would in turn cause poor compression. But what is causing the smoking? Is this where the bad valve seals come in?

Should I do another leakdown test?

KB

150 PSI is within 10% of 164 (and who knows if you were spinning at 350 RPM or not (a little valve timing overlap can allow RPM to have a huge impact on compression readings...) ) so nothing needs to be done for compression baswed solely on the compression test. A very leaky valve should yeild far lower than 150 PSI anyway.

No idea why the seals would go but I can't imagine it's from lack of adjustment. They (or more likely "it") may be defective. Perhaps the little spring broke inside one of them or the seal popped off the head and is just rinding up and down on the valve stem.

What were the results of the first leakdown test? I don't see it mentioned in this thread other than you could hear a leak. The test should yield a numerical (% if memory serves) result that you can compare to the specs in the manual.

[KB]

I am unclear of the exact method to obtain the % of leak. My first test I did was to determine more or less if it was rings or valves. Not so much to determine the % of leakdown.

I am going to start ripping the bike down tonight. Tanks plastics and everything that is in the way of access to the heads. I really want to get this fixed soon. It's very embarassing and my new nickname "smokescreen" is cool and all but I've had it.

BTW the bike uses about a qt of oil every 3000 miles. Depending on how hard I ride it.

Thanks for all your replies. They are much appreciated.

KB

[stoinkythepig]

Originally posted by rmbbikes
Thanks for all the replies. I have found the compression ratio in the book. It should be at 164psi at 350 rpm. I've got 150. I'm going to look into a valve adjustment and replacing the valve seals. Put her back together and see what I come up with. That's the quickest and easiest option at this point. No need to tear down the heads or any of that crap. I have the manual and I am ready to go. Just don't want the bike to be down for a week or two. I got the bike with about 14,000 miles on it and the guy swore up and down that he had a valve adjustment done. But I think he's full of cah-cah!!!

So if the bike has never had a valve adjustment, and the tolerances got tighter, this causing the valve to never close all the way, would in turn cause poor compression. But what is causing the smoking? Is this where the bad valve seals come in?

Should I do another leakdown test?

KB

150 PSI is within 10% of 164 (and who knows if you were spinning at 350 RPM or not (a little valve timing overlap can allow RPM to have a huge impact on compression readings...) ) so nothing needs to be done for compression baswed solely on the compression test. A very leaky valve should yeild far lower than 150 PSI anyway.

No idea why the seals would go but I can't imagine it's from lack of adjustment. They (or more likely "it") may be defective. Perhaps the little spring broke inside one of them or the seal popped off the head and is just rinding up and down on the valve stem.

What were the results of the first leakdown test? I don't see it mentioned in this thread other than you could hear a leak. The test should yield a numerical (% if memory serves) result that you can compare to the specs in the manual.

[TLRMan]

Oil smoke on decel is usually valve seals(as well with a show during starting)......If you don't put enough pressure in the cylinder during a leakdown, the rings won't seat and the air leaks past both comp rings, and sneaks out of the holes behind the oil rings as well as past the piston skirt. 150 seems fine with 40k on the engine.

Wet/Dry are the same readings so the rings are fine.

The exhaust valve drops ARE controlled by the camshaft lobes, but since they run hotter, are more apt to snuggle themselves a little deeper into the seat than the intake valves. Now days the camshaft profiles are not symetrical, and will allow the valve to drop faster. One of the limiting factors of holding an exhaust valve open longer is that when it's time to close it, it's gotta be fast, and a hot valve hitting the seats, will cause things to bend. Ducati and the desmo valve actuation are the only ones that can affectively have (aggressive) valve closure without any undue damage, but because of this, the valve train clearances have to be dead on.

If you can pressurize the cylinder and get the keepers and retainers off, good deal, but if you are planning to pull the head, might as well freshen up the valves and seats....

[KB]

I think I am going to just run the bag out of it and then come winter I'll pull the motor and do some work to it

Maybe some port and polish work on the head, high compression pistons, cams, and I think that should give a few more ponies.

Then we'll see what's up with those RC's

I'm still looking for a motor to drop in. If that comes through I will just swap and then I can REALLY build up the spare motor.

Thanks for all your replies and help. I owe you all a or 10

KB

[KB]

UPDATE:

I forgot a friend of the familia is a long time 20+ year rice burner motorcycle mechanic.

I explained all that I have explained to him here and he says I have a "collaped oil ring". He says in all his years of being a Japanese motorcycle mechanic he has never seen a set of valve guides go. He has however from my symptoms said he has seen alot of collapsed oil ring. He claims that my mile long standup wheelies have starved the front cylinder of oil thus the oil ring has gone south. Which would give a good compression/leakdown test reading.

I haven't torn the engine apart yet but he claims if it's not a collapsed oil ring he'll eat shit.

So I will keep you kids updated!!!

KB

[Awesome]

I'll help you do it. (AKA - drink beer and hangout) And if it's not it can I watch him eat the shit?