Would you notice a 50% power reduction?

[dcarver]

My 23k 06 A model is now in the shop with cylinders 3&4 at 60/80 psig. 1 and 2 at 180/190. Leak down test indicates leakage through intake valves through throttle bodies.

So... it seems that 1/2 of the engine is making 1/2 the horsepower..

So why didn't it run badly? Just 2 days before going in for normal service, it ran 130 no problem. Fast to accelerate,

Fuel efficiency had reduced from ~40 to ~34 but then again the gas reformulated and I've been running higher speeds with the warmer weather. Just did a 1,000 mile + ride two up, and except for some minor burbling, experienced by another rider on another FJ too, the bike ran great. The burbling was at a stop sign, I had to wing the rpm's to get her to launch, then it just stalled. The consensus at the time was improper ecu mapping due to being below sea level to well above sea level, I'm guessing Beatty is about 4000 feet and we had just left from - ~270 feet below sea level.

Anyway - the one nagging question is why didn't I notice the performance decline? I can say positively it didn't decline all at once.. Matter of fact, as far as I can tell, the bike ran as it did when new.. which makes me wonder if it was this way from the very start?

Sorry for the rambling, just confused, that's all. :glare: Would you notice a 50% decline?

 

[BrunDog]

The bigger and more pressing question is: why are the valves leaking?

-BD

 

[Barabus]

It will feel like a new bike with a turbo charger when you get it back!!

 

[weekend rider]

Lets hope they did not use some of there early technologiclal ideas when they came over here and were selling a lot of small cars during the first gas crunch. And that would be using inferior material for valve seats and valve guides, they incorperated brass and had nothing but problems.

Maybe it is just a standard production flaw and only your bike slipped by and made it to market, before they found the problem and correcteed it.

Just some info to help you think it through.

Good luck on the repair .let us know what the problem was

Maybe J.D. power and associates should call for a recall oh! it's not an American product

weekend rider

 

[kaitsdad]

My 23k 06 A model is now in the shop with cylinders 3&4 at 60/80 psig. 1 and 2 at 180/190. Leak down test indicates leakage through intake valves through throttle bodies.
So... it seems that 1/2 of the engine is making 1/2 the horsepower..

So why didn't it run badly? Just 2 days before going in for normal service, it ran 130 no problem. Fast to accelerate,

Fuel efficiency had reduced from ~40 to ~34 but then again the gas reformulated and I've been running higher speeds with the warmer weather. Just did a 1,000 mile + ride two up, and except for some minor burbling, experienced by another rider on another FJ too, the bike ran great. The burbling was at a stop sign, I had to wing the rpm's to get her to launch, then it just stalled. The consensus at the time was improper ecu mapping due to being below sea level to well above sea level, I'm guessing Beatty is about 4000 feet and we had just left from - ~270 feet below sea level.

Anyway - the one nagging question is why didn't I notice the performance decline? I can say positively it didn't decline all at once.. Matter of fact, as far as I can tell, the bike ran as it did when new.. which makes me wonder if it was this way from the very start?

Sorry for the rambling, just confused, that's all. :glare: Would you notice a 50% decline?

Let's think about this - if the head gasket was pinched or open between 3 & 4 from the factory - gasses moving between the cylinders when they shouldn't have - intake valve seats over time start to burn - (and this is pure conjecture, mind you, cause I don't know jack about this) and finally reach the point when they no longer seat properly.

I remember your bike from WFO5 when we did the CO mod - and it ran fine at that time. Or seemed to.

So - here’s my ‘hypothesis’:

A leak down test if I understand it correctly, measures the loss of pressure within a cylinder when the piston is at the top of the compression stroke. The piston is NOT moving - so the pressurized air is 'held' in the cylinder. If the valves are not able to seat, the pressure leaks out.

The burning of the valve seats would happen during the power stroke on one cylinder 'bleeding' burning pressurized gas into the cylinder next to it, while that cylinder is on a different stroke - perhaps intake? I don't know - but it would be interesting to study the firing sequence of the cylinders, and to understand what is happening on each cylinder at the same time. Probably a small window of time during the two cylinders' cycles that allow this to happen.

When the engine is running, there is a very small window of time that the cylinder is at TDC on the compression stroke - it fires, the gases expand, the piston travels down on the power stroke. A small amount of burning gas escapes through the compromised head gasket - burning the open intake valve guide of the other cylinder. An engine running at 1,000 RPM means that each cylinder completes a rotation (up and down of the piston) 1000 times per minute - or 16 times per second.

2,000 RPM = 32 times per second

4,000 RPM = 64 times per second.

So - running at 4K RPM, each piston reaches TDC on the power stroke 31.25 times per second – (intake, compression, power, exhaust) that’s 32 milliseconds for TDC power to TDC power- but being a 4 cycle engine, that piston is actually moving up and down 64 times per second - or TDC is hit every 15.625 milliseconds.

Not a very long time for gases to move from one cylinder to the other during the power stroke.

And that is probably why this was a very slow, very long process over time. All those little 15.625 millisecond 'bits' of time (assuming you averaged 4k RPM engine speed - I wouldn't be surprised if it's even a bit higher) slowly burned the valve seats in the adjacent cylinders - till the valve seats reached the point that they would no longer seal well enough to support proper expansion of the gases. Viola ! The noticeable loss of power happens at this point - it appears suddenly.

I think jestal will be proven correct - it's probably an improperly installed head gasket. You might want to talk to your mechanic and ensure that he’s careful when lifting off the head in order to preserve the gasket as best he can. I'm really looking forward to knowing what this is.

And I didn't touch it - so I know I didn't pinch it. Unlike my FI orings.

EDIT: Is my math right ? Does a 4 stroke engine have 4 revolutions from TDC Power to TDC Power? Or is it 2 revolutions?

I'm sorry, but my 9th grade auto shop class is but a vague memory.

EDIT: Math correction - Thanks, Toe !

 

[Toecutter]

Maybe you should give your Harley a polygraph exam.

EDIT: Is my math right ? Does a 4 stroke engine have 4 revolutions from TDC Power to TDC Power? Or is it 2 revolutions? I'm sorry, but my 9th grade auto shop class is but a vague memory.

4 strokes - two up, two down = Two revolutions.

 

[kaitsdad]

Maybe you should give your Harley a polygraph exam.

EDIT: Is my math right ? Does a 4 stroke engine have 4 revolutions from TDC Power to TDC Power? Or is it 2 revolutions? I'm sorry, but my 9th grade auto shop class is but a vague memory.

4 strokes - two up, two down = Two revolutions.

Thanks, Toe,

I'll revisit the math and edit my post.

 

[feejer222]

Its only a 25% power loss if its down half on only 2 cylinders. You should have noticed it even if it happened over a period. Maybe you didn't, the only other explanation is, as you say it was there from new. (Very doubtful). Strange it should happen at all.

 

[charismaticmegafauna]

k/d -- 2 revolutions.

Back to the original question: some anecdotes: It's been said that you can kill a frog in a pan of water on the stove by slowly increasing the temperature so the frog becomes adjusted to the increases and doesn't jump out. There have been manufacturers of competition motorcycles that included with the crated bike a dynomometer run of that engine -- the ones I've seen varied very little (< 10%). Someone who rode FJRs regularly; a tech at a big shop who regularly worked on FJRs; a test rider for Yamaha; a very active and experienced rider of high performance m/c (maybe an LD rider?) may have noticed this particular FJR to be "off-song". All good FJRs will run right up to 150 mph with no problem -- I know it may not be the smart thing to do but it does tend to take the place of a dyno.

I don't recall reading why you took it to the shop -- periodic service? Or, was it exhibiting running problems (related to what we now know is low compression on two cylinders)?

 

[kaitsdad]

k/d -- 2 revolutions.

Thanks, CMFauna!

 

[racer157]

This is a guess, but an educated one. Normally intake valves don't burn unless there is a radically timing change( ignition) or the valves have tightened up due to soft seats or soft valve. My thought is you may have missed a shift and tagged some valves. On a carburated bike this would be instantly noticed but on a fuel injected bike the system would try to compensate as much as it could thru the computer. The compression numbers you gave were low but still runnable. Most of us drive below 70 and this is normally in the first 1/8 of a turn of the throttle. With the weakened engine you may have used a slightly larger throttle opening not aware the bike was hurt. The tear down will tell for sure. Lets us know what your mechanic finds. Good Luck and keep the rubber side down.

 

[Vacman]

Ya they run the best right before they blow!

 

[v65]

Would you notice a 50% decline?

A 50% decline in what? My guess is that loss in compression did not result in the extreme loss of horsepower you think it did. It would be interesting to see a dino run with the loss of compression, obviously not going to happen. Maybe somebody with some experience can guestimate how much horsepower was actually lost? I 'll start the guessing at 10-20%.

 

[double_entendre]

Ya they run the best right before they blow!

I would have thought you'd notice just because it would run so rough with two cylinders not running right. My M3 just blew its head gasket between cylinders 5 and 6 and it was immediately obvious that something was seriously wrong. I'm really surprised that the bike would rev at all without seriously vibrating with two nearly-nonfunctional cylinders.

Not bagging on you, but wondering why the bike would run well enough to ride on essentially two cylinders.

Bob

 

[Geezer]

If I snapped the throttle open in second gear and the steering didn't get very light I would know that the power is below normal.

 

[jestal]

The cylinders were not totally dead...just a little weak. Unlikey you would notice it especially if it degraded over time. There is such a small window of time during the compression and power strokes for "leakage" to occur (no matter where it leaks to) that the leak becomes much less apparent to the power the engine is making compared to the relatively long time interval (slow RPM) during a compression check and the constant pressure of a leakdown test. The cylinders were still making compression and the leakdown wasn't totally zero (like with a hole in a piston) so those cylinders were far from dead.

Production engines have a lot of "tolerance" for high leakdown numbers and "low" compression. Don't be mislead by the leakdown and compression numbers that the racers like and quote. Production engine valve seats and rings and such are designed for the long haul not perfect sealing for only 1 or 2 hours of operation like on a race motor. As a result there is inherently a little more leakdown and compression loss under "normal" conditions so the numbers you saw are not as bad as you might be lead to believe. Granted, they certainly indicate something is wrong, particularily due to the mismatch with the other cylinders but the cylinders were far from dead.

Also keep in mind that at part throttle, where you are spending 99% of your time anyway, you are controlling the amount of power the engine is making with your wrist. Even if the engine is slightly down on power due to two weak holes the engine is SO far from full power that the overall effect of two weak holes is going to be even less evident. As before, the two holes were far from dead, just a little weak and you are making them all far "weaker" anyway by the heavy throttling at low power outputs. Fuel economy would start to show up a little due to the inefficiency of the two weaker holes but you as the driver are unconciously compensating for the slight loss of power by just opening the throttle a little more. So you notice little or nothing at part throttle.

My guess, off the cuff, based on the compression comparisons and leakdown is that the motor might have been down 5 or 10 % on power not 50% or more.

The other thing that is often misleading is when you might have a fouled plug or disconnected spark plug. That cylinder is not just dead. It is actually sapping power from the engine overall due to the severe pumping losses. Disconnect two plugs on an FJR and it would only be making about 35 to 40 percent of the normal power at WOT. The dead cylinders would obviously cut the power in half (down to 50%) and then pumping air in and out of the two dead cylinders would take at least 10 to 15 % more power away. So, disconnecting plugs (a typical "dead" cylinder comparison from a bad plug) losses a LOT more power than just weak compression. The weak compression cylinders are still running and at the very least making some power so they are nowhere near as "dead" as a cylinder you might have experienced with a bad plug or coil or ???.

Along this thought process, keep in mind that the production auto engines that disable cylinders for improved fuel economy (DOD) do not just turn off injectors or disable the spark. That would cause huge pumping losses that would kill power and fuel economy. A DOD engine deactivates the valve train on the disabled cylinders so as to keep the intake and exhaust valves closed all the time. This way the charge trapped in the disabled cylinder acts like an air spring. The piston compresses it on the up stroke and the compressed, trapped charge pushes the piston back down on the down stroke. Just like an air spring. There are only slight losses and the deactivated cylinders take almost no power from the rest of the engine while they are deactivated.

That is not a bad idea on the bent valve thought. Hadn't really considered that a valve might have tagged a piston on a severe overrev at some point. Certainly possible I would guess particularily if you happened to remember such an event. Since the tech mentioned that the intakes seemed to be leaking on the leakdown test it adds more credence to that idea. Usually the valve train on overhead cam engines like the FJR are pretty tolerant for overrevs so it might not be the first thing you would suspect. The engine is protected by the rev limiter on upshifts and missed shifts but if the transmission were downshifted too far at too high a speed the engine can be mechanically overreved and the rev limiter will not be able to prevent it. If I think about it long enough I might change my bet to a bent valve instead of the head gasket.......

 

[Inlaw1]

In regards to over revving the engine and tagging a piston, my FJR has a rev limiter on it to keep that from happening.

 

[jestal]

In regards to over revving the engine and tagging a piston, my FJR has a rev limiter on it to keep that from happening.

Read post above.....

If you are going 80 and downshift into 1st the rev limiter will be helpless as the drivetrain spins the engine into oblivion. Even turning off the key wouldn't help in this case. And it isn't that hard to shift down two gears instead of just one in the heat of the moment.

 

[Toecutter]

That is not a bad idea on the bent valve thought. Hadn't really considered that a valve might have tagged a piston on a severe overrev at some point.

So, will the repair be covered under Y.E.S., assuming you were smart enough to deny any overrev events.

I think Carver's got himself a blue lemon there.