Camshaft float ???
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New User
Joined: Oct 2008
Posts: 14
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From: Glasgow, Ky.
Camshaft float ???
Has anyone had a miss or what seems to be a timming problem? I have been told that the cam has a thrust plate that can wear & let the cam move away from the CPS, thus loosing the signal while changing the timming. I have changed ,CPS, IDM, Injectors, UVC wireing, Fuel pressure is good at wot, batterys AT 12.7 VOLTS. Anyone had this problem?? I have been looking for this fix for a while. This is worse at low rpm & med to high torque , cold or hot. Need a way to tell if the cam is moving& do I have to take out the motor to replace the thrust plate. Thanks to all that read & looking for someone that has had this problem. T.Tolle
Post Fiend
Joined: Feb 2006
Posts: 11,892
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From: Middle Tennessee
Has anyone had a miss or what seems to be a timming problem? I have been told that the cam has a thrust plate that can wear & let the cam move away from the CPS, thus loosing the signal while changing the timming. I have changed ,CPS, IDM, Injectors, UVC wireing, Fuel pressure is good at wot, batterys AT 12.7 VOLTS. Anyone had this problem?? I have been looking for this fix for a while. This is worse at low rpm & med to high torque , cold or hot. Need a way to tell if the cam is moving& do I have to take out the motor to replace the thrust plate. Thanks to all that read & looking for someone that has had this problem. T.TolleThere is a shim procedure if clearance is out of tolerance but it is rarely used. I have never heard of anyone doing it. I do not even know for sure how to go about measuring/doing it even after reading about it.
I doubt your cam situation is related to where the CPS aka CMP sensor gets it's signal. Seems to me, the darned thing ought to be called the crank position sensor though I am sure someone with real thick glasses and a pocket protector can explain why it is called a cam sensor.
Hotshot
Joined: Jan 2002
Posts: 17,988
Likes: 207
From: La La Land
Mike,
The cam position sensor "reads" differing-width "windows" in the camshaft gear. Most of the "windows" are the same size, but one is narrower and one is wider. The output from the CPS is square-wave pulses of DC voltage, in direct relation to the width of the windows passing next to it. It's how the PCM figures out which cylinder is where in the firing order, and allows it to figure when to send pulses to the IDM to fire the injectors properly.
Tony,
I understand your question, and can see how a thrusting cam would cause a small timing change, but there's been no discussion of it happening, at least not in this forum, that I can recall. It strikes me that it would be a small change, however.
Pop
The cam position sensor "reads" differing-width "windows" in the camshaft gear. Most of the "windows" are the same size, but one is narrower and one is wider. The output from the CPS is square-wave pulses of DC voltage, in direct relation to the width of the windows passing next to it. It's how the PCM figures out which cylinder is where in the firing order, and allows it to figure when to send pulses to the IDM to fire the injectors properly.
Tony,
I understand your question, and can see how a thrusting cam would cause a small timing change, but there's been no discussion of it happening, at least not in this forum, that I can recall. It strikes me that it would be a small change, however.
Pop
Post Fiend
Joined: Feb 2006
Posts: 11,892
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From: Middle Tennessee
Pop, I will not argue that. The CPS is mounted right above the harmonic balancer and may well read from a crank driven gear on the cam. Knowing you and your dealings, you are probably right.
Hotshot
Joined: Jan 2002
Posts: 17,988
Likes: 207
From: La La Land
Yes, Mike, the cam gear is exactly twice the diameter of the crank gear driving it, meaning also that it is turning half of the crank RPM.
Remember, these are four-stroke engines. Intake, compression, combustion, exhaust, (repeat).
Up, down, up, down. Twice around is one complete "cycle". Running at 500 RPM? You're getting 250 power pulses per minute. The cylinder only fires every SECOND time around. Two-to-one ratio.
If the sensor were on the crank, it would detect #1 cylinder EACH time it came around, not every-other time.
Here's an animated shot of a gasoline engine, which is the same except for what sets off the fuel. Look at the spark plug in this drawing as being the fuel injector, and it should become clear.
http://www.keveney.com/otto.html
Pop
Remember, these are four-stroke engines. Intake, compression, combustion, exhaust, (repeat).
Up, down, up, down. Twice around is one complete "cycle". Running at 500 RPM? You're getting 250 power pulses per minute. The cylinder only fires every SECOND time around. Two-to-one ratio.
If the sensor were on the crank, it would detect #1 cylinder EACH time it came around, not every-other time.
Here's an animated shot of a gasoline engine, which is the same except for what sets off the fuel. Look at the spark plug in this drawing as being the fuel injector, and it should become clear.
http://www.keveney.com/otto.html
Pop
Post Fiend
Joined: Feb 2006
Posts: 11,892
Likes: 2
From: Middle Tennessee
Yeah, that's right Pop now that I think about it, thanks. At least the question is not languishing away without an answer. So can we answer his question? Thrust plate or shim the CPS. Do you think it is walking? I am leaning towards shimming i am not sure how to do it from from previous reading in the shop manual. I guess I am not equipped and have not read about it in such a long time. Sorry OP.
Sorry OP.
Cargo Master
Joined: Apr 2004
Posts: 3,162
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From: Vilonia Arkansas
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Hotshot
Joined: Jan 2002
Posts: 17,988
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From: La La Land
You won't have to remove the motor. It's not going to be easy, though, and you could end up with a pan leak if you're not real careful about sealing it around the bottom of the front cover.
Given the way the gears are cut, it seems that the cam should always be thrust one way at all times, and not able to move in and out while operating.
Before you go much further, however, I'm a bit concerned about having only 12.7 volts while running. If the glow plug relay has "timed out" (after a couple of minutes, max) and shut off the glow plugs, you should be seeing about 14.4 volts across the batterys' posts.
There's an adapter that allows you to take compression readings through the glow-plug holes, too, and would tell you if you've got a valve going south. That might cause a condition that could be interpreted as a "miss" during high-load, low RPM conditions.
Pop
Given the way the gears are cut, it seems that the cam should always be thrust one way at all times, and not able to move in and out while operating.
Before you go much further, however, I'm a bit concerned about having only 12.7 volts while running. If the glow plug relay has "timed out" (after a couple of minutes, max) and shut off the glow plugs, you should be seeing about 14.4 volts across the batterys' posts.
There's an adapter that allows you to take compression readings through the glow-plug holes, too, and would tell you if you've got a valve going south. That might cause a condition that could be interpreted as a "miss" during high-load, low RPM conditions.
Pop
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Postmaster
Joined: Mar 2008
Posts: 4,158
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From: Paramount, Ca
Never heard of cam float, valve float is another story. There is a lot of problems with big rigs wearing out the cam lobes. They idle like crap and run horrible. It happens from them idling to much. I doubt that's your problem but it's possible. Good luck.
Bump.
Bump.
Post Fiend
Joined: Jul 2005
Posts: 14,582
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From: 21791
The cam/crank gears are helical cut. That means that it is constantly pushed one direction under load, the resistance from the valve springs keeps a constant load on the camshaft, which would probably not allow it to walk in and out. If they were straight cut, i could see that happening. Mike, here is a picture of the cam gear
Post Fiend
Joined: Feb 2002
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From: Carhenge
The early powerstroke CPS were a lot more sensitive to air gap, they ran closer and occasionally the cam gear would get too close and wipe them out. International actually offered a shim a shim kit for them, but I haven't heard of anyone having clearance issues for a long time, the newer CPS sensors must work at a wider gap.
Elder User
Joined: Oct 2005
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From: Reno nv
my thoughts and $.02:
if it were really the cam walking back and forth, it would affect the sensor since hall effects need to run in a minimum gap mode. too much gap will cause a miss read and result in errtatic typical bad CPS mode....
easy way to kinda check: take off sensor and see if the cam moves much backwards when you push on it with a dowel or other soft thing that will fit through the hole.
with a helical gear you'd advance about 2 degrees, which I don't think would affect much of anything at 2600 rpm where we operate at
if it were really the cam walking back and forth, it would affect the sensor since hall effects need to run in a minimum gap mode. too much gap will cause a miss read and result in errtatic typical bad CPS mode....
easy way to kinda check: take off sensor and see if the cam moves much backwards when you push on it with a dowel or other soft thing that will fit through the hole.
with a helical gear you'd advance about 2 degrees, which I don't think would affect much of anything at 2600 rpm where we operate at