Measuring cam lobes on IO-360

[Flying Ant]

Is it possible to measure the health of a cam by measuring valve lift therefore measuring how much of the cam lobe is worn of any?

Can a cam be replaced by itself if it is worn or pitted?

By the way, I don't think I have any problems with mine but it's a conversation I was having with a friend.

 

[Tom-D]

Is it possible to measure the health of a cam by measuring valve lift therefore measuring how much of the cam lobe is worn of any?

Can a cam be replaced by itself if it is worn or pitted?

By the way, I don't think I have any problems with mine but it's a conversation I was having with a friend.

Yes cams can be measured, and yes any part in the engine can be replaced as a repair.

 

[Skylane81E]

Yep, if the cam is eatten up the lifters should have a good hard look taken at them as well.

 

[Let'sgoflying!]

cam lobe is worn of any? Can a cam be replaced by itself if it is worn or pitted?

I don't believe individual camshaft lobes are routinely built back up in light a/c engines; I have only heard of replacing the entire camshaft with new. (?)

 

[Piloto]

Yep, if the cam is eatten up the lifters should have a good hard look taken at them as well.

Hmm... wonder what they taste like. Never ate one.

José

 

[Skylane81E]

Crunchy

 

[N801BH]

Is it possible to measure the health of a cam by measuring valve lift therefore measuring how much of the cam lobe is worn of any?
Sure... Use a Dial indicator on the rocker arm...

Can a cam be replaced by itself if it is worn or pitted?

If the cam is toast it needs to be replaced and the lifters too at the same time.

By the way, I don't think I have any problems with mine but it's a conversation I was having with a friend ( end Quote)

 

[Flying Ant]

I was thinking because they are hydraulic lifters that the amount of valve movement will depend on how much oil they have in them. So it's a valid test to simply take the rocker covers off, pull the prop through and measure the valve lift?

 

[Let'sgoflying!]

Theoretically they will bleed down when there is no oil pressure.
Also I think a lot of destructive activity can happen on the lobe surface with little change in valve action, so you really need to eyeball the camshaft if there is concern about its health.

 

[Henning]

Yep, if the cam is eatten up the lifters should have a good hard look taken at them as well.

The tappets (in a plane with a hydraulic cam, the lifters are a separate unit within the tappet, the thing that rides on the cam) must be replaced with the cam as the wear surfaces have to wear in together. You can replace a tappet onto an old cam with no problem, however putting used tappets on a new cam will damage the cam.

Thing about measuring lift at the rocker (how you would measure the cam) is that it has to be pretty destroyed by then. There's a lot of pitting and flaking that can happen before you ever measure the problem.

 

[Dan Thomas]

I was thinking because they are hydraulic lifters that the amount of valve movement will depend on how much oil they have in them. So it's a valid test to simply take the rocker covers off, pull the prop through and measure the valve lift?

To get a good idea of the lift you have to take the guts out of the lifters and get all the oil out, then put them back in and measure the dry lift. This requires removal of the pushrod tubes, pushrods, rockers and so on, all of which is put back together to do the lift check, and hopefully someone doesn't turn the crank and pump the lifters full of oil again before you get the check done. You could turn the crank backwards to avoid that.

Dan

 

[Henning]

To get a good idea of the lift you have to take the guts out of the lifters and get all the oil out, then put them back in and measure the dry lift. This requires removal of the pushrod tubes, pushrods, rockers and so on, all of which is put back together to do the lift check, and hopefully someone doesn't turn the crank and pump the lifters full of oil again before you get the check done. You could turn the crank backwards to avoid that.

Dan

Vacuum pumps aren't fond of that.

 

[Skylane81E]

The tappets (in a plane with a hydraulic cam, the lifters are a separate unit within the tappet, the thing that rides on the cam) must be replaced with the cam as the wear surfaces have to wear in together. You can replace a tappet onto an old cam with no problem, however putting used tappets on a new cam will damage the cam.

Thing about measuring lift at the rocker (how you would measure the cam) is that it has to be pretty destroyed by then. There's a lot of pitting and flaking that can happen before you ever measure the problem.

Correct, lifers laymans term...

IIRC ECI reconditions tappets

 

[Henning]

I was thinking because they are hydraulic lifters that the amount of valve movement will depend on how much oil they have in them. So it's a valid test to simply take the rocker covers off, pull the prop through and measure the valve lift?

They'll all collapse pretty much equally. If you pull the prop through very slowly for a couple of turns, you'll bleed down all the lifters and you'll notice if one is hanging because it will be higher than the rest. By the time you notice a performance issue enough to make you suspect a cam, you don't need to do anything, it will be obvious as hell just watching the rockers as you pull it through even without a dial indicator. Once a cam goes through the thin hardened surface, the lobe goes down very quickly.
If I'm looking for early spalling, what I look for is a twitchy needle on my dial indicator, but not having one is not an indication that I haven't a problem. IOW, it can show a positive but not a negative.

 

[Henning]

Correct, lifers laymans term...

IIRC ECI reconditions tappets

Yep, just recoat them.

 

[Tom-D]

To get a good idea of the lift you have to take the guts out of the lifters and get all the oil out, then put them back in and measure the dry lift. This requires removal of the pushrod tubes, pushrods, rockers and so on, all of which is put back together to do the lift check, and hopefully someone doesn't turn the crank and pump the lifters full of oil again before you get the check done. You could turn the crank backwards to avoid that.

Dan

How much pressure does it require to operate your dial indicator?
All that is needed to be done is remove the rocker arm, bolt the dial indicator to the rocker box, and align the indicator pointer with the push rod, find lowest point on the cam, and set the dial to "0" and rotate the cam to the highest point and read the indicator.

Dry tappet clearance is a whole different routine, for a whole different reason.

 

[Tom-D]

I was thinking because they are hydraulic lifters that the amount of valve movement will depend on how much oil they have in them. So it's a valid test to simply take the rocker covers off, pull the prop through and measure the valve lift?

Yes, it really does not matter how much oil the lifter has in it, the lifter has a spring it it that will hold it extended, during the check with the rocker arm off. that spring will be stronger than the required pressure to operate the dial indicator.

the lifter is only 2 cylinders that have a spring that holds them extended to suck oil in when they are at the lowest point on the cam, as the cam trys to collapse the 2 cylinders, a check valve closes and prevents the lifter from being compressed, which then acts as a solid object. Each and every time the lifter reaches the lowest place on the cam lobe it will be pumped open to remove all the clearance in the valve train. that is why they are commonly know as "0" lash lifters.

 

[Tom-D]

Yep, just recoat them.

Nope they are never re-coated, they are ground to specific measurements, and rehardened if that is required, when they get too short, they are thrown away.

I require new tappets (AKA lifter body) and hydraulic units at overhaul, the "lifter" is the assembly of the tappet, hydraulic unit, and cup.

 

[Henning]

Nope they are never re-coated, they are ground to specific measurements, and rehardened if that is required, when they get too short, they are thrown away.

I require new tappets (AKA lifter body) and hydraulic units at overhaul, the "lifter" is the assembly of the tappet, hydraulic unit, and cup.

I forget what it was Ed told me they do on their tappet faces but it was a process after the hardening. I wouldn't use anything but new tappets on a new cam, not worth the savings unless they were unobtainium as new.

 

[Tom-D]

I forget what it was Ed told me they do on their tappet faces but it was a process after the hardening. I wouldn't use anything but new tappets on a new cam, not worth the savings unless they were unobtainium as new.

To modify any internal engine part requires a STC. the lifter bodies have allowable undersize measurements written into the over haul manuals.

The only exception to that is when you develop a patented process such as channel chrome as ECI did. And I'm not sure how the paper reads on that.

 

[denverpilot]

Vacuum pumps aren't fond of that.

Depends on the vacuum pump. Ever seen a cutaway of a dry pump?

Unless the vanes are so worn down they'd be breaking soon anyway in the forward direction, this is absolutely an OWT for most of them. Exacerbated by folks who "run them to failure" (granted a lot of us do) and don't know how close they are to failure.

 

[Henning]

Depends on the vacuum pump. Ever seen a cutaway of a dry pump?

Unless the vanes are so worn down they'd be breaking soon anyway in the forward direction, this is absolutely an OWT for most of them. Exacerbated by folks who "run them to failure" (granted a lot of us do) and don't know how close they are to failure.

I've taken them apart and swapped vanes in them even (no, not for re-installation on an airplane, I made a vacuum pump for doing a lamination/lay-up project)

 

[Let'sgoflying!]

when is a cam follower a 'tappet'?

 

[Dan Thomas]

Depends on the vacuum pump. Ever seen a cutaway of a dry pump?

Unless the vanes are so worn down they'd be breaking soon anyway in the forward direction, this is absolutely an OWT for most of them. Exacerbated by folks who "run them to failure" (granted a lot of us do) and don't know how close they are to failure.

That's right. I have never busted a pump by turning the prop backwards. We always bought the pumps with the vane wear inspection ports, and changed them once they reached the limit, and that limit was conservative enough that you could turn the thing backwards as long as you liked.

Before the inspection-port pumps we did run them to failure and they almost always broke up before low vacuum warned us. After all, the engine will sometimes kick back on starting, and a worn pump might fail at that time.

Dan

 

[Let'sgoflying!]

I broke vanes on the pump in a newly purchased plane by moving the prop backwards out of the way of the towbar. (I could actually hear them snap.) So, it does happen and it's not an OWT.

In this case the vanes were short (well worn) and it was a blessing in disguise, to discover it this way.

 

[Tom-D]

when is a cam follower a 'tappet'?

My old Chevy 235 has tappets in it because that is what they did, tap, tap, tap
But the box I received today had 8 Lifter bodies in it along with 8 hydraulic units including cups.

When I get them together, I will have 8 new Zero lash lifter assemblies.

 

[Henning]

when is a cam follower a 'tappet'?

The piece that rides the lobe of the cam I have always known to be a tappet regardless type. Or are you including non engine specific cams as well?

 

[Tom-D]

I broke vanes on the pump in a newly purchased plane by moving the prop backwards out of the way of the towbar. (I could actually hear them snap.) So, it does happen and it's not an OWT.

In this case the vanes were short (well worn) and it was a blessing in disguise, to discover it this way.

The only way that can possibly happen is to have the vanes worn to the point they will not retract into the cavity they normally operate in.

the vanes are designed to be at a tangent to the rotation of the rotor, centrifugal force brings them out of the groove, and they slide around inside of the pump, when you turn them backwards the friction of the side wall of the pump housing will force them back into the center of the rotor. simply because there is no centrifugal force to hold them extended.

I'd bet the pump was shot long before you touched the prop, and all you heard or felt was the backlash of the accessory gears, or as you pushed or pulled the prop you felt the crankshaft end play. on some engines that is very pronounced.

 

[Tom-D]

The pictures are of a Pesco wet pump, but the operation of all wet or dry pumps is the same theory.

 

[Henning]

The only way that can possibly happen is to have the vanes worn to the point they will not retract into the cavity they normally operate in.

the vanes are designed to be at a tangent to the rotation of the rotor, centrifugal force brings them out of the groove, and they slide around inside of the pump, when you turn them backwards the friction of the side wall of the pump housing will force them back into the center of the rotor. simply because there is no centrifugal force to hold them extended.

I'd bet the pump was shot long before you touched the prop, and all you heard or felt was the backlash of the accessory gears, or as you pushed or pulled the prop you felt the crankshaft end play. on some engines that is very pronounced.

I've taken apart every failed pump I've removed, and I replaced at least 3 of probably 40 in 2 years working a CRS where the reported failure was on turning the prop back. It doesn't have to be all that worn out. What I found is that dust and moisture make a scrud that gets in that crack a keeps the vane from retracting into the slot.

 

[Tom-D]

The piece that rides the lobe of the cam I have always known to be a tappet regardless type. Or are you including non engine specific cams as well?

Have you ever looked in the part break down and seen the actual nomenclature ?

 

[Let'sgoflying!]

I'd bet the pump was shot long before you touched the prop, and all you heard or felt was the backlash of the accessory gears, or as you pushed or pulled the prop you felt the crankshaft end play. on some engines that is very pronounced.

You ever have that sickening feeling when you hear something go, 'crack', and you instantly know you broke something unintentionally - you immediately blurt "oh, ****"?
I did all that when it happened because I knew something had broken. Confirmed it by starting it up again; shonuff - zero on the gauge. Opened pump and found busted, and short vanes.
I could be wrong, and I often am...but I wasn't this time. I will take that bet!

 

[Henning]

You ever have that sickening feeling when you hear something go, 'crack', and you instantly know you broke something unintentionally - you immediately blurt "oh, ****"?
I did all that when it happened because I knew something had broken. Confirmed it by starting it up again; shonuff - zero on the gauge. Opened pump and found busted, and short vanes.
I could be wrong, and I often am...but I wasn't this time. I will take that bet!

I used to hear it. Owners would walk in and say "Hey"... They knew it.

Change your vacuum filters, they're cheap insurance against this.

 

[denverpilot]

I broke vanes on the pump in a newly purchased plane by moving the prop backwards out of the way of the towbar. (I could actually hear them snap.) So, it does happen and it's not an OWT.

In this case the vanes were short (well worn) and it was a blessing in disguise, to discover it this way.

Right. But those would have been beyond the limit through one of those little inspection ports, and I assume it probably had well over 500 hours on it, right?

If so, it was overdue to fail. And you're right, turning the prop backward was a blessing in disguise... since it saved you having an in-flight failure. (Hopefully not in solid IMC.)

If the vanes aren't worn out, backwards doesn't hurt them unless something else has already gone wrong inside.

 

[Tom-D]

I guess we now add this to the pre-flight list, turn the prop backwards to see if the dry pump is worn out.

 

[Dan Thomas]

Right. But those would have been beyond the limit through one of those little inspection ports, and I assume it probably had well over 500 hours on it, right?

If so, it was overdue to fail. And you're right, turning the prop backward was a blessing in disguise... since it saved you having an in-flight failure. (Hopefully not in solid IMC.)

If the vanes aren't worn out, backwards doesn't hurt them unless something else has already gone wrong inside.

When we bought the Tempest or Rapco pumps with the inspection ports, the requirement was to make the first inspection at 500 hours, then every 100 thereafter. We were getting around 1200 to 1400 hours out of a pump mounted on any of the six Lycomings we were operating.

Continentals spin their pumps much faster than the Lyc and those pumps will wear out faster. Pumps that get hot wear out faster, too, as do any that get oil or cleaning solvent into their drive ends. They don't have much for seals into the pump itself, and the only oil seal is to keep engine oil in the engine, not out of the pump. The dry side of that seal is vented to the atmosphere and external oil or solvent can get into that area and at the pump itself.

Dan

 

[Tom-D]

When we bought the Tempest or Rapco pumps with the inspection ports, the requirement was to make the first inspection at 500 hours, then every 100 thereafter. We were getting around 1200 to 1400 hours out of a pump mounted on any of the six Lycomings we were operating.

Continentals spin their pumps much faster than the Lyc and those pumps will wear out faster. Pumps that get hot wear out faster, too, as do any that get oil or cleaning solvent into their drive ends. They don't have much for seals into the pump itself, and the only oil seal is to keep engine oil in the engine, not out of the pump. The dry side of that seal is vented to the atmosphere and external oil or solvent can get into that area and at the pump itself.

Dan

The old Pesco wet pumps on the 0-300-D we ran to failure but they never failed, at engine overhaul we would disassemble inspect and replace vains when necessary.

 

[Let'sgoflying!]

Change your vacuum filters, they're cheap insurance against this.

against worn-down vanes? Cool, I had no idea.

 

[Let'sgoflying!]

If the vanes aren't worn out, backwards doesn't hurt them unless something else has already gone wrong inside.

I agree with your statement, Nate.

I guess we now add this to the pre-flight list, turn the prop backwards to see if the dry pump is worn out.

And to the prebuy inspection, I missed the worn vanes (no inspection holes back then). Logbook might have told me but I don't place any faith in logs, and was focused on bigger issues.

 

[Skylane81E]

I forget what it was Ed told me they do on their tappet faces but it was a process after the hardening. I wouldn't use anything but new tappets on a new cam, not worth the savings unless they were unobtainium as new.

O-320-H2AD...

Reconditioned were well worth the price of admission.