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Engine guys; how to inspect a cam???

flyboy1963

Well Known Member
So I need to inspect the cam in my 0-320, FP, has anyone done the 'thru the nose' method, and what are the issues with pulling the plug, and sticking a scope thru the crank, as some guys seem to do?
can you only see the front lobes for cyl #1? The typical Lyc. cut-away leaves me scratching my head.
I prefer NOT to pull a jug, or two.
 
To get a look at all the cam lobes and follower faces, you need to pull some jugs. No other way around it.
 
hmmmmmmmm

ok Gary, that makes sense, if you gotta see 'em all!

....but can you see the front one or two? If they were pristine, I would take the odds that all were in reasonably good shape. if one was pitted, then would do further investigation of all.
 
Just seeing some of them means nothing. I have seen where all but one is perfect, the last one was garbage.
 
On my one hand I have 4 1/2 fingers. If you only look at one of my fingers you might assume that I have 5 :)))) so there you have it.
The point is, if you want to INSPECT the camshaft, pull a cylinder and look at the entire camshaft. You be glad you did regardless what you see. Larry
 
Gentle reminder, for the forgetful and inexperienced

The jug pulling technique is pull the piston out of the cylinder ONLY enough to expose the piston pin and pull the pin, leaving the piston in the cylinder.

Saves a hone@
!

mjb
 
So I can quickly think of a couple reasons you would want to inspect the cam. The first being the engine has sat for an extended amount of time and your concerned that the cam has rusted. Or, you've found metal in the filter and think it's possibly from the cam.

If you've found metal the first thing you can try is put a dial indicator on the rocker arms which will show you how much lift the cam lobes have. If you find one or more that aren't comparable then it's time to dig deeper.

My O-320 had one bad lobe on the cam that was almost half gone and all others were like new
 
Seriously? How 'bout some specifics?

Ya, seriously, why would I make that up? The last follower was worn so badly there was a grove in the face from what was left of the cam lobe. All the other lobes and followers were in perfect condition. This was on an IO-540.
 
Ya, seriously, why would I make that up? The last follower was worn so badly there was a grove in the face from what was left of the cam lobe. All the other lobes and followers were in perfect condition. This was on an IO-540.

WHY? How does only one lobe go sour? What causes such specific, localized damage?
 
I'd agree with Gary, it's typical to find only one or two bad lobes. Also, you'll typically find the followers gone before the cam lobe so it's more important to look at them first and that means all the rocker shafts will need to be pulled.
And last comment, you'll have to pull a front AND rear cylinder to see the entire cam and all the followers.
So I wouldn't inspect it unless you have ferrous metal in the filter and you know it's not a impulse coupling or something that can be fixed without major surgery, or I was buying it as a used or stored engine.
My dos centavos
Tim Andres
 
My O-320 had one bad lobe on the cam that was almost half gone and all others were like new

Same here, O-320 E2D. The bad lobe was one that activates two lifters. Compare the profile of the good lobes with the bad one:

overhaul-13.jpg


This is what kills a cam lobe:

overhaul-6.jpg


What was interesting is the engine still ran smoothly, matter of fact it took me half-way across the USA and back! Steel in the oil screen is what indicated something was happening in the engine.
 
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okay, so the verdict is.............

so is it POSSIBLE to see anything thru the crank?

...why do 'people' mention this method?

what's a reasonable amount of hours for a shop to roll the plane in, remove cowls, exhaust, intake tubes, all the primer lines, baffling etc. etc. etc. to pull 2 jugs, scope, inspect, and then re-assemble it all.???
10 hours?

sounds like you might as well do a top overhaul while you're at it! :confused:
 
so is it POSSIBLE to see anything thru the crank?
...why do 'people' mention this method?
what's a reasonable amount of hours for a shop to roll the plane in, remove cowls, exhaust, intake tubes, all the primer lines, baffling etc. etc. etc. to pull 2 jugs, scope, inspect, and then re-assemble it all.???10 hours?
sounds like you might as well do a top overhaul while you're at it! :confused:

I'm not sure what you are saying. You cannot see any part of the cam "thru the crank". The only thing you can see through the crankshaft is the inside of the crankshaft.
 
Maybe he means looking up with the sump removed? Answer is no, you can scarcely see the crankshaft through the oil drain slots in the case.
If there is steel in the filter it almost for certain is from a follower and the lobe it rides on.
Dial indicating the lift at the rocker will only tell you if you have a severe failure, it cannot tell you if the parts have spalled and are making metal.
Bottom line is pull two cylinders to know, or wonder and wish.
Tim Andres
 
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Cam troubles

My experience has been that the rear cam lobes and tappet bodies show wear or spalling more often than the forward ones. Several times have seen where a tappet quit rotating and the cam lobe wore a vertical "trench" in the contact face of the tappet body. Unfortunately the only real way to get a good look is pull 2 cylinders on one side. Shouldn't take more than 8 hrs in a average shop.

Don Broussard

RV-9 Rebuild in Progress
 
Same here, O-320 E2D. The bad lobe was one that activates two lifters. Compare the profile of the good lobes with the bad one:

overhaul-13.jpg


This is what kills a cam lobe:

overhaul-6.jpg


What was interesting is the engine still ran smoothly, matter of fact it took me half-way across the USA and back! Steel in the oil screen is what indicated something was happening in the engine.

You can find the bad lobe location by doing a compression check with a compression gAUge screwed into the spark plug hole and cranking the engine, just like you did with your car. A low number will show the valve was not open as much as the others. Do a differential test first to confirm the valves are sealing first.
 
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