Engine guys; how to inspect a cam???

[flyingriki]

Originally Posted by C-FAH Q

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?

[tim2542]

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

[Sam Buchanan]

Originally Posted by birddog486

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:



This is what kills a cam lobe:



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.

[flyboy1963]

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!

[BillL]

Originally Posted by flyingriki

WHY? How does only one lobe go sour? What causes such specific, localized damage?

Same reason all the links in a chain don't fail at the same time. Yes, Seriously.

[Mel]

Originally Posted by flyboy1963

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!

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.

[tim2542]

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

[cajunwings]

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

[gasman]

Originally Posted by Sam Buchanan

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:



This is what kills a cam lobe:



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.