Checking Cam Lobe Condition

[jetdriven]

On 4/26/2020 at 12:59 PM, Nukemzzz said:

When I called and talked to Jewel about rebuilding my engine I asked about roller lifters and they reported that there is one thing to consider. Apparently with a prop strike you must replace all 8 of them at $750 each. I’m not one to plan on preparing for a prop strike but that is one thing maybe to consider. 

Im planning on giving DLC coated lifters a go as a compromise. 

Jewell, from what ive seen, marks parts up threefold or more.  When my friend asked for new lycoming cam and lifters rather than reground on his cracked case teardown, they told him nearly 7k more. When he asked why new 89$ lifters and a 400~ cam cost 7K, he was snapped at with "we dont negotiate parts prices". The rollers are ~250-300$ each

[chrixxer]

Engine monitor data could be useful to access engine condition including cam. Plus you can see how the engine was run.

How so? Savvy and I were pouring over the logs from the 830 and none of us caught the intake lobes issue; I had an A&P run a valve lift check and that caught it.


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[ArtVandelay]

How so? Savvy and I were pouring over the logs from the 830 and none of us caught the intake lobes issue; I had an A&P run a valve lift check and that caught it.


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The above is a graph of the EGTs during leaning at cruise.

I’ll leave it to the y’all to figure out which cam node was bad and why.
;-)

[Ragsf15e]

5 hours ago, ArtVandelay said:

The above is a graph of the EGTs during leaning at cruise.

I’ll leave it to the y’all to figure out which cam node was bad and why.
;-)

Was there only half the lobe left?!

[ArtVandelay]

Was there only half the lobe left?!

[jetdriven]

2 hours ago, ArtVandelay said:

geez look at all the rust on the rear journal and the cam gear !

[Ragsf15e]

Looks like it wasn’t flown and sat outside in a coastal jungle!

[A64Pilot]

10 hours ago, jetdriven said:

geez look at all the rust on the rear journal and the cam gear !

Surely that occurred after the cam removal, i’d guess he still has it and it sat around in a shop etc and rusted.

‘However I believe how or where an aircraft is kept as well as frequency of flight has a lot to do with it, an airplane kept outside will get corrosion faster than one in a hanger and a Florida airplane will get it before an Arizona airplane.

I now live in Fl and from my little bit of looking at aircraft to buy, would recommend avoiding Fl aircraft, and if its been kept on the ramp to most likely don’t even go look.

I went to look at a 79J, new paint in 05 and new interior a couple of years ago, thought it sounded real good.

Airplane wasn’t in my opinion even airworthy from excessive corrosion, sad to say but I think he killed it, I didn’t even bother looking close, the liner in the wheel wells actually had holes in them from corrosion.

‘School aircraft usually makeTBO or well beyond, and if you think about it, they are operated in a manner we were always told will kill engines, not properly warmed up, excessive, repeated full throttle excursion and pulled back to idle after full throttle over and over

 

So far as checking can lobe condition, about all you can do is pull two cylinders and look. and even that’s not a guarantee, as was said, all it takes is a small defect and it will spread, once you get through the exceedingly thin hardened surface, it goes fast.

‘How will DLC protect from cam corrosion? Is it the cam, or the lifter or maybe either one that starts it?

Edited March 22, 2021 by A64Pilot

[ArtVandelay]

geez look at all the rust on the rear journal and the cam gear !

It’s been sitting on my hangar floor for 3 years, it’s a good door stop. It’s usually stored vertically so the cam gear gets the dust and moisture.

[Mooney-Shiner]

On 4/25/2020 at 6:28 PM, philiplane said:

Yes, this will only identify lobes & lifters that are already unserviceable. It won't detect corrosion pitting that leads to spalling of the lifter faces. It's already easily done with a dial indicator mounted to the rocker cover bolt holes. You compare the lift of all intakes to each other and all exhausts to each other.

Thank you for posting this.  I would like to develop this a little more. 

1. Is there a SI or SB on exact procedure?

2. Besides all intake/exhaust comparison, is there an absolute number that we are looking for on the measurements?

[MBDiagMan]

Since this is aviation it might be bound by a specific procedure, but nothing could be simpler.  As long as you have a dial indicator and some standard Mount apparatus just remove the rocker covers, set up the dial indicator and turn the prop. Read the dial indicator and record the measurements. Easy Peasy.