How to check cam in IO-360

[Morgan3820]

The partnership is wanting to upgrade the panel but before throwing money at the panel, I would like to check the engine health. As cams are often an issue, is there a way to inspect at least some of the cams without too much disassembly?

The engine runs fine with consistently good compressions, filter inspections. We have thought of starting oil analysis but I figure that would be of little immediate use. The engine has ~1300 hrs. since factory reman about 23 years ago.

 

[mondtster]

You’re likely going to need to pull at least one front and one rear cylinder to see much of anything.

 

[kyleb]

If you have a hollow crank, you can fish a borescope into the engine via the crank.

Alternately, you can measure valve lift at the rockers to get a sense of whether the cam has worn lobes.

But pulling a cylinder is the typical approach.

 

[mondtster]

If you have a hollow crank, you can fish a borescope into the engine via the crank.

That will only work on some engines, and having a hollow crank is not the only deciding factor.

This is why I didn’t waste my time mentioning it.

 

[Magman]

Cams are only hardened to a depth of a couple thousandths.

Once you wear through that the wear accelerates.

I think measuring lift will tell if it is shot.

Pulling cylinders if the most practical.

 

[Morgan3820]

Thanks. Is there a specified lift?

 

[MooneyDriver78]

I was able to tell my cam shaft was bad and which node was bad, just by reviewing my engine monitor data. But by then I needed to have it overhauled.

 

[Clip4]

The partnership is wanting to upgrade the panel but before throwing money at the panel, I would like to check the engine health. As cams are often an issue, is there a way to inspect at least some of the cams without too much disassembly?

The engine runs fine with consistently good compressions, filter inspections. We have thought of starting oil analysis but I figure that would be of little immediate use. The engine has ~1300 hrs. since factory reman about 23 years ago.

I believe you are justified in questioning the panel upgrades when you are running a 23 year old engine. If the partners aren’t willing to pony up the cash for the upgrades, stand your ground.

 

[nrpetersen]

(Is there a specified lift?)

Not that I've ever seen. Use a dial indicator to measure the valve spring cap motion, checking all cylinders. They should all be within a few thousands.

Bear in mind that on Lycoming engines around the center of the camshaft length, there are two cam followers running on each cam lobe. These are probably the ones most likely to be scored.

 

[mondtster]

Bear in mind that on Lycoming engines around the center of the camshaft length, there are two cam followers running on each cam lobe. These are probably the ones most likely to be scored.

Only the intakes are paired. And yes, they are most likely the ones to be spalled. The 540 I’m overhauling right now had every intake tappet spalled and every exhaust was fine.

 

[aftCG]

Cams are only hardened to a depth of a couple thousandths.

Once you wear through that the wear accelerates.

I think measuring lift will tell if it is shot.

Pulling cylinders if the most practical.

Curious because i don't know, but how do they regrind cams if that's true? Are they hardened again after grinding?

 

[Magman]

Is it possible to really get a meaningful determination with hydraulic lifters?

Would you have to bleed them down? Even then ; variation in the

Dry Lifter Clearance Range of .028 to .081 (?) would skew any lift results.

My thought is you would need a test that will alert you of wear of 1 to 2

thousandths. Any figure larger than that will show that the wear has progressed

through the hardened surface and into the material underneath that will wear

rapidly.

So you may be able to identify a BAD Cam : but not one about to go BAD.

 

[mondtster]

Curious because i don't know, but how do they regrind cams if that's true? Are they hardened again after grinding?

Ive never been present when one gets ground but that is my understanding of how the process works for aircraft cams and lifters.

Is it possible to really get a meaningful determination with hydraulic lifters?

Would you have to bleed them down? Even then ; variation in the

Dry Lifter Clearance Range of .028 to .081 (?) would skew any lift results.

I would question any measurements made with the hydraulic units in place. If they were removed and a dial indicator was placed directly on the tappet then I think you could get close enough. This sort of measurement and approach is commonly used when degreeing cams.

Regardless, the measurement would only tell you if you have a cam or tappet that is already bad, but likely wouldn’t provide any indication of one that is just starting to spall.