Camshaft Photo

[AndyFromCB]

The camshaft is the one that came out of my 1600 hour TIO540AF1B, the camshaft in question is actually only about 1100 hours old as it was replaced by previous owner during engine repair. That lobe is about 3 millimeters shorter than the rest. The oil analysis was showing elevated steel starting about 1450 hours. So the engine flew for about 150 hours with this happening, never missing a beat, still climbing like a bat out of hell. The good news, oil filter did its job, the crank, connecting rods, cylinders are still all standard size after the overhaul. TIO540AF1B overhaulled with all accesories for 33K (other than the turbo which would have been another 1500 or so), granted I kept the cylinders, but all new pistons, springs, valves, guides, etc. But the cylinders only had 1100 hours on them and still measured standard.

[KSMooniac]

Do you know the history of the cam?  Was it new when installed 1100 hours ago, or serviceable, or reground?  

[AndyFromCB]

Brand spanking new last time 1100 hours ago with a new set of cylinders, turbo and few other goodies. That's why I kept the cylinders during this overhaul, 1200 vs 2800 for new.

Andy

[jetdriven]

Our cam looked just like that, but 3 lifters were completely chewed up as well.

[AndyFromCB]

What's funny is 8 out 9 lobes are within new limits and one is so far gone. Out of the 12 tappets, 1 was a goner, 1 was starting to go, you could tell it quit rotating, others looked brand new. Other than the oil pump housing, the rest of the engine looked new upon opening. It was 1600 since major but only 1100 since almost major (case work, new cam, new cylinders) and 400 since tear down by G&N for prop strike inspection. I'm a strong believer G&N killed it during the inspection and reassembly.

Hopefully the guys at Central Cylinder where you can eat of the floor in the assembly room did better. Everyone I talked to around here has never had an issue with their engines and they do all work inhouse including fuel, turbos, controllers, etc. One of the better equipped shops in the nation that doesn't just look at lycomings price list and knocks a grand off like most big name shops. I'm not going to name names but they do a lot of work for few of the big ones.

On the other hand they showed me an engine done by a big name shop they were tearing apart at 100 hours because it was making metal.

[Skywarrior]

My gut tells me roller tappets have to be less injurious to cam lobes than old-style. For example, if you have any valve float, the tappet could impact the lobe around halfway up the rise, rather than smoothly following the surface of the cam. IF that happened, the tappet would gouge the 'upward rising' side of the cam lobe.

However, if a *roller* tappet ever hit the side of the lobe (vice rolling uphill smoothly), it would not gouge the lobe. The roller wheel would transfer the impact force into spinning itself on its 'axle'.

The fact that astelmaszek's cam is nearly pristine except for just 1 lobe makes me think he did not have a corrosion problem. Corrosion is not that selective. Manufacturing flaw? Maybe. Oil distribution not homogeneous across the cam? Maybe. Heat problem? Maybe. A&P hamfistedness? Maybe. Cam heat-treated or quenched incorrectly at the factory? Maybe.

Conclusion? I'm gonna try really hard to minimize possible ways my engine can lunch itself. The more knowledge we can gain about engine operation and failure modes, the better off we will all be.

[AndyFromCB]

Corrosion definatelly was not an issue. Airplane was based in Lake Tahoe, flown weekly between Tahoe and LA. I'm not crying too much, I paid next to nothing for it (I knew the engine was going to go sooner rather than later) and now I have a TKS Bravo with a new engine, overhauled gyros/autopilot, upgraded GMX200/GDL69/WX500, fairly new paint and interior, 400 hours on prop/governor/exhaust, new everything else and I'm still in for less than vRef.

Granted, it's been fun 8 months getting everything in top shape and writting lots more checks. Keeping N767RD for a while. Now time to get back to work, write the next big app to make good photos look bad and buy me a TBM.

Andy

[jetdriven]

Quote: Skywarrior

My gut tells me roller tappets have to be less injurious to cam lobes than old-style. For example, if you have any valve float, the tappet could impact the lobe around halfway up the rise, rather than smoothly following the surface of the cam. IF that happened, the tappet would gouge the 'upward rising' side of the cam lobe.

However, if a *roller* tappet ever hit the side of the lobe (vice rolling uphill smoothly), it would not gouge the lobe. The roller wheel would transfer the impact force into spinning itself on its 'axle'.

The fact that astelmaszek's cam is nearly pristine except for just 1 lobe makes me think he did not have a corrosion problem. Corrosion is not that selective. Manufacturing flaw? Maybe. Oil distribution not homogeneous across the cam? Maybe. Heat problem? Maybe. A&P hamfistedness? Maybe. Cam heat-treated or quenched incorrectly at the factory? Maybe.

Conclusion? I'm gonna try really hard to minimize possible ways my engine can lunch itself. The more knowledge we can gain about engine operation and failure modes, the better off we will all be.

[Skywarrior]

Quote: jetdriven