Does Camshaft failure affect Crankshaft?

[cctsurf]

I have a camshaft failing in one of my planes, I've been thinking about a rebuild and wondering if any of those who have had camshaft spalling have also had trouble with the crankshaft when the engine was torn apart for replacement.  (this is one of the possibilities that my mechanic has warned of).

Thanks!

[ShuRugal]

depending on the way the cam failed, you could have debris contaminating and wearing the crank.

[AlexLev]

I just had my engine overhauled after a camlobe spalling + two lifters. Crankshaft was in good shape. A lot of the crankshaft is protected by the bearings, so I'm not sure what sort of failure you had...whether it's just some shavings coming off, or something more spectacular, but if it's the former I'd bet that your crank is fine.

My cost to overhaul the engine was about 13.5K all in including the R&R. No accessories except ignition harness + fuel pump + oil pump housing.

Edited March 8, 2018 by AlexLev

[cctsurf]

My cam is doing the standard metallurgy spalling issue, small shavings were coming off...  Actually we haven't seen metal in the oil filter for some time, however, one of the lobes is worn and I'm thinking that it might be time to do the bottom overhaul, I'm just balking at the price if I have to eat a crankshaft too.  We've been watching it for some time, and its been running strong; however, it may be getting some extra use this summer and I'd prefer to have a fresh engine.

The accessories were overhauled when it had a top overhaul not long before I bought it and that was a couple hundred hours ago.  We didn't realize it, but the spalling was already happening then.  That means 2 things to me: They had the opportunity to look at the camshaft and didn't.  At the same time, they had to mess with the crankshaft and it didn't throw up any red flags for them...  If their eyes were as careful on the crankshaft as the camshaft, no help, on the other hand, they had direct contact with the crank and it didn't stop them in their tracks.

[AlexLev]

26 minutes ago, cctsurf said:

My cam is doing the standard metallurgy spalling issue, small shavings were coming off...  Actually we haven't seen metal in the oil filter for some time, however, one of the lobes is worn and I'm thinking that it might be time to do the bottom overhaul, I'm just balking at the price if I have to eat a crankshaft too.  We've been watching it for some time, and its been running strong; however, it may be getting some extra use this summer and I'd prefer to have a fresh engine.

The accessories were overhauled when it had a top overhaul not long before I bought it and that was a couple hundred hours ago.  We didn't realize it, but the spalling was already happening then.  That means 2 things to me: They had the opportunity to look at the camshaft and didn't.  At the same time, they had to mess with the crankshaft and it didn't throw up any red flags for them...  If their eyes were as careful on the crankshaft as the camshaft, no help, on the other hand, they had direct contact with the crank and it didn't stop them in their tracks.

How do you know a lobe is worn? How severe? If metal is not showing up anymore, that’s a good sign. You could replace the cam/lifters for about 8K, I imagine..or do the whole overhaul for about 12-14.

[cctsurf]

1 minute ago, AlexLev said:

How do you know a lobe is worn? How severe?

We know because we had a bent push-rod tube that we replaced and noted that the tube had rubbed on the push rod and left a mark of how much lift it was getting.  It has ~3/8" lift, I've hear different things from different mechanics, however it should definitely be more.

[kortopates]

41 minutes ago, cctsurf said:

My cam is doing the standard metallurgy spalling issue, small shavings were coming off...  Actually we haven't seen metal in the oil filter for some time, however, one of the lobes is worn and I'm thinking that it might be time to do the bottom overhaul, I'm just balking at the price if I have to eat a crankshaft too.  We've been watching it for some time, and its been running strong; however, it may be getting some extra use this summer and I'd prefer to have a fresh engine.

The accessories were overhauled when it had a top overhaul not long before I bought it and that was a couple hundred hours ago.  We didn't realize it, but the spalling was already happening then.  That means 2 things to me: They had the opportunity to look at the camshaft and didn't.  At the same time, they had to mess with the crankshaft and it didn't throw up any red flags for them...  If their eyes were as careful on the crankshaft as the camshaft, no help, on the other hand, they had direct contact with the crank and it didn't stop them in their tracks.

You can't tell what might be going on with the crankshaft just doing a top unless you also start pulling connecting rods off. Then you can at least see the rod journals, but you still won't be able to see more (main journals) until the case is cracked.

But I wouldn't be too concerned. Even if some finer metal particles did get into the bearings creating some  minor damage there is good chance the crankshaft may still have enough meat to turn the shaft down, line bore the case and go to the next oversize bearings. Its very common to do so, and for lots of reasons that have nothing to do with metal contamination. If your worried though, you should be able to look at your engine's last overhaul records for the crankshaft dimensions (or receipts) and see if it still has enough meat for another turning or its had it last reconditioning so to speak. In which case if it needs it, you'll need a new crank. But you really won't know till the case is cracked and it all inspected.

Edited March 8, 2018 by kortopates

[KSMooniac]

I lost a lobe on my cam as well, and my crank polished out to normal specs and didn't need to be ground down.

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[cnoe]

Paul is right; pulling the jugs tells you nothing about the crank. But neglecting to inspect the cam and tappets while the jugs are off borders on negligence (on a Lycoming 360) since cam/tappet spalling seems to be an epidemic. Oil travels from the sump through the suction screen, the pump, and then the filter. With a cold start or plugged filter the oil will bypass and carry metal into the crank bearings. It’s a crapshoot, but if your crank hasn’t been turned too much already it can likely be reused (after turning, or not if you’re lucky). It’s very helpful to know what your current crank specs are (as noted above). A good indicator of contamination is to pull your prop governor and check for metal on its screen. Metal there means your filter has bypassed. Too much metal in the sump may cause damage to your cylinders and pistons from splash lubrication erosion. Oil analysis should put you on alert. Significant metal in the filter means repairs are in order.

 

 

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[cctsurf]

Just looked through the logs, it appears that the crankshaft was Inspected and polished at the previous overhaul, the yellow tag notes "std--std", which I'm hoping means that it was original size.  The engine was new 2100 hours before that.  It would appear that the crank has not been turned and the case hasn't been bored.  The info you have provided gives me a lot more confidence going into this!

[Guest]

Generally the crankshaft is protected by the oil filter, the oil pump body bores get scored by the steel particles passing through the pump. The pistons in line with the failing cam and lifter get their skirts impregnated with steel particles.  Left long enough this will “hone” your cylinder walls until they are scrap.

Clarence

[cctsurf]

1 hour ago, M20Doc said:

The pistons in line with the failing cam and lifter get their skirts impregnated with steel particles.  Left long enough this will “hone” your cylinder walls until they are scrap.

And still, this damage is cheaper to replace than if I have to replace a crank...

[nels]

9 hours ago, cctsurf said:

We know because we had a bent push-rod tube that we replaced and noted that the tube had rubbed on the push rod and left a mark of how much lift it was getting.  It has ~3/8" lift, I've hear different things from different mechanics, however it should definitely be more.

What is the published lift for that engine. Off hand 3/8 doesn’t sound too bad. I assume the rocker ratio is 1.5 or so? That would bring lift up to 9/16 inch. I’m not an airplane mechanic but I’d compare the lift with an indicator at each push rod.

[mike_elliott]

9 hours ago, KSMooniac said:

I lost a lobe on my cam as well, and my crank polished out to normal specs and didn't need to be ground down.

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The fact that most only lose a lobe when they fail, and it is usually the common intake lobe, just screams of metallurgy issues vs the official fall guy "corrosion" cause and generally points to the tappet as the weak part. The centrilube mod would seem to help and of course the new Lycoming tappets are available. But they are  not saying the old ones were junk.....

[KSMooniac]

The fact that most only lose a lobe when they fail, and it is usually the common intake lobe, just screams of metallurgy issues vs the official fall guy "corrosion" cause and generally points to the tappet as the weak part. The centrilube mod would seem to help and of course the new Lycoming tappets are available. But they are  not saying the old ones were junk.....

I opted for the centrilube mod and new Superior tappets, and hope that does the trick. Lycoming has put out several variants of tappets over the last few years, apparently throwing crap on the wall to see what sticks.

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[jetdriven]

The newest ones have a DLC “diamond-like coating” which seems to not corrode or spall. After a long talk with the owner of LyCon he has quite a few engines out there with these tappets and none have come back. 

[mike_elliott]

10 minutes ago, jetdriven said:

The newest ones have a DLC “diamond-like coating” which seems to not corrode or spall. After a long talk with the owner of LyCon he has quite a few engines out there with these tappets and none have come back. 

.hummm..... that says something itself. I know of an io360 engine that was hangared in a climate controlled environment, flown 2x a week, oil changes every 25 hrs, Aeroshell 100w, and it spalled tappets at less than 500 hrs. 

Corrosion was not the cause, even though that is what they told her.

[jetdriven]

Did it have the DLC tappets?

[cnoe]

But they are  not saying the old ones were junk.....

 

Lycoming may not be saying it Mike but plenty of others are (including me). Here’s a pic of the 4 (previously new Lycoming) intake tappets from my less-than 800 hour engine. This engine was flown weekly, 150 hours/yr for the previous 4 years, though the prior owner only managed 40/yr for the 5 before that.

 

 

I’m hoping the new DLC-coated steel tappets, frequent flying, Camguard, and my engine dehydrator get me well past the 2000 hour mark now.

 

 

Like [mention=6924]KSMooniac[/mention] my previously unturned crank was fine having caught the warning signs early through a rise in Fe (iron) on a routine oil analysis. I had the case split within about 50 hours and 3 more oil changes/inspections. Being in south Texas I wasn’t too worried about bypassing the filter with a cold start but once the filter started showing obvious “visible” metal the engine came off.

 

 

 

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[jetdriven]

You take a few of these stock iron lifters and bake them in straight w100 oil then hang to dry. In 3-5 days they will be covered by a bright orange bloom of rust. 

[mike_elliott]

Prior to moving to florida in 2012, I threw away a camshaft I took out of a Datsun 1200 in 1975. 

37 years of sitting around in a shed without any oil coating etc, not a bit of rust or pitting. Granted it was in Indiana, where it is only 90% humidity a few months of the year and full of days condensation occurs on cold parts regularly, not in a climate controlled hangar with a dehimidifier on it.

 

[jetdriven]

Yep that was then. A Lycoming cam from 1975 would probably do the same thing.  

All these spalled tappets and ruined cams, how many of them are from engines built before ~1995?  Two friends of mine have a 1987 built engine at TBO hangared on the gulf coast.  The Piper Arrow was built in 1989 but t flies about 2 hours a year for the past 15 years. No spalling it just Goes and goes. Another friend had a 1977 Aerostar with original engines. Never overhauled. 

[MB65E]

If your crank is of original size and never ground it should be fine. If it is polished .010 under now and there is damage you might be out of luck. I’m .010 under and I’m hopefully on the 2nd to last run on this crank. 

I bet your crank is fine.

-Matt 

[Browncbr1]

What years were known bad metallurgy for tappets?   Were all lycoming tappets from that time bad or was it hit and miss?   My 1998 overhauled Io-360-a1a with about 700 hours and a lot of leaky gaskets, but otherwise seems smooth and makes good power. Never found any traces of metal.  Flown every week, 25hr oil changes with Exxon elite and avblend.   

[mike_elliott]

On 3/8/2018 at 9:51 AM, jetdriven said:

Did it have the DLC tappets?

no I dont believe they were an option at the time she had it rebuilt. She now has a roller cam engine in it and it is the slowest J I have ever flown.