What to replace Cam with?

[garytex]

If you want you can skip the mental torture description below and cut straight to the chase, I'm looking for advise on what to do about my cam and lifters during an upcoming overhaul.  IO 360 A1A.  How about it fellows, what do you think would be best, and why?  I have had good luck with AEA in Dallas before on ferrous, and that is my first inclination, just OH the existing cam and lifters, but I'm wondering.

This is one of those tales about what happens when your engine talks.  Mine was burning 1 qt in 4 hrs, not bad, but had been burning 2 then later 3 in 50.  The quickening burn rate had kind of snuck up on me over the summer.  I had been doing long WOT 2700 rpm target EGT climbs to cooler altitude, and thought that might be where the extra oil had been going.  I also noticed one little transient change in vibration for maybe 3 seconds in cruise, not much, barely noticeable.  My mechanic checked compression, borescoped, found nothing.  Last few oil analysis from Blackstone showed slightly high iron, aluminum, nickel.  I flew it some more, still burning oil.  Two of the cylinders remained from a field limits overhaul about 10 years previously (overhauled jugs) and had 1400 hrs on them. Two are recent (400 hrs) overhauled jugs from Custom Airmotive, nickeled at that chromer in Tulsa to replace one that had cracked, one with a burned valve almost immediately after I had bought the airplane. I flew a few more hours, and something wasn't right.  Still burning 1 qt in 4.  I had been wanting to do the wobble test (valve stem to valve guide clearance) for a while, so my mechanic did that.  One of the old jugs had 40 thousandths, the other 25. The two new ones were fine.  With the spring off you could feel the slop in the valve.  So, ordered two new Lycoming cylinder kits from J and J airparts, a cylinder overhauler in Pleasanton, TX thats been around forever.  There was a little delay as we got the right wrist pins that matched the other side, but all good.  Now for the break in.  On take off, engine only turned up to 2500, but I hadn't done a very long warm up-run up, and sometimes with cold oil she only turns 2600, so no big deal.  I circled up to 5000 above the field, WOT, full rich, now up to 2600.  The replaced Cyls. were 2 and 4, 2 is the front, 4 the back both on the left (pilot) side.  2 was running hot, 435df, but 4, the rear cyl. was cool at about 375, and cyl temp on it fell about 25 df in the first 10 minutes.  I went about my business and flew another 3 hours.  4-5000 feet, wot, full rich, 2600 rpm.  Man, #2 just didn't want to break in, hot hot hot.  Always over 420, the rest of the cyls. 350-375.  I noticed that the engine seemed tight after shutdown.  The prop would stop quickly on shutdown.  Pulling the prop through took more effort than normal. But I had overhauled engines before, and they were all a little tight at first.  I flew another two 1.5 hr legs, and on the last part of the last leg, I climbed to 8500, then descended at 20", and about 250 fpm and finally got the #2 cut down to 395df.  The other jugs were all around 300-320.  Something wasn't right.  Shut down, got gas, and the starter (a newish NL starter with almost new Concord glass mat battery) barely got the 6 or so blades that my hot start always takes.  After shutdown at parking, I tried the prop.  With 3 fingertips on the backside of the prop, I could barely turn the prop.  With almost nothing to gauge it by I estimated more than 15 lbs of pressure, less than 25 to move the prop with the engine hot.  This required some puzzling.  Next morning, cold engine, engined pulled through with normal pressure, however it took almost all my effort fore and aft on the prop to feel the clunk of the prop hitting the end of the crank endplay. The obvious smoking gun was a cylinder, but I've been around the block a time or two with recalcitrant motors, trapped offshore, trapped out in the middle of the ranch, and was suspicious.  The painful lesson has been: If you are really hosed, there is usually more than one thing wrong, and you are sometimes wrong about or unaware of what the second (or even first) problems is.  The obverse of that is, in the specific case: I can probably get the 30 miles to the mechanic if it's just the jug, but if a thrust bearing is stressed, or one of the main bearings has spun a bit due to loss of bearing preload while the jug was off, I'm going to be hosed.  So I got out my trusty Hawkeye borescope (meant to inspect the inside of rifle barrels) and looked.  Nothing definite, maybe come scratching, maybe not.  Turns out the hot jug was 6 thousands out of round, and had 15 thousands choke, as reported in another post.  We put a replacement new jug on, it didn't run hot, but the engine still tight.  Then put two overhauled jugs on, that didn't have too much choke, engine still very tight when hot. Also there is zero crank endplay now, I mean none.  I've checked with enough engine overhaulers (smart old guys, and one old test cell guy) that have told me the same thing, which is that the engine is just about to seize, that I'm going to crack the case, but two more new jugs and major the engine.  Probably use Divco or ECI for the case.       

[carusoam]

Additional data points...

my factory reman engine (IO550) has a very small but noticeable movement from pulling vs pushing on the prop.

my original engine was slightly more.

my O360 in my C was measured in parts of an inch.

from this experience it tells me to expect some motion, or look for an explanation why no motion is acceptable...

Temperature dependent rpm sounds like a different problem that you are looking for.  Being off 200 rpm from Max, is about 10% power.  Which equates to a 50% increase in T/O distance in my O. This is the difference of 400' for going from 2700rpm back to 2500 rpm.  800' vs 1200' in T/O distance....280 hp vs 310hp.  That may be a govenor challenge.  

I would expect a tightness that slows the engine down that much would be turning something incredibly red with heat and burning the oil and turning it really dark with the aroma of being cooked.

This observation probably doesn't mean much coming from a PP without a mechanic's background.

Best regards,

-a-

Edited October 18, 2015 by carusoam

[MB65E]

What a bummer. Hail and now this. "love the one your with"!!

Keep the cam and re-grind it. Make sure the shop nitrates it. New lifters. Or overhauled lifters and new cam. I'd try to keep the cam if you can.

I needed a new cam to get rid of the two piece. Went with the Lycoming part. I used re-ground lifters from AIrcraft specialties services. I was going to mention century lube as well.

good luck.

-Matt

Edited October 18, 2015 by MB65E

[KSMooniac]

I opted for the centri lube STC mod for my cam during overhaul. I used new lifters and tappets too FWIW.

Some crank end play/movement is required. If you have none, something is very wrong IMO. The limits are in the overhaul manual. It sounds like it is time to open your engine.

Sent from my VS985 4G using Tapatalk

[garytex]

Yes, KS, the Centrilube might be a pretty good idea.  I knew about that but forgot about it which is of course shows the benefits of having multiple memories floating around to tap into.  I think the jury is still out as to the true proximate cause of cam failure, and I'm not sure additional lubrication when running would help if the true proximate cause is corrosion or bad metallurgy.   Ultimately it's probably a combination of factors. I'll take a look at the centrilube guys stuff and  prices. Thanks.

[N601RX]

I went with the Centrilub cam 4 years ago, no problems so for.  I purchased a new cam and sent it to them for the mod.  Cost was around $500. I used Divico for the case, Rick Romans and Aircraft Specialties for steel parts.  Aircraft Specialties balanced all the internals including a set of flow balanced lifter internals.  It runs very smooth. At the time Aircraft Specialties had the best prices on parts and I got most of the internal parts from them.  They had everything in stock.  I also got a few things from Aero-In-Stock. If I were doing it over again the only thing I would do different would be to port the cylinders.

Also lifters are purchased in 3 parts.  The body, hydraulic internals, and pushrod cup.

Edited October 18, 2015 by N601RX

[jetdriven]

If you are shredding bearings there is going to be heaps of metal in the oil filter.  

 

Also, when you regrind hard parts Ty can't re-nitride the surface unless you have ground all the previous nitrided layer off.  And there is no way to verify that. 

My previously overhauled engine made it 1250 hours on a new cam and aircraft service specialties reground lifters.  

The only solution for lifters is a roller cam but this is only available from one source and we know some folks have had problems with that source 

[garytex]

"If you are shredding bearings there is going to be heaps of metal in the oil filter. "

You know there wasn't anything that we could see when we had the jugs off.  Additionally, as mentioned there wasn't much in the filter after the first 6 hrs on the jugs.  I haven't had the filter open since.  The engine didn't seem to get tight till the last 2 of the 6 hrs, and hasn't been run 30 min since then.  It seems to be losing endplay with time.  I do not have a good explanation/understanding of what's going on.  

Byron, the only way to get rollers is to buy a new 390, right?  Either that or get really creative at the National Airplane Parts Association store, and put a big X on your data plate.  I don't see that as in the cards.  

But I'm still wondering what to do about the cam.