I have this option for my exchange engine.
Conventional wisdom is that both should be the same, both conforming to the same mfg spec. And the secondhand one is field proven.
OTOH could Lyco still be having the same QA issues which they had years ago?
FWIW I would buy a new camshaft given the option. Any wear at all on the lobes and you are down on power. I know when I overhauled my own engine in the Cub it was a must change item for me. I am not sure about the quality issues from Lycoming, but you don’t hear much about them in the field if they are present. Do you know the tolerances for the used one, and where yours sits within the range?
An overhauled cam would be reground with a slightly smaller base circle. All wear would be ground off, tolerances would be the same as for the new part.
An overhauled cam would be reground with a slightly smaller base circle. All wear would be ground off, tolerances would be the same as for the new part.
Fair point @ Silvaire. I must go back on the Cub forums and search for the logic that prevailed in getting the new cam and lifters etc. I forgot what exactly made my decision clear at the time.
You get the same lift but it is other factors I would be thinking of eg case hardening depth.
My old Lake Amphib had the Firewall Forward STC pressure lubricated camshaft, which was seen as a desirable mod at the time. Just a curveball to consider.
http://thenewfirewallforward.com/tnfwf_2012-2013_new_007.htm
Indeed, though that cam is IIRC an FAA-only approval so an engine with it will block the plane ever going on an EASA-reg. Not that this would worry me, but also that camshaft is ineffective while stationary, obviously, so the great corrosion vulnerability is still there.
IMHO the argument for using an old camshaft, reground and re-casehardened as required, is that it probably doesn’t have internal defects in it. It will be NDTd anyway, but that picsk up only surface cracks, not ones which are wholly subsurface.
There is another argument, concerning Lyco’s QA, but I have never seen any evidence of bad metal in their camshafts. There was (for example) a poster here whose Lyco engine disintegrated with metal everywhere and it was traced to a shagged camshaft and tappets, and they got a lab to test it all for hardness and the report was that all the metal was exactly to spec and very uniform in hardness too… so the verdict was, again, corrosion, apparently under a previous ownership of the aircraft (and a period of inactivity which was either not evident from the logbooks or was disregarded as a prebuy factor). I was not able to get a permission to post the lab report or to get him to post it.
So I think a new camshaft is not going to be any worse than an overhauled one, though I am sure both will drive the valves the same way – due to the hydraulic tappet system.
Peter
What is the difference in $$ between the new and the refurbished? Very little.
What is the cost in $$ of re-opening the engine due to camshaft failure? Very much.
I have a friend who followed the advice of the O/H shop and fitted a re-furbished unit (I went for a new unit). After 500h the camshaft fail and he had a bill of > £10k to reworked the engine.
I say go for new. You can replace a cylinder, a pump, anything external very easily, internal parts are a different story. Go for the best you can afford because the other end is very costly.
That was my decision too. As I indicated earlier the main factor otherwise would have been whether Lyco have current QA issues.
For example with crankshafts, the ones they made approx 1997-2002 were crap, and eventually got hit by the AD. So in say 2001 you would be looking for a pre-1996 one, and I am getting one such in this engine, which is an ex Israeli Air Force VIP transport TB20 one. Unfortunately those “vintage” cranks were crazily expensive back then because everybody in the trade knew that the whole Lyco engine scene was about to hit the rocks due to the AD, and if you had one it was a great chance to make a fast buck out of some poor sucker. One “maintenance” company wanted £8k for a ~ 1960 crank but luckily I discovered it was a different type with something called “slush tubes”.
Sludge tubes 
