skykrawler Posted August 16, 2020 Report Share Posted August 16, 2020 Here is an interesting report http://www.kathrynsreport.com/2020/08/loss-of-engine-power-partial-cessna.html of a C206 with a big Lycoming that had roller tappet/cam failure. Lots of good pictures. I know some recommend getting IO-360s exchanged for roller tappet versions. I don't know when roller tappets were incorporated into the larger Lycomings. 1 Quote Link to comment Share on other sites More sharing options...
Hank Posted August 16, 2020 Report Share Posted August 16, 2020 There's surprisingly little structure holding the roller in place! Quote Link to comment Share on other sites More sharing options...
mike_elliott Posted August 16, 2020 Report Share Posted August 16, 2020 Just now, Hank said: There's surprisingly little structure holding the roller in place! aside from cost, I wonder why it was not made from a billet vs cast Quote Link to comment Share on other sites More sharing options...
skykrawler Posted August 16, 2020 Author Report Share Posted August 16, 2020 That was my thought as well. Things usually break at the smallest cross-section. Quote Link to comment Share on other sites More sharing options...
Hank Posted August 16, 2020 Report Share Posted August 16, 2020 (edited) 12 minutes ago, mike_elliott said: aside from cost, I wonder why it was not made from a billet vs cast Ha, ha, ha! "Aside from cost"! You're funny this morning! Aside from cost, how do the accountants tell engineers which one to buy? Been there, done that, lost the rodeo and was stuck with the sh!t option because it was cheaper. And had every problem I expected to have, plus some others, many of which would not have happened had Accounting let me buy a more expensive system. Instead, we bought the cheaper one and paid much, much more in downtime, lost production, replacement parts and bad product. But those losses did not come from the sacred Capital Budget . . . . Edited August 16, 2020 by Hank 1 Quote Link to comment Share on other sites More sharing options...
Sixstring2k Posted August 16, 2020 Report Share Posted August 16, 2020 Wouldn’t an oil analysis catch something like this? Or the beginning of it? Just asking out of curiosity. 1 Quote Link to comment Share on other sites More sharing options...
mike_elliott Posted August 16, 2020 Report Share Posted August 16, 2020 2 minutes ago, Sixstring2k said: Wouldn’t an oil analysis catch something like this? Or the beginning of it? Just asking out of curiosity. Most likely not. Tensile failure of the tappet roller shaft boss, then the Ca Ca hit the rotating oscillator so to speak. Not much time for an oil change in this event Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 16, 2020 Report Share Posted August 16, 2020 The pics are amazing... Everything was going along swimmingly well.... until the roller‘s shaft got part way out.... Cast or machined, won’t make much of a difference when parts get out of line and crash together.... It appears that something may have caused the roller shaft to become loose and unconstrained... It looks like there were some odd tracks displayed on the cam lobe over time... Words often used to describe damage caused by oxidation were used... Roller cam followers, I thought, were better able to handle the rough surfaces of a pitted cam... Something let the axle out... Once broken free... what kept the rest of the engine from soldiering on? Five other cylinders in good working order? How do we get to see the data from that JPI? Those trends will be extra interesting.... @kortopates There may be some signs from five flights earlier, or only five minutes earlier... +1 for the PIC recognizing the single cylinder going off line... and successfully landing amongst trees in the dark! Inviting the usual MSers that enjoy Sunday Engine discussions... @jetdriven @M20Doc PP observations only... not a mechanic... Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
kortopates Posted August 16, 2020 Report Share Posted August 16, 2020 (edited) 17 minutes ago, carusoam said: How do we get to see the data from that JPI? Those trends will be extra interesting.... @kortopates its here: https://dms.ntsb.gov/public/63500-63999/63917/636469.pdf You can see the event at 2:30 in the data Or if you want the EDM-900 data file: 636471.csv Edited August 16, 2020 by kortopates 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 16, 2020 Report Share Posted August 16, 2020 Wow! Thanks Paul!!! There is possibly more to be learned here... Partial power for another 20minutes... Then something else happened... in the dying throws and fits... ? It would be interesting to hear the pilot’s first hand account... Thanks for sharing the graphs... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Guest Posted August 16, 2020 Report Share Posted August 16, 2020 7 hours ago, Hank said: There's surprisingly little structure holding the roller in place! The material is wafer thin. I snapped this picture of one from my junk drawer. Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 16, 2020 Report Share Posted August 16, 2020 Any idea if there is some kind of retainer holding the shaft/axle for the roller in place? Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Hank Posted August 16, 2020 Report Share Posted August 16, 2020 15 minutes ago, M20Doc said: The material is wafer thin. I snapped this picture of one from my junk drawer. Quote Link to comment Share on other sites More sharing options...
Guest Posted August 16, 2020 Report Share Posted August 16, 2020 13 minutes ago, carusoam said: Any idea if there is some kind of retainer holding the shaft/axle for the roller in place? Best regards, -a- I’ll have a look to see what holds it in place. Clarence Quote Link to comment Share on other sites More sharing options...
cferr59 Posted August 16, 2020 Report Share Posted August 16, 2020 19 minutes ago, M20Doc said: The material is wafer thin. I snapped this picture of one from my junk drawer. This doesn't exactly make me want a roller tappet engine. Is this the first documented failure of this nature or has this happened before? The tappets in my Harley are beefier than that... Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 17, 2020 Report Share Posted August 17, 2020 There is probably a way to look up engine issues as they get recorded... They don’t necessarily need to cause an accident... If they become a significant issue... the AD system has a way of notifying owners... PP thoughts only, not a mechanic... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
skykrawler Posted August 17, 2020 Author Report Share Posted August 17, 2020 .....'The engine's 11 other roller tappet assemblies were found in overall good condition, and each of their respective shafts remained staked. ' My take is the cam led to the roller failure....rough ride. Should oil analysis reflect the wear on the cam? Quote Link to comment Share on other sites More sharing options...
mike_elliott Posted August 17, 2020 Report Share Posted August 17, 2020 13 hours ago, M20Doc said: I’ll have a look to see what holds it in place. Clarence the shaft repositioning itself outside its operating environment surely had to be a design consideration if this was the primary cause. That said, I left a very sweet engine in ittty bitty pieces entering turn 5 at Elkhart Lake back in the day because a wrist pin retaining clip (O Jesus clips, you see them and say "Oh jesus...") slipped from its groove. Cause was sloppy care in installation and putting a slight rounding on the groove's upper square edge allowing it to creep out. Anthony could be spot on about the shaft creep being the primary cause of the boss destruction, vs "value engineering" 1 Quote Link to comment Share on other sites More sharing options...
ArtVandelay Posted August 17, 2020 Report Share Posted August 17, 2020 .....'The engine's 11 other roller tappet assemblies were found in overall good condition, and each of their respective shafts remained staked. ' My take is the cam led to the roller failure....rough ride. Should oil analysis reflect the wear on the cam? I like to know if the cam node that failed is an intake or exhaust node, the intake (on 360 anyway) are shared, so if it caused the failure there should be 2 failed rollers. Quote Link to comment Share on other sites More sharing options...
jetdriven Posted August 17, 2020 Report Share Posted August 17, 2020 The valve could have stuck, then the roller tappet was then overloaded and failed. But usually the pushrod bends. These things have been in service fifteen years now, and this is the first failure of that mode that we've seen. 1 Quote Link to comment Share on other sites More sharing options...
mike_elliott Posted August 17, 2020 Report Share Posted August 17, 2020 1 hour ago, jetdriven said: The valve could have stuck, then the roller tappet was then overloaded and failed. But usually the pushrod bends. These things have been in service fifteen years now, and this is the first failure of that mode that we've seen. That would suck if the new weak point of failure is the roller tappet axel vs the pushrods. The valve stem lubrication and resultant cooling hasnt really changed, and the stuck valves will still be as common roller tappet or not. It would be interesting to see how many roller tappet engines have had "issues". Just because we havent seen them, that doesnt mean it hasnt happened of course. Quote Link to comment Share on other sites More sharing options...
jetdriven Posted August 17, 2020 Report Share Posted August 17, 2020 All engines have issues and failure modes. The question is, is the roller tappet more reliable than the flat tappet? I'd guess mostly yes, but economically, whats the tradeoff? I havent seen any cam failures requiring engine teardown due to rollers, besides this. But plenty due to the flat tappets. So, you trade 1 accident in a million for a "run to TBO" engine, vs one thats 2/3rds as likely, due to risk of lifter spalling. Totally made up numbers, BTW. Quote Link to comment Share on other sites More sharing options...
LANCECASPER Posted August 17, 2020 Report Share Posted August 17, 2020 2 hours ago, jetdriven said: The valve could have stuck, then the roller tappet was then overloaded and failed. But usually the pushrod bends. These things have been in service fifteen years now, and this is the first failure of that mode that we've seen. Must be at least two if @M20Doc has one in his junk drawer. Quote Link to comment Share on other sites More sharing options...
mike_elliott Posted August 17, 2020 Report Share Posted August 17, 2020 27 minutes ago, jetdriven said: The question is, is the roller tappet more reliable than the flat tappet? Ill disagree, Byron. My question is if the roller tappet engine has any less chance of exhaust valve coking and hard pointing the pushrod vs the tappet itself. If as you suggest, normally the pushrods fail first in compression, but perhaps now the tappet does instead, this is a much more serious point of failure. The problem of coking the valves caused by excessive CHT's is a different problem than the lack of lubrication/poor metallurgy tappet fix the roller cam offers. Quote Link to comment Share on other sites More sharing options...
kris_adams Posted August 17, 2020 Report Share Posted August 17, 2020 20 hours ago, cferr59 said: This doesn't exactly make me want a roller tappet engine. Yeah...the same exact thought was going through my mind... Quote Link to comment Share on other sites More sharing options...
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