Lycoming Roller Tappets

idahoflier

idahoflier

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idahoflier
Since roller tappets have been around over a decade, does anyone have any operation experience with them?

I know HP remains the same and they add additional weight. Do they make it to TBO? If you converted due to an overhaul, would you do it again?

Thanks!
 
From what I've read, they cut down on friction but cam and lifters must be replaced at TBO, vs tappets that can be re-used if within tolerance. Primary advantage is for high RPM engines, which our engines are not.
 
The other benefit is for aggressive cam ramp profiles and environmentally friendly high-pressure lube additives, both of which are in the automotive realm. I suppose if wiping cam lobes, spalling lifters, and corrosion are issues, maybe it has aviation benefits as well.
 
Raymo said:
From what I've read, they cut down on friction but cam and lifters must be replaced at TBO, vs tappets that can be re-used if within tolerance. Primary advantage is for high RPM engines, which our engines are not.
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Their primary advantage in the Lycoming is their ability to work with minimal oil, such as at startup. Lycomings long had problems with cam/lifter scuffing due to the placement of the cam above the crank, where oil didn't readily reach them until the oil started flowing and was thrown off the crank at them.

We ran the roller lifter engines in the flight-school airplanes. They were just fine.
 
My recalled Superior engine had roller lifters. My newly ordered Lycoming engine will also have roller lifters. I wasn't offered a choice in either case. They've become standard equipment.
 
Dan Thomas said:
We ran the roller lifter engines in the flight-school airplanes. They were just fine.
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Based on your experience do you think they are worth the upgrade?

Based on the amount of flying I do this would likely be the only overhaul I would need for my aircraft so the added costs at the next overhaul after roller tappets wouldn't be a factor. My understanding is that the only way to get roller tappets is through Lycoming and that limits options for the overhaul I'm going to need.

The other consideration is that my engine has never been overhauled. If I go the Lycoming route I don't get my engine back and could potentially receive an engine that has been through several overhauls. I understand in theory that shouldn't matter as everything will be within limits, but at the same time Lycoming offers incentives on first run cores, so there has to be a reason for that.
 
idahoflier said:
Based on your experience do you think they are worth the upgrade?

Based on the amount of flying I do this would likely be the only overhaul I would need for my aircraft so the added costs at the next overhaul after roller tappets wouldn't be a factor. My understanding is that the only way to get roller tappets is through Lycoming and that limits options for the overhaul I'm going to need.

The other consideration is that my engine has never been overhauled. If I go the Lycoming route I don't get my engine back and could potentially receive an engine that has been through several overhauls. I understand in theory that shouldn't matter as everything will be within limits, but at the same time Lycoming offers incentives on first run cores, so there has to be a reason for that.
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We bought Lycoming factory overhauls because they didn't cost us any more than getting our engines overhauled locally, and we were able to have the engine on hand and not have to ground the airplane for a long time at engine change.

If your engine has many years on it the overhauler might find extensive corrosion that mandates a new crankshaft and some gears and whatever else is rotted away. That's expensive. Lycoming has the advantage of being able to pull brand-new parts off the shelf, and I suspect that it's actually cheaper to do that rather than trying to reclaim worn stuff. Their engines get new cylinders and cam and lots of other stuff. A couple of times I received entirely brand-new engines for overhaul exchange because they were short of cores.
 
Take a look at a cam and a standard lifter and ask yourself what would be the value of a roller here. Other than expense of the OH, I don’t understand why all aicraft engines don’t have roller.

With that said, cams do not wear out before TBO on planes that are flown a lot.
 
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In automotive applications there are plenty of cases where the roller lifters have stopped turning and ruined the lifter and cam. My reservation with the Lycoming rollers would be seizing due to disuse and rust. Does anyone know of any problems with old, low time Lycoming engines with roller lifters?
 
My O-360 has roller lifters and about 1350 hrs since overhaul in 2009. No lifter issues, but it has been flown regularly by both the previous owner and me.

The one time it gave me some problems the shop was able to remove the lifters and test/inspect the mechanisms from the outside (they were fine). I'd guess that if we wanted to inspect the camshaft, it would be possible to pull some lifters and insert a borescope.
 
bkspero said:
My O-360 has roller lifters and about 1350 hrs since overhaul in 2009. No lifter issues, but it has been flown regularly by both the previous owner and me.

The one time it gave me some problems the shop was able to remove the lifters and test/inspect the mechanisms from the outside (they were fine). I'd guess that if we wanted to inspect the camshaft, it would be possible to pull some lifters and insert a borescope.
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If you don't mind sharing, what was the nature of the problem that required looking at the lifters? Thanks!
 
idahoflier said:
If you don't mind sharing, what was the nature of the problem that required looking at the lifters? Thanks!
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Im guessing he’s thinking of the hydraulic units, as I don’t believe the roller lifters are removable without splitting the case. I may be mistaken however, as the last roller engine I had apart was a couple of years ago now.
 
idahoflier said:
If you don't mind sharing, what was the nature of the problem that required looking at the lifters? Thanks!
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I had 2 cylinders repaired due to out of limits valve wobble tests and one of the repaired cylinders just about always lagged the other 3 on cold starting. Its EGT lagged the others by about 20 seconds and the engine ran rough until its EGT substantially caught up to the others. One theory was that one or both of that cylinder's lifters were collapsing and taking some time to resume operation and properly open the valves. The lifters were fine. Eventually my local shop sent the cylinder back to the repair shop to be reworked. They sent the reworked cylinder back with another set of rings and it has been fine since.

I was not at the shop when the lifter work was done, so its possible that the lifters were not removed if the hydraulic units can be examined and tested without removing the lifter.

I am also ready to be corrected, but for now I still think that they can be removed. See this Lycoming Service Bulletin, and specifically the paragraph under the first "WARNING". It talks about things that must be done if the roller lifters are removed prior to overhaul. I take this to mean that removal is possible without splitting the case.

https://www.lycoming.com/sites/default/files/SI1514C Roller Tappet Part Info Update_0.pdf

And if you compare roller lifters to Lycoming old standard lifters, the diameter of the roller appears to be no larger than the diameter of the body so it makes sense that it could be extracted from the case (as Continental lifters can). OTOH, old standard Lycoming lifters have a wide face that is too large to fit through the cavity in which the lifter body slides. See this web page near the bottom for a comparison:

https://www.lycoming.com/parts/tappets#section_2
 
bkspero said:
I had 2 cylinders repaired due to out of limits valve wobble tests and one of the repaired cylinders just about always lagged the other 3 on cold starting. Its EGT lagged the others by about 20 seconds and the engine ran rough until its EGT substantially caught up to the others. One theory was that one or both of that cylinder's lifters were collapsing and taking some time to resume operation and properly open the valves. The lifters were fine. Eventually my local shop sent the cylinder back to the repair shop to be reworked. They sent the reworked cylinder back with another set of rings and it has been fine since.

I was not at the shop when the lifter work was done, so its possible that the lifters were not removed if the hydraulic units can be examined and tested without removing the lifter.

I am also ready to be corrected, but for now I still think that they can be removed. See this Lycoming Service Bulletin, and specifically the paragraph under the first "WARNING". It talks about things that must be done if the roller lifters are removed prior to overhaul. I take this to mean that removal is possible without splitting the case.

https://www.lycoming.com/sites/default/files/SI1514C Roller Tappet Part Info Update_0.pdf

And if you compare roller lifters to Lycoming old standard lifters, the diameter of the roller appears to be no larger than the diameter of the body so it makes sense that it could be extracted from the case (as Continental lifters can). OTOH, old standard Lycoming lifters have a wide face that is too large to fit through the cavity in which the lifter body slides. See this web page near the bottom for a comparison:

https://www.lycoming.com/parts/tappets#section_2
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I think you're confusing the "hydraulic unit" that sits inside the lifter body with the lifter. Those can be removed without any invasive disassembly and checked to make sure they aren't bleeding down. Even if there was no problem with them they need to be removed and collapsed prior to reassembly so you're not trying to compress oil while reassembling the valvetrain.

The picture you linked is hard to see but I believe the flats that keep the roller lifter from rotating also keep it from being pulled from the case. Like I mentioned earlier, it has been a couple of years since I did cylinder work on a roller engine but I probably would have removed the lifter body if it was removable, and I know I didn't do that. :)

As a tangent, everyone loves to hate the Lycoming "76" engines but they did have removable lifters that allowed inspection of both the cam and the mating surface.
 
Spring Ford said:
Harvey J. Crane Jr of Crane Cams patented the roller tappet in 1963.
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And he got it from the old big radial engines which were using it prior to WWII.
My 1937 Warner 165 horse had roller tappets in it.
 
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