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Bleeding Lycoming roller lifter

Bill.Peyton

Bill.Peyton

Well Known Member
I'm looking for the procedure to bleed the new style Lycoming roller lifter. I want to check the dry tappet clearance.
 
I think the bleed down part is the same as with conventional lifters. Let it sit on a valve-open part of the cycle for 5 minutes and that lifter should be fully compressed. Keep pressure on the pushrod while you rotate the prop to TDC and measure the gap.
 
Using the method of having it sit so they get compressed can make it easier to get the rocker arms off but it doesn't mean they are compressed enough to get an accurate measurement of dry clearance. It really is best to remove them and bleed them using a tooth pick or other non-marring device.

Vic
 
Vic, I agree with you in principle. But what is your experience, since you do a lot of work observing others, in practice? My thinking is for us amateur mechanics, that the chance of a screw up in pulling,bleeding, reinserting a lifter (along with push rod and rocker arm) likely exceeds the chance of an inaccurate reading done by bleeding in situ? Especially for a field check?
 
BobTurner said:
Vic, I agree with you in principle. But what is your experience, since you do a lot of work observing others, in practice? My thinking is for us amateur mechanics, that the chance of a screw up in pulling,bleeding, reinserting a lifter (along with push rod and rocker arm) likely exceeds the chance of an inaccurate reading done by bleeding in situ? Especially for a field check?
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I suppose this is relative to how tight the lifters are (I am sure there is some variability in the tightness / bleed down rate). In my engine, they will not fully bleed down with just valve spring pressure. I have to use extensive mechanical leverage just to get the rockers back on. I would have no confidence that they are fully bled down for a lash check after this though. Other than using a magnet to get the plunger assemblies out, not sure there is much to screw up. Once out, they are easy to bleed down and not many ways to damage them, unless you take them apart.

Larry
 
lr172 said:
I suppose this is relative to how tight the lifters are (I am sure there is some variability in the tightness / bleed down rate). In my engine, they will not fully bleed down with just valve spring pressure. I have to use extensive mechanical leverage just to get the rockers back on. I would have no confidence that they are fully bled down for a lash check after this though. Other than using a magnet to get the plunger assemblies out, not sure there is much to screw up. Once out, they are easy to bleed down and not many ways to damage them, unless you take them apart.

Larry
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I agree with Larry and Vic - if the lifters bleed down sufficiently to allow an accurate measurement with just spring pressure, then there's a good chance they are leaking. I have always collapsed them fully, according to the Lycoming manual (and the technique taught at their school), in order to get an accurate measurement.

Paul
 
BobTurner said:
Vic, I agree with you in principle. But what is your experience, since you do a lot of work observing others, in practice? My thinking is for us amateur mechanics, that the chance of a screw up in pulling,bleeding, reinserting a lifter (along with push rod and rocker arm) likely exceeds the chance of an inaccurate reading done by bleeding in situ? Especially for a field check?
Click to expand...

Honestly, it's not that hard and a reading without bleeding it down isn't really worth much. These engines are really old technology and most everything is out in the open and easy to get at. It's easy to compress the valve springs with the right tool and there's a great chance someone at the airport has one. Heck, I'll mail you mine if you want. 😀

Once you compress the valves it's super easy to slide the rocker arm shaft sideways to remove the rocker arms and then the pushrods slide out and you can remove the pushrod shrouds and then the lifters, using a piece of safety wire. No magnets.

Checking all of the dry clearances takes a few hours, so don't expect it to be a quick check.

Vic
 
The roller tappets are totally different than the flat tappets, At least that's the way it appears. The rollers tappets have a small oiler assy that fits over the end of the pushrod. This oiler fits into the hydraulic lifter. The lifter itself does not want to come out of the bore easily. I am very familiar with the removal and bleed down of the flat tappet assy., but this looks completely different, and does not want to come out. The bore has two flat sides to keep the roller lined up. Am I missing something here with the removal.
I bore scoped my cylinders for this last annual and found a valve on it's way to failure, so I replaced the cylinder. Only 680 engine hours! Lycoming may warranty it even though it is over 2 years, so I am sending the cylinder back to them for evaluation. I want to be sure I have the minimum tappet clearance before I button it up.
 
Bill.Peyton said:
The roller tappets are totally different than the flat tappets, At least that's the way it appears. The rollers tappets have a small oiler assy that fits over the end of the pushrod. This oiler fits into the hydraulic lifter. The lifter itself does not want to come out of the bore easily. I am very familiar with the removal and bleed down of the flat tappet assy., but this looks completely different, and does not want to come out. The bore has two flat sides to keep the roller lined up. Am I missing something here with the removal.
I bore scoped my cylinders for this last annual and found a valve on it's way to failure, so I replaced the cylinder. Only 680 engine hours! Lycoming may warranty it even though it is over 2 years, so I am sending the cylinder back to them for evaluation. I want to be sure I have the minimum tappet clearance before I button it up.
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SI1011J mentions that both a body and a plunger assembly inspection are required for both flat tappets and roller tappets. This implies a separate plunger assembly and I just can't imagine that it is captive. That would be a big change for them and see no reason for them to do it and a lot of reasons not to. The oiler you referred to is probably a redesigned pushrod socket that overcomes the lycomings poorly designed oil flow on the flat tappets. If you pull the oiler/socket, I suspect you will see the familiar plunger assy. A traditional captive lifter assembly will have a very visible c-clip around the top pushrod socket piece holding it together. If you cannot see a clip of some sort, it will come apart.

Larry
 
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