ROTAX HYDRAULIC LIFTERS

[Kyle Communications]

I hve never heard of lapping lifters ever..only valves of course

 

[facthunter]

It's precision stuff and most just replace the whole lifter. They are relatively cheap as they fit a lot of motors. IF there's much leakage in the lifter the motor will clatter and maybe run roughly till it pumps up and you have a risk of a pushrod jumping out of place and maybe bending. I don't like them in an aero motor as it's something else to go wrong and I've experienced a partial failure that nearly put me amongst a field of tree stumps In an 0-300. Continental. A bit of dirt in the oil can cause this. That's all it takes.   Nev

[Area-51]

Thanks for lifter deets there Kyle. Much appreciated.
 

Lapping in lifters to the camshaft is a lost art and there is the science as well that comes from years of experience working with metal and machines; so there is no break in period required as it is done by hand prior.

 

The camshaft lobes have been scrutinised and wear marks present all lifters operating slightly off center as required.

 

I have had more time to sit and nut this situation out and go through the many possibilities.
 

Firstly the worst presenting lifter was put in the lathe and polished up with cotton and brasso, then the contact face was lightly lapped and then brasso polished. The lifter surface was pretty slippery afterwards. Then the diameter was mic'd again 0.8745", unchanged. The face was checked with a dial gauge, 0.004" convex and 0.00025" deep trough mark from not spinning. Then the lifter was placed into the cleaned bore lubricated with diesel. While sliding down the fit was somewhat tight until fully in place where it could rotate freely. The rotation of the lifter operation was checked. It rotated until the trough aligned with the lobe crown; so that lifter as is is cactus.

 

I am not at all happy with the tightness of the lifter when it reaches the top of it's stroke, which may be a mitigating cause toward not spinning. Will have to mic up all the other bores and compare. However at this stage I am leaning toward operator error as the cause of this abnormal early lifter failure.

 

Allowing the engine to sufficiently heat stabilse before going WOT into the sky is so important; reason being. These lifters are operating in a chunk of alloy that takes a whole lot longer to reach operating temperature than the lifter does. And the lifter is clearly operating at a very minimal bore clearance. If the lifter heats up and grows before the crankcase has had sufficient time to equalise then this clearance is again reduced. And what can be expected to happen when sustained WOT is selected too early? Lifters that don't spin is one answer of many. Which is what I think has happened here.

 

So a new set of lifters will go in and the if not sufficient an extra 0.0005" bore clearance at the unused section of the upper bore will be dialled in. To be honest these lifter bores should be interference sleeved with bronze or EN31, but I get that the crankcase only has to reach the TBO. May opt to have this done while the crankcase is apart.

 

Regarding lifter leak down rates. I have read a few posts about lifters leaking down overnight. This is not an issue so long as the lifter operates correctly while the engine is running. The concern is greater if the lifter does not leak down. Leak down rates vary greatly. The standard automotive (rotax) lifter can have a leak down rate  of anywhere between 80-160 seconds, and this is why some engines idle rougher than others. Higher precision lighter weighted lifters can have a leak down as low as 20 seconds balanced across all lifters; while operating at high rpm the lifter stays pumped up; while at low rpm idle the lifter leaks down reducing valve lift and duration resulting in a smoother idle and easier startups because the high speed valve timing has been altered to a more sedate manner. The lighter weighted competition lifters will also help reduce valve float as well as the reduction in extraordinary level of reciprocating inertia of the valve train is affected so lighter valve springs can be implemented reducing this inertia again even more.

 

 

 

 

Edited August 29, 2023 by Area-51

[facthunter]

That last bit is not right. Where did you get such information? It's difficult to get any lifter full of oil to depress. The amount of clearance when empty of oil is about .10 inches (about  2.5 mm. minimum) Just ask anyone that's done it properly Any loss of lift will bring in a very sharp/abrupt contact and should not be happening. Any of that would be dangerous.  A new motor is best pre pressured with oil to make the engine start easier. Any ONE being depressed will make the engine run rough. New camshafts and followers can be moly coated to assist break in. It's more critical when extra strong valve springs are used. The Revs a 912 does, valve float should never be an issue.  Bushes in the block are going to weaken it and there would have to be NO chance of it moving when used for the follower . You'd be better to get an oversized follower and bore the hole a bit. They don't turn properly till there's a bit of load on them also. Nev

[Area-51]

A couple of more sessions on the 914 and some more answers emerging from the mystery of early lifter failure.

 

After frustrating and inaccurate results from the trusted mitutoyo kit some specific sized gauges were turned up and mic'd on the lathe and finished off with a polish. The one on the right measures for flogged out lifter bores upon tear down and will go in the Special Tools draw. The one on the left is matched to the 914's current lifter bore diameter; it measures 0.8748". The diameter on all the hydraulic lifters is 0.8745"; that's a 0.00015" operating clearance. I think somebody at the factory has maybe pushed '0' on the CAM console one too many times?

Either way 0.00015" wall clearance on a hydraulic lifter is pretty tight. All the more reason to warm up that engine before WOT or suffer early valve train failure. I would expect this issue has been sufficiently rectified since the engine's 1998 production date; 0.0005" to 0.0015" being the standard wall clearance. Not  sure what Rotax actually specify.
 

upon writing I have just heard from someone that rebuilt two pre 1998 9XX engines that upon tear down both engines had chronically hammered grooved lifter faces. So maybe this was an endemic production issue. Glad to of identified a source of and reached a conclusion on this one.

 

 

 

[facthunter]

Motors using non roller followers are all having problems these days as the anti scuffing additives needed are not permitted in road use oils as they muck up the CAT. Convertor.  Nev

[onetrack]

I've already mentioned this ZDDP problem in the 19th post on Page 1 of this thread, and got told Shell Aero Sport is the recommended oil and is presumed to have the appropriate level of ZDDP in it.

I reckon either the Shell Aero Sport oil is suffering from a deficiency of ZDDP, or someone has been using another brand of oil that has inadequate ZDDP in it. The lifter/camshaft damage due to reduced levels of ZDDP is well known.

[facthunter]

It's complicated by the CONFLICTING needs of the drive clutch. They say the clutch will risk slipping if those additives are used. Why not get around it with ROLLER followers?. Any of those surfaces failing contaminates the oil with metal particles. Once the surface is destroyed on the cam or follower face it will continue to deteriorate..  Nev

[Area-51]

Ok so some update on this subject...

 

Just pulled out a new 916 lifter from its bubble wrap packet. It appears slightly brighter in colour than the 914's HT-900 ford unit; so will assume that is indicative of a change in base material with a reduction in nickel to chrome ratio; i.e harder wearing.

 

The 916 measures 0.8742" against the 914's 0.8745"; the really early build 912 80hp lifters measured up at 0.8747"; so we see a progressive increase in lifter bore clearances being dialled in over the years. Fitting the 916 lifters the operating clearance has gone from 0.0001" to 0.0004". Does not sound a lot but after a really light hone things should be sitting pretty within the nominal 0.0005" to 0.0015" nominals.

It would be safe to assume non rotation of lifters has been an operational challenge for quite some time. Let's hope it has finally been sorted by the white coats at the factory.

[skippydiesel]

FYI: Rotax Owner Forum has a lot of very well informed information on lubricant choice. "AeroShell Sport +4" being the current oil of choice (there are others).  Rotax now offer a full synthetic oil "XPS"  that may suit some pilots.

[Area-51]

27 minutes ago, skippydiesel said:

FYI: Rotax Owner Forum has a lot of very well informed information on lubricant choice. "AeroShell Sport +4" being the current oil of choice (there are others).  Rotax now offer a full synthetic oil "XPS"  that may suit some pilots.

The subject presented has nothing to do with choice of oil; it's a mechanical and materials related design matter resulting in reduced component longevity. It would not at all be surprising if multiple engines exhibit these aspects of lifter wear if inspected at the end of TT.

[skippydiesel]

1 hour ago, Area-51 said:

The subject presented has nothing to do with choice of oil; it's a mechanical and materials related design matter resulting in reduced component longevity. It would not at all be surprising if multiple engines exhibit these aspects of lifter wear if inspected at the end of TT.

Okay let's not get all hot & bothered 😎 - just responding to some earlier comment about oil choices possibly contributing to accelerated wear.

[Area-51]

13 minutes ago, skippydiesel said:

Okay let's not get all hot & bothered 😎 - just responding to some earlier comment about oil choices possibly contributing to accelerated wear.

Trying to keep the data relevant; subject of oil should be fodder for never ending story 🙂