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Area-51
Joined: 03 May 2021
Posts: 372
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 Posted: Tue Aug 22, 2023 12:37 am Post subject: ROTAX 9XX Hydraulic Lifters |
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If anybody has extended field experience overhauling early and late production 9 series engines I am needing some clarity on the following:
• Some forums make mention of an SB some 10 years ago related to faulty hydraulic lifters. Is this true? I cannot find any SB on the FlyRotax website other than (SB-912-051/SB-914-034). Are there any relevant others?
• I am tearing down a 1999 914 with 105hrs TSN. It has Johnson HT-900 (Ford 351 Windsor) lifters fitted. 50% of the lifters are presenting signs of early failure at the lobe contact face. There is no EDM oiler port on these units. Were Johnson lifters ever fitted as OE components on the 9 series engines?
• I have removed the lifters from another earlier +2000hr 912UL. They do not have any branding laser etched. The lifters also have an EDM pinhole port in the center of the lobe contact face. The lobe contact face on some lifters are just beginning to present troughing. Do genuine Rotax hydraulic lifters still support an EDM oiling port on the base of the hydraulic lifter?
• The current part number for the lifter is 854099 (915is), and 881832 for the Set. So far I have found references to eight part number changes prior to 881831 (set) in 2008, working backwards; 881830 (set) / 854098 / 884094 (set) / 854092 / 854090 - and two since, 854099 / 854097. So clearly there has been a somewhat constant unresolved issue with lower valve train reliability prior to 2008. Can anyone shed more light upon this?
Any factual industry knowledge is appreciated.
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| A good lifter, rotating in service |
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| Starting to fail after just 100hrs due to not rotating in service. |
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| Johnson HT-900, Ford 351 Windsor |
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Area-51
Joined: 03 May 2021
Posts: 372
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| Posted: Sun Sep 03, 2023 5:31 am Post subject: Re: ROTAX 9XX Hydraulic Lifters |
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So an update on the 914F tear down and a correction on earlier assumptions.
At first my initial thoughts were leaning toward operator error of insufficient engine warm up prior to T/O where the lifter to crankcase expansion lag was causing the lifter to not rotate; which was somewhat correct and not correct.
The second 912 being torn down does not have an oiler port at the lifter face. The markings thought to be EDM ports were just deterioration of the surface material.
There is always a reason for early component failure. Determining the root cause is not always that easy as there are often layers of factors to be thrown into the diagnostic possibility field.
One thing noticed on the 914 while removing each lifter was how tight they each were during extraction and insertion through the unused portion of the lifter bore. Could this indicate the clearance upon assembly at the factory?
Some gauges were turned up on the Czech Hobbymat lathe. One gauge was made oversize to determine unserviceable bore sizing of ^0.0015". The other gauge was matched to the 914's unused portion of the bore. It was a good exercise with the added benefit of learning how to perform 0.0005" precision passes.
In the end the gauge revealed that the engine left the factory with 0.00015" operating clearance. This alone would prevent the lifter spinning in the bore as required. Introducing lifter to crankcase expansion lag would reduce this clearance further again. There is minor scuffing on the bore indicating metal to metal contact binding. So far information filtering in has this situation presenting in 1999 and prior manufactured engines.
With a cause now identified the lifter bores will be correctly sized and a new set of lifters fitted and lapped to the camshaft.
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| The special special tools |
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| Mostly torn apart for inspection |
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dmac7
Joined: 05 Apr 2019
Posts: 46
Location: Canada
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| Posted: Mon Sep 04, 2023 4:08 pm Post subject: Re: ROTAX 9XX Hydraulic Lifters |
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Very interesting, Ford lifters. I would be a little surprised if those were put there by Rotax in Austria! I will ask someone with Rotax experience and get back here. I know old american V8's mostly.
The Rotax service manual's & parts catalogue show very conventional lifters without those Ford part numbers, actually when I looked that Johnson HT-900 I get a aftermarket part. Made in USA , they claim to be best in the world.
Looks like that one lifter was not always rotating, on most flat tappet engines the cam is taper ground, this should be visible in the cam wear pattern. When the lifter rides the lobe it will rotate if all is well. The taper will wear off on the nose of the lobe first but it will still rotate unless the whole lobe is worn down.
Pull the valve covers on a engine and run it, if some push rods are not rotating or some are rotating slower, you have a problem!
Some engine's offset the lifter from the cam lobe instead of taper grinding the cam, they still rotate.
If the lifter had corrosion or deposits on the lifter body it would be hard to remove, and may not rotate.
Was reading about a guy in Australia who sent his 912 cam to Melbourne for regrind after 1800 hrs. and re-nitride (surface harden) and bought new lifters. Your cam should be good with only 100 hrs. though.
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Area-51
Joined: 03 May 2021
Posts: 372
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| Posted: Mon Sep 04, 2023 4:40 pm Post subject: Re: ROTAX 9XX Hydraulic Lifters |
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Thanks, would really be interested to confirm who actually supplies Rotax their OE hydraulic lifters.
The wear pattern upon the camshaft is indicating correctly on all lobes. So I am placing the root of all issue upon the tight bore clearance only and not the lifter unit itself.
Need to have a custom sized ream ground up to reset the bore clearances.
There is one guy here in Australia currently building a big bore 912ULS on a TBO'd 2015 production engine base. The camshaft has been reground and nitrated and Johnson HT-900 lifters fitted.
Good service dodge on removing valve caps to see if pushrods spin. It will be messy though :)
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dmac7
Joined: 05 Apr 2019
Posts: 46
Location: Canada
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| Posted: Tue Sep 05, 2023 2:21 pm Post subject: Re: ROTAX 9XX Hydraulic Lifters |
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Was talking to my Canadian Rotax expert who has been to Austria for training a few times over the years.
The Johnson Lifter company did indeed supply Rotax with Lifter's for some years.
There was a SB regarding wearing through the hard surface on the Cam, he thought around 2002 maybe? They had gone to a highly polished cam face on the lifter's for a time but not anymore. The new lifter's he said are much more costly to purchase for some reason & he didn't know who is supplying the new lifter's
He told me the Cam is taper ground, I forgot to ask him about the tight clearance issue, but Rotax is famous for tight clearances'
Those Johnson HT 900 lifter's will fit all the old Ford V8's, 260, 289, 302, 351W, 351C, 429, 460, I'm sure I missed a few but you get the idea, and Rotax 9 series
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Area-51
Joined: 03 May 2021
Posts: 372
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| Posted: Tue Sep 05, 2023 7:35 pm Post subject: Re: ROTAX 9XX Hydraulic Lifters |
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Thanks again for that support information. Factory must have deleted that SB mentioned but older forum posts do make mention of it.
Will bypass using the HT-900's and supplement the latest 915is spec'd units.
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