What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Superior XP-400 Service Bulletin

Jim Ellis

Well Known Member
For those who may not have already seen it, Superior Air Parts published a new Service Bulletin, XPB02, on January 14, 2019 that changes the advance timing from 25 degrees BTDC to 20 degrees BTDC.

It also calls for removal, disassembly and inspection of any engine that has flown with the 25 degree timing advance setting.

The XP-382 that I have is not included in the Service Bulletin.

You can read the Service Bulletin by clicking here.
 
Last edited:
Wow, that's going to be painful for both customers and Superior.

But good for them for jumping in and taking care of it, if it was me, I'd push for a new crank.

Dramatic evidence of what can happen with a "minor" timing change on a high performance engine.
 
Last edited:
No doubt a result of the 2016 fatal RV-8A accident due to a fractured crankshaft in an XP-400. Although compliance not required, good judgement would necessitate the required teardown.
 
Timing recommendation is now in line with Lycoming IO-390s.

I'd be very surprised if this crank failure was due solely to too much timing though. Short of long duration detonation, a few more degrees of timing shouldn't put much more load on the crank. They should have a massive safety factor in there. We triple the power output of Lycomings and Continentals at Reno (yes 300% over the stock rating) and they don't break cranks.

I hope Superior ran at least one at full rated power for the full TBO period to prove the design is robust. Anybody know how these were tested and validated?
 
Well...

I am almost to 600 hours on my XP-400, serial #2. My data plate says 28 degrees at 3,400. Obviously I have never done 3400, but I did run the engine from when I got it (32 hours) for a fair amount of time at 28 degrees. I ended up backing it off to 25, and later to 23, which is where I have been running it for the bulk of its life. 20 degrees does slow it down a noticeable amount, but also lowers all the temps, which shouldn't be a surprise.

So the real question I have (and have had since I bought it) is why is this engine so freaking good? My talks with different Superior guys over the years never yields much information, although I haven't tried to contact them in a long time. My engine is pre-bankruptcy, back in the Thielert days, and supposedly was assembled in Germany. You can say what you want about how that whole deal went down, bankruptcy, etc.. but the guys knew something because I have the fastest 4 cylinder in my class at Reno for a seriously long time. It, is, awesome. How/why it runs so well is a bit of a mystery. It just runs too well to tear open and find out. Maybe, now I will find out, if I'm supported under this service bulletin. Or...

My engine goes back, and what is returned is a 'stock' XP-400, which would be a real shame. I'll have to think about this one. I'm not sure if I should call them or not. Hmmmm
 
CALL THEM NOW!!

Well...

My engine goes back, and what is returned is a 'stock' XP-400, which would be a real shame. I'll have to think about this one. I'm not sure if I should call them or not. Hmmmm

Life or death, Tom! You gotta get rid of that engine!:D
 
Timing recommendation is now in line with Lycoming IO-390s.

I'd be very surprised if this crank failure was due solely to too much timing though. Short of long duration detonation, a few more degrees of timing shouldn't put much more load on the crank. They should have a massive safety factor in there. We triple the power output of Lycomings and Continentals at Reno (yes 300% over the stock rating) and they don't break cranks.

I hope Superior ran at least one at full rated power for the full TBO period to prove the design is robust. Anybody know how these were tested and validated?

5 degrees has a big effect on peak pressures and the crankshaft torsional loads. Do you measure torsional loads on cranks on your dyno Ross? I would hate to be a crankshaft :eek:
 
If you go back and look at the the crank failure on the Titan 400, and this one, it was a classic pressure induced fatigue of the inside fillet on the underside of the pin at TDC. Force on the rod at TDC tends to spread the cheeks against the main bearings.

Just because it was pressure induced, does not mean the crank fatigue strength was correct. There is a lot of processing that ensures the fillets are the toughest part of the crank.

If a chain breaks, either reduce the load or make the chain stronger.
 
Back it Goes....

I have serial number 4 and spoke with Superior for a while today regarding the history and proposed fix. From my conversation and as stated in the SB, there is a history of detonation induced damage with some cranks. Superior's analysis has included finite element analysis of the crank based on recorded cylinder pressures while running at both 25 and 20 degrees of advance. At the 20 degree setting, pressures and resulting computed stresses were greatly reduced and resulted in an "infinite" fatigue life cycle for the crank.

The SB work will include ND testing of the crank, pistons, and rods, installation of new bearings and gaskets, and run time in the test cell. All shipping, shop labor, and parts associated with SB related issues will be covered by Superior. Turn around time is currently running 4-6 weeks from the time the engine arrives to the time they initiate the return shipping.
 
I have serial number 4 and spoke with Superior for a while today regarding the history and proposed fix. From my conversation and as stated in the SB, there is a history of detonation induced damage with some cranks. Superior's analysis has included finite element analysis of the crank based on recorded cylinder pressures while running at both 25 and 20 degrees of advance. At the 20 degree setting, pressures and resulting computed stresses were greatly reduced and resulted in an "infinite" fatigue life cycle for the crank.

The SB work will include ND testing of the crank, pistons, and rods, installation of new bearings and gaskets, and run time in the test cell. All shipping, shop labor, and parts associated with SB related issues will be covered by Superior. Turn around time is currently running 4-6 weeks from the time the engine arrives to the time they initiate the return shipping.

Long term detonation would certainly explain failures and the 20 degree timing recommendation would do a lot to nix any detonation. From the discussion above, the design sounds a bit marginal IMO and if this was known for some time, why wasn't the lower timing setting mandated before?
 
XP-400 Crank failure

They have 5 documented crank failures now. One occurred last week with an engine only running 20 degree timing. It’s being shipped to a reputable repair station for tear down. If your flying a 382 or 400 I would ground it. When people’s lives are at stake the only responsible thing we as members of this small community of experimental aviation can do is spread the word. I’m told they made 200 of these crankshafts and I wonder how many of the participants know of the risks they’re taking.
 
Last edited:
My understanding is that most owners of XP-400s have been contacted by Superior (subject to the limits of owner records accuracy) by phone, and well before the SB was actually issued. I received a call (grounding my plane) on Dec 3 - I think the delays in the SB being issued were bureaucratic (legal review). I also had the advantage of being an hour+ drive from their facility. My engine was in their shop 4 days after the call and back in my hands 2 weeks later - probably a best case. The engine was installed before year end and I have 25 hours logged on it since the tear down - no issues.
I was treated very well by Superior and commend them for their customer service (I describe the experience as the best possible outcome from an unfortunate circumstance).
 
Anyone know???

Anybody know how they got the extra 1/4" of stroke?? Is the rod pin the same diameter as the 4.375" stroke (360)? i.e. same rod bearings?
 
Forged in Germany, machined in the US. Rod journals are 2.125", same as 320, 360, 390, etc. Mains are 2.375" however, while a late model 390 is 2.625".
 
Best I know, Walt is right, same 4.625 stroke crank.

Dan (or others), 382 owners (one is a customer of mine) are being told the cyl pressures are lower on the 382 vs the 400 so not to worry.
So set me straight, if both engines have the same comp ratio and the same timing, are the cyl pressures less? I thought PP was basically a result of CR and timing?
 
Dan (or others), 382 owners (one is a customer of mine) are being told the cyl pressures are lower on the 382 vs the 400 so not to worry.
So set me straight, if both engines have the same comp ratio and the same timing, are the cyl pressures less? I thought PP was basically a result of CR and timing?

Could be. Same CR and same timing would not necessarily result in the same cylinder pressure. There are variables like VE, and turbulence, the differences between parallel valve and angle valve.

The same cylinder pressure would result higher crank load for the 400...more piston area. And a larger piston would also make recip inertia higher.

I say give Superior a round of applause. They're doing the right thing.
 
I have serial number 4 and spoke with Superior for a while today regarding the history and proposed fix. From my conversation and as stated in the SB, there is a history of detonation induced damage with some cranks. Superior's analysis has included finite element analysis of the crank based on recorded cylinder pressures while running at both 25 and 20 degrees of advance. At the 20 degree setting, pressures and resulting computed stresses were greatly reduced and resulted in an "infinite" fatigue life cycle for the crank.

The SB work will include ND testing of the crank, pistons, and rods, installation of new bearings and gaskets, and run time in the test cell. All shipping, shop labor, and parts associated with SB related issues will be covered by Superior. Turn around time is currently running 4-6 weeks from the time the engine arrives to the time they initiate the return shipping.

Remember who you spoke with? I might give them a call. I have not been contacted at all.

Thanks,
Tom
 
382/400= 95.5%. Given that the VE is probably slightly better on the 382, they are probably splitting hairs on how much less stress is on the 382. These are not failing at the 2000 or 3000 hr. mark- far less and that fact doesn't speak well for large safety factors in the design.

Any correlation on crank failures and type of props fitted?

Any specific batches of cranks in all the failure cases?

Superior is doing the right thing in stepping up but do they really have a solid cause and solution?
 
382/400= 95.5%. Given that the VE is probably slightly better on the 382, they are probably splitting hairs on how much less stress is on the 382. These are not failing at the 2000 or 3000 hr. mark- far less and that fact doesn't speak well for large safety factors in the design.

Any correlation on crank failures and type of props fitted?

Any specific batches of cranks in all the failure cases?

Superior is doing the right thing in stepping up but do they really have a solid cause and solution?

Seems to me like once again the EAB folks are unknowingly being used as the test program for these engines.
 
Last edited:
XP-Crank failures

Due to one of those happenstance change in travel plans I ended up being Present at the tear down of the latest 400 failure. This one broke through the #4 rod journal at aprox 45 degree angle. Because of the angle of the break the #4 rod captured the cranks 2 half?s if you will, together and prevented the engine from becoming a total threshing machine. A Superior rep was present and from what I heard they truly are committed to doing the right thing.
These cranks are breaking in different places and with different props so there doesn?t seem to be a specific pattern. This engines data plate was marked as a 20 degree BTDC and when it was test run before customer delivery it was set at 20 degrees. As you can imagine The timing was throughly checked but with the discontinuity of the crankshaft front and back end it was difficult to be presise and was within an aprox 3 degree range that I will just say, it looked to be between 20 degrees and 25 degrees.
This shop has called all their 400 and 382 customers and asked that they ground their planes and send their engines back to them for evaluation. Some of their customers had not heard anything about the crankshaft issue but this could be because some of these cranks and rods were sold seperate from complete engines and engine shops built up there own versions with these parts. So far I haven?t heard of any 382 failures but they utilize the same crankshaft. Apparently there are 80 XP 400?s out there with either 5 or 6 crank failures.
I reiterate my previous post if you fly a 400 ? Ground It !! ?. This is serious with 2 fatalities already. I?m not in anyway associated with any of the parties but I?ve seen enough to know this is something to be taken extremely serious.
 
Remember who you spoke with? I might give them a call. I have not been contacted at all.

Thanks,
Tom

Tom - I sent you a PM with the contact info.

I sent Superior an e-mail following my phone conversation requesting additional information. By the way, I wasn't contacted either...I reached out to them after reading about the SB here. Hard to believe it was because they didn't have my contact info as I had many e-mails and phone calls with them a year ago after discovering the incorrect build when I received the motor due to the cam to crank timing issue (i.e., the "Coughing XP-400" thread). :confused:

While the information I've see to date suggests a classic fatigue failure, I hope they're continuing to investigate since the failures don't seem to consistent with known loads (i.e., a highly modified/high hp engine crank hasn't failed while an apparently "stock" engine crank failed within 20 hours). Intuitively this doesn't make sense....if the cranks were (hypothetically) all identical, the crank in the engine with high hp should fail first.

The questions/comments from my e-mail to superior are below for reference:

What data, if any, is Superior collecting from the owners of the motors? It would seem the type of information should include, at a minimum:

How many hours in service?

Constant speed or FP propeller?

EI or mags?

If EI, is there a timing advance feature?

Oil change frequency?

Oil additives?

Climate/typical area of operation?

Any use of auto fuel?

Typical cruise settings (rpm/MP)?

Per-heat during the winter?

Dynamic prop balance?

This information would be critical in order to ?connect the dots? between not only the failed cranks but also the cranks that seem to be fine.

It concerns me that there is no obvious cause of the crank failures. My understanding is that some low time ?stock? motors have failed cranks yet other higher time, highly modified motors with much higher than stock hp figures have not failed. This would suggest that the root cause is not simply the pressure peaks associated with ignition timing. I assume Superior has full traceability of the manufacturing process associated with all cranks including metallurgy, heat treating, and machining. Have these items been fully investigated for all cranks to look for potential patterns that might point towards a failure mode?

While I realize the change in ignition timing from 25 degrees to 20 reduces cylinder pressures thereby reducing some of the internal stresses, it alone does not explain the apparent random nature of the failures. What is Superior doing to further investigate the root cause(s) of the failures?

How many XP-400 cranks have failed (both raw number and as a percentage of the total) to date and how many are in service (i.e., 5/200 or 2.5%). How do these numbers compare with a similar engine (i.e., Lycoming IO-390) in terms of crank failures?


I hope we get some answers...I'll pass along anything I learn going forward.
 
Good questions, will be interesting to see their answers. While on the subject, any know Lycoming IO-390 crank failures?
 
Just curious after looking at the cross sectional view of the crankshaft that is cut lengthwise in the article linked in a previous post.
Be curious to see how the 45 degree break in the number four journal mentioned in previous post aligns to the rod journal lightening bore shown in that cross sectioned crankshaft.
Haven?t built a lot of aircraft engines but have built many racing automotive, motorcycle and marine engines. Never seen a crankshaft rod journal done that way. Seems there are locations of less material area with the lightening bore done on an angle like that.
Only crankshaft holes done on an angle like that were for cross drilling oiling hole and they are typically about 3/16?-1/4? diameter.
Not an engine design engineer and didn?t stay at a Holiday Inn last night, just an observation.
 
Just curious after looking at the cross sectional view of the crankshaft that is cut lengthwise in the article linked in a previous post.
Be curious to see how the 45 degree break in the number four journal mentioned in previous post aligns to the rod journal lightening bore shown in that cross sectioned crankshaft.
Haven’t built a lot of aircraft engines but have built many racing automotive, motorcycle and marine engines. Never seen a crankshaft rod journal done that way. Seems there are locations of less material area with the lightening bore done on an angle like that.
Only crankshaft holes done on an angle like that were for cross drilling oiling hole and they are typically about 3/16”-1/4” diameter.
Not an engine design engineer and didn’t stay at a Holiday Inn last night, just an observation.

I agree. Very odd way of boring the lightening holes on the rod journals. Might make it lighter than a bore running straight through the journal but almost certainly weaker in a critical, high stress area. I've never seen any other crank machined like that. While it sounds like they did an FEA on the design, FEA is only a tool and doesn't prove much without actual validation by running the design at peak stress on the dyno for a long time.

FEA is only as good as the model and plugging valid numbers in to begin with. I've seen a number of broken parts now which proudly stating having had FEAs done. Backing your math analysis with actual running (lots) is the safer way to do things. You're not done after the FEA is complete.

Would be interesting to see photos of all the breaks. Yes, could be forging or heat treatment issue in the end on a small number of cranks but this doesn't look like a robust design IMHO.
 
Last edited:
I assume you are talking about this photo?

O-360-crankshaft-cutaway.jpg
 
Forged in Germany, machined in the US. Rod journals are 2.125", same as 320, 360, 390, etc. Mains are 2.375" however, while a late model 390 is 2.625".

There is no pin overlap on the XP-400 crank from the photo. Pin overlap makes things much stiffer and stronger, especially on a design which doesn't have a pair of mains for every throw. Lycoming made a good choice by increasing the main size on the 390.
 
Due to one of those happenstance change in travel plans I ended up being Present at the tear down of the latest 400 failure. This one broke through the #4 rod journal at aprox 45 degree angle. Because of the angle of the break the #4 rod captured the cranks 2 half’s if you will, together and prevented the engine from becoming a total threshing machine. A Superior rep was present and from what I heard they truly are committed to doing the right thing.
These cranks are breaking in different places and with different props so there doesn’t seem to be a specific pattern. This engines data plate was marked as a 20 degree BTDC and when it was test run before customer delivery it was set at 20 degrees. As you can imagine The timing was throughly checked but with the discontinuity of the crankshaft front and back end it was difficult to be presise and was within an aprox 3 degree range that I will just say, it looked to be between 20 degrees and 25 degrees.
This shop has called all their 400 and 382 customers and asked that they ground their planes and send their engines back to them for evaluation. Some of their customers had not heard anything about the crankshaft issue but this could be because some of these cranks and rods were sold seperate from complete engines and engine shops built up there own versions with these parts. So far I haven’t heard of any 382 failures but they utilize the same crankshaft. Apparently there are 80 XP 400’s out there with either 5 or 6 crank failures.
I reiterate my previous post if you fly a 400 “ Ground It !! “. This is serious with 2 fatalities already. I’m not in anyway associated with any of the parties but I’ve seen enough to know this is something to be taken extremely serious.

I am confused on the approach here. Cranks that, in theory, were inspected for defects before being placed into service are failing prematurely. How does another inspection of the crank reduce the likely hood of a premature failure on a crank that was already inspected? Are they inpecting to a different level than the initial inspection after manufacturer? What am I missing here? Unless they are questioning their QA process, I fail to see how another inspection will prevent premature failure, unless they have found a root cause they are looking for that wasn't known during initial manufacturing inspection. If it can happen 200 hours after passing inspection at manufacturer, why can't it happen 200 hours after a passing a second inspection ?


Larry
 
Last edited:
There is no pin overlap on the XP-400 crank from the photo. Pin overlap makes things much stiffer and stronger, especially on a design which doesn't have a pair of mains for every throw. Lycoming made a good choice by increasing the main size on the 390.

What is pin overlap?
 
What is pin overlap?

Listening . . . . I think he means overlap of the main diameter and rod pin diameter, but that is only for short stroke engines. The cheek thickness is primary for longer strokes.

The beach marks are very shallow on that pin and the progression of the brittle failure was odd. There is something else going on in this engine (design).
 
Last edited:
Looking at the second picture in the link from theduff.

Looks like crack started at that thinnest section area between journal surface and the angled lightening hole.

From the different colors of the crack surface the crack stayed in that starting area for a bit, darker color of the crack surface. Then cracked clean through shown by the lighter colored crack surface.

Wonder what the theory was behind the angled lightening holes.
 
Yes, Bill has it right. On the 390 with the larger mains, they may have a couple mm of pin overlap which makes it a bit stronger in bending.

I have seen failures like this one in race engines which were stroked with aftermarket cranks. No analysis, little proper long term testing. Despite being forged, heat treated, shot peened and having rolled fillets, one crank broke in less than 6 hours.

My theory was that these lacked proper damping and were ringing like a bell the whole time, ramping up the fatigue cycles rapidly. Seen similar breakages when folks removed the OE damper and went with a lightweight pulley instead. Fairly immediate failure again. The factory setups never broke cranks, even with hundreds of hours at or near redline.

Further instrumented running needed here to find the smoking gun.
 
XP-400 Buy Back

Just got a call from Superior and apparently they're buying back all the XP-400s to get them out of service. Time for a new motor I suppose....
 
This is the type of thing that worries me about going to a 370/375 versus a standard 360 configuration which have a multitude of operational hours on them. It appears that at least Superior is doing the right thing here by buying back the engines. I do understand the business demands that can be placed on the design team too. How do you get enough test time on a new product like this in a cost effective manner?
 
Just got a call from Superior and apparently they're buying back all the XP-400s to get them out of service. Time for a new motor I suppose....

This certainly improves the company technical image. Now, how about the Titan 371 engines?
 
Last edited:
Titan 371 ????

Now, how about the Titan 371 engines?

What's a Titan 371? I just installed a new Titan IO-370 in my plane and never heard of a 371.

Titan and Superior are two unrelated companies and this thread is about Superior engines.
 
This certainly improves the company technical image. Now, how about the Titan 371 engines?

I have a friend with a Superior 382, same crank, he's paying out of pocket to have an almost brand new engine converted back to a 360. I understand Lycon has advised all it's 382/400 customers to ground the planes that have those engines.
 
Back
Top