Just finishing the 15 hr service after rebuild on my UL350iS.  Required a torque check on the cylinder head bolts.  If torque has loosened (not uncommon) you need to retorque all 16 cylinder head bolts.  Each cylinder has two of the bolts which are not accessible without a bit of extra work.  The bottom cylinder bolts required removal of the valve cover, lock tab and cylinder head plug.  Get at it while checking and setting the tappets.  The top cylinder head bolts require lifting the inlet manifolds about an inch or  two to access.  When going to remove the inlet manifold bolts, I discovered one that was completely loose (despite nordlock washer) and could be removed with my finger. Closer inspection revealed stripped threads!  I already had a proper helicoil kit for the M6 bolt size since I had inserted one helicoil already for a stripped exhaust bolt hole. Anyway, got it done today and should be able to do test runs later this week.  The good news is that the engine so far has been running well, no prop flange issues as of yet with the new crank and prop flange and WW prop.  Also note that the 5 and 15 hr prop flange bolt torque check has been eliminated if new engine or rebuild by factory/authorized repair station.  The picture below shows the freshly tapped hole ready for helicoil insert.

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Hi David, how many hours did you get on your UL Power 350IS before needing a rebuild?

David, I had approx 160 hrs on the engine when I experienced a catastrophic and complete loss of oil while in flight.  Successful forced landing with no damage to the aircraft other than the engine which I sacrificed to make a suitable landing area...hence the major overhaul.  Pulled the engine again after having crankshaft and prop flange issues, replaced both and went to a new prop system.  So far no issues.  The airframe has 198 hrs of hobbs time.

Hope that answers your concerns...Cheers! Dave

Wow, that must have been a scary moment!...so happy to hear you managed to get the airplane down safely with no damage. Interestingly enough...my UL Power 350IS engine is approaching 160 hrs and so far has been running excellent. Is there anything you learned from your experience with this failure that you can pass on?



The loss of oil was caused by the oil filter backing off.  I suspect this occured due to the harmonics of the engine and prop.  The mx manuals for the ULPower engine (and the Rotax engines I've been told) do not call for using safety wire on the oil filter.  I now use safety wire on the oil filter and on my oil sump drain plug.

Thanks for the lessons learned  David..appreciate it!

Best of luck with your rebuild and fly safe!




I'm considering putting a CH750SD on order.  As the majority of my flying would be in the Rockies and tI'd often be close to gross, the engine I'm leaning towards is the UL520iST as it has a turbo.  

Although the 520iS has been out for several years, the turbo model has just come out as of this month with all testing, etc. being completed.

Any comments on Ul engines, support, etc?



Hi Bob, I am happy with the support from UL.  Ray Lawrence of Kaolin Aviation is knowledgable and readily available regarding any questions or support requests.  Robert Helms is also a good POC and is easy to reach.  The company keeps an up to date website with service bulletins, manuals, and additional tech support.  Response from the company is prompt and effective, though there are time zone and occasional language challenges. There has been continuous improvement from when I started out with my 2011 UL engine in terms of overall knowledgeable and accessible support.  Wick's aircraft is doing a good job in parts availability and increasing on hand items as well. There are more people using UL engines in the U.S. now I think that will bode well for continuous support.

Hi David

Sorry for not responding sooner but I'm not familiar with this site as yet and missed your response.  

I've spent countless hours (sitting at home due to Covid) on the internet exploring various aircraft.    But just a little history of where I'm at - I've been flying since 1982, have a Seneca II, IFR certified but not current and probably won't take the check ride as I'm now 75 and not flying enough to be proficient, spend the winters in Phoenix but not this year. 

Having considered most of the alternatives I've decided a Zenith CH750SD would meet most of my "mission" and may order the kit over the next week or so.  In general terms I would instal the UL520iST with a Airmaster prop, Dynon VFR avionics with an autopilot.  

I've spoken to Ray at Kaolin Aviation and he is/or will be testing the UL520iST in the Zenith CH750SD along with the Airmaster prop that is recommended by Airmaster.  He will provide the FWF kit including the cowling, etc. - he appears to be knowledgeable. 

Zenith tell me they can have a Quick Build fuselage to me within about 4 weeks with the remainder arriving in about 4 months.  Just a little hesitant to order the kit as the time commitment is huge - but I have a quote with the Quick build fuselage which helps a lot - just trying to find someone local for builder assist.

It's always reassuring when knowledgeable folks like you lend a hand.  I'll try to be more responsive in the future when I'm familiar with this site - not even sure if this conversation is universal or just between the 2 of us?




Bob sounds like you're going to have a very nice combination!  The QB kit does save some time, but in the overall scheme of things for me as a first time builder it was of minimum consequence.  I think the bigger factor is from a motivation perspective.  Having a fuselage on wheels allows you to hang an engine and visualize your panel and cabin layout while working on the project.  Good luck with your project, can't wait to see it fly!  Cheers!


David, would be curious as to how you safety wire the oil filter. I have been using a hose clamp around the filter to secure the wire. Regards, Joe


The easy answer to safety wiring your filter is to switch to a K&N oil filter HP-1004. Has holes pre drilled for wiring. Just drill a hole in your should to wire to and you are in business. Available at auto parts stores nation wide. 

After reading about David’s I switched brands. Safety wire is cheap.

I also switched brands of the fine fuel filter. Went to the auto parts with the old one and they used their cross index to find the filter in WIX. $15. 

Ordered NGK spark plugs to replace the Bosch at Six dollars and change each, Wicks is asking $15, each for Bosch.

Still looking for a Bosch part number for the fuel pumps supplied by UL. 

I do not mind showing support for Wick’s, but at twice or three times the price of other dealers…


Interesting.  I also use the K&N Filter and have not had any issues with it.  What are the part numbers for the fuel filters and spark plugs you purchased.  I have also been looking for a alternative to the Fuel pumps...will share if I find one.


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