I received a text message with a link to the Warp Drive website informing me of a new service bulletin they just issued.

The bulletin applies to the "HP" hubs that are used on the O-235, O-200 and C-90 engines.

The SB is for cracking of the prop hub.

It is also onerous in that it requires inspection "every 15 hours of flight or 12 months". Since you have to pull the prop bolts this takes a bit of time and effort - especially for people like me who fly a lot of hours every month.

They do offer a hub trade-in plan for $150 (a 50% discount according to WD) which apparently eliminates the problem. Guess I'll be spending some more money....

You can read about it here:


Probably not one of those SB's you can ignore.

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I have everything on my shelf to install an Ed Serba 68/57 wood prop and Saber extension and bolts. Your right about cost, everything came out to a little over $1,200.00 dollars. Problem is, parts are  for a Lycoming 0-235 C1B & my flying 601 has an L2C 0-235. They have different mounting hubs.  First I will check and see if I can just change the hub on the engine. I'm told the two blade prop offers better performance, but that I don't know. 

I don't want to influence anybody and think everybody oughta do the 15 hour inspection.

The info I got was that 2 out of hundreds have cracked. The hub looks to me like it might be susceptible to overtorquing. My Craftsman torque wrench is technique sensitive and will go beyond the desired setting if not held just so and it's not always very noticeable. I wonder how many more are out there like that. And we all know that some of us can tear up an anvil so that may be a factor in the 2 that failed. The answer I was looking for was that the failures aren't due to harmonics. If so that would have been a mandatory change to a different prop for me. I didn't know there was a mandatory torque check every 15 hours(did I really tell that?) and the only time I've ckd it was when I removed the prop for some reason. It's got 500 hours or so on it. All that seemed favorable to me when I was evaluating this SB. OTOH if you go online and search WD history there have been hub cracks and blade separations but all those have been corrected long ago. Search it for yourself, I was unaware and a little surprised. Maybe the engraving will actually cause another series of failures WD will know/correct in time.

WD has liability to think about; I understand.

I've been told.

Don't mind me, do the inspection.

Hi Gil

I have had both a wood prop, Sensinich two blade 68x57

and the warp drive three blade 68 inch tapered blades.

Yes, technically the two blade is slightly more efficient, but you lose

the ability to fine tune the prop to your airframe and engine. You can 

set the prop to a cruise prop or a climb prop and anywhere in between.

i can certainly tell you the three blade is a lot smoother. My oil filler access

door used to vibrate a lot with the two blade prop, which had been dynamically balanced.

with the three blade warp drive no vibrations at all and it has not

been dynamically balanced.

So that’s why I prefer the warp drive, my Sensinich is hanging on the wall as decoration.


I heard back from Warp Drive and I have the older hub, so all I need to do is check my torque on the mounting bolts. I bought a protractor and they told me on the 0-235 I should be between 9 and 12 degrees for 2300 RPM. My static RPM is about 2400 rpm so I'm not sure if I should increase the pitch or any idea what to expect if I do. It is all uncharted territory for me.


Hi Gil

you may not have to adjust the pitch at all.

Retorquing the mounting bolts does not loosen the blade 

pitch setting. 

if the plane performs well the pitch might be correct.

how can you tell? I’m not sure of the max rpm of your engine,

if its 2700 rpm, what rpm’s do you see at maximum power in cruise

properly leaned?

if you are at the max rpm for your engine in top cruise you are ok.

if you want higher top end at the expense of climb you can increase the pitch very

slightly, I usually use 1/4 degree increments. So measure your pitch, if you are at 10.5 you can try

10.75. If you are looking for more climb, reduce the pitch 1/4 degree 

test fly the plane and if you find your sweet spot, that’s it.

the higher your cruise speed the lower your climb rate and vice versa.

my  Continental 0-200 likes between 10.25 and 10.75 degrees

since you have more power with a 0-235 your numbers may be different than mine, I would expect you could 

dial in more pitch than mine.

but like I said if you are happy with your cruise and climb, it’s not necessary to adjust it at all.

I would suggest taking the hub off your plane and clean the surfaces of the hub and crank hub.

i found some corrosion which is not unusual when you have dissimilar metals in contact with each other.

i removed the corrosion and treated the surfaces with corrosion x



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