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Prop won't cycle

nigelspeedy

Well Known Member
Ok, I need a little tech assistance. I have an IO-360 with an RV-74 prop and a Jihostroj P-920-028/A governor. I did the first engine run on the weekend and the good news is the engine fired right up and ran like a champ. The bad news is that doing a prop check at 1500 rpm with 70 psi engine oil pressure results in no change in the prop rpm/MAP or oil pressure. After shutting down I disconnected the governor output line that runs up to the front of the engine case and there was no oil in it. The crank does not have a plug in the front. The prop lever cable is attached to the lever on the governor and it does move over its full range of motion. When I pulled the governor off the back of the engine what seemed like about 1/2 a quart of oil ran out. Any ideas on troubleshooting or possible causes would be much appreciated. I'll even report back when I find out the rookie mistake I've undoubtedly made.
Thanks
 
MUCH higher RPM to get that oil up there flowing and working for you. Run it up to at least 2300 and watch it work. Tie it down.
 
Ditto on what Mike said, try that before you put a wrench to it.

And, Congrats on the first engine run :D
 
FLAPS UP!!!

If the airplane is light you dont want to risk the tail coming up and getting a prop strike.
 
Hi Nigel,
I agree with what others said previously. I have the same governor as yours and a whirlwind 200RV (which I believe shares the same hub as the 74RV).
On mine, the prop will not cycle below 1800RPM and I usually do it at 2000RPM.
 
Another small check........

You stated that the crank does not have a front plug.

You must also be sure that the crank DOES have a solid plug in the aft end of the front cavity?
 
Thanks for the tips.

I did have it tied down and chocks but that is certainly a good and timely reminder.

Mel it did have the aft plug but not one at the very front.

Doing the check at low RPM was an attempt to be nice and cautious on the first ground run, I was not aware that higher RPM would be required to get it to work.

Thanks all.
 
Initially the prop may be a little tight and need more oompth to get it to move. After a while it may not take as much.

Mine will cycle fine at 1700 rpm but it is a different prop.
 
Actual RPM to cycle at run-up varies by what prop and/or gov., but it usually takes at least 1700 and sometimes 1800+ to get it to cycle (especially when new).
2000 RPM should be more than enough to safely get it to go. It still may require a few pulls of the knob though.....
 
In some (Lycoming powered) piston twins, the feather check is done at 1500rpm because the prop WILL NOT cycle conventionally. Any rpm change is due to the prop going towards feather. Hence why that RPM was picked.
 
As above, there is a balance between power, new engine, and checking Prop works.

I would suggest these things usually work fine, or not at all. If you follow that school of thought, then now try 1600 - 1800 RPM to see if you can get any joy out of the prop. Be careful - certainly the Superior manual implies until broken in, you only want to "drop RPM" by max 100RPM (if you can keep it to that well done!).

Once you see a drop, restore ASAP, confirm once more and leave it at that until flying...
 
SI1462A

IF it still does not work at higher RPM, it is time to conduct Lycoming Service Instruction SI1462A (or latest version) to make sure the rear plug is Seated correctly. I know of one instance where this test failed and the recently overhauled engine had a poorly seated and leaking rear crankshaft plug.
 
new prop/ engine installs will take longer for prop cycle due to air in system I have seen some to take a long time to purge system, also you need higher rpm
 
The winner is Kahuna

So the correct answer was from Kahuna in 10 minutes. After pulling the governor and making sure all the gasket holes matched up with oil galleries I put it back together and gave it another ground run. This time after it warmed up I did a prop check at 2000 RPM and it worked a treat. Thanks for all the help and such speedy responses.
Cheers
Nige
 
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