Norvel .074 Crank Seizure
11-08-2004, 08:23 PM
#1
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Norvel .074 Crank Seizure
I flew my Norvel .074 on my HOB Spacewalker out of fuel (intentionally, last flight of the day) for the first time Sat. Upon landing the crank had become hard to turn. Upon disassembly, the piston/liner and rod big end looked fine and there was plenty of residual oil in the crankcase.
This engine had not leaked oil out the front when running like my .049, whcih leaks excessively in my mind. Is this seizure a unique occurance, or is this a known .074 problem? After reassembly, I have been able to loosen the crank up with after run oil and spinning it with the electric starter. Compression is as good as it ever was. I'll try to run it again next weekend.
Fuel was Powermaster 25% nitro, 18% castor/synthetic mix. Engine has a bit over a quart of fuel through it. I've been flying for just under 50 years, and this is the first engine I have 'stuck'.
Thanks for your comments, JOhn C
This engine had not leaked oil out the front when running like my .049, whcih leaks excessively in my mind. Is this seizure a unique occurance, or is this a known .074 problem? After reassembly, I have been able to loosen the crank up with after run oil and spinning it with the electric starter. Compression is as good as it ever was. I'll try to run it again next weekend.
Fuel was Powermaster 25% nitro, 18% castor/synthetic mix. Engine has a bit over a quart of fuel through it. I've been flying for just under 50 years, and this is the first engine I have 'stuck'.
Thanks for your comments, JOhn C
11-08-2004, 09:15 PM
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RE: Norvel .074 Crank Seizure
John, Good Evening,
I address that very problem in my Jan.05 Flying Models CL Combat column. I wasn't thinking of the .074, but rather any of the current small engines. Unless the shaft to case fit is pretty loose on these plain bearing (really no bearing) engines then they can easily gall and seize.
The good news is that there is usually no serious damage done and cleaning the aluminum off the shaft (if any is transferred to it) and refitting will return the engine to service.
I have reamed the case on some engines that were real tight and lapped the shaft to the case (with Boni Ami power mixed in light oil) on others. If you lap, then work real hard at getting the compound off the surfaces (use a bottle brush and lots of soap and water on the case journal) so you don't run it through the engine when you crank it up.
I use and recommend 20% all castor in plain bearing 1/2As and the .074 may be close enough to call a 1/2A for fuel and oil considerations.
Also, try putting a drop of light oil, or fuel, behind the thrust washer before cranking each time to help with the lubing until the engine is well broken in.
I address that very problem in my Jan.05 Flying Models CL Combat column. I wasn't thinking of the .074, but rather any of the current small engines. Unless the shaft to case fit is pretty loose on these plain bearing (really no bearing) engines then they can easily gall and seize.
The good news is that there is usually no serious damage done and cleaning the aluminum off the shaft (if any is transferred to it) and refitting will return the engine to service.
I have reamed the case on some engines that were real tight and lapped the shaft to the case (with Boni Ami power mixed in light oil) on others. If you lap, then work real hard at getting the compound off the surfaces (use a bottle brush and lots of soap and water on the case journal) so you don't run it through the engine when you crank it up.
I use and recommend 20% all castor in plain bearing 1/2As and the .074 may be close enough to call a 1/2A for fuel and oil considerations.
Also, try putting a drop of light oil, or fuel, behind the thrust washer before cranking each time to help with the lubing until the engine is well broken in.
