gmcjetpilot
Well Known Member
Rvator51 asked about motor mounts and I miss read. He wanted to know about the rubber isolators. Any way I deleted my post on that thread and decided not to waste it and just post this as information. IF YOU HAVE ANY SERVICE PROBLEMS WITH THE STEEL Weldament post it here:
Metal fatigue and hidden weld defects are always a cause for cracks in steel. Do RV's have a particular problem with engine mounts? No. (with a RV-4 caveat, below)
Inspect it with a bright lights, good eyes, magnification and take your time. If you don't trust your inspection skills get a good A&P or AI. Also strip the wires and tape and clamps away. If you need to, by all means wire brush the paint away and clean it well. Of course repaint it after. If the engine mount is off the plane, by all means strip all the paint off and inspect it. You could even send it to one of the GA plane engine mount OH companies for inspection. They will use Dye Penetrate or Magnetic Particle Testing. You can by a dye inspection kit. One brand is "Zyglo", a fluorescent dye penetrate. You use a black light to expose cracks.
You also may want to up your inspection schedule. Frankly every oil change you should have a good visual inspection at it. Cracks start slow and grow. So it's not like it will fail immediately.
A mount may last in theory forever? Well that is a long time but in GA flight time longer than we will be around. It also depends on the kind of flying. Unpaved operations (aka soft fields that are not really soft) can be tough on the gear. The engine mount of course takes gear loads. If you do aggressive aerobatics, again a factor.
The RV-4 like most tail wheel RV's takes the landing load through the engine mounts. If you have had a hard landing, inception is a must. The older RV's had cracks in the corner bulkhead fittings on the aft side of the firewall, especially the the bottom ones. Changing those out is a bear but can be done. Some cracked and some did not. Again visual inspection. Remove the bolts (one at a time) and have a good look. Theses where only an issue on early RV's and the design was changed for the later RV-4's and all RV-6's and so on.
The answer is hard to put your finger on but there is no LIFE LIMIT on it. There are very very old planes, Cessna, piper, stinson, aeronca, sterman.......basically antiques with the original engine mounts 50 - 70 years old. Some times the FAA puts out AD's in contemporary airplanes for motor mount cracks.
RV's don't have AD's and I personally have not heard of any common or prolific engine mount cracks (except for the corner bulkhead fittings in early RV-4's). They do happen from time to time but its not systemic. Again operations is a big factor. There is always a chance a bad weld could happen, but from my experience Van has pretty good welds.
THE BIG KILLER IS CORROSION, hidden damage and pitting inside the tube. Hard to inspect but unless its a float plane on salt that should not be an issue for at least 50 years? (Trivia: hard core aerobatic planes with a steel tubing fuselage, fill the tubes with inert gas through a fitting. A pressure gauge in the cockpit indicates a crack if pressure is lost!)
I guess a question for Van is where are the critical locations to inspect on the engine mount or where have cracks been found before?
Metal fatigue and hidden weld defects are always a cause for cracks in steel. Do RV's have a particular problem with engine mounts? No. (with a RV-4 caveat, below)
Inspect it with a bright lights, good eyes, magnification and take your time. If you don't trust your inspection skills get a good A&P or AI. Also strip the wires and tape and clamps away. If you need to, by all means wire brush the paint away and clean it well. Of course repaint it after. If the engine mount is off the plane, by all means strip all the paint off and inspect it. You could even send it to one of the GA plane engine mount OH companies for inspection. They will use Dye Penetrate or Magnetic Particle Testing. You can by a dye inspection kit. One brand is "Zyglo", a fluorescent dye penetrate. You use a black light to expose cracks.
You also may want to up your inspection schedule. Frankly every oil change you should have a good visual inspection at it. Cracks start slow and grow. So it's not like it will fail immediately.
A mount may last in theory forever? Well that is a long time but in GA flight time longer than we will be around. It also depends on the kind of flying. Unpaved operations (aka soft fields that are not really soft) can be tough on the gear. The engine mount of course takes gear loads. If you do aggressive aerobatics, again a factor.
The RV-4 like most tail wheel RV's takes the landing load through the engine mounts. If you have had a hard landing, inception is a must. The older RV's had cracks in the corner bulkhead fittings on the aft side of the firewall, especially the the bottom ones. Changing those out is a bear but can be done. Some cracked and some did not. Again visual inspection. Remove the bolts (one at a time) and have a good look. Theses where only an issue on early RV's and the design was changed for the later RV-4's and all RV-6's and so on.
The answer is hard to put your finger on but there is no LIFE LIMIT on it. There are very very old planes, Cessna, piper, stinson, aeronca, sterman.......basically antiques with the original engine mounts 50 - 70 years old. Some times the FAA puts out AD's in contemporary airplanes for motor mount cracks.
RV's don't have AD's and I personally have not heard of any common or prolific engine mount cracks (except for the corner bulkhead fittings in early RV-4's). They do happen from time to time but its not systemic. Again operations is a big factor. There is always a chance a bad weld could happen, but from my experience Van has pretty good welds.
THE BIG KILLER IS CORROSION, hidden damage and pitting inside the tube. Hard to inspect but unless its a float plane on salt that should not be an issue for at least 50 years? (Trivia: hard core aerobatic planes with a steel tubing fuselage, fill the tubes with inert gas through a fitting. A pressure gauge in the cockpit indicates a crack if pressure is lost!)
I guess a question for Van is where are the critical locations to inspect on the engine mount or where have cracks been found before?