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rotorwrench · 11-08-2019, 02:09 PM

Do you know of problems with PM gears? If originals are in good condition and check to have minimal wear then they can be reused. Model A engines run at a lower rpm level than a lot of others and I haven't heard of problems yet.

Sintered iron and steel gears have been tried in several applications on different helicopters that I've worked on over the years and they had troubles with them. It seems that the PM technology works well for automotive connecting rods and other structural engine parts but not so well with some gears. On Lycoming engines they first used sintered iron with problems, then they tried aluminum ones that didn't work well, and finally they changed to a nitrided steel gear for one and a carburized steel gear for the other and this worked OK. On the Rolls Royce/Allison 250 military turbine engines, they tried a sintered steel gear for the output shaft and they started failing right & left till they took them all out of service.

The technology is getting better but that's due to the intense need of auto & auto parts manufacturers to make parts cheaper. They are easier to manufacture with no hobbing technology required and they are easier to heat treat but you never know how the ones for model A engines are made. If they cut corners, there is a lot better chance for problems.

11-08-2019, 02:09 PM	#5
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,440	Re: Oil pump replacement gears Do you know of problems with PM gears? If originals are in good condition and check to have minimal wear then they can be reused. Model A engines run at a lower rpm level than a lot of others and I haven't heard of problems yet. Sintered iron and steel gears have been tried in several applications on different helicopters that I've worked on over the years and they had troubles with them. It seems that the PM technology works well for automotive connecting rods and other structural engine parts but not so well with some gears. On Lycoming engines they first used sintered iron with problems, then they tried aluminum ones that didn't work well, and finally they changed to a nitrided steel gear for one and a carburized steel gear for the other and this worked OK. On the Rolls Royce/Allison 250 military turbine engines, they tried a sintered steel gear for the output shaft and they started failing right & left till they took them all out of service. The technology is getting better but that's due to the intense need of auto & auto parts manufacturers to make parts cheaper. They are easier to manufacture with no hobbing technology required and they are easier to heat treat but you never know how the ones for model A engines are made. If they cut corners, there is a lot better chance for problems.