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Pinion gear grenaded

Krsowles

Krsowles

New member
New member, hi all. Thanks in advance! Got a new used fishing boat and attempted to social distance Saturday. Had a great day on lake even though no fish caught but motor had acted like it was stumbling for fuel as day went on. Primer bulb was hard and fuel filter looked good. Running back to launch, stumbling seemed to get worse and would fluctuate between normal rpms and dog down. Last time it came up to full rpms and there was a loud bang from motor, rpms screamed and both forward and reverse gears stopped working. After I collected my thoughts and emptied my drawers (did I mention it was loud?) I started motor up again and it ran fine but gears definitely gone. Used the kicker to get back to launch. I removed propeller and shaft and found the pinion gear in 3 pieces. Forward and reverse gear look good. Lower unit oil was fresh (first day out) and when drained had traces of brown and lots of metal flake in it. The motor is a 1986 75 hp 2 stroke 4 cylinder. I’m asking the brain trust, any guesses what might cause this failure? I don’t want to replace all this and have it happen again because I missed something. All thoughts appreciated! 🍺
 
That happened to me, water caused the gear to rust weaken and break, there must have been water in it, look at the teeth of the gear for pitting.
 
Thanks for the input! I saw no pitting on broken gear (I have a so so picture of it) and haven’t cleaned the forward gear or housing yet. The reverse gear also showed no pitting. I will add a friend suggested prop may have spun and the motor wasn’t stumbling on fuel. I saw no evidence of a spin prop but not 100% sure. My other question would be can a spin prop jam up the gears?
 
My other question would be can a spin prop jam up the gears?​
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Nope....

I’m asking the brain trust, any guesses what might cause this failure? I don’t want to replace all this and have it happen again because I missed something. All th​
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Slamming in gear, pinion bearing fail due to water intrusion or oil break down. Don't waste your time trying to rebuild as unit needs special tools to shim.Just find a used on and seal and bolt on. Only a 4cyl 2:3: ratio will work correctly
 
Thank you for the input! I assumed I could replace driveshaft, bearings, pinion gear and all seals and go. I remember hearing a saying long ago about assuming though...
 
This takes an experienced mechanic to repair, skilled in lower units. Try Tim's Outboard in Hackensack MN.....see what Mike or Dan has. 218 682 2331.
 
So next chapter of saga is that I’ve found a nice, used lower unit for sale that has been through professionally two years ago. The previous owner has been very accommodating and replies I’ve received on another forum as well as discussion with several professionals indicates rebuilding a lower unit may be beyond my skill level. This nice lower unit was made available to me at a price comparable with just buying the new parts, so I went that route. Thanks for all the help! ������
 
Lower unit repair has been a pretty large part of my business here. Between all the rocks, freezing temps, lack of skilled aluminum and stainless MIG welders, ignorance of proper maintenance, and incredibly high replacement parts......it's not a bad deal for 'ol Tim.
 
Great job. Make sure the unit was pressure tested PROPERLY to 15 psi. A more accurate test is accomplished with ambient temperature above 70 degrees F. and before unit is filled with lube. Furthermore shafts are to be moved, rotated and/or shifted WHILE AIR PRESSURE IS BEING APPLIED. Otherwise the test will not effectively duplicate operating conditions. This proceedure is often overlooked.
 
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Don't forget to replace the water pump impeller because even if it was replaced two years ago it's just about half worn out. Why? 70% of rubber today is synthetic polymer, made from petroleum by-products. It's terrible for applications like impellers. I don't understand why they don't make small components like impellers out of real latex rubber polymer. I also play with old turntables, VCRs, and tape players where the original belts are still good after over 40 years.....got a Radio Shack Realistic high-power in my old pickup that still works great with the original belt....... manufacture date 1978. My son has a 5 month old rock tumbler that just blew the belt. WTF? Why do these engineers want to dick around with something as critical as an impeller?
 
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I’ve already got the impeller kit but thanks for the heads up! As far as pressure and vac test goes, I’m headed out now to get it, 5 hours away. I’m hoping to find someone there open and able to do it. Otherwise I’ll have to buy it and hope for the best. I can have a local test it when I get home but I realize that’s less then perfect, it’s better than the one I currently own. For a $200 unit, I won’t drive back, I’ll have another lu with all parts and replace all seals.
 
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