Sniper
Well-Known Member
I think I know the answer to this, but I’d like to check with those who have greater knowledge.
I have recently bought a second hand but well looked after Engine from a reputable private source. Originally fitted to a sail drive, the engine has been married to a conventional gearbox for shaft drive. I have fitted the whole outfit as a direct replacement for the ageing 1GM Which has done well for 30 odd years but is now starting to corrode badly. New engine runs well so I have no concerns about this. However, the gearbox seems to be an issue. Gears seem to engage ok, but there is no way the engine is making peak revs going ahead, leading me to think that the gearbox ratio is wrong for the propeller that I have already fitted (Previous gearbox ratio was 1:3.22, and the old engine was still capable of spinning up to 3,200 rpm given time).
This to me seems like the new gearbox is a different ratio and I am therefore overpropped. I will check the ratio next time I am on the boat. However, when I put the engine astern, there is clearly a lot of slippage , I assume in the reverse cone? The engine spins up no problem but the prop shaft can easily be prevented from turning by putting a foot on it (don’t ask!)
seems I have two problems - one an installation issue, the other a mechanical fault. I still have the old engine with gearbox attached and the gearbox always worked well and seems to be in good condition. I am thinking therefore of putting the old gearbox onto the new engine. As far as I can tell, this is simply a case of undoing the 8 flange bolts and swapping them over. Propellor issues sorted and decent performance astern.
Am I on the right lines? Any obvious problems? I will of course be having a chat with the vendor but I do appreciate that buying secondhand is caveat emptor and these things happen.
I have recently bought a second hand but well looked after Engine from a reputable private source. Originally fitted to a sail drive, the engine has been married to a conventional gearbox for shaft drive. I have fitted the whole outfit as a direct replacement for the ageing 1GM Which has done well for 30 odd years but is now starting to corrode badly. New engine runs well so I have no concerns about this. However, the gearbox seems to be an issue. Gears seem to engage ok, but there is no way the engine is making peak revs going ahead, leading me to think that the gearbox ratio is wrong for the propeller that I have already fitted (Previous gearbox ratio was 1:3.22, and the old engine was still capable of spinning up to 3,200 rpm given time).
This to me seems like the new gearbox is a different ratio and I am therefore overpropped. I will check the ratio next time I am on the boat. However, when I put the engine astern, there is clearly a lot of slippage , I assume in the reverse cone? The engine spins up no problem but the prop shaft can easily be prevented from turning by putting a foot on it (don’t ask!)
seems I have two problems - one an installation issue, the other a mechanical fault. I still have the old engine with gearbox attached and the gearbox always worked well and seems to be in good condition. I am thinking therefore of putting the old gearbox onto the new engine. As far as I can tell, this is simply a case of undoing the 8 flange bolts and swapping them over. Propellor issues sorted and decent performance astern.
Am I on the right lines? Any obvious problems? I will of course be having a chat with the vendor but I do appreciate that buying secondhand is caveat emptor and these things happen.
