mercruiser on a pontoon with noise

[mayjean123]

I have a 24 foot pontoon with a 120 4 cly mercruiser out drive that is bad will a out drive off a 165 6 cly work

 

[wrench 3]

The gear ratio is different. It can be compensated for by changing the prop pitch, but you'll loose some efficiency.

 

[mayjean123]

that's what I figured but had to try thanks

 

[Rick Stephens]

I would still do it in a heartbeat. The compensation for the gearing is not very big. Somewhere around 7% difference in the ratio of the drives would be the default factory gearing. 1.98:1 for the 4 cylinder versus 1.84:1 for the 6 cylinder engine. And with more HP you'd want to increase pitch as well. But the ratio difference is minor compared to the HP difference. Say you're at a 17 inch pitch now, you'd probably have to go 21 or 23 inch pitch with a engine producing half again as much HP. Once prop'd properly it would be nearly the same efficiency as with a 1.84 gearbox.

If you have a good donor motor, the only way to really do this without getting spendy, I don't see any reason it couldn't be done.

 

[thumpar]

Rick from the OP he is going the other way. He has a 120 and wants to use a 6cyl ratio drive. Being the size that it is you can try to go lower in pitch but might run out of room depending on where it is at now.

ETA: What is wrong with the drive? If the upper is good you could just swap lowers as long as it is not shreaded gears that got in the lube. That would keep the ratio the same.

 

[mayjean123]

the problem I'm having is that when I run the engine I get a rattle noise when I rev up engine and turning the outdrive right or left going straight no noise it has new u-joints and gears look good and it has new gimbal bearing

 

[thumpar]

I don't think a drive will fix it if it doesn't doing it when the drive is straight. Nothing in the drive changes when turning or going straight.

 

[mayjean123]

I,ll see if I can get a video of it thanks

 

[Rick Stephens]

Rick from the OP he is going the other way. He has a 120 and wants to use a 6cyl ratio drive. Being the size that it is you can try to go lower in pitch but might run out of room depending on where it is at now.

.

DOH

 

[mayjean123]

cant seem to load video but the sound is like a rattle it is comeing out of the 165 6 cly unit as well as the 120 4 cly unit I,m lost

 

[thumpar]

Are you sure it is ONLY while turning? The flappers make a rattle when the rubber wears off.

 

[mayjean123]

I removed the flapper

 

[wrench 3]

Do you have the drive most of the way down?

 

[mayjean123]

its down about level

 

[mayjean123]

here is a video of what it sounds like matbe this will help

 

[mayjean123]

what would make it sound so tinny

 

[Rick Stephens]

Your video is set to private.

 

[mayjean123]

try one of these sorry

 

[Rick Stephens]

Sure sounds like CV joint. Wow, loud. Input bearing OK (behind the yoke)?

 

[mayjean123]

tell me I,m going to try new cvs the ones in there are new but maybe ?????? thanks for looking