Pre Alpha and gen 1 question

[Climber513]

Somewhat new to boating and was wondering if I can use a gen 1 with a pre alpha outdrive? It all bolts up together but someone told me the gear ratio may be different? I dont know any help would be great.

 

[alldodge]

Don't worry so much about gear ratios unless your unable to find a prop with low or high enough pitch to use it.

Example:
If you had a 1:50 drive with 21P prop, and went to a 2:00 drive, you may not be able to find a 30P prop if needed.

Or if you had a 1:50 drive with 21P prop and went to a 1:30 drive, you may not be able to find a 13P prop if needed

Numbers about are not real but just what needs to be thought about.

What was the original drive ratio and what is the one your going to?

 

[achris]

First up, no such thing as a 'pre-Alpha'. It's a MerCruiser-1, or MC1 for short.

Next, what engine are you mounting this up behind?

Chris...

 

[Climber513]

Not sure on the ratios. What happened is I was in a pinch and down to the last day to get my boat water ready. It was getting hot so I had a 250 6cyl with what I was told a pre alpha outdrive. I also had a mercruiser 228 with an alpha 1 outdrive so the lowers looked to be the same so I swapped them due to one having a new impeller in it. Took it out and it's still getting very hot even with new impeller. So I'm changing the water pump on the 250 engine and double checking the impeller but I'm not sure if the outdrive would get hot due to engine overheating or if I have two separate things going on. That's when someone said something about the ratio.

 

[achris]

The 250 (an old Mercruiser '165') ran a 1.65:1 drive. The 228 runs a 1.5:1 drive. So the 165 will be overloaded without a prop change.

However, that's not the reason for the overheat. You have a new impeller, and I assume the 228 wasn't overheating, so we can assume the water pocket cover's not the problem. New water pump on the 165 didn't fix anything. The problem is likely a blocked up exhaust elbow. Very common on those engines. Once you have the elbow off, have a good look in the manifold passages too.

Chris.........

EDIT: Just re-read the post. You only swapped the lowers... Your drive ratio didn't change. Ratio changes are in the upper, but your water pocket cover could still be the problem...

https://forums.iboats.com/forum/eng...0645-i-m-running-hot-help?t=556903&viewfull=1