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30 to 57 mercruiser swap gearing question

G

gewtersnake

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"I'm in the process of swa

"I'm in the process of swaping a 3.0 for a 5.7, and I've got a few questions about the mercruiser stern drive. Do I need any special tools to swap gears? Is it a pretty straight forward swap or should I let the local marine mechanic do it? Can I leave the 2.00 gears in there and just rum a diffrent pitch prop? I've done plenty of swaps in cars but this is my first boat, I'm im in "uncharted waters"... Ha! Thanks for you input in advance guys!"
 
"The ratio you need is 1.47.

"The ratio you need is 1.47.
The different ratios are all determined in the upper gear case. The lower case is the forward and reverse gears and they are the same for all ratios.

You can do it, but it takes a few special tools.
The new gears must be properly shimmed to get the proper mesh.
You must also set the preload on the input shaft bearing pack correctly.
You would be well advised to pick up a manual for your drive before proceeding. If you are friendly with your local boat shop, you may be able to borrow the tools you will need.

The water pumps is driven by the vertical shaft which rotates whenever the engine is running. With the 1.47 ratio this shaft turns faster than with the 2.0; and your pump would not likely push enough water to cool the 5.7 without the gear change, even if you could prop up enough to compensate for the power difference.

It might be easier to sell your drive on ebay and either pick up a 1.47, or buy a new one complete from SEI. This would be especially the case if your drive is a few years old and tired already. With a new drive you get all new u joints, etc.

What year is it? Alpha or pre-Alpha?

Rod"
 
"It is an alpha drive, It'

"It is an alpha drive, It's only about two years old so i'd hate to sell it... but I haven't really looked into it yet. I think I'll swing by the boat shop and see what it would cost me to have my drive re geared vs a new unit. Has anybody heard of anyone doing this swap before on the web, somewhere I might find a good write up or more info? I've had troble finding any myself so I will be posting my experience along with pictures once it's complete..."
 
"Adam;
Last year I swapped ou

"Adam;
Last year I swapped out a carbed 4.3 V-6 in my boat for a new 6.2 MAG MPI V-8.
It went well in that both engines are the same width, but the 6.2 is about 4-1/2" longer. My boat has plenty of engine bay space.
I had to change from the 1.81 ratio drive to a 1.47; which I did by swapping the upper gear case complete. I had no trouble selling my old upper gear case on ebay.
The 6.2 came with a standard 10 pin barrel plug which fitted up to the boat harness with no issues at all. I had to do some special wiring for the shift interrupt switch, but no big deal.

Your swap is more complex in that the 5.7 is completely different than the 3.
You will need a new exhaust Y pipe to bolt up to your inner transom plate, as well as the different ratio drive leg. All else in the transom assembly will work fine.

You will have a hefty weight increase in your boat. I hope it is at least a 20 footer. In my case I don't think I added more than 100 lbs going from a V-6 to a V-8. But I went from 180 to 320 propshaft hp. Yahoo!

Rod"
 
"320 propshaft hp? on an alph

"320 propshaft hp? on an alpha? I thought they where only good for 300 hp? (of course thats manufacturers recomendations, they have liability issues and etc.) It's a 19 ft bowrider, I'm doing some other things to compensate for the weight like aluminium headers (saves 80 pounds!), mini starter, and such... I can't wait to get this little boat on the water. It should fly with 270 hp!"
 
"I just found the 1.47 unit on

"I just found the 1.47 unit on SEI's sight, really nice price vs the new mercruiser unit. I think I'll go that route and sell the 2.00 on ebay..."
 
"Adam;
So far so good on the

"Adam;
So far so good on the Alpha; but you're right, the 320 hp is over the published limit. I try to be a little gentle with the throttle from a dead stop.

I also have an entire spare drive leg sitting on the bench ready to go in case of disaster. It's made up of a new Merc 1.47 upper and a new SEI lower unit.

I think you are doing the right thing with the SEI upper case. Good luck on your swap.

Rod"
 
"so tell us hows it going and

"so tell us hows it going and you got any pics???????? sounds like something I would be interested in doing....
"
 
"Ken:

Welcome. Please st

"Ken:

Welcome. Please start a new thread instead of hooking onto another's. Click on TOPICS above, select MERCRUISER and then START NEW... in the dark blue area.

One question: Is the 350 engine's HP rating under that which is stamped on your Coast Guard boat info. placard?"
 
"19 much better...that would b

"19 much better...that would be scary in a 17 footer... although 1 tempest brochure I have shows the V8 as an option in the 17. those Quebec-ers are a bit crazy speed wise...60 is pretty impressive...is that GPS? or the speedo on the dash?
The good thing for you, Ken is the discontinuation of the single vessel lic program in Canada. That was a PITA trying to get rating plates for repowered boats... luckily I just hid out with my old Grew...You should still write to whoever makes Tempest boats and ask what the rating of the hull is....they will of course tell you that Tempest is a different company now with no support of older products....and that way you are covered as you "tried" to find the rating. I can also copy the brochure if you want if your boat is early 80's"
 
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