How-to: convert your Merc raw water pump to crank-driven Johnson (take 3)


According to this picture from PerfProTech/Merc, I guess I can move to a shorter belt and just skip having an idler.


MC336.jpg
 
I wonder if the alternator is adjustable in that picture. You need some way to take up the slack in the belt. In my case (350 mag), I just looked at the parts diagrams for a version that didn't have the engine mounted pump (hint alpha drives have the raw water pump in the lower unit), and copied that setup. Don't know if such an animal exists for the big blocks...
 
undercover said:
I wonder if the alternator is adjustable in that picture. You need some way to take up the slack in the belt. In my case (350 mag), I just looked at the parts diagrams for a version that didn't have the engine mounted pump (hint alpha drives have the raw water pump in the lower unit), and copied that setup. Don't know if such an animal exists for the big blocks...
Click to expand...

The idler on the port side above the PS pump adjust the tension
 
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AllDodge said:
The idler on the port side above the PS pump adjust the tension
Click to expand...

I?m not getting rid of my tensioner. The tensioner for this big block is located above the power steering pump on the odd bank. It?s similar to the picture I posted above. My questions were more around trying to figure out if it was necessary to provide a more graceful belt route to the alternator versus having the switchback as in the picture.
 
Just bringing this back up with an important PSA. 4 years later, this is what that billet aluminum hose adapter looks like. Not good, and my boat is used in salt water but always flushed and stored in fresh water (come through the locks into freshwater Lake WA). The purpose of this piece was to adapt the 1 1/2" output of the merc pump to the 1 1/4" output of the Johnson pump. I'm doing a cooling system refresh (replacing all hoses on the seawater side) and found that this isn't necessary. The 1 1/2" merc hose necks down to 1 1/4" before the PS cooler. Just run a fresh hose from the PS cooler to the output of your Johnson pump, and you're GTG.
 

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TurboJoe said:
Does Volvo also offer a vdrive version like merc does? This would put the pumps way in the back, and might be part of the reason merc kept the pump in the same location they always have.
Merc also packaged it with the special pump drain system and is in a great spot to get the hose from the bravo transom assembly. These are the two immediate things that pop out. I don't think their first requirement was to make a pump that was very expensive to replace, though I'm sure they didn't mind that. Every previous water pump was in the same post also. I do wish the stuck with the 7.4 style cheap easy to rebuild pump. Either way, I just went with the hardin marine.
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Yep. Here's a video of an older one. Some of the accessories and harnesses have changed, but basically the same as a more modern setup. Water pump/impeller astern. Would not be fun to change, but on the I/O boats, it's a breeze.

 
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