7.5 and 9.8 differences

R

Rmoore45

Seaman
Joined
Aug 4, 2011
Messages
68
Hi, my name is Ranger and I'm new to this forum. I joined to ask a question about the differences between the 7.5 and 9.8.

I have a 1978 Mercury 9.8, the powerhead and pistons are shot. I'm looking for a complete powerhead but I'm having some problems locating one, my local outboard repair shop doesn't have one so I have resorted to the internet.

I found a 1977 mercury 7.5 powerhead on eBay that was removed from a running outboard, will this powerhead fit? On the outside they look the same however I have heard rumors about different port sizes. I think that it will work but I want to be sure.

Thanks
 
79Merc80

79Merc80

Senior Chief Petty Officer
Joined
Nov 22, 2007
Messages
673
Re: 7.5 and 9.8 differences

I believe the blocks are identical, the only difference being the port timing. You will have to change props to make up for the different gear ratio in the 9.8's lower unit.

Others with more know how will chime in soon.

Craig
 
B

bob1340

Petty Officer 1st Class
Joined
Jun 12, 2010
Messages
287
Re: 7.5 and 9.8 differences

I don't know about a '78 model, but on my '69 model 7.5 the only difference is the carb. I did a cross check on all the parts and found the only difference to be the carb. I did not check the prop part #'s, just the powerhead stuff. Same crank, rods, pistons, case, ignition, intake componants, yada, yada. Just different part numbers on the carb.

You may want to check on someplace like this:

http://www.crowleymarine.com/parts.cfm
http://www.marineengine.com/parts/mercury-outboard/index.php
 
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