merc 9.8 & 7.5

[jwsimmons]

I bought a 1971 mercury 7.5 hp (75 model) from a garage sale the other day. I would like to know if the lower unit off that can be put on a 1967 merc. 9.8 (110 model). Probably not but if anyone knows, I'd appreciate advice. <br /> ^thank you

 

[joblo33]

Re: merc 9.8 & 7.5

If they're both the same shaft length and both the same type (electronic ignition, same cowling release system) then yes. I have a bunch of those 9.8's and 7.5's and swap everything but the carbs and the powerheads between the two models.

 

[jwsimmons]

Re: merc 9.8 & 7.5

I took the 7.5's lower unit off. They are identical. I decided to try and switch prop's but now I can't get the one off. The nut, I would say, was a little rusted shut. I think maybe the prop has just rusted itself to prop shaft. Does anyone have any little tricks for this? Thanks again

 

[dajohnson53]

Re: merc 9.8 & 7.5

So it's the nut that is frozen? I'd say you need to soak with something like liquid wrench or PB Blaster. <br /><br />If the prop itself is stuck there are a lot of ways to try to get it unstuck (same stuff), but you often have to ruin the prop to get it off. With the price of a new prop for this engine being around $70, I wouldn't waste a huge amount of time trying to save it. Some times the path of least resistance is to just carefully cut these things (nut, prop) off and replace the parts. YMMV of course! Search various Iboats forums for stuck prop type subjects. I have my experience in a thread entitled "9.8 stuck prop adventure" Good luck.

 

[dajohnson53]

Re: merc 9.8 & 7.5

Oh, PS: the nut itself is most likely simply a nylon insert type lock nut which is easy to replace - in case you decide to cut it off.

 

[jwsimmons]

Re: merc 9.8 & 7.5

Actually I've already got the nut off. The prop won't pull off the lower unit. It probably doesn't make a difference but I thought I'd add that just in case.<br /> Thanks for the advice though.

 

[dajohnson53]

Re: merc 9.8 & 7.5

You can find out if there's a difference between the recommended prop for the 7.5 and the 9.8 by going to a parts web site and comparing. I've found that most of the props websites, including the IBoats prop finder, often don't list props for the older, smaller engines -you have to call. I think you can find recommended props for both of these engines at Mercruiserparts.com. Then it's up to you to decide if you want to change the bugger

 

[joblo33]

Re: merc 9.8 & 7.5

I'd just leave it on and put a new prop nut in front of it. I've tried time and time to get them off and haven't succeded yet. Those old mercs sieze up there often.