1976 7.5 HP. merc. Shear pin or hub.

[billybones]

Hello all. I just put in an order for a manual for this. My problem is a short amount of time. not sure I will recieve it in time. I recently purchased a boat with this motor and will be taking this to a far away place from parts. 10 years ago I caught bottom in this lake an broke a shear pin. did not have one. My question is, does this motor use a pin or a hub? would like to take a spare just in case. serial no. is 4402748. Merc. 7.5 outboard. Any info would be appreciated. Part of the reason for this is I did a search and found nothing. I am sure a dealer could tell me but want to put it into the archives of this place.. Thanks for your time.

 

[Sotestar]

Re: 1976 7.5 HP. merc. Shear pin or hub.

I had a 1976 25hp Johnson and it had a shear pin, broke it as well but easy to come by. I would stick my neck out and say that it has the shear pin as well. That is what they used on nearly all the lower hp models back then. The hub is is used on higher hp models due to the loads put on them. Go buy a pin for 2 bucks, it should fix your situation

 

[Sotestar]

Re: 1976 7.5 HP. merc. Shear pin or hub.

I had a 1976 25hp Johnson and it had a shear pin, broke it as well but easy to come by. I would stick my neck out and say that it has the shear pin as well. That is what they used on nearly all the lower hp models back then. The hub is is used on higher hp models due to the loads put on them. Go buy a pin for 2 bucks, it should fix your situation. Or just pull the prop nut off and look at it. Should take about 5-10 minutes

 

[billybones]

Re: 1976 7.5 HP. merc. Shear pin or hub.

Thanks, for some reason I did not think of that.. to much on my mind.:$

 

[emckelvy]

Re: 1976 7.5 HP. merc. Shear pin or hub.

Your Merc does not have a shear pin.

The prop is rubber-bushed and if your motor is revving up when underway either the rubber hub is slipping, or your crankshaft splines are bad.

If the motor is pumping water OK it's an indication that the driveshaft is turning and the crank splines are at least connecting crank to driveshaft.

You can do a cursory check of the prop by first disconnecting the plug wires then shifting to reverse. Note you may need to turn the prop while shifting in order to engage reverse.

Then, hold the flywheel to keep it from moving and try to turn the propeller. Apply a good amount of force and if the prop turns at all the hub is bad. Time for a new or rebuilt prop.

You can also pull the prop off and inspect the forward side (gearcase side). You can see the center metal splined insert from that side and also the rubber hub. If the rubber is all chewed up it's probably shot.

HTH and keep us posted........ed

 

[billybones]

Re: 1976 7.5 HP. merc. Shear pin or hub.

Thanks emckelvy and sotestar. I will do this monday. And will report back. I was unaware that the hub was in the prop itself. Not happy about that. The 944 had a rubber bushed clutch. failed with age alone,. so if its bad I need a new prop? Must be why when I put in the dates and numbers no one has a prop for this engine...It has a chip off of it. not bad just an 1/8" nick on the side of the blade.. Monday it goes into the barrel and gets ran. after the slippage check. Thanks again guy's.

 

[billybones]

Re: 1976 7.5 HP. merc. Shear pin or hub.

Well being way to busy I finnaly got the engine out and tested the hub. A-ok there. thanks for the info. Found the motor bushings a bit shot though. Did start on the 3rd pull. Local kid stoped by and waited for me to start it in the garbage can I filled with water... LOL he ran as fast as his legs would take him when it fired up... the handle ain't quite right where it should be.. start is high throttle.. Plus tension was set way high. I freaked a bit myself. tell tale is a bit non exsistant at idle though in neutral. low speed. about 2 and a 1/2 on idle screw. Know this is not good. but it seems OK in gear. I will try and find an impeller tomorrow. sunday I leave for up north in MICH. Today i could not find one..(late in day) Everyone is waiting on 8-11-06..for restock Strange but true..out of stock. Where I am going it is about a 4 minute ride up wind full throttle then you float for about 2 hours and troll with the wind..so will only use motor in that time frame. Motor seemed strong.. just wished for a better tell tale stream. Do have a trolling motor. will use that at slow speeds. and oars.. total rebuild after I get back.. I learned a lot today about outboards and how they work. I thought the entire lower unit below the power head was the bottom. bought a 2 quarts of lower unit lube... Didn't need any.. Thanks again for your help. Will post a rebuild of power unit and lower unit rebuild this winter. pics included..

 

[billybones]

Re: 1976 7.5 HP. merc. Shear pin or hub.

this will close out this thread. I wanted to say thanks to this forum for basically saving my vacation. On the way up stopped at a marine store, they had an impeller kit. Like a dummy thought I packed the manual.. did not. once up north pulled the lower unit anyway because I was worried. Put it in from what I remembered from the original post that brought me here..How to change an impeller. (man that sucker is tight and the engineer that made that key should be at least slapped on the hand with a ruler). got it back together.. that was rough. why would all three things lineup at once? Did not work at all now.. original impeller was missing one blade stuck in the upward hole and next blade ready to crack off. and now it does not work. did not realize that the outlet side of the pump had a guide tube. this was stuck up inside of the motor. My kid found it and lining up the tube and 2 splines came a lot easier. also was not aware that the gearing is all in the bottom.. learned a lot. memory of an old thread from here helped and now the book goes into the takle box. Thanks again.d