Merc prop 68-70 vintage

[anotherhassel]

I was wondering if anyone could help me find a propeller for a 1970 4 hp merc? I spun the hub and it won’t run at speed. Just revs. If I take it easy it goes but not like beforethe prop. I would hope this rule out the lower unit. Thanks in advance!

[jeff-register]

Before pitching drill & pin the prop & retest to be sure it is OK

[billw]

48-47944A1 8 7/8 by 5 pitch. 8-spline.

http://www.ebay.com/itm/PROP-48-47944A1 … 14&vxp=mtr

COUNT your splines, though. If you have an odd ball lower unit on it or it’s not really a 1970 (SERIAL NUMBER!) it could have a different spline count.

Take the plug wire off and take out the spark plug. Put the shift in forward. Hold the flywheel and attempt to turn the prop counter clockwise by hand. If it spins but the prop nut doesn’t, the hub is spun. You can do this on a little motor.

Long live American manufacturing!

[anotherhassel]

Ok so I tried the test. The prop didn’t slip. Is it possible it is only slipping when the hub gets warm under a load? I am gonna try to run the boat tomorrow. This is my duck boat engine and I love it. I need this boat to run right. When it was running correctly it would plane my 10 ‘ jon on plane with me in it 235 lbs and so light gear. I had 105 lbs compression on the cylinder. So I would assume that the engine is healthy. Can’t pull the engine with the recoil stater as it is in the hood so it was done with a drill.

[billw]

Well, I was just talking about turning the prop by hand. I have done it before so I know it can work on these little props. Anyway, the alternative method that these guys like is to take the prop off, take a Sharpie and make index marks on the inner hub and outer part of the prop. Put the prop back on and run the engine where the condition exists. Then, take the prop off and see if the index marks are still in alignment….or not. If not, the hub slipped.

Long live American manufacturing!

[slim60]

What BillW said. I checked my 110 the same way. As far as starting that motor, if it starts easy with the recoil it should start without the hood by spinning the flywheel by hand.

[billw]

Motors with that type of cowl/recoil are another reason Mercury sold the tiny, screw-in compression tester. Not much taller than a spark plug, you could screw it into the plug hole, put the cover on, pull it a few times, then take the cover off and see the reading.

Long live American manufacturing!

[anotherhassel]

My engine has way to much compression to start it by hand. I have tried. I took it for a ride yesterday and it ran as it should. I am going nuts with this old girl. I scribed the hub and the prop and there was no movement at all. I hope that it was something as stupid as the prop wasn’t seated properly and was cavitating.

[billw]

Maybe you just picked up some weeds on the prop. That can have a similar effect. (Yeah, I know it’s a weedless type but it’s a guess anyway….)

Long live American manufacturing!

[anotherhassel]

Bill and others thank you. I appreciate the help. Bill hopefully you are right and that is all it was.

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