Prop hits trim tab

Changing my old prop out and put a 10 5/8 prop on my 1971 mercury 500 50hp....checking to make sure everything fits I notice that the prop is going to contact the trim tab.......Curious since the prop is actualy 1/8 smaller than the one the spec sheet calls for. So, was wondering will it hurt anything if I grind a bit away from the trim tab, trying to keep the same angle on the front? Or can I run without it? Any help is appreciated.
Terry

Re: Prop hits trim tab

Using the right prop would be best but sure, you can grind the trim tab. Mercury makes several different configuration trim tabs for some of their motors to clear long props. You could run without it and some of the higher HP mercs dont have them but they do use a fin on the skeg that does the same thing.

http://www.mrcool.us/822777q1-mercruiser-trim-tab-anode.html?gclid=CNjF3pzF87cCFWYV7Aodfj4AOg





http://www.ebay.com/itm/ZINC-MERCUR..._Accessories_Gear&hash=item232c06e771&vxp=mtr

Re: Prop hits trim tab

skaggst said:

Changing my old prop out and put a 10 5/8 prop on my 1971 mercury 500 50hp....checking to make sure everything fits I notice that the prop is going to contact the trim tab.......Curious since the prop is actualy 1/8 smaller than the one the spec sheet calls for. So, was wondering will it hurt anything if I grind a bit away from the trim tab, trying to keep the same angle on the front? Or can I run without it? Any help is appreciated.
Terry

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Does your "new" prop have significantly more pitch than the "old" one? I'm thinking this could be the cause of the interference. I doubt that grinding a small portion of the trim tab away will be detrimental especially in fresh water use. In salt water, the trim tab is, of course, the sacrificial anode.

Re: Prop hits trim tab

Are you using the right thrust washer?

Re: Prop hits trim tab

wired247 said:

Are you using the right thrust washer?

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Yep it's the thrust washer that came with the Prop....it is a Mercury quick silver.....same pitch as old prop.. according to the spec sheet for 1971s it should take up to 10 3/4 and this prop is 10 5/8......however now that you mention it I think the old thrust washer was about and 1/8 in. thinner and I bet thats what it is......I may try to use the original thrust washer and see if it clears....in the mean time I ground off about 1/8 in of the skeg and the prop clears fine now. But I am going to switch it out the thrust washer and see if that was the problem.
Thanks for the help.
Terry

Re: Prop hits trim tab

skaggst said:

Yep it's the thrust washer that came with the Prop....it is a Mercury quick silver.....same pitch as old prop.. according to the spec sheet for 1971s it should take up to 10 3/4 and this prop is 10 5/8......however now that you mention it I think the old thrust washer was about and 1/8 in. thinner and I bet thats what it is......I may try to use the original thrust washer and see if it clears....in the mean time I ground off about 1/8 in of the skeg and the prop clears fine now. But I am going to switch it out the thrust washer and see if that was the problem.
Thanks for the help.
Terry

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Unless the new prop is the exact same part number as your old one, it is possible to have the same pitch and even diameter prop and still not fit properly. There are so many variables to props that your new prop could have more rake built into it then your old prop and therefore it will rake (slant) back further when installed. So even if it is the same pitch, it still isn't the same part number... Rake effects the lift to the boat's bow and will slant backwards as compared to non-rake props to achieve that effect... Just saying...

Re: Prop hits trim tab

gm280 said:

Unless the new prop is the exact same part number as your old one, it is possible to have the same pitch and even diameter prop and still not fit properly. There are so many variables to props that your new prop could have more rake built into it then your old prop and therefore it will rake (slant) back further when installed. So even if it is the same pitch, it still isn't the same part number... Rake effects the lift to the boat's bow and will slant backwards as compared to non-rake props to achieve that effect... Just saying...

Click to expand...

The mercury dealer had to cross reference two numbers to get one that was supposed to be a match.....I have figured out the problem the barrel of the new prop is about 1/4 inch longer than the old one which pushes the blades just back far enough to run into the trim tab. So......I talked to the merc dealer and he said, I could grind off enough so it would clear.....so got out the trusty grinder and modified the trim tab now I have a good 1/4 in clearance between the trim tab and the outer edge of the propeller.....it doesn't come close now.....I dressed up the trim tab (made a nice curved front line the old one, and I think I am good to go now. I think I will look for an offset trim tab that has the fin back about two inches compared to the old one. But for now going to try it out.