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STV Bob K

Prop Spacers

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I have a prop shaft spacer that seems to bee siezed on my Merc 2.5. I have an 8" puller but the it won't fit under it. I tried a light hit with a lead hammer ende of the shft (prop nut on the shaft) & a wedge under the spacer. I am a little nervious about hitting harder. Any suggestions on removal? ohmy.gif

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I have a prop shaft spacer that seems to bee siezed on my Merc 2.5.  I have an 8" puller but the it won't fit under it.  I tried a light hit with a lead hammer ende of the shft (prop nut on the shaft) & a wedge under the spacer.  I am a little nervious about hitting harder. Any suggestions on removal?  ohmy.gif

smile.gif

I used some heat on the spacer and tried the wedge and hammer again. The spacer broke free. I been using white zink lube on the shaft and the spacers.

Any suggestions on this subject?

Also, I am told that some props like to be spaced out farther on the output shaft. Can someone comment on the use of thicker prop spacers?

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You talking about the thrust washer? Goes on the propshaft before the prop and has a taper that matches the taper on the propshaft?

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You talking about the thrust washer?  Goes on the propshaft before the prop and has a taper that matches the taper on the propshaft?

Yes. Thrustwahser. I belive the some drag boats are using modified/thicker "thrush washers" to improve performance.

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Wonder if the spacer taper is worn some. May want to just start with a new one.

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Use anti-seize on the prop shaft taper where the thrust washer fits. And lube it regularly.

Spacing the prop back on the prop shaft with a thicker thrust washer is an OLD trick. It is part of dialing in any prop.

The water running along the gearcase is disrupted each time it is forced to make a change in direction. Even the nose of the case will cause the water to seperate from the case.

By spacing the prop farther back on the prop shaft, you are trying to do several things:

The first is to locate the "sweet spot" where the main flow of water is feeding the prop. This gives the prop the thrust it is designed to have, and makes the prop more efficient - especially at speed.

Another is that spacing the prop slightly back on the shaft will allow more water to feed into the center portion of the prop, causing more bite. This loads the engine more when coming on plane. For drag racing, this allows you to bend the lower portion of the blade (near the root) so that it acts like a smaller pitch than the blade root angle SHOULD give the prop. It also allows you to better make use of ALL of the blade area.

At higher speeds and rpm, spacing the prop back more can make the boat drive better and continously load the engine so that it makes more power. If the engine is not loaded, the engine will be richer than it should be, and will not make the power it is designed to have.

The stock Mercury thrust washer is about 1/2 inch thick (as are the ones for Yamaha props). I have used spacing up to 1 inch (1/2 inch more) with good results. I generally make spacers from 1/2 inch to 3/4 inch thick in 1/8 inch increments for dialing in my racing props.

On lake boats, like my STV, I have found that setting the prop back farther can reduce the mid range pourposing by a large amount, and I can get a bit less slip from the prop at speed.

The angles on the forward edge of the thrust washer can help performance as well. At speed, the water is rushing past the gearcase and actually sucking the exhaust out through the case. If the angles on the forward face of the thrust washer are done correctly, they will increase the flow of exhaust air through the gearcase, and can actually cause a slight vacuum in the midsection. If they are done incorrectly, the exhaust gasses and air will be fed into the outer edges of the prop blades, and reduce the efficiency of the prop.

The more you space the prob back away from the case, the more load you put on the prop shaft and the rear bearing in the gearcase. Something to think about.

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Wayne,

I would lke to try your spacers. I have two different round ear props.

The spacer that came with the 22 Drap prop you sold me looks like OD is too small for the SRX/DAH 27 and a 26 prop from Randy. If your interested, I could post some pictures of these props. Please advise. Thanks. cool.gif

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Dale Hill can make any kind of spacer you want for your props... I will send him an email to post his info over here. He goes by lazer65 on the byuboyz site

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Mikej i had sent him an email a while back and he said he didn't think he was making them anymore, I'd like to get a couple from him if he still makes them.

Thanks

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