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Old 28 May 2013, 17:43   #1
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tohatsu 9.8 prop

Just bought a new prop for the above on ebay. When I put the old and new side by side it is now clear that the previous owner has filed the prop big time assume to get rid of some dinks.

Going to be interesting if I notice any difference in performance. I assume with a thinner edge it will bite more and the bigger surface area will get my 2.9 Sib on the plane quicker.
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Old 28 May 2013, 22:23   #2
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Buying spare props without installing a induction tach on engine for wot testing can turn into a very bad & costly wrong purchase. Must test both props with you alone, preferably on flat cal no wind waters and check max rpm achieved at wot with each prop.

Then compare both readings to factory stated min-max wot rpm parameters to know if engine is running in the safe side. Which are the pitch numbers stamped on the old & new prop ?

Happy Boating
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Old 29 May 2013, 04:50   #3
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Hi Loco,

Thanks for the reply, the prop that I have purchased (white one) is as per the Tohatsu 9.8 manual. I have the long shaft so purchased 12 spline 8.5"x7.5 and is a genuine Tohatsu prop (also came in Tohatsu packaging) PART NO. 3B2W64515-0.

I have not got a tacho but feel I would be safe with selecting the manufacturers recommendation.

I assumed the original prop was standard but it wasn't until I compared them side by side that I noticed the difference. The stamp on the new prop clearly states 7.5 the one that came with the engine has H7 and on closer inspection has been seriously filed down as the leading edge is quite thick and you can see the filing marks where the paint has come off following a respray. The old prop will be used as an emergency spare and now I know should I ever use it again I wont be taking this prop to WOT.
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Old 29 May 2013, 10:36   #4
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Hi AJ,

If you are going for an induction tach, better go for a hour/tach meter which is a must install. Test your white prop, specs for both 9.8, 2,4 strokes are 5000-6000 rpm. If near 6000 rpm or slight less with you alone you'll be fine, bear in mind that if placing extra mates wot rpm will decrease accordingly, but still inside safe wot parameters.

Hardline induction hour/tachs are very simple, reliable and small to install outside engine. Will need to set firing sequence to read well. 7.5 is the standard factory delivered prop, if over reving will need a 8.5 pitch to lower max rpm if boating full throttle with you alone, but that can only be determined with a tach.

Happy Boating
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Old 29 May 2013, 13:30   #5
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AJ, isn't that motor an auxiliary as well?
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Old 29 May 2013, 14:00   #6
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AJ, isn't that motor an auxiliary as well?
I thought that..but I wonder if that was just a justification...let's be real..it's never going on the back of his boat...

Comment was passed this afternoon he should just sell it and get a ss for some sib action.
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Old 29 May 2013, 14:01   #7
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Hi AJ,

If you are going for an induction tach, better go for a hour/tach meter which is a must install. Test your white prop, specs for both 9.8, 2,4 strokes are 5000-6000 rpm. If near 6000 rpm or slight less with you alone you'll be fine, bear in mind that if placing extra mates wot rpm will decrease accordingly, but still inside safe wot parameters.

Hardline induction hour/tachs are very simple, reliable and small to install outside engine. Will need to set firing sequence to read well. 7.5 is the standard factory delivered prop, if over reving will need a 8.5 pitch to lower max rpm if boating full throttle with you alone, but that can only be determined with a tach.

Happy Boating
Hi Loco,

This engine is just for playing around on with a little SIB, the main purpose of it was as NOS points out below as an Aux.

Having spent quite a bit of money on it in repairs as it looks like it wasn't looked after that well by previous owners I don't want to spend a great deal more on it.

How much are these hour/tacho things?
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Old 29 May 2013, 14:10   #8
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AJ, I've got a Quicksilver tiny tach your welcome to borrow if you want to test you props.
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Old 29 May 2013, 14:16   #9
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Thing is, IF you're going to use it as an aux, you're probably better off propping it so it overrevs a bit on the sib and don't use full throttle. If you need to actually use it as an aux, it could be an issue if you don't make full power.

If realistically you aren't, just prop it right-but then, you might as well chop it in for a short shaft.
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Old 29 May 2013, 14:16   #10
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Cheers Sam, are you around this Sat?
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