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Old 10-15-12, 06:19 PM   #1
maxwell.riddle
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Default bore out 90hp

if you bored out a 90hp, it wouldnt be a 90hp anymore would it? what would be a normal jump from 90 if you bored one out?
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Old 10-15-12, 07:13 PM   #2
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It would then be an over bore 90 hp,it makes no sense unless rebuilding as its normal over 30,very costly to rebuild without needing it just to overbore.Change jets and go to fiber carbon reeds will cost less gain about the same hp.Even more gains if you can stick a 115 tuner on it.Most motors blocks and cubic inches are used for more than one hp say 90,115,125
The 2.6 yamaha 150,175,200,225 as an example one cannot easily make a 150 into a 225 as internal changes like as in porting but can make a 175/200 fairly easy.
Talk to a yammer mechanic yours can be a 115 or more for around 600 bucks,river pkgs more expensive from hydro tech would gain more at more cost.
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Old 10-16-12, 12:25 PM   #3
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boring will gain you nothing noticable
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Old 10-16-12, 12:46 PM   #4
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Overboring the cylinders of any internal combustion engine will produce an increase in torque and power roughly proportional to ratio of the new engine displacement to the old one. This will hold true for small, real-world overbores.

I'm not sure what the cylinder bore size on a 90hp outboard is (would need to know make and model), but let's look at one I'm familiar with, the Mercury Optimax. It has a bore/stroke of 3.63/3.00 (inches). That makes the cylinder volume of 31.04 cubic inches. (It's a 3-cylinder, so 3 x 31.04 = 93.12 cubic inches, almost 1 hp per cubic inch, sort of a golden rule for non-supercharged engines.)

If you were to bore the cylinders 0.030 (3.66 inches), the new displacement would be 31.56 cubic inches per cylinder.

The ratio of new to old is 31.56/31.04 = 1.017

So your 90hp outboard should now be putting out 91.5hp.

Congratulations...you've just spent $4,000 on machine work and new pistons to make 1.5 more horsepower. But hey, you will get to your honey hole 3 seconds faster than your rival, right?

This should tell you overboring is almost always to clean up wear or damage, not increase performance. The only time you would "max bore" something is if it already needed cleaning up, and you didn't already have your pistons in hand.
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Old 10-16-12, 01:04 PM   #5
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Well I am paying 1400$ for boring, new pistons and rings, head shaved, carbs rebuilt, new water pump, new oil pump and lower unit oil change.

I lost a cylinder. Had 0 compression. So that's the reason for getting worked on. All the other stuff is to fix the problem that may have caused the cylinder going out.

So tell me if I'm wrong, but 1400$ sounds pretty good for all that work.
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Old 10-16-12, 01:37 PM   #6
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Are you sure you're getting new pistons? Many shops if they only bore it .0010 over will re-use the pistons and install an over-sized ring. Going with oversized rings would save a chunk of that $1400 (if it includes "new" pistons). You could also sleeve the cylinders, and re-use pistons (assuming they are not damaged). Lots of options. Whatever, a $1400 rebuild is better than a new outboard, but you won't see a noticible increase in th HP output. Just make sure you get what you pay for.
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Old 10-16-12, 02:35 PM   #7
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$1400 sounds like a great deal for that amount of work. Make sure they do quality work. Peace of mind is very expensive.
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Old 10-16-12, 05:58 PM   #8
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1400 sounds scary cheap and over size rings and/or bore on same size piston is not only wrong, but will probably explode soon.
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Old 10-16-12, 06:02 PM   #9
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well i was sent to the guy by a very reliable source, and they told me he just did the same thing for another guy a month or so ago. supposed to be new pistons and rings.

oh and my mistake, its $1600. but still great deal.
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Old 10-16-12, 08:41 PM   #10
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ok, i am NOT a mechanic, nor do i know much aobut prices on rebuilds. BUT i DID ask my dealer what the average price was on a rebuild. HE said to replace the power head was around $2500.00. so......in my opion ONLY, if oyu are having the entire motor rebuilt for $1600.00 it SOUNDS like a good deal. as long as they are a reputable shop. you WILL find out afterwards.

did they say what kind of WARRENTY you would be gitting on this?
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Old 10-17-12, 10:47 AM   #11
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Boring and pistons can cost that little,not doing a lot more id say,and a 90 hp rebuild costs a tad less than say a 250 hp one.As for any gains they are minimal more in torque than anywhere,and during break in period with double oil wont even notice.
Often the cure can be a used motor that may cost less,Id sell you a decent 150 hp 1989 2.6 yamaha for 1800,low hrs to boot,with associated wiring oiler and shifter.
That might be above what you need hp wise but a good reference also have 1977 140,and a franken rude costs a tad more.
Used outboards are like from 1500 up from 90 to 150 hp,between private sellers not dealers.

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Old 10-17-12, 04:20 PM   #12
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muley...i ain't forgot about that motor bud. but if oyu can sell it, sell it pal. if i can...we'lll talk when i get dad to give the ok bud.
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