repower question for a 17 ' center console

[hydrasports cc]

I have a 1996 Hydra Sport 17 ' center console that is rated for 90 hp max. It currently has a 90 Yamaha 2 stroke with a bad # 1 cylinder. I am weighing my options and going four stroke is a possibility. But I have no way of knowing if the hull can handle the weight of a four stroke. And is a 75 horse at the prop close to a 90 at the prop ? Or is the price difference between a 75 and 90 not that great so go for a 90 ?

[robert graham]

If you go from a 90HP 2 stroke to a 90HP 4 stroke you'll add about 100 lbs. hanging off the transom....maybe search around for a good used motor very similar to your old one and keep the old one for parts....it would be real nice having all those spare parts for future use....

[TownsendsFJR1300]

Here's a Yamaha link for checking props;


Performance Bulletins | Yamaha Outboards

As for the additonal weight/load, my 4 stroke (in-line 4) is definitly heavier than my old V6, Evenrude 150, 2 stroke.

My boat is also rated for a 150 hp. Short of the boat sitting a little lower (maybe an 1"-1.5"), its fine. The hull is 1997 vintage, before 4 strokes were popular...

The drain scrubbers are definitly closer to the waterline...

If you currently have a 90, I would pop for another 90hp...

Double click to enlarge

[hydrasports cc]

If you go from a 90HP 2 stroke to a 90HP 4 stroke you'll add about 100 lbs. hanging off the transom....maybe search around for a good used motor very similar to your old one and keep the old one for parts....it would be real nice having all those spare parts for future use....

I like this plan but finding a decent Yammie 90 2 stroke is in the hard pile. I've looked for three weeks now and only found one. I'm leaning towards a local rebuild but not sure yet.

[hydrasports cc]

Well right or wrong today I pulled my rig to a local marina that rebuilds engines. The two guys have about 50 years experience and said no problem rebuilding the 90. The only " if " is the condition of the crank, if that has to be replaced it will add 500.00 to the rebuild. If the crank is good we go with boring the # 1 cylinder to whatever the next size is based on the depth of the scoring of the cylinder. Will get three new pistons/rings along with new crank/connection rod bearings. The pistons will be balanced within a gram based on weight. All new seals, carbs rebuilt with factory parts, a new water pump/impellar and two hours of break in time in the water. Price is 2495.00 plus or minus any surprises. I just couldn't justify the cost of a new motor. Should get it back in about three weeks. Fingers crossed.

[TownsendsFJR1300]

Well right or wrong today I pulled my rig to a local marina that rebuilds engines. The two guys have about 50 years experience and said no problem rebuilding the 90. The only " if " is the condition of the crank, if that has to be replaced it will add 500.00 to the rebuild. If the crank is good we go with boring the # 1 cylinder to whatever the next size is based on the depth of the scoring of the cylinder. Will get three new pistons/rings along with new crank/connection rod bearings. The pistons will be balanced within a gram based on weight. All new seals, carbs rebuilt with factory parts, a new water pump/impellar and two hours of break in time in the water. Price is 2495.00 plus or minus any surprises. I just couldn't justify the cost of a new motor. Should get it back in about three weeks. Fingers crossed.

That's not bad at all and un-less you beat the snot out of it, the crank should be fine..

Please post your final fix, etc..

[robert graham]

Well, good luck on your rebuild.....hope it goes very well!....

[hydrasports cc]

That's not bad at all and un-less you beat the snot out of it, the crank should be fine..

Please post your final fix, etc..

Will do hope all the news will be positive

[hydrasports cc]

Also going to disable the oil injection and go with manual mix, in my opinion a safer way to go. Will use 40:1 during break in and then 50:1 after that. I'm old school prefer to mix manually.

[rodbolt17]

let me wrap my busted brain around this.
your going to disable a rock solid mostly bullet proof oiling system, why?????

[hydrasports cc]

let me wrap my busted brain around this.
your going to disable a rock solid mostly bullet proof oiling system, why?????

Their shop is full of various brands of outboards that went lean for whatever reason so they like to go old school and premix. I'm OK with that. I've read enough online horror stories and my own experience with this motor so I'm not convinced on its rock solid ability. To be fair as I type this I don't know the fault that caused my engine to destroy # 1 cylinder but my guess is it didn't have enough oil.

[TownsendsFJR1300]

They should be able to tell you if it was a leaned out A/F mixture issue or lack of oil..

Do you know if the cylinder got scored, or what exactly happened with it yet?

[hydrasports cc]

They should be able to tell you if it was a leaned out A/F mixture issue or lack of oil..

Do you know if the cylinder got scored, or what exactly happened with it yet?

A few weeks ago when she shut down I took it to another marine mechanic. He determined cylinder # 1 had 30 lbs. compression and with a bore scope stated the cylinder wall was scored. They pushed for a Yamaha rebuilt block but that was 6k. Found these local guys been in business a long time so we'll see. They guarantee their work for one year however they want it run on premix only. I guess they are old school but I'm OK with pre-mixing it's not a big deal. I hope to hear something in 7-10 days. Yes I know I can make a mistake with pre-mix but nothing is perfect. They will leave the tank and everything in place they will just disconnect it so it can be reversed in the future if need be.

[rodbolt17]

oil related failures typically take out bearings.
heat or lean A/F mix typically takes out pistons.

as that system does NOT rely on fuel to oil its rare that its an oil failure.

oil is injected behind the carb and not through the carb.
boring one cyl is kinda sketchy.
if your going to rebuild it then rebuild it.
otherwise its a patch.

[99yam40]

I hope they pull the pump drive gear when they disable the oil system.

Even Yamaha recommends adding the oil while filling with gas to make sure it mixes well in tanks, kind of hard to do that in large tanks.
Small tanks are easy to shake up and blend the fuel better.

Maybe adding the oil to some gas in small tank, mixing that and then add to big tank as you fill big tank will help make sure it mixes better.

Or Have a large funnel and slowly add oil as filling with with gas.

A good clean oil injection system is so much better

Seems that if the jets are not engineered/ speced to flow oil and gas mix with a different specific gravity then there could be a difference in the volume through the jets, Somthing to think about.

Might look to see if the fuel and air jets in a C90 are different than a regular oil injected 90

If they have to balance 3 new pistons it seems it would be a lot easier to have them all the same size, so bore all 3 to the same size for the 3 new pistons