2 questions re: '90 Merc 115

[wassup]

I hope I am posting this under the right forum...

A few months ago I acquired a '90 Searay 16' o/b boat.
I have used it probably a dozen times and I am hooked! I have rediscovered fishing and am having a ball. I have 2 concerns that you folks might shed some light on.

When I turn to the left the steering feels like it's 'hanging up'. I kind of wiggle it back and forth and it seems to release itself and turns more smoothly. I am by no means mechanical, but I played with it while it was out of the water and I noticed that the electrical cable that comes out of the engine and is attached by 2 clamps seems a little tight. I showed it to a buddy that is very car-knowledgable and he felt that wasn't it. The steering is basically 2 hydraulic tubes, 1 on each side (don't know correct term).

The second question is does anyone know the redline for a '90 115hp Merc. It came with a 5 blade prop if that helps. It seems like it is revving very high, but maybe I'm used to my car's tach, lol. It hits around 6000 rpm at around 35 mph. Also, not sure the speedo is accurate as I have easily gone over 40 mph and I don;t think I was really going that fast.

Any help/ideas are greatly appreciated!

 

[Chris1956]

Re: 2 questions re: '90 Merc 115

Speedos can be very inaccurate. Usually we use a GPS to determine true speed. I do not know the max RPM for that motor, but is it likely 5500-5800. It therefore sounds like your are overreving it. You can post a prop question in the prop section of this forum. Kenny is pretty up on motors and props.

 

[OldMercsRule]

Re: 2 questions re: '90 Merc 115

I don't think there was a 1990 115, could have been a 1989. Check for the serial number on the motor bracket to verify vintage. The 1989 inline 6 115, (the last year of that great line of engines), had a WOT range of 5000 to 5500. Some of the people on this site (who know a lot more then me) run their inlines up to 6000. I would make sure you were getting performance worth reving it that high. Most inlines have a sweet spot. Use a GPS to tell where that is on your engine. Hope this helps .JR

 

[WillyBWright]

Re: 2 questions re: '90 Merc 115

Inline-6s like 6000. Inline-4's shouldn't rev above 5300 (cranks snap around 5600). Lower 40s on a 16' SeaRay wouldn't suprise me with either motor.

 

[Texasmark]

Re: 2 questions re: '90 Merc 115

4750-5250 per the '94 sales brochure which should be the same 4 cyl engine.....I think '90 was 4 not 6 cyl in that hp range (my '89 was 6 and agree that '89 was the last year for it, but personally have no proof).

I ran my 115 inline at 6000 WOT and it is still running (son in law has it) and no wrenches on the powerhead power part in all those years. Had no problem running over 40 mph on a 17 1/2 \ ft. Ranger fisherman and waterskiing with the same prop.

If they didn't make a 115 that year the 100 is the same rpm range as is the 125 so it looks like that's your numbers.

All the experts on here (and I agree) say that 2 cycles like to rev and I keep mine actually above the rpm limit and they love it. Have yet to blow an engine from overrevving........but Willy indicated a problem with the 4 cylinder; he must know about that engine, I don't.

35 mph on a 16' boat (even if it is a Searay which is probably heavy but should have a fast hull) is sloppy slow for that much hp.

And, what on earth do you need a 5 blade prop for on that setup? With what you've told me, you must wear a neck brace (to prevent whiplash) when executing your hole shot! :%

Mark

 

[WillyBWright]

Re: 2 questions re: '90 Merc 115

It turns out that HighFives are great for speed and great for underpowered boats. In each case I believe it has to do with the relatively small blades and smaller diameter. Less Hp is required to spin them and thus more Hp is transferred to push the boat. They can also allow the motor to be hung very high on the transom. I've seen them run with the top of the bullet of the gearcase running just below the waterline but you have to be very careful to keep all of the water intakes in the water. Waterskiers like them too because they spin-up nice and quick and give the boat good holeshot. But they're not so great for mulitple skiers because you need a lot of blade area and horsepower for that.

 

[wassup]

Re: 2 questions re: '90 Merc 115

Thank you everybody for the great input. I went and took her out this weekend and paid more attention:

1st off it was the 5,000 - 5500 range I was running in not 6,000. I guess the newness of looking down and seeing such high numbers caused brain lock. I drive an old 4 runner and anything over 3,500 makes me sweat a little.

I looked at the i.d. plate and it does show as an '89. You guys know your stuff!

Again, any idea why it is hard to turn left but is smooth turning to the right?

Thanks again everyone. It is impressive that you spend time helping others.

 

[Chris1956]

Re: 2 questions re: '90 Merc 115

Wassup, Usually prop torque (with a right hand prop) causes the motor to pull right. if you trim up the motor, it should lessen. At a normal trim (say 1/2 of max trim) the steering should have no or little pull in either direction. If this is not the case, you can adjust the zinc fin above the prop to compensate. I would think you would turn it counter clockwise (from above)to conteract a right pull from the motor.

 

[wassup]

Re: 2 questions re: '90 Merc 115

Thank you Chris, I'll check it out!