What to look for in a rebuilt 90 hp powerhead?

[tfbrown1270]

I traded my 1989 Force 85 hp (Piece of junk) in on a 92 Johnson 90 hp; the shop I deal with here is rebuilding it for me, they sent the block out and It came back .040 (40 thou) oversize.
They are putting in new pistons, rings, rods but are reusing the crank. They said that it was fine.
They tell me that some kind of line or tube feeding the right bank of pistons was pinched. This decreased fuel flow and resulted in some piston wear.
I examined the bores before they were done and noted some "chatter" marks on the right bottom cylinder below the exhaust port and some fine scrapes on three of the cylinder walls.
In order to get all the damage out they machined all .040 over.
Will this will result in more displacement and more power...yes or just wishful thinking.
My primary concern is that so much material came off the cylinder walls. Will this make them more prone to problems because there is less material between the piston and the water jacket?
What else should I be looking for them to do?...
They have said they are going to install a new VRO improved pump not the old one; and they are giving me a one years warranty on their work.
Thanks for any thoughts.

 

[kynolan2183]

Re: What to look for in a rebuilt 90 hp powerhead?

4 Mils over in my opinion is on the edge of being to much but it will be fine. I have machined many a four stroke 4 banger to 3 Mils. The cylinders, more than likely, were so out of round on them that 4 mils was the best thing to do. Each engine company has specs for how much you can machine an engine. The cheapest way to look it up is to search the net for Pistons and rings for your engine and if 4 mils is the max over size you can buy then that will tell you on the milling. For example 3 mils is the biggest I can get for my engine (or that I have seen). If they will give you a year to destroy it then I would think you are ok.

On the power issue it is theoritical.
Increasing the bore will make the engine have more displacement but for that displacement you need more fuel to get more power and since the carbs will not change my answer is no or so small you will not see it.

Engines are listed as 3 types
Over square, Square, Under square.
Over Square i think is bigger bore than stroke (means higher rpm and faster to your horse power)
Square is even-steven Horse power to Torq
Under Square is Torq before Horse Power.

Your engine will be even more Over Square thus you might see an increase in your rpm speed to WOT. But again I think that a computer dyno could only see it.

However new Rings will increase compression and thus give you more power which you might see depending on the compression of the engine before the rebuild.

While they are working on it have them replace all of the old crapping hoses and check the wiring for any cracks in the insulation. Since it is apart pay the 13 bucks for a thermostat if you motor has one. And have a new water pump put in (always have a new water pump put in)
No water means heat and death.

Good luck
Kyle

 

[tfbrown1270]

Re: What to look for in a rebuilt 90 hp powerhead?

Thanks for the reply. I'll have the water pump changed out and a new thermostat (or two?) installed as well.
I have a performance question, once I get this engine up and running will it be much faster than the 85hp Force...
I managed 38 mph (GPS) with my 16 ft alum Princecraft and the Force.
Its not a deep vee rather more of a shallow vee and flat at the stern. It weights about 800-1000 lbs I think, has a solid front (not a bow rider).
I'm hoping for mid 40's???????

 

[ondarvr]

Re: What to look for in a rebuilt 90 hp powerhead?

I had a 90hp Force and a 90hp Evinrude, the Force would suck down 12 gallons of fuel so fast I thought the tank must have been leaking. The Evinrude ran better, was faster and used about half the fuel, and crossflows (this type of 90hp Evinrude) are considered thursty.

 

[Dhadley]

Re: What to look for in a rebuilt 90 hp powerhead?

I'd be a bit leary of that dealer. There is nothing on a 90 crossflow that will "pinch off" to starve the starboard bank. Each carb feeds two cylinders, each across. The top carb feeds the top 2 cylinders, the bottom carb feeds the bottom 2 cylinders.

I'd also ask what pistons they're using. Wiseco makes a .044 over but if they've bored it to .040, that's a problem. Check it out!

You'll not notice the power from std bore to .044. That block will bore safely to .064 over. You will notice the difference between the Force 90 and the OMC 90.

Make sure they aren't putting a VRO pump back on. Make sure it's the newer OMS pump.

The warranty sounds good but some of their other comments throw up a red flag. Without knowing anything about the motor I'd be willing to bet it was being lugged and the starboard pistons coked up and stuck rings. Very common but they should know the difference.

A complete cooling system service is a part of any rebuild. Don't pay extra for it. Nor for carb cleaning, that's part of it too.

 

[R.Johnson]

Re: What to look for in a rebuilt 90 hp powerhead?

Before getting to the bottom of this post, I some how knew Dhadley was going to catch those pinched off hose's.

 

[Dhadley]

Re: What to look for in a rebuilt 90 hp powerhead?

I've seen a couple V4 crossflows in my time but I'm not sure where these magic hoses would be.

 

[tfbrown1270]

Re: What to look for in a rebuilt 90 hp powerhead?

I'll be asking some "pointed" questions and get back to the group...these are some great thoughts and I'm learning a lot.
I trust these guys they seem to know their stuff, perhaps I misunderstood what they told me, I'll try to learn more. I'll report back what I learn and ask for some more enlightenment...
Thanks

 

[kynolan2183]

Re: What to look for in a rebuilt 90 hp powerhead?

I would expect your rig to top out at 42 to 48 MPH depending on load. You say the boat is 1000 pounds plus you the motor the fuel the batteries and any other stuff. So I would think that you might be about a true 2200 pounds when all is said and done.
I don't know the foot's gear ratio or the WOT RPM of that motor but 90 hp is 90 hp.
I would look to prop it at 19 pitch to 21 pitch but find out the gear ratio and Wide open throttle before propping it.
A higher gear ratio like 2.43 would be better for the 21 while a lower ratio like 2.0 might prop out at a double cupped 17 or an uncupped 19.

Propping out a boat is Black Magic the science is very complicated and no prop is ever perfect since the conditions on the water are never perfect.

good luck
Kyle

 

[tfbrown1270]

Re: What to look for in a rebuilt 90 hp powerhead?

I dropped by the shop this morning and spoke to the boss to address these concerns.
He is using new Bombardier parts, .40 over pistons and ring kits and a new Bombardier pump, I saw the stuff still in the boxes; the pistons have 0.40 stamped in the tops. As for the mysterious tube that got pinched to cause all this I must have been smoking dope cause he says he never said that (and he is likely right) That the failure was under oiling because the previous owner failed to "ever" change the oil in the oil tank and it got dirty and stopped flowing properly. He didn't think it was the fault of the original VRO pump rather that the oil tank was gummed up. In any case the tank has been cleaned, new hoses are going on as well as the stuff I already mentioned. I am getting excited about getting this thing up and running and in the water.
That is when the water is a liquid again not a solid like it is now