Bore/Hone Cylinder Question

[Vile]

Heyo,

My 92 Johnson 40HP motor blew a few weeks ago. The damages include some minor scaring on the bottom cylinder wall where the top cylinder is in good shape. This means we will have to bore it out to 0.20 or 0.30 depending on the last inspection this week. Due to that, I have been told that this could increase performance of my motor because it will have a bigger bore and oversized pistons to boot.

Does anyone know how much power I could see from the new fixes? Some have said it will not be noticable, others have said you can notice the change because it's clean and bigger.


Another question I had is the size. We can go up to 0.40. Would going that size be useful, or should we stick to the smallest amount in case further issues happen down the road for the engine? I would hate to do 0.40 and then later in life something happens where we can't fix the walls.


Cheers!

 

[rockyrude]

Re: Bore/Hone Cylinder Question

The performance difference will not be noticable. I always go with the smallest oversize necessary to fix the problem, leaves room for later even though resleeving is an option.

 

[Vile]

Re: Bore/Hone Cylinder Question

Thanks!

Is there anything that can be done to a boat engine that does greatly improve the performance at my engines age?

 

[boobie]

Re: Bore/Hone Cylinder Question

Not to much unless you have plenty of $$$$. Just keep it tuned good and well maintained.

 

[nwcove]

Re: Bore/Hone Cylinder Question

The performance difference will not be noticable. I always go with the smallest oversize necessary to fix the problem, leaves room for later even though resleeving is an option.

i will have to respectfully disagree. unless the motor was an extremely low hrs unit, you will notice a difference in performance on a 22 year old motor after your bore job. but dont expect to go from " chevette" to "corvette"!!
also do you know why the engine failed? its important to fix the cause also.

 

[Vile]

Re: Bore/Hone Cylinder Question

i will have to respectfully disagree. unless the motor was an extremely low hrs unit, you will notice a difference in performance on a 22 year old motor after your bore job. but dont expect to go from " chevette" to "corvette"!!
also do you know why the engine failed? its important to fix the cause also.

If you're referring to my engine, the oil reservoir got turned over due to large wakes on the lake. This caused the oil to not mix into the gas all day and blew the motor. Upon taking off the powerhead we could see the gasket and rings blew causing damage in the lower cylinder wall. It wasn't major damage, but enough to warrant boring/honing to 0.20 or above.

To fix the problem, we are going to just disconnect the oil reservoir and mix the gas from now on. The clamps on the oil reservoir are not good enough for the boat when it's on a large lake. Of course, we can secure it more, but that doesn't mean the oil lines won't go one day and cause issues either. We rather know for sure the oil is mixed and getting into the engine right away because obviously if the gas is not flowing to the engine, it won't start at all right?

Luckily, my dad is a master machinist with his own machine shop. He will bore/hone the two cylinders and rebuild the engine. It will be a nice learning experience for me and I plan to film to rebuild as much as possible to show others how you can possibly do it yourself rather than dropping 2K to 3K on a engine rebuild.

That's why I'm asking if there is anything else we can do while we are in the engine to make it have more pickup/power. If it's something we can do via the machine shop, we can surely tweak it out.

 

[rockyrude]

Re: Bore/Hone Cylinder Question

If money isn't a problem, then go ahead with both cylinders, with outboards oversize pistons are weight matched to standard pistons. You can just do the problem cylinder without worries about out of balance like with an auto.

 

[Vile]

Re: Bore/Hone Cylinder Question

If money isn't a problem, then go ahead with both cylinders, with outboards oversize pistons are weight matched to standard pistons. You can just do the problem cylinder without worries about out of balance like with an auto.

I wasn't aware you could just fix the one bad wall and not do the other(s). We were planning on boring/honing both walls and add two new pistons. But, my father is more of a car mechanic than a boat one. He has fixed boats before (as he owned bass boats all his life too), but most of his engine work is on cars.

 

[SparkieBoat]

Re: Bore/Hone Cylinder Question

chalk up another one for the premix guys.....If you want more power sell your 40 and get a 50 or 70. If your motor was in good running condition, you will not notice much difference in the power..maybe slightly. be sure to check your crank and bearings, no oil condition probably messed them up. I think you can bore up to 020 on one hole and not do the others, past that and you need to bore all.

 

[Vile]

Re: Bore/Hone Cylinder Question

It only has two cylinders.