Building for low rpm reliable power

dmak

New member
Hello all,

I realize that this post may not be totally in line with the theme of this forum, but I was hoping to tap into the wealth of knowledge present here. I live in Alaska, and I have a boat with a "long tail" motor platform. These platforms use your choice of 4 cycle engine, which has led me here. I use my boat and this engine to access some very remote areas by river so reliability is my first priority. That said, if I can reliably make a little more power out of a given engine at it's governed rpm, I can install a larger propeller and go faster and have more thrust which in some cases means an increased safety margin when running sketchy portions of river. My current setup is a bone stock power ease 420cc that came with the boat when I bought it. It blew the head gasket on the last trip and I'm looking at switching to a kohler ch440 for a couple of reasons: 1. They are supposed to be very reliable. 2. It's close to the same weight of the power ease, which is important. 3. It's the same engine that my sawmill has and it would allow me to buy spare parts for 1 engine instead of 2.

My questions for the experts are:

1. Should I slap a new head gasket in the power ease, carry a spare and forget spending the money on the kohler?

2. What modifications would you make to either engine to reliably increase power at governed rpm?

3. Is there another option that you think would be superior to either one that I have presented?

I appreciate any insight you all might provide.
 
Did you limp home on the blown head gasket ? If so then thats option #1 .
New engine bigger cc a plus . Cost is your choice . Of course only you know how many hrs on the 420 .
Power wise think of it , as a airplane you should only be using 60% the rest is reserve . I doubt thats the case except for the governor which does provide limits . I know myboat is either full on or trolling .
If you change head gaskets use a dab of yama bond on it that will practically gaurentee it holds .
 
I floated home. Luckily I was upriver of the truck, so I just had to be patient. There was ZERO compression after it blew. I tried removing it entirely, adjusting the valves accordingly and seeing if there was enough compression, but still nothing. I'll try the yamabond when I put the new gasket on-thanks for the tip.
 
Check the head with a level or a straight edge to see it it is warped. If it is then a new gasket isn't going to help you. You can mill it level if it isnt too bad, or replace it.
 
I would do #3 as long they are a direct bolt up from the 420. fix the 420 for ground work around the plantation.
with product availability and shipping time in your case location you could be up a creek without a paddle for some time.
use the sawmill engine as backup part till new part show up for boat
 
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If this motor uses a thin(.01 thick) metal gasket with no coating you may consider using Honda or Toyota bond on the gasket. I've had trouble with clones blowing head gaskets before. A guy at dyno cams said he uses toyota bond to coat both sides of the gasket.
 
Too epand on the honda / toyota bond . Even sillycone .
Lay the gasket on a sheet of coated cardboard . Then wipe it on both sides with your finger . Its messy but will give you a thin coating .
Not 1/8 th inch thick just a nice thin coverage .
 
Flattop1, I use nitrile gloves. I squeeze out small portions around the edge of the gasket. Maybe 5 or 6 spots each side. Then, with gloves on, work the silicone over the gasket making sure its covered well. It will be uneven at this time. Then i start patting my hands with the gasket between them. Even use the backside of my hands if there is too much on it still. This removes the silicone leaving just a thin coating. When I place it on the block I try not to touch the flat surface. I will handle it on the edges.
 
I think stick with what you have and solve the HG issue.

Marine application tends to be much more severe than road because you will have a sustained load for a long period of time, keeping temps under control is crucial. Might be worth watching head\plug temp to see if it's getting hot.
MLS head gasket of course would be a good way to go too. Definitely check the head and deck for true while reassembling it.

For more power, I guess my first question is do you still have the stock airbox and exhaust on it? If yes, then those are the first things to swap out, you will have to increase the main jet size to compensate. In fact it might be worth richening a point or two since it's a marine application just to give you some headroom. I'd be cautious with raising compression or adding ignition advance until you have a way to watch temps.

After junking the stock airbox and exhaust, you could look into a hotter cam and or larger carb maybe. Slide or butterfly at your choice. NRRacing have a very nice three circuit 24mm carb that perks up a stock big block quite nicely. If you really want to run a bigger prop you might have no choice but to start turning the engine faster than the stock governor though which puts you nearer to the point where you should consider swapping the stock rod and flywheel.

I've found the stock flywheel in big blocks to be OK to hold together up to sustained 5200 RPM, but don't constitute this as a recommendation. Safety first :)
 
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