New old boat - wrong prop?

[highangle]

Just got a 1961 16' Seaswirl runabout - closed bow. The front looks like a tug boat, not much rake to the bow.

It has a 1964 Mont. Ward Sea King 60hp, finally got it running well, but can't really pop out of the hole and top speed is only 24-25 mph (gps). Out of the hole it has some hesitation. Can pull the kids on a tube and skis, but it really doesn't seem like it is running full out.

Pulled the prop, and it has around the shaft "Michigan SMC 864" Stamped on one of the blades it reads (very poorly) "10 1/2 / 8" and looks like it was stamped with just hammer stamps. Is this 10 1/2 inches with an 8 pitch?

Reading about the props for this engine, it seems like this is WAY underpropped, if it is indeed a 10 1/2 inch, 8 inch prop. I see that these pin drive props available now are 10 to 12 pitch.

Still want to ski, but it seems like if it would do better since it can't ever get up to the open throttle rpm's. Tachometer is on order....

Am I reading this right? Would an 11 work better?

 

[Silvertip]

Re: New old boat - wrong prop?

If it can't get out of the hole now, increasing diameter and pitch will make it worse, not better. Are you sure the engine is running right? Reving it in neutral proves nothing. To many folks, a two stroke running on half its cylinders "sounds normal".

 

[highangle]

Re: New old boat - wrong prop?

That's kinda what I was afraid of.... Is this an 8 pitch you think? From what I have read here, it seems like if it were running at all 5000rpm on all 4, an 8 pitch outta get up pretty good?

Hasn't been run since 1984, so I'm going through it.... It sounds like it is running pretty strong, but now I'll wait for the tach to see what's going on..... Rotor and cap were pretty corroded, have not replaced the coil yet, so I'll get to confirming the spark again.

Or is the 60 just too small for this boat? It gets up on plane, even got me up on two skis (175lbs). If it weren't running well, should I expect this kind of performance? Is it just at it's limits?

Thanks for all the help!!!!!

 

[Frank Acampora]

Re: New old boat - wrong prop?

I think you are expecting too much out of that 60 hp. In those years they were rated at the power head not the prop. And on a 16 foot boat, the speed you are now getting is pretty much what you can expect.Maybe 1 or 2 miles more but that old 60 is never going to get you to 35 or 40. Example: I had an old 55 on a 15 foot runabout deep vee. It did 27.

 

[EricR]

Re: New old boat - wrong prop?

Once you have a tach on it you'll have a better idea of what it is doing, I would also do a compression test and if that works out go through the timing proceedure to make sure it is getting full advance. It just sounds sluggish to me. But an 8 pitch is more like a pontoon boat prop!

 

[steelespike]

Re: New old boat - wrong prop?

If that is the Gale built 4 cylinder 60.It developes its power at 4,500 rpm.
These are known for good low end grunt.As stated a 8 inch prop is pontoon
pitch.It should leap out of the hole! But run out of legs early.Easily over rev.
It has a 2 barrel carb;each with a low speed needle and a fixed high speed orifice.Throttle shutters are independent and should be syncronized to close at the same time.Don't remove the high speed nozzle unless you have the installation tool 378014.

 

[highangle]

Re: New old boat - wrong prop?

Some of this info is posted in the Johnson forum as well, but prop related info here.

First, I think they sent the wrong tach. Adjusting the idle, could get it down to where the tach said about 1200, but anything below that it would die. Then took it out to see what WOT did - sounded really smooth, but tach read 8500!!! Engine plate says 4000 to 5000 rpm operating range - Finally decided that tach was showing double the real rpm, adjusted carbs to get to 9300 at top end (4650). Does a plug fire for every one or two rpms?

It still doesn't really punch it well. It takes maybe 10 seconds to get up on plane. Starting to think I am just expecting too much. All the prop info I can find shows 10-12 pitch props. Think I'm going to toss the 8 pitch (it is chipped anyway) and go to the 10 1/2 x 10 pitch. What should I expect? It almost seems like this motor takes a bit to get the 8 pitch spinning - too much resistance/not enough torque?

I have done the link-n-sync proceedure umpteen times, and am getting the same results.

I know that going to a 10 pitch should cut my WOT back 400 rpm.

 

[steelespike]

Re: New old boat - wrong prop?

Have we done a compression check?Should be at least 100 psi.And within 10% between cylinders.As far as the hp rated at prop or flywheel I don't think you could tell the difference without a speedo.

 

[highangle]

Re: New old boat - wrong prop?

steelespike - thanks for your replies. I really don't know where to go from here - first boat/engine. Here is a link to the other thread I have going related to the function of the engine: http://forums.iboats.com/showthread.php?t=209782

Compression is 65-70 in all cylinders. Told in earlier that this probably is not bad. Keep spraying DeepCreep in the cylinders a day or two before we take it out. Need to do another SeaFoam decarb. Engine did was not started since 1984. 1st owner stated that he had it tuned "to go real slow" for trolling.

Below is from the last post in the above thread:

If running at 4250 rpm, should I be concerned? Where should I be looking to increase that? Have rebuilt the carb, link-n-sync, plugs, plug wires, decarb....

When replacing the plug wires, I checked some of the bolts on the head/jacket/etc and found that the bolts under the flywheel holding down the cover plate were loose - not "if I crank on them they will move" but easy to turn with a 4" wrench. Should I retorque everything?

The carb is rebuilt and adjusted, but the gaskets (body to manifold) seem to be wet/weeping. When wiping a finger under the orifice plugs, I get gas. The orifice plugs do not screw in evenly, and are just plugs (no head). Should these have a head and a gasket of some sort on them? Could any of this be causing problems?