wooden boat engine mystery

[kibotas]

Greetings,
My old Monk Sedan cruiser has a engine problem that I'm a bit perplexed by.
She is a 1953 31' cruiser. The power comes from a 1976 Ford Seamaster engine. This is basicly a marine version of the the 300 cubic inch pickup engine that has been around forever. It is keelcooled and backed up by a Borg-Warner velvet drive gear.
I've had the boat for 3 years. When I first got it I ran it the same way as the previous owner did, 1950 RPM which showed 13" of vacume and 190 degrees F of temp. If I try to run it at that now it overheats. At 1950 RPM the vac is down to 10" or so (I.E. the engine is working harder to go the same speed). The bottom is clean and the wheel is clean with no bends in it. I can turn the shaft easily by hand, with the engine off of course, so I don't seem to have a shaft problem. This is a problem that has steadly and slowly gotten worse. I'm not sure how man hours are on the engine and I havn't done a compression test yet but it use little to no oil, maybe a quart in the last 100 to 150 hours. The engine runs smooth its just working harder. The embarssing part is that I am a automotive mechanic! Any old gas boat fans out there that can HELP!?
Dan

[nedL]

Interesing problem. The only thing I can think of to check right now is the exhaust, are there any colapsed/restricted areas? Did someone stuff a potato in there ?(LOL) I would think an exhaust blockage could cause both your symptoms (higher operating temp. & reduced intake vacuum), just an idea. I'm real curious what this will turn out to be.

[Classic Boatworks - Maine]

Check your exhaust (are you in an area prone to zebra mussels?) Do your compression test and look for a leak in the head gasket.
Check other hoses for collapse. Are your pumps and alternator driving hard?
Low vacuum might also be an intake gasket.
Good Luck!

[rodcross]

The model-year of the engine (1976) reminds me of the hassles we had during those years with automobile engines built to the newer emissions standards. During those years, my cars were super-sensitive to timing and condenser issues. If the timing or the advance mechanism was off, the engine would lose power and I'd blow the radiator cap. These engines wouldn't have a vacuum timing advance mechanism, would they?

[HizzenanHern]

One other crazy thought:

When you turn the shaft freely, there's no forward stress on it, as there is when the screw is pushing the boat and the equal-opposite thrust is being supplied by the thrust bearing in the tranny. Could it be a bind which occurs only under load? That would explain the slow, gradual worsening of the problem.

Another thought: The engine should turn up its maximum intended operating speed in gear and underway. It it will turn up significantly more rpm in neutral than underway (not tied to a dock) there is a problem just with that--usually caused by being overpropped. But here I'm probably into another topic altogether.

[Henning 4148]

Another idea: How much weight did you add to the boat in the meantime? If she is much heavier now than she used to be when you got her this would also result in higher engine loads.

[kibotas]

Thanks for the prompt advise coming in. Yes the distributor has vac advance but I've checked the timing. I've replaced the head gasket and intake gasket due to the fact that the head was leaking a bit from the back of the gasket. No weight has been added. I think the exhaust and the gear are the prime canidates. The exhaust is "wet" and exits at the transom a little bit under the water line. No Zebra mussels here but a VERY active barnacle population. They are so fast that during the spawn season they can cover any unpainted surface within a few months. Thanks again for the great ideas. I'll let you know as soon as I can. Dan

[TerryH]

If you don't have a tranny temp guage might be a good idea to install one.
I had a 30' boat with 6v53 DD and velvet drive that was cooled through engine heat exchanger, tranny temp was running around 210. Installed an inline cooler and that reduced temp to around 170 at full load.

Good luck

[steve sparhawk]

With as much added strain the engine appears to be working against you'd think there would be a lot of heat being produced in some rotating part if resistance was the culprit. Anything like that should be easy to find in the few areas where friction could be an issue.

If the head gasket was replaced you have probably checked for any carbon or valve problems. I'd guess ignition and compression would be fine if you are a mechanic familiar with chasing down the simple things. Power-robbing friction-breathing at the engine and spark are covered--leaves just fuel and exhaust.

I for one would like to know the final and tie=breaking answer too. I hope it's a clam in a pipe. That's easier than an engine job.

Maybe lagging valve timing-a stretched chain? (Probably gears in that one.)You know how to check that. A puzzler for Click and Clack.

This is a progressive thing. Hmm, have you been driving it up to the mountains? Higher altitude-----

[Bob Adams]

This might sound a bit off the wall, but if your directional valve in the transmission allows a little leakage to the reverse clutch pack while you are in forward, that will put one hell of a drag on your engine. my 2 cents

[rodcross]

Why would you have 'keel-cooled' and 'wet exhaust'? I thought keel-cooled meant that engine coolant circulated through an exchanger that was mounted on the bottom. There'd be no need to pump sea water into the boat to then be injected into the exhaust, unless its sole purpose was to cool and quiet the exhaust.
Funny, I just realized how elegant the sea-water to exchanger to exhaust link is. You cool the motor, then cool the exhaust which reduces the noise dramaticaly(where's my spell checker when I need it?) and eliminates mufflers and the need for fancy exhaust fittings and the insulation thereof. I hope the person who designed that process died a millionaire or is a millionare. I wish the same for the designers of nylon ties, duct tape, C-clamps and garlic presses.

[Mr. Know It All]

It's a Ford.....check the pcv(positive crankcase ventalaton) valve.

[Ken Liden]

My first guess would be a restricted exhaust system. I would also check for a vacuum leak or incorrect air/fuel mix. Remember "lean makes heat" as does advanced or retarded timing. I am surprised that the distributer is vacuum advance. Normally a marine unit is centrifical advance. A low vacuum condition would have a significant adverse effect on ignition timing thru inadequate advance resulting in retarded timing. Check also for smooth advance with no more than 3 degrees variation in dwell.

You know the stuff, you just ain't got there yet.

[yachtdoc]

One thing not mentioned yet is check timing chain wear. One way is to bar the eng back and forth with a wrench and see how much crank movement is required to make the distributor turn.
A better way is replace the chain/sprocket set with new whether it needs it or not. You should get a "performance" timing set which gives you the option of "streight up" valve timing rather than the 4 degree retard on smog auto engines.

Most speed shops and auto machine shops have several sources for less than $100 and with gaskets and front main seal.

If the chain is badly worn, it is just a mater of time before it skips a whole tooth and then you will need to paddle home.