No Power/No Compression

[redpigg]

I bought the motor from my favourite shop ( The Dump )
for fifty bucks.

The 45Hp Chrysler had almost no corrosion and the paint was bright and shiny.

Ran it in the tank, it started easily, had a good idle, pumped
lots of water.
Would start and run on either cylinder.

Put it on the boat, went for a drive, there was no power
couldn't get on the plane.

Checked the compression 60PSI both cylinders.


Took the head off, no holes, no corrosion.

Took the exhaust cover off, no corrosion the rings free to move in their slots.

On a car with lots of miles on the clock there is usually a
10-15thou ring at the top of the piston travel, the O/B had
no such ring.

QUESTION

Will a set of new rings bring the compression back?

 

[JB]

Re: No Power/No Compression

Howdy RP.

Welcome to iboats.

I don't see a problem with the compression, as long as the cylinders nearly match. If compression was a problem it wouldn't start and run on either cylinder.

You have some other problem, but you don't give us enough info to go further.

What happens if you pump the primer bulb or spray fuel mix into the carbs?

Are the throttle plates in the carb opening fully?

When you advance the throttle does the stator advance the timing?

When you advance the throttle under load, does the engine rev but the boat doesn't accellerate?

Let us know.

 

[Frank Acampora]

Re: No Power/No Compression

60 psi is a bit low; I would expect to see about 90-100 since brand new, compression would have been 115-130.

Sometimes when an engine like that is overheated, the ring lands at the bottom of the piston, between the bypass and exhaust ports wear and gall, and while the ring you can see through the ports may move, it is stuck in part of the piston, reducing compression.

But, you leave out some of the most important info. What size boat? That 45 will comfortably push a 14-15 foot fiberglass runabout, but no more. Even a 15 footer will only go 20-25 mph with the engine in top condition, and most boats of that type plane somewhere around 18 mph. So you can see it might be marginal, and lacking a bit of HP would not get the boat on plane. What was the load inside the boat? Are you adding 1 pint TCW-3 oil to each 6 gallons of gasoline?

Since outboard engines get a fresh shot of oil with each revolution, frequently you can see high hour engines with the hone marks still visible, and, typically, they don't form a wear ridge as auto engines do.

There is no really good way to check base crankcase compression, however, if the piston skirts are worn, the engine will not induct a full charge of air/fuel and will only run about 1/4 throttle--even with rings in excellent shape, and the fuel pump will not deliver its 2-6 psi. --Won't matter though because you would not be able to use the full amount of fuel capable of being delivered. However, If the fuel pump is not delivering 2 psi at idle, (Assuming the pump is in good condition) then it is suspect that base crankcase compression is low.

Another thing to check would be loose crankcase halves bolts. Two are on the top, two are on the bottom and one of the center ones is inside the manifold--behind the carb. they are 3/8 bolts and if they are loose, pressure will bleed between both crankcases of both cylinders, thus reducing power significantly. These bolts should be about 280 inch pounds torque.

Remember two cylinder, two cycle outboards are like two separate one cylinder engines cast together. Anything that compromises their integrity and separation will reduce horsepower.

 

[redpigg]

Re: No Power/No Compression

Thank you for your suggestions.

The boat is 14ft, but has a cuddy cabin,this would make the boat heavy.

I have set the points, checked the timing, the advance works OK , the
carby jets are clear and both choke and throttle butterflies ( lift, escalator?)
function.

I initially thought that the prop had too much pitch, so stuck it in the vyce
and with a couple four foot planks fined it up a bit, to no avail.

The boat tries to plane, if you screw in that screw on the front face of the carby almost all the way in, you appear to get most power, but then the
motor won't start untill you unscrew it about two turns.

The motor hasn't been cooked, the paint is too good, do rings loose their tension with age. the motor is Mod 457HH Ser 7174.
Perhaps the bores are glazed ( death for a diesel) perhaps I should purchase
a Hone and rought 'em up a bit?

I have a second motor which runs well (magneto) has good compression, though requires a pump impeller,I will try it(after fitting new impeller) if all else fails that will at least show whether 45HP is sufficient.

I quite like the chrysler, there is the absolute minimum of electronic crap
hanging off it,if the bridge rectifier goes you can get a replacement from
Radio Shack.

redpigg

PS Your boat prices on Ebay are positively mouth watering, in this part of the
world Noah would be a rich man from the proceeds of selling his Ark.

 

[roscoe]

Re: No Power/No Compression

""The boat tries to plane, if you screw in that screw on the front face of the carby almost all the way in, you appear to get most power, but then the
motor won't start untill you unscrew it about two turns.""

By turning that carb screw in, you are leaning out the fuel mixture, depriving the engine of fuel, AND the lubrication it needs to stay in one piece. Do not turn that screw in !!