Loss of power in Century

[OverseasSoul]

OK - Thank you all, we have a diagnosis. The compression is low, I think there are fuel supply problems and I need to clean the spark points. Do you think the piston wear has been caused by running her inappropriately at 1:25, instead of 1:10 mix?
So I will be getting some parts - Can you advise on the best supplier to ship to the US ( or in the US)? Please advise on the list:
1) New piston rings and gaskets for block and cylinder head.
2) New brass fuel cap plunger - a PO had substituted o-rings for cork, and they are deteriorating.
3) New throttle cable - original is in bad shape.
4) 1:25 conversion needle
5)New carb gaskets and banjo fitting fiber washers.
6) Spark plug cap
7) Order some SAE140 oil online in the US. It's used for racing gearboxes as it sticks to the gears in high G-forces.

And for work I will change the piston rings and fit parts as above, check the magneto points and get a better spark, and clean the fuel system again. One last question, there was a comment that the hull was overloaded for the engine- I thought the Century plus ( with a 5 bladed propellor) was one of the more powerful motors and managed heavy displacement boats up to 25 feet. My lightning is a featherweight by comparison at 900lbs. With good compression can I expect her to zip along?

iain

[Charles uk]

Your never going to water ski, but that is a big hull for a Century 100 plus to push!

What do others use on theirs?

Boats like women don't tend to get lighter with age.

At 50 years old, now might not be the best time for restricting it's supply of lubrication!

[Michael]

On the compression test, I agree that those numbers obtained are very low. Did you pull make several (3-4) pulls to make sure you get the highest reading? One pull is not normally sufficient. Guess my concern is that it seems to start pretty easily for an engine with that low or compression (ie 2 pulls).
I am sure that pulling the engine apart would be a good thing. Might find that the low compression is due to stuck as opposed to worn rings. But if going that far, might as well put the new rings in there after a light honing of the cylinder.
I tend to agree with Charles, leave it to run on 10:1.
Re the fuel tap - you can just get a new cork, do not need a new brass plunger unless yours is damaged.
Shouldn't need a new spark plug cap unless broken, but maybe a new plug would be a good idea.

[OverseasSoul]

Hi Michael,
The compression test numbers - 28 to 32 PSI - are firm from about 10 pulls, most quite hard. I've emailed John Williams about my parts list; I hope I can buy from him and ship to the USA. The forum has been great and I can't thank you enough. I'll keep in touch after the rebuild with the results and probably to ask advice when I get stuck.
Iain.

[phil]

Those are lower numbers than I have ever seen on a similar motor. Hopefully it is just a head gasket. Otherwise they must have run on 50:1, if so it will likely take more than rings to fix it.

[Michael]

Or from a gauge that is faulty. I have a hard time beleiving the engine would run as well as it did on numbers that were truely that low

[Keith.P]

That's not uncommon at all, even seeing the motor running, I've seen it quite often on this forum over the years, as soon as its put in gear, or ask the motor to work, it dies a death, had it happen myself on other motors.

[OverseasSoul]

Hello everyone. The parts are on their way from the UK and I've been reading as much as I can about changing piston rings, which must be the main culprit. I was able to extract better performance from the engine adjusting the spark plug, taper needle depth and fuel mix ( it likes 16:1 better than 10:1, and a Champion D21 better than a Champion D16), but the compression remained firmly in the 30's. Admittedly that was extremely low for the gauge I was using - It's first notch was 25PSI and last 300PSI - so gauge error is certainly possible.
Another question - I am deathly concerned about removing the Cylinder head bolts given all I have read. I will not have the skills to recover if I break them, so I'd rather not take the cylinder head off. It looks in great condition anyway. All I have seen and read shows me that removing the block from the crank case and exhaust are the necessary moves for replacing the piston rings. Can I get away with doing this? Seems the block nuts are an easier proposition than the cylinder head bolts. Is that true and advisable?

PS I took the gearbox apart and removed the sludgy brown oil - to reveal almost perfect condition. replaced it with a US GL-4 SAE 140.

Iain.

[Stelios_Rjk]

Hi,

Gearbox oil is fine. API GL1 is the original but it's OK.

Usually a flex hone increases the compression. You can hone the cylinder when you will remove it from the crankcase. You won't escape that!

The cyl head is advised to be removed to inspect the water jacket but it's a task. After removing it a couple of times and putting it back you will have get the experience.

Somewhere I had described the process. Search with the words "surface, preparation, acetone, heat, annealing". Sorry I can't help further, I am typing from my mobile.

[Stelios_Rjk]

Found it!

viewtopic.php?f=5&t=4212&p=32841&hilit= ... ket#p32841

[Michael]

If the engine has been used in fresh water, the cylinder head bolts will most likely come out pretty easily. If salt water use, all bets are off. Since it is pumping wtaer fine at the moment, I would be inclined to leave cylinder head alone. If need be later, you can attempt to remove it without dismantling the whole engine anyway.

[phil]

Why not borrow a gauge and try that maybe something wrong with the one you are using. It is a screw in type I'm assuming.

[OverseasSoul]

Thanks everyone once again for your helpful comments. I've realized I'm going to need a set of Whitworth tools (5/16 BSF) before attempting anything on the head/block, and will have to special order those in the US. I don't want to burr up the edges of any fasteners... From Stelios' response its seems it is possible to change the piston rings without removing the cylinder head, particularly as the water flow seems to be pretty good. Please confirm if you can...
The overall condition of the motor is good. When I get home, I'll post some pictures of the motor and perhaps you can help me in my decision of whether to go after those cylinder head bolts!

Iain.

[Michael]

Here is a place in the US that sells whitworth:
http://www.britishfasteners.com/index.p ... l-kit-4010

I have not used them, just did a quick google search

[phil]

It's an excellent place to order. Nice guy runs it, good service.