Loss of power in Century

[headdownarseup]

there's another reason for NOT TRUSTING somebody else's information.

whenever i get hold of a "new" seagull, the very first thing i do is completely dismantle the thing.
precisely for this reason, closer inspection of the engine internals will tell you far more than the outside condition does.

shiny on the outside DOESN'T mean shiny on the inside as well?
made that mistake before!

definitely need a new piston and rings. thats the only way to go from here.

another possible reason for the corrosion on the piston is where the motor is not correctly mounted on the boat properly i.e the exhaust tube is too low in the water. you will end up with water getting splashed back up the exhaust tube to a certain extent which in turn, if the motor hasn't been dried out properly between every use, then corrosion starts on the bottom of the piston around the exhaust port. broken rings are the next thing to happen and then scored bore etc.
very lucky its not done any more damage than that.

jon

[OverseasSoul]

.. The piston rings were intact when I first removed the block from the crankcase- I broke one of them removing the ring from the piston. Did not realize how fragile they are. The erosion was under both rings as shown in the photo. No evidence of scarring of the cylinder itself.
I was able to work on a couple of other items.... The drive shaft was quite rusty, but the water pump impeller was in excellent condition compared to many pics I've seen ( see the pic of all my parts). I used wire wool and a drill/wire brush to clean the shaft down to bare metal with lots of pitting from the rust, but not enough to seriously reduce its strength. Covered it with an oily film for now. Here's a question- is it worth painting the driveshaft with a rust protecting/spray galvanizing product to prolong it's life even though its unseen, or is the rate of decay on these slow enough to last my lifetime? The drive tube is still in good condition and I intend to just clean and polish up the chrome.
I've also decided to paint the block as well for the same protective reasons, following advice i've seen elsewhere on the forum, though it will be black, not silver.
Iain.

[headdownarseup]

whenever i dissmantle a gearbox, the driveshaft is one of the components that i will paint even though you wont see it.
as to how long you can keep rust/corrosion at bay is anyones guess? i do it because i can.
any colour you like as long as it will slow down the rust.
engine blocks i always paint them after i've cleaned out the waterjacket. i use a good quality heat resistant paint (either brush on or spray) try and find one that is fairly resistant to chipping or you'll forever be touching up!

examine closely the condition of the piston particularly around the ring lands. any heavy corrosion/pitting in this area could lead to more trouble later on. i like to partially polish the piston with wire/steel wool and maybe a little metal polish (reduces friction a bit) before i reassemble. A good amount of neat 2 stroke oil all over the piston and down the bore helps it go together sweet. smokes a bit when you first start up but that'll soon clear.

sounds like you're nearly there with it.
videos next of the big start up

jon

[OverseasSoul]

Progress report:
Last weekend I received a new piston and rings, and some Whitworth tools. I completely deconstructed my Seagull down to its major components and cleaned everything with kerosene, wire brushes and whatever it took. The cylinder head came easily off the block and Jon was right - well worth doing. The block was full of brownish, rusty grunge. I cleaned it up and repainted it with some high temperature engine paint. Pic attached.

The piston rings and new piston were easy to install using the boiling water method, and it was a delight to put the cleaned engine back together again with some of the new parts I'd had shipped from the UK ( Villiers throttle cable, new fuel tap, new gaskets etc). One challenge was the Villiers magneto - when I span the flywheel one of the magnets scraped the coil housing block,and, being unable to move the coil housing, I chose to file the magnet down. After this, you could feel the magnets opposing the coil on spinning the flywheel. The spark from this action, and cleaning all the points, looked much improved. Another challenge was the exhaust junction with the lower unit - the fit was very loose and the exhaust rattled around. The previous owner had filled the gap with a circular shim of resin, but that made breaking down the engine a bear. So I elected to let it wobble, knowing the drive shaft was very strong and structural.
Once all in one piece, it was clear that compression made this a completely different engine. Turning the flywheel met strong resistance at TDC. Fitted the champion D16 spark plug, cleaned the fuel system again, used 1:15 mix and the original jet needle at 1 turn deeper than the throttle piston on the Villiers carburettor.
Engine didn't start on the 1st pull, disappointingly, but on about the 5th or 6th and never looked back. After that started on the 1st or 2nd pull every time. Made a completely different noise. A much sharper, tinnier bark.
Next up was true boat test, so we put our Lightning sailboat in the creek without her mast and headed out. Performed beautifully - another pic attached.

Only snag - and the reason to do a boat test - we started to flood the boat when we got out into some significant waves. The Lightning has a scupper on the transom on a very rudimentary shock cord fixing; all very low in the water. When this was knocked out of position back into the boat, the backwash from the engine poured water back through the scupper, flooding the boat with several hundred gallons. Fortunately we have lots of closed cell flotation installed when I rebuilt the sailboat, so it was fine to just ride along with a foot of water in the boat, and we got home. I need to redesign the transom scupper using a robust flap, and that'll fix it.
All in all a great success. Thanks to you all again.
PS At the end of an hour's boat test, I had to wipe a lot of unburned fuel from my Seagull's "nose" - it kept dripping. Is there any way to optimize or reduce this?
Iain.

[headdownarseup]

when you mean "wipe it's nose" do you mean a lot of wetness around the carb inlet?

well, this has come up in previous posts under the term "blow by".
you will often see fuel being thrown out of the carb at most throttle settings except for very low settings. (same with the amal carbs)
have a little play with the mixture screw again when you have the engine running in a test bin. this time, put your hand in front of the carb cowling and see if you can feel your hand getting wet? careful use of the throttle should find the best setting.
also worth mentioning with the mixture setting, the more you turn the screw down you will lean the mixture. you want to try to get the motor running at 3/4 throttle (thereabouts) but with no fourstroking. you'll know when its right? then count how many turns it took? (you might be surprised) it took 4 1/2 turns down from flush on my LLS but i'm still using 10:1 fuel mix.

glad to see the old girl came good in the end.

corrosion is always going to be an issue on pump housings and exhaust tube connections. do you know anybody local to you that could weld the top of the flange, that way you'd effectively remove the "wobble" from the tube and do away with the "resin repair".

they get under your skin these seagulls dont they!

jon

[OverseasSoul]

Jon - thanks for your comments. I saw "wipe its nose" on a previous post on the forum and should have been more specific; I meant wiping the grey gunk that drips from the exhaust after use, and in my case, also from the leaky exhaust/lower unit junction. It's clearly unburned fuel and 2 stroke oil, suitably carbonized. There is no leak at all from the lower unit gearbox- bearing seals must be good.
I'm sure that some of this is natural, but I was a bit shocked at how much there was - would estimate an egg cup full overall. Can the unburned fuel amount be reduced by using a leaner mix, a lower 2 stroke fuel ratio and other optimizing tweaks (ie run at 3/4 throttle, with lower back pressure etc)?

[headdownarseup]

i wouldn't reduce the oil content in your mix. Try to stay at 10:1 (15:1 at a push if you must) also try a semi synthetic 2 stroke oil instead of a mineral oil. The modern oils are much better (usually less smoke)

The "dripping nose" has a bit to do with the corrosion on the pump housing, if you've got a decent (tight-ish) connection between the exhaust tube and pump housing then most of the exhaust will end up going straight out of the outlet instead of collecting around the bottom of the tube.
You might be able to reduce the amount of "dribble" by tweeking the fuel mixture on the slide screw, run it in the tank and see how it goes, try to get the engine running without any fourstroking (you'll know when it's right) shut down and then leave it to cool for an hour. Try and restart it, if you've got it right it should start right up (within a couple of pulls) then try it again on the boat.
It might just need a bit more running time to settle down. Usually the only thing you can "tweek" on a seagull is the fuel settings, a smaller/larger gap on the points will advance/retard the timing a bit (if it helps any)
With more practice, you'll be able to see/hear the best throttle setting for optimium performance and economy.

Another thought, how deeply immersed is the engine on the transom? if its too deep you'll end up with more water in the exhaust tube and increased back pressure (that's why there's usually 2 little flute holes on the exhaust tube to help combat this)
Try to get the waterline around 1 inch above the pinch bolt at the bottom of the torque tube and you should be fine.

jon

[OverseasSoul]

Unfortunately there was no wind this weekend, so couldn't take my sailboat out but got down to a couple of jobs on my Seagull and the boat itself. I did try to fix the leaking exhaust per one of the other posts I've seen, by creating a ring of DAP 230 Exterior Ultra sealant pushed into the gap between the exhaust and the pump housing ( a very loose fit that leaked), built up into a ring around it and cleaned up with a high quality hose clamp. See pic. Ran the motor for a good 1/2 hour ( and tuned it up for 1:15 mix) and was pleased to see the only exhaust fluid coming out where it should. So now I can put a small plastic baggie over it with a cable tie and catch all the drips. The hose clamp isn't perfectly centered because it kept moving when I tightened it up - this was the best I could do. This arrangement will make my Seagull very acceptable at the local dock surrounded by all the Yamaha's, Honda's, fishermen, families, kids and their inner tubes.
Iain.