Upset century

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red42hj
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Upset century

Postby red42hj » Wed Aug 23, 2017 7:56 pm

my s.century ( ws) suddenly began to misfire after a good run. It has been reliable for several years. Despite much work on it recently, I cannot find the problem .I could almost write a short book on everything I've done:
Stripped entire fuel system and tank( twice)
Tried another carb of same type
Checked fuel mixture (new fuel)
Checked float bowl operation( fuel flowing through ok)
Tested coil ,ht lead, plug
Tried other new leads and plugs, spark is good at all times
Points are good. It will start but runs very erratically then dies. The plug is very wet and black. Getting desperate now; taking the block apart! Looks good though. Any ideas? Much appreciated. Regards

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Keith.P
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Re: Upset century

Postby Keith.P » Wed Aug 23, 2017 9:01 pm

Any diagnosis at this stage would be premature without an extensive examination, So just going on a hunch, I think it's broken.

fleetingcontact
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Re: Upset century

Postby fleetingcontact » Wed Aug 23, 2017 9:45 pm

On a more positive and helpful note...

Assuming that you have successfully eliminated fuel and spark issues (sounds like it) - and based on the state of the spark plug - the next most likely issue is in the bore - so barrel off, check for cracks and scoring, check rings (maybe stuck, maybe broken) and check piston for damage and wear.

New rings can bought if you want new, as can pistons. Barrels are a bit trickier but if its not cracked then you may consider getting it re-honed. If you remove the piston from the con-rod replace the circlips while you're at it. Piston rings are rather brittle - care required.

NB: Its possible that simply de-coking everything then re-assembing may be the answer.

If spares are needed, they are findable! (Check Sheridan Marine - or Jon@SOS of course - for spares).

There's a great thread discussing some points of finesse on rebuilds - search 'SJP2497 Continued'.

Good luck, have fun.

Martin.

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Keith.P
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Re: Upset century

Postby Keith.P » Wed Aug 23, 2017 10:17 pm

SJP's are common and parts are interchangeable with most other forty seagull, also see what if any sideways movement you have with the flywheel, could be crank bushes, parts for this motor are easily found.

fleetingcontact
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Re: Upset century

Postby fleetingcontact » Wed Aug 23, 2017 11:01 pm

Hey Kieth, was your last comment intended for a different thread?

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Keith.P
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Re: Upset century

Postby Keith.P » Wed Aug 23, 2017 11:48 pm

Sorry I noticed SJP, It's a century your working on, just ignore my post, most do.

red42hj
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Re: Upset century

Postby red42hj » Thu Aug 24, 2017 9:06 am

Thanks fellas, the head is off, and today I'll examine it closer. I'll let you know how it goes!
Red.

red42hj
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Re: Upset century

Postby red42hj » Thu Aug 24, 2017 10:03 am

One other thing; should the crankcase gasket be fitted dry? Reading all the posts, I'm a little unsure.

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Keith.P
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Re: Upset century

Postby Keith.P » Thu Aug 24, 2017 2:18 pm

Some use RTV, myself I just anneal the copper gasket before fitting, depending on the state of the gasket would be my answer.

fleetingcontact
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Re: Upset century

Postby fleetingcontact » Thu Aug 24, 2017 7:26 pm

And once again the wrong answer...

I suspect that the gasket in question is the base gasket, some fit it dry, others use rtv, others saturate it in oil or grease or even vaseline, as I recall. The crankcase does not have a gasket.

Its all in the thread dude.

headdownarseup
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Re: Upset century

Postby headdownarseup » Thu Aug 24, 2017 11:50 pm

Whichever motor i'm working on, i go through everything systematically.
As you've already been through the fuel system twice now i'd leave this alone for the moment.

If you've already got the engine stripped down, now would be a good time to double check the crank bushes for excess wear. If they check out ok then re-assemble after you've re-lapped both case halves. A good flush fit is what's needed on the crankcase with no gaps.(a little smear of rtv helps but don't overdo it with the gloop) Gaps mean air leaks which can result in poor running. Eliminate the possible air leaks and you're halfway there.

Compression is the next step.
The cylinder needs careful checking for scoring or scratches in the bore. Some light rubbing marks from the piston is ok, but deep scores and scratches can lead to low compression and you'll be chasing your tail. If you can feel any deeper scores with your fingernail the chances are that your cylinder has had a hard life and it's now time to look for another cylinder. Head gaskets can very easily be re-annealed by simple heating. Paper gaskets at the cylinder base can either be made yourself, or bought readily from various sources. Rtv (used sparingly) at both ends of the cylinder will help get over any uneven surfaces and help with a better seal.

Ignition is your next step.
I'm no expert here but everything must be top notch. Points gap, ht lead, spark plug, general cleanliness of the connections etc. must all be attended to. Points gaps can be reduced a bit to obtain a stronger better spark. You'll often find that coils in these seagulls are well past their best by now. New ones are available to buy, but it can be a tricky job to strip down a baseplate to replace a faulty or dying coil. Only tackle this job if you're confident you have the skills to do it. If not leave it in the hands of a professional or buy a replacement ignition that you know is reliable and working 100%. Leave NOTHING to chance here. No spark no go.

Carb.
I'm guessing you have an Amal 46n 2jet carb with your Silver Century?
Cleanliness reigns supreme in here. There's a small fuel filter inside the banjo bolt. This must be clean (so you can see through the fine mesh). If it's not clean the fuel flow will be restricted. If your carb hasn't got a banjo filter then you need to fit one.Same with the fuel tap. There's a small filter in here as well. They get clogged with debris from the tank which also restricts the fuel flow into the carb.
I make my own filters for the fuel tap from fine mesh brass matting. Really simple to do.Takes me 20 minutes from scratch, all soldered into place when it's finished just like it's supposed to be.
If in doubt, shop bought carb cleaner reaches those hard to get to bits inside the carb. By all means take the carb to bits if you need to BUT BEWARE that the threads inside the banjo bolt are fragile and are very easily damaged.(they corrode badly in here)

Fuel mix.
Provided your engine was made after 1978 you should be running at 25:1 petroil. Anything made before this was set to run at 10:1
Now go and check to see which jets are fitted in your carb. The longest of the 2 jets needs to be removed to see the numbers stamped into it.
(don't ask me which numbers are supposed to be on what jet, you should find the answer on an older discussion somewhere)
Steady as you go when you're in here. These jets are delicate little things and don't take too kindly to rough treatment.


I'd say you've already got a pretty good handle on things so far. It must be something fairly simple to my mind. It was running before, it will run again.
If you get stuck one of us will jump in somewhere :P


Jon

red42hj
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Re: Upset century

Postby red42hj » Fri Aug 25, 2017 12:05 am

So far so good, the block looks good, its soaking in caustic soda now, will clean it tomorrow. The water jacket near the top of the cylinder was blocked on one side I noticed. Not helpful for cooling. While I'm doing all this I'm also prepping a TC102 for next season. Works in the barrel but not tried on a boat yet. Having a lot of agro with fuel connection leaks on this ; need new washers.
With the century though, I feel its a toss up between the block and the ignition. I think its going to run and run.......

red42hj
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Re: Upset century

Postby red42hj » Fri Aug 25, 2017 12:13 am

Ps thanks Jon, I'm taking note of all you say. I'll keep you posted as I go.

fleetingcontact
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Re: Upset century

Postby fleetingcontact » Fri Aug 25, 2017 11:46 pm

Jon,

assuming that all issues relating to fuel delivery and a good spark have been addressed (the original post seems to indicate a healthy approach to dealing with potential problems) what else (apart from coking or excessive wear in rings/piston/bore) might result in a wet, black plug? (Not a rhetorical question)!

There is no scope for adjusting ignition timing or carb mixture (jet and needle swapping aside) either on purpose or by accident ...right or wrong?

At the moment, the greatest expense that has to be met is the price of a new base gasket, some RTV, and some time. If stuff is worn (like crankshafts at the point thay pass through the cases) or the bushes in the crankcases themselves then admittedly this is a problem. But if no discernable play can be detectd at these points (also con-rod ends) then I'd still say just get everything nice and spotless and re-assemble is the thing to try first. Having got the head and barrel off without falling foul of siezed bolts etc, it'll be easy to undo it all again if you have to.

I know it's not in any manual but a pot scourer, lots of WD40, and a bit of patience can work wonders. I have a 40 I put together using only parts I considered sub-standard using this 'methodology'...a great runner.

Red,

were the piston rings coked up?
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fleetingcontact
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Re: Upset century

Postby fleetingcontact » Fri Aug 25, 2017 11:49 pm

Damn, ignore the attachment, that was a mistake!


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