Hone a cylinder bore before re-ring er no?

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joe28
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Hone a cylinder bore before re-ring er no?

Post by joe28 » Wed Apr 15, 2015 6:29 pm

This is on a '75 Silver Century.
I haven't taken a compression test, but I can almost bet it needs to be re-rung.
My low hour '69 Century is much harder to spin over and I can spin the '75 by hand-almost.
This outboard has been "ridden hard and put away wet", by the looks of it.
So, I'm just trying to get a plan of attack when I do finally start on this "project', and a parts list.
I've read I should put some silicone (high temp), on the head and base gasket.
I'll check bore for size and taper when I get it apart.
Clean carbon off piston.
Flush coolant passages out.
Clean up the threads
new S.S. head bolts
(great info here)! :mrgreen:
Now the question.............
Do you "break the glaze" off the cylinder with a hone, or just clean/inspect?
If the cylinder has a coating (chrome or??) like bikes, it's a bad no-no, but if not, I was taught YEARS ago, the rings won't seal.
Do I or don't I?
Joe
If this was easy, doctors and lawylers would be working on them

headdownarseup
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Re: Hone a cylinder bore before re-ring er no?

Post by headdownarseup » Wed Apr 15, 2015 7:23 pm

Joe
i'm guessing that you are quite capable of weilding a wrench on something old like these.

seagull cylinders are cast iron (so no chrome plating to the bore) so "glaze busting" is something i would definitely do.
A few reasons why some (not all) seagulls seem to have low compression. Sticking or stuck piston rings, a lack of any oil in the bore (motor been stood for a long time) cylinder head gasket failure to name but a few. Or something far more serious in what i term as the "Spanner Monkeys" might have gotten to this motor at some time in the past! You know the sort, the guy who thinks he knows what he's doing but ends up making a hash of things..... :roll:

Open the motor up and you'll see what's wrong.

I have a 78 silver century plus which has low compression (around 50psi) which for most of them seems about right. Even my older 102's run around the same at 50psi (ish)
Nothing too out of the ordinary so far! Most of the square block century's you can spin by hand with little effort. (compare the difference in a smaller 40 series motor if there is one close to you and you'll see what i mean)

All good so far buddy

jon

Keith.P
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Re: Hone a cylinder bore before re-ring er no?

Post by Keith.P » Wed Apr 15, 2015 7:32 pm

Do you "break the glaze" off the cylinder with a hone, or just clean/inspect?
As you are going to fit new rings, its always best to clean or even lightly hone before hand so the new rings can re-seat, don't go in to hard as they don't do over sized rings.

joe28
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Re: Hone a cylinder bore before re-ring er no?

Post by joe28 » Thu Apr 16, 2015 3:10 pm

Thanks!
I'm dying to see what the compression is, but the anal mechanic in me says, "just re- do it and get it over with! This way we start fresh"! :mrgreen:
I've got a great set of "ball hones", (it's got a million balls of honing stones material on the tips of wires that works great for this stuff, and a nice flexible fine stone cylinder hone, both have been "sleeping" too long in the bottom of my one tool box.
Seems "Glaze breaking", like points and dwell are lost arts :lol:
I spray kero in the bore, soak the hone, put it in and give her hell!
A few strokes up and down to get that nice 60 degree cross hatch, and POOF!
My old shop instructor would be proud! A good wash out with brake clean or Kero, lube the walls with 2 smoke oil, and we're ready to go!
Now to get the time and parts order together!
I dunno how many "projects" I've gotten where I had to "fix" the P.O. "attempts" to fix them.
You always get the, "No, I didn't do that! It's the way I bought it"! :P
There should be a written test BEFORE you are allowed to pick up a wrench, order parts! :roll:
A lot of these I got cheap cuz they were SO screwed up, the P.O. gave up on them!!
Joe
So many toys, so few hours

Keith.P
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Re: Hone a cylinder bore before re-ring er no?

Post by Keith.P » Thu Apr 16, 2015 4:26 pm

That's why the parts sales are on the up, someone else always knows best. :lol:
Seems "Glaze breaking", like points and dwell are lost arts
I always found glazing more problematic with Gas run engines, I have never tried, or even know the dwell angle of a seagull, a little hard to do with the flywheel spinning though.

phil
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Re: Hone a cylinder bore before re-ring er no?

Post by phil » Thu Apr 16, 2015 9:39 pm

The best Century or Silver Century I've seen has about 72 psi, I'm happy if I find one that is 60 cold and dry. They seem to run well at 50 psi and I've seen them run with 35 psi. I don't put any oil in before checking comp. it does not give you a proper base for comparison between motors, in my opinion and many others opinions, but it is a somewhat controversial position, as I'm well aware.
Don't forget that you need good crankcase comp. as well, check the upper and lower crankcase bushings (or bushes as they prefer to call them in the U.K.) You may want to consider running 40 wt.oil in mix on low comp. motors. I use low ash Aeroshell 80 which is a 40 wt oil.when I run old motors other than Seagulls as many call out for 40 wt.oil and do not seal properly on TCW 3 which appears to be about 20 wt. at normal temps.

headdownarseup
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Re: Hone a cylinder bore before re-ring er no?

Post by headdownarseup » Sun Apr 19, 2015 12:20 am

I'd concur with Phil, 50psi seems to be a good average for a century or century plus motor.
As you mention earlier,40wt oil is also a good idea with regards to helping crankcase sealing (particularly if the bushings are worn like a lot of them are by now)

Tear the motor down Joe, you should find it easy to see what's wrong.
I bet when it's all finished you'll end up with around 50-55psi (best guess) which should be ok for what you want to use this for.

jon

joe28
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Re: Hone a cylinder bore before re-ring er no?

Post by joe28 » Wed Apr 22, 2015 6:50 pm

hmmmmm,
I hadn't thought about the crank bushings or seals? if they have them, (on all the bikes I've done, I had made up a pressure tester.
(really all it is is a few "expansion plugs? Soft plugs? casting plugs?, Soft Plugs? many names for same thing. I drill and brazed on a air chuck fitting).
Take the carb. off, bring piston to TDC, fit the plug in, tighten the clamp to seal it, pump 2-3 PSI into the lower end of the motor and listen or watch to see if the air PSI goes down. 9 times out of 10, it is the flywheel side, sucked some dirt or?? and took out the seal.
I'm thinking that these motors don't have crank seals?
How do I check/test the crank bushings? seals??
Thanks
Joe
Yep! This $54 E bay outboard is going to coat $3 less when I'm all done than if I bought a new one! :lol:

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