Much appreciated Tam

[headdownarseup]

Keith

An LLS motor is 102cc. Same crankshaft as a 102 or century. Same con-rod design, same piston design etc. but with (mostly) 2 rings on their pistons.
The only major difference as far as i can see is that their powered by a Villiers carb and not an Amal. They even have the same narrow (square/oblong) transfer port as the century/silver century cylinders.
The one i have in the shed i've just measured the compression at 49psi dry. Pretty much in line with what i've been talking about for all the other 102cc variants.


So Charles. What you're saying is that by reducing the reciprocating weight will help to increase maximum revs (slightly) and partially reduce friction at the same time. Is this correct.(is it really as much as 12-14 grams?) I was thinking more along 8-10 grams.
Why not polish the piston skirt to achieve similar levels of friction reduction? Less heat soak resulting in slightly more power.There's plenty of oil floating around inside there after all, and depending on how tight the tolerances are between the cylinder wall and rings, the amount of oil provides something of a "cushion" anyway. As you say, with a 10:1 fuel/oil mix having this oily mixture has probably prevented a lot of sideways wear inside the bore and the corresponding "scuff" on the piston.

I still maintain that 2 rings in this case works better than 1, especially for a low revving low compression engine in the seagull.
For a higher revving application with a much thinner ring, then perhaps 1 ring works even better. The shape of the piston crown becomes more of an issue here though. Higher revs = higher temps. Flatter topped pistons provide a better way of increasing the compression. (and to some degree a better air flow) Chop a bit off the head for a tighter squish band. Difficult to achieve the same things with a square block seagull as it has a deflector. However, if there's a way of mimicking the shape of the piston crown inside the cylinder head itself (like a 40 series head for example) then i can see good things happening and the resulting increase in compression. Typically around 100psi for a 40 series. That's nearly twice as much compression as a century/102.
Do you see where i'm going with this?

Jon

[Charles uk]

Ask Keith about the weight saving, he weighted it.

Check your LLS cylinders again, the majority have bridged ports, I think it was the late ones that had the small ports, probably 4 different cylinder patterns on these & the CPs.

Have a read up on the rings to see how they work, then my comments will become clear.

The 40 series at 60% of the Silver Century's cubic capacity produces 50% of the Silver Century's Bhp.

Seagull must have agreed with you about the 2 rings, as the cost savings using one, would have been significant!

All Seagulls except the 170, 160 & the 125 have deflectors.

[tambikeboy]

All Seagulls except the 170, 160 & the 125 have deflectors


My FVPS have tafficators. .....

[Keith.P]

Don't Ask ME.
What do I know.
It's got a ring missing, I worked that out myself, that's me happy.

[Keith.P]

Back to the job in hand, sorting out the ignition system now.
Pulled out a multimeter and tested the coil, as people keep saying, one end to the points and the other to the HT connection and yes I have a resistance, open the points and I still have a resistance.
That's why I always remove the points cable and just test the coil.
So I have a small resistance out of the coil (on its own) and a large resistance out of the points as I should when they are closed.
I also got a large resistance with the the points open, this would point to a dead short, but as the coil wire has been removed it must have a duff condenser, I re-tested the points with the condenser disconnected and no resistance with the points open.
That's the way I test them and it saves a lot of head scratching when you get bogus readings, you test them as two different parts, which they are, as both can, and do fail, plus you can performed this without removing the flywheel.
I could have just changed the condenser, but as all the bolts were rusted pretty much away, I have removed all the parts from the stator plate and I will be replacing them, so they can be removed at any other time in the future.

[headdownarseup]

What has a bridged port got to do with cubic capacity Charles? (nothing as far as i can see)
Keith was asking what cc's an LLS was!
102 if i'm not mistaken.

If we're talking about weight saving, there are other ways to do this at perhaps the expense of increased wear on some other components.
You'd know much more about these sorts of things being a "racer" Charles. I'm not, i'm just a "user" like many others out there.

Radial tension, ring groove to piston ring side clearance, blow-by and ring flutter etc. etc. I can read too
Brilliant if your engine's running at close to 9000 rpm's, but most typical gull engines don't get anywhere near this of course. Due to the design characteristics most run out of puff well before this. Whether some of this is due to frictional losses is debatable, is 1 ring better than 2 in a gull engine? For my money... no. There isn't the compression there to begin with to worry too much about this sort of thing. For starters there's more than enough oil residue to overcome most frictional losses inside a typical gull cylinder. I'd be more concerned about how much leakage there is around the crank bushes before i worried about what's happening around the piston.
High rpm's is one thing, friction and heat transfer different again. Air flow characteristics for the most part are largely down to the surface finish of the casting inside the cylinder ports. Shape and size play their part too. To get all these things to work together correctly takes time and effort.

As a standard cylinder a seagull works just fine for most of us mere mortals. It's already stood the test of time for most folks already. Why mess with perfection!

I'm done with this topic now.

[Charles uk]

Maybe I miss read what you were saying about the same shaped transfer ports in the LLS & the century the many people will notice they will have a wide bridged transfer in theirs & think they've got the wrong cylinder.

I was talking cost saving not weigh.

[Keith.P]

So far so good, building it up is not normally a slow Process, but finding where I put the parts in the first place is.
One good thing, I'm finding parts I didn't know I had.

IMG_1365.JPG

Thanks TAM.

[Charles uk]

That's starting to look quite honest Keith, & you've even got the notch in the right place!

You've done this before.

[Keith.P]

To be honest, I did put it on upside down first time, but the motor was upside down at the time, so it wasn't my fault.

[Hugz]

Notch?? Exhaust clamp?

[Keith.P]

Hugz, I think Charles is on about the flat lip on the edge of the exhaust ring clamp, some have more than others, it holding the gear lever when it's out of gear.
I know, notch is not quite the right word, but he is getting on a bit now, so we have to cut him some slack now and then.

IMG_1365A.jpg

[Keith.P]

A little more added today.

IMG_1368.JPG

[tambikeboy]

Looking good china