Differences between Century and Plus models

[whigum]

Hello, I'm wondering what the differences between the Century and Century+ models are? I see they have different gear ratios and props, and the Plus model has a twin jet carb.. is the carb the only reason for the higher HP rating?

[Oyster 49]

Century plus models have a larger prop, that is slower running but a coarser pitch. So more suitable for a heavier displacement hull that needs a push, but not necessarily going to go that fast.

Silver centuries have the twin jet amal 46 carb mounted on the opposite side to a century that has a villiers carb.

[Charles uk]

There are 2 styles of Century outboards,

The Century 100 & the Silver Century.

On the Century 100's only 3 types of lower units were used, the 3.5:1 & the plus, 4:1 fixed & 4:1 clutched box.
All of the above used Villiers carbs.

On the Silver Century's 5 different lower units were used, the 2.5:1 clutched, the 3.1:1 FNR clutched box, the 3.5:1 fixed, & the plus boxes, the 4:1 fixed & the 4:1 clutched.
Up to circa 1979 Silver Centurys were fitted with the Amal 46N carb after this the Amal 416 was used.

[whigum]

Thanks, very informative. What I'm left to understand is the difference in power ratings. Is this due to different carburetion? The seem to have very similar power heads? Are all the Century models essentially re-branded/updates to the same basic design?

[cobbadog]

I think you might find that it is a combination between prop, gear ratio and carby, not just one thing.

[whigum]

cobbadog, as far as my understanding goes (and I do not claim to be an expert, correct me if I'm wrong!), The gear ratio does not effect the HP rating, same with the prop. The power going into the gearbox is converted to produce the desired rotational speed/torque, the pitch of the prop does the same thing - a balance of speed and torque to suit the application. 5HP is still 5HP whether it's geared for low speed and high torque, or the opposite, right? So then, the power is actually produced in the power head, which is down to the design of the unit... back to my original question, what's the difference that changes the HP rating between the Century models? Anyone know?

[headdownarseup]

When most of the original documentation was written about these engines from way back when, the horsepower figures were based on a comparison of other engines of comparable size.
Most of what was originally written was from a time before the trade description act so they could probably get away with it then.

Probably the more accurate power ratings came from the later designed motors in the QB range. These pretty much did what they said they could do due to a complete re-design of the powerhead and a different carb. The original design of the "classic" range, good as they are for most of us are shall we say adequate.

The AMAL 2 jet carb was fitted to a whole range of motors from pre-war right up to the late 70's with very little change to speak of except for a small tweek to the jet sizes in later years (1978 onwards) to allow for slightly less oil content in the fuel mix. Apart from that they're basically the same carb all the way through.There are a few small detail changes to them but nothing that would increase or decrease the power output.

As for gearboxes etc. there's an easier way to identify them at a glance.
The PLUS gearboxes are generally much bigger (and some would say uglier) than their conventional and smaller sized boxes with corresponding props.
Plus gearboxes are much slower turning as they've generally got a very large prop to try and spin. Coupled with a meager power output they're not going to be anywhere as speedy as the smaller gearboxes.Better suited to very heavy boats that don't need to go fast as Oyster has mentioned.
I can testify to that.

Pics below might help, but century motors follow a similar pattern.

Jon

[Charles uk]

Seagull quoted their horse power figures on the basis, of which horse power motors does this model of Seagull, push a boat as well as.

If a Seagull featherweight was labelled as a 10 horsepower, obviously you wouldn't sell many, as they would fail badly in comparison with a 10 horse Evinrude, so whatever Seagull claimed for a motor had to be credible in the comparison game, so a Century 100 which was quoted as 4 hp had to perform as well as every other 4 hp outboard available at that time, otherwise they wouldn't have sold very many.

They must have got that right as the estimates say circa 1 million passed through the factory gates.

[whigum]

headdownarseup, thanks for all that information, very interesting, particularly regarding the trade description act. I wonder what's a better way of doing things? The old fashioned "that should do it" or the modern "precisely that, according to the computer model".. I think the answer is clear I still use old 60s/70s Black & Decker drills.. they may lack reverse and speed control, but they sure don't break! In fact, the majority of my tools are older than I am.

So, the picture I have is that that Seagulls were rated based on the competition. Fair enough. I could then assume the differing power ratings are more a matter of perceived performance based on the target market for the outboard? That would mean the larger props on the Silver models are going to put out more pushing power, and if they were aimed at heavy displacement boats, then they probably would perform more like a 5hp machine? Am I getting it now?

But then.. to get technical, what about pistons/rods/cranks/cylinders? Are they all the same among all the Centurys? Or did they get their designs revised to put out more power?

[headdownarseup]

Errr... Yes to the early part of your question. Boxes and props etc aren't that good a percecption of power, but you're on the right track.
But definitely the ratings (whatever they are) were based on a comparison of other "similar" motors about at the time. During the 1980's is where things changed and BS started to refrain from quoting HP figures in favour of thrust output. Hence what we once knew as a 40- or featherweight for example became known unceremoniously as the model 45. It's not the same is it.

I'm not saying i'm an expert by any stretch of the imagination, but i have dismantled quite a lot of these seagulls now (well over 50 of them) both big and small.
Crankshafts,con-rods,pistons etc. for the most part have very subtle changes. Hardly noticeable for a mention, and certainly not the kind of thing that's going to improve power output. It's more to do with the cylinder as this is where most of the action happens. Over the years (with the 102's at least) i've noticed some very small changes, nothing to do with the port timing as this is pretty much untouched throughout the 102's, but the shape and size of the ports does seem to change a bit. Some of the square block models i've stripped seem to follow a similar set of changes, but it's worth mentioning that a roundblock 102 has some different "architecture" shall we say compared to the century/silver century cylinders. Again, nothing that will increase or decrease power output. Think of them as a tractor and not a sports car and you'll start to understand what these engines are all about.

It's not till we get into the mid 80's when there's a complete re-design of the powerhead (64cc and 102cc) and it's these later motors that are the full 9 yards in terms of power. Ask Charles L, he'll tell you as this was more his area of interest.

With the older "classic" engines they are what they are. Simple tough and durable (provided you look after them), and have stood the test of time partly because they've got so much oil content in the fuel (often 10:1) which saves the cylinder bore from wear.There's no roller bearings to worry about either (like a lot of the later engines have) and generally they're a lot simpler with less to go wrong. True, carbs have changed a bit over the years but again it's not necessarily going to make an engine produce more or less power. I think nowadays the biggest area of concern is with the ignition systems.Particularly the Villiers. The coils go bad and loose their spark rendering a once loved gull into a headache for some folks and we see 'em for sale in the usual places. Apart from that they'll just keep on going and going and going with a little bit of tlc once in a while.

The fun starts when you tinker with 'em to try and make them go a bit better than normal, but that's another topic of conversation.

Jon