Hi I have what may be a silly question and the answer may be obvious but I need to ask. I have a 100 century direct drive with a 40 gearbox on it with a prop marked 40 plus and all is good. I have a prop marked 100 only and have tried to fit it on the prop shaft of the 40 gearbox. This is where it sounds silly - 100 only and I am trying to fit it on a 40 props shaft. I had a flash of brilliance and thought duuuuh maybe they are different gearboxes. Do the 100 and 40 gearboxes have different ratios and shaft sizes or am I trying to fit a flogged out 100 only prop to the 40 shaft?. If they are different would I gain an advantage from trying to get a 100 century direct drive gearbox to replace the 40 gearbox with thrust/hp. Have some good news though the wife has taken to seagulls and says I should get another one OR TWO sorry she is not for sale then again decent offers considered but no free postage
cheers
Bob
The gearboxes on the 40plus and 100 direct drive motors are the same. Same gear ratios etc. The only visual difference between them will be in the pumphousing where the exhaust tube attaches. Smaller diameter exhaust attachment will be for a 40, larger diameter is for the 100.
The drive shaft (that the prop attaches to) will be the same diameter so will be a straight fit with your larger prop.
If you have both props on the bench, lie one on top of the other and measure the difference in the prop length. (hub centre to blade tip) Bigger prop= bigger motor (usually)
Your 100 only prop, is it a 4 or 5 bladed prop? Square edged blades (hydrofan) or rounded blades (cloverleaf as we call them)
Using a smaller 40plus prop on your century motor as it is now, may end up with a slight increase in engine revs with little advantage over speed. Swapping over to the correct prop might reduce the engine revs a little in favour of a little more thrust. Try it and see with both props if there is any real advantage or disadvantage over either of them.
Thanks for your information Jon it has sorted out what I have been wondering for a while. The prop is a clover leaf and appears to be the same dimensions as the cloverleaf prop I have with 40 plus written on it. The issue must be the centre bush has been worn as it is a sloppy fit on the shaft and when I did try it on the 100 century with the 40 gearbox (whoops! probably shouldn't say that any more because of the similarities) on the 10 foot tinny there was a vibration when running. The prop has a couple of nicks on one blade which could put it out of balance a bit also? Combined with the looser fit on the shaft I think it might become an ornament to hang in the shed somewhere.
Thankyou
Bob
Im always changing bits, all it takes is the construct a large to small exhaust tube and change the water supply tube.
At the moment I have a 102 power unit on a 40+ gearbox, last I had a Century 100 to the same 40+ gearbox. Cant say I've really notice any change in power or speed.
And as others have said C100, Silver Century and any 40+ propellors will fit.
That seems like a lot of work Rob, that could have been avoided if the correct water pump housing had been used, & would probably would have cooled better with the higher cooling water output from the correct 102 cc water pump & impeller.
All classic Seagulls had 1/2" prop shafts & the bronze prop bushes are still available from John Williams & British Seagull.
But you've still done a very nice tidy job!
The only difference between the props is a little more pitch for the higher power motors.
Make it idiot proof and someone will make a better idiot.
Bob
Props can be "reworked" and re-bushed quite easily. I've "re-worked" a couple with good results. Quite satisfying actually when you get it right. It's also quite surprising how much of a difference it makes, not only in reducing vibration but improving the efficiency of the prop as well.
I have a couple that need re-bushing. Simple enough job to do if you know someone with a lathe and suitable phosphor bronze material with which to make the bushing from. Hardest part is removing the old worn out bush.
Hi Jon
It would be a good project to redo the prop but I can't access the tools to do it. Anyway on a brighter note I'm going to look at a 102 this weekend that's in the original box apparently and hasn't been started for a very long time. I'll update the data for you when I know more.
Cheers Bob
Still trying wrote:Hi Jon
It would be a good project to redo the prop but I can't access the tools to do it. Anyway on a brighter note I'm going to look at a 102 this weekend that's in the original box apparently and hasn't been started for a very long time. I'll update the data for you when I know more.
Cheers Bob
The props are very easy to rebush all you need is a 5" length of 5/8"mild steel round bar with one end turned down to 1/2" for 1 inch, I'm sure you've got a bearing press at work Jon, drop the 1/2" end of your mandrill down into the bush & press the bush out.
If you now place a thick 1/2" washer on your tool, you can now press in the new bush to the correct depth.
Often there is quite a bit of corrosion between the bush & the aluminium, in this case it can be beneficial to drill out the hole in the prop 1 size & fit a larger OD bush.
As these bushes are not acting as a bearing, so there is no need to use expensive phosphor bronze, you can get them made from brass or Oilite, the bore of them was 0.5015" the same as the gear case prop shaft bearing, this tool will remove & replace them as well.
John has stock of the prop shaft bearings & prop shafts for almost all Seagull lower units, so if your going to go to the effort of rebushing the prop it might be a good idea to fix the oil leaks by renewing both at the same time!
Make it idiot proof and someone will make a better idiot.
I'll look into getting some oversize bushes and have a go myself. And yes, i have access to a press so no biggy
It was more the "re-working" aspect i enjoy. Some props are a bit too far gone to economically rejuvinate by "garden shed" mechanics, but some are more than up to a bit of smoothing, a bit of polishing, a tweek here and there, maybe even a blob of weld or two. It's this side of things i quite like doing to most of my props now. I'd even go as far as saying i quite enjoy balancing them despite taking an age to do without any powertools just good old fashioned elbow grease.
Picked up the 102 this morning. Pulled it out of the box for a look at his place and it all looks original as far I know anyway. Old fella I got it from reckons it hasn't run since the 80s, this will be fun . Can't do anymore today as I have to go to an Orchid show with the misses ( which I reckon is as exciting as going to work on a Monday morning ) Anyway works both ways I guess, her and her orchards and me and my seagulls. Cheers Bob
Thanks BP.
When I bought it this morning old mate says "She is a bit hard to turn over you know and I never figured out why". Anyhow first thing I did was drop the gearbox off and everything turned fine thought better have a look inside and this was the contents of the gearbox no wonder it had difficulty rotating. Pinion and crown gear seem ok? Really good clean out and a dash of oil to fix this up I hope. Also a picture of 102 without box so I can make sandcastles with contents and the flywheel plate has no words on it? Oh well, I get sick of reading most of the time .
and thought duuuuh maybe they are different gearboxes. Do the 100 and 40 gearboxes have different ratios and shaft sizes or am I trying to fit a flogged out 100 only prop to the 40 shaft?. If they are different would I gain an advantage from trying to get a 100 century direct drive gearbox to replace the 40 gearbox with thrust/hp. Have some good news though the wife has taken to seagulls and says I should get another one OR TWO 
sorry she is not for sale 
) Anyway works both ways I guess, her and her orchards and me and my seagulls. Cheers Bob
