Avon Sportboat

haccor · 30 May 2013, 23:30

Hi all,

Recently , I have acquired an inflatable RIB and am now at a complete loss! From what I gather, it's a Avon Spoartboat S3-40, which came with a Black a Blue labeled 20HP Mercuery Thunderbolt(maybe?) engine. The RIB (or should I say SIB?) Inflates well and comes with all they plywood but not controls/steering. The Mercury engine starts and runs well (although I do need to try and source a fuel tank...), but has clearly been used alongside some steering gear is it has no tiller. Has anyone any experience with this engine, with regards to some sort of service and cleanup? Have had a quick look online and can't find a manual, but intend on cleaning up the wiring and carb.

What I can't work out is the remote steering and throttle controls. I gather I have two choice, either (A) try and source some sort of steering and throttle mechanism, and try and build some sort of ply/metal console to mount it on- but can't work out what I need for this. Or (B) take a (possibly) more simple approach and buy a second hand tiller. Problem is, this leaves me with two questions. Is the steering mechanism any old generic type that is the correct length for the boat, or do I need to be looking for mercury stuff? and secondly, which tiller do I go for? Oh and (C) is it worth it!!!

Sorry for such a long winded post, but I am REALLY struggling to find info on this SIB(or RIB!) and engine.

Cheers
Jake

Nos4r2 · 30 May 2013, 23:48

The tiller and throttle are combined if you fit a tiller.
You'll need the correct tiller for the motor-is there a 'gear' sticking out of the port side of the motor? If there isn't, you'll need to source the throttle linkage that goes inside the cowl from the tiller as well. Probably better to buy a scrap motor to remove them from-there's quite a few about as most have died of abuse/ old age by now.

However,before you try and do anything,get a manual (you'll need it to find all the bolts) and try and get the gearbox off it-those motors are a steel driveshaft from memory and you might find the gearbox seized on because the driveshaft is rusted solidly into the powerhead.

It can't be serviced properly if it's stuck as you won't be able to replace or inspect the water pump impeller. I wouldn't use it without at least inspecting the impeller-it could be 40 years old. If it fails, you'll be stuck.

Nos4r2 · 30 May 2013, 23:55

This should be the manual you need:-

Mercury Repair Manual 1965~89 by Seloc | eBay

Nos4r2 · 30 May 2013, 23:58

BTW, you might find the seller of this has a tiller setup:-

Scrapping Mercury 20hp 2 stroke outboard manual start. crank cases | eBay

It's the same motor as yours

haccor · 30 May 2013, 23:58

Quote:

Originally Posted by Nos4r2

The tiller and throttle are combined if you fit a tiller.
You'll need the correct tiller for the motor-is there a 'gear' sticking out of the port side of the motor? If there isn't, you'll need to source the throttle linkage that goes inside the cowl from the tiller.

Before you try and do anything, try and get the gearbox off it-those motors are a steel driveshaft from memory and you might find the gearbox seized on.

It can't be serviced properly if it's stuck as you won't be able to replace or inspect the water pump impeller. I wouldn't use it without at least inspecting the impeller-it could be 40 years old. If it fails, you'll be stuck.

Hi Nos4r2, many thanks for the reply.

There is a gear sticking out the motor. When we tested it in a bucket of water- it seem to manage reverse-neutral-forward okay. I'll try and get the gearbox out and give it a check- is there any gaskets I need to replace if/when it comes out? I may replace the impeller (if easily source-able?) before I take it out. In the meantime I have a 5hp Yamaha engine I can have a play with when the weather gets better (although, will be a while with my broken collarbone, not boat related!!!)

I guessed the tiller and throttle (and therefore, steering) are combined. Is it easy to find the correct tiller, would any mercury one do or is exclusively a thunderbolt I should be hunting for?

You seem to have roughly guessed the engine, any rough ideas as to what model I should be looking for? So far my research has roughly pointed to a thunderbolt 200, but I could be way off...

Thanks for the help.

Nos4r2 · 31 May 2013, 00:01

Post a pic-it'll be a Mercury 200 (20hp) Blueband from what you've said. Is it a wraparound aluminium cowl or a plastic cowl? If it's aluminium it'll probably be 1970s, maybe earrly 80s.

Sounds like all you need is the tiller unit then.

You WILL need to fit a killcord to that motor though if you use it, it's quite easy-they just plug in to the wiring of the stop button.

I'd replace the impeller as a matter of course. Be careful removing the old one-the key for the impeller on those is tiny and easy to lose.

haccor · 31 May 2013, 00:02

Quote:

Originally Posted by Nos4r2

BTW, you might find the seller of this has a tiller setup:-

Scrapping Mercury 20hp 2 stroke outboard manual start. crank cases | eBay

It's the same motor as yours

Super- thanks very much. I have emailed the seller, so finger crossed.

haccor · 31 May 2013, 00:07

Quote:

Originally Posted by Nos4r2

Post a pic-it'll be a Mercury 200 (20hp) Blueband from what you've said. Is it a wraparound aluminium cowl or a plastic cowl? If it's aluminium it'll probably be 1970s, maybe earrly 80s.

Sounds like all you need is the tiller unit then.

You WILL need to fit a killcord to that motor though if you use it, it's quite easy-they just plug in to the wiring of the stop button.

I'd replace the impeller as a matter of course. Be careful removing the old one-the key for the impeller on those is tiny and easy to lose.

Will try and get a pic tomorrow, but as you said, it's a black aluminum cowl with blue writing, with a little foam on the inside. Bit dented, but not too bad!

Nos4r2 · 31 May 2013, 00:08

Oh, and you may need to very very carefully split the impeller from the driveshaft. They stick. I used a dremel to remove the last one I did.

They are VERY responsive to the throttle when you first open it by the way. Be careful. I nearly turned a 3.4m Zodiac over backwards finding that out.

haccor · 31 May 2013, 00:19

Quote:

Originally Posted by Nos4r2

Oh, and you may need to very very carefully split the impeller from the driveshaft. They stick. I used a dremel to remove the last one I did.

They are VERY responsive to the throttle when you first open it by the way. Be careful. I nearly turned a 3.4m Zodiac over backwards finding that out.

Woah, pretty reasonable engine then! I have dremel at hand, thanks for the tip. Will make sure I do before I take it out. If it drives through the gears si the gearbox likely to be knackered?

In your opinion- is it worth spending the extra ins steering gear for this boat, or should I just have fun enjoying it with a tiller? Part of me is tempted to get a good price tiller and see what happens from there....

I guess it depends if it's a good boat worth spending money on....

Nos4r2 · 31 May 2013, 02:14

Get a tiller. You'll never recoup the money for buying steering gear and remotes and you'll lose a lot of space.

Not sure about 'reasonable',but they are quite torquey. I think the 3.4 Zodiac hit about 20 knots in a flat calm, but the initial acceleration was more than I first expected..

They are ok if they run right, but there's all sorts of issues with older Mercs. The wiring decays, driveshafts seize to powerheads,impellers seize on, sometimes the driveshaft will corrode and frag the gearbox seals, and all the bolts are American sizes and threads. Don't be tempted to try using anything metric on it.

if it goes wrong, be VERY careful if you put a spanner anywhere near it. It'll be the devils own job not to shear every bolt/stud off.

If the gearbox is working, as long as there's no water in the gearbox oil it should be OK. Make sure you use proper Quicksilver gear oil in it though, and change the gearbox fill/vent washers every time you remove the screws

Landlockedpirate · 31 May 2013, 12:36

If you don't get a response from the Ebay seller give Bill Higham Marine a try, he has hundreds of tillers hanging round his work shop. Agree with above, not worth the effort or expense of fitting a steering wheel, stick with the tiller.

haccor · 03 June 2013, 21:06

Cheers for all the very helpful advice. Have a tiller on the way so happy now! Quick update- did a quick compression check today on both cylinders, 153 psi on 1 and 148 ish on the other, which seems to be pretty good? Had a bit of a pain with the wiring though, one wire immediately snapped pretty much as I touched it, but I had been warned about this! I am going to see if I can find good wire if I trim back, and try and solder/heat shrink some replacement. Failing that, I have had some good info on a method of removing the resin from the switch box and replacing all the wires for new wire, so figure I'll have nothing to lose! Hopefully it won't come to it though.....

Anyone know if there is a free manual on the net for this engine, or is it all paid for copyrighted manuals only that exist? Is removing the gearbox completely away from the engine necessary, or is a oil change, carefully inspecting the oil removed, good enough? I still have an impeller change and a kill switch on the to do list.... Just need to wait for the tiller and fuel hose connection to check it will run first!

Nos4r2 · 03 June 2013, 21:53

you need to remove the lower unit (ie , drop the gearbox) to change the impeller.

You don't need to dismantle the gearbox

Those compressions are VERY good for a motor that old. Nice one for getting a tiller that easily too

haccor · 03 June 2013, 21:56

Quote:

Originally Posted by Nos4r2

you need to remove the lower unit (ie , drop the gearbox) to change the impeller.

You don't need to dismantle the gearbox

Those compressions are VERY good for a motor that old.

Excellent. That makes complete sense. Thanks for clearing that up nicely!

That's good to hear, I though they seemed pretty good.

Jake

haccor · 03 June 2013, 21:59

Quote:

Originally Posted by Nos4r2

Nice one for getting a tiller that easily too

I owe you big time for that, so thanks. Sent an email to the guy on eBay and he sorted me out. Called him and he was a REALLY knowledgeable and friendly chap- I feel it got it for a very fair price too.

Nos4r2 · 03 June 2013, 22:02

No worries, I hope you have fun with it!

Ref the manual, I haven't seen a pdf manual for it anywhere. I'd have one if there was one available free

haccor · 05 June 2013, 12:42

Quick update- a bit of further progress on this...

I have stripped the wiring and flywheel off, and gave the block a quick wire brush in the view to wack a bit of paint on to protect it. I need to do some minor repair work to the switch box loom- one wire has snapped which I will try and cut back/repair, and I'll check the state of the other wires and shrink wrap as necessary. I was going to attempt to remove the resin and solder all new wires on, but decided this is too risk and, at the the moment, not really necessary.

I have removed the lower gearbox unit and ordered a new impellor. The old one looked okay, but I'm taking no chances! The gearbox came away no problems and hardly has any surface rust on the shaft. No rust at all on the shaft as it meets the engine at the top, so that's a relief. The gearbox oil has been drained, and there appears to be zero water and zero bits of fine metal. New quiksilver oil on the way.

The tiller turned up today and looks a great fit, but has made me realise I need another part (the bit that joins from the square shaft in the engine, to the external tiller connection). Silly me!

Oh and I managed to get a manual for around £2.50 which I was happy with. Cover engines from 1965-1991 2hp-40hp. Bought from here:

1974 Mercury 200 20 hp 2 cyl Outboard Service Manual PDF Download

Thanks for all your help so far. I will try and upload pictures when finished.