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Old 12 August 2020, 15:34   #1
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Country: UK - England
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Yamaha 75hp reiiability/rebuild costs?

Hi all,

Have been a long time lurker on here whilst waiting for a deal to go through with a 7m rib that I was supposed to be getting. This unfortunately fell through and to 'tide' me over, I have had a look at a little speed boat (i know, i know) and wondered what the reliability of the yamaha 75 outboard is like?

It is a very favourably priced boat for a 'quick sale'. One owner from new (2002) but admits that in the second half of ownership it hasn't been serviced as often as it should have. He said everything runs as it should although the trailer needs attention.

So my question is, how robust the engines are? I'm happy for the reduced price to be because of niggles that I can fix including trailer etc but I don't want to get caught out if later on I find the engine needs work. As a worse case, if it required a rebuild, what would this cost?

I realise this is quite an open ended question but i'm just trying to build up my knowledge of the engine rather than buying it blind.
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Old 13 August 2020, 03:12   #2
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Country: UK - Scotland
Town: Aberdeenshire
Boat name: Sula
Make: Ribcraft 4.8m
Length: 4m +
Engine: Tohatsu 60hp + aux
MMSI: 235087213
Join Date: Jun 2007
Posts: 3,969
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They are robust. Based on Yamaha 90 block, 3 cylinder 2-stroke. In service with RNLI usually set up as twins, etc.

Before spending anything on the engine, you need to determine its current health. Start it from cold and see how it idles. If the carbs are in sync it'll purr like a kitten after the usual throaty start (will need choke to start). Don't worry about smoke at start unless it's excessive, that could just be oil residue in the carbs.

Also get yourself a Draper compression tester to test cylinder pressure £20 or so. More details here: https://www.boatus.com/magazine/2016...ard-engine.asp

What you're checking here is the cylinder compression is equal across all 3 cylinders, give or take 5-10 psi or so. Anything greater, then you're looking at new piston rings or cylinder sleeves.

Assuming that turns out well, then factor in a full service. It's entirely possible to do it yourself but if your not mechanically minded, put it to a marine engineer.

1/ Drop gear oil to check for emulsification (sign of water entering gear box). Can be pressure tested to identify source of leak. Refill with fresh oil and new fibre washers.

2/ Replace impeller, visual check of water pump today see if scoring.

3/ Remove propeller, grease prop shaft and thrust washer, check for fishing line or other debris that can cause issues. Check propeller. Slight dings are fine, anything untoward then ship it off to Steel Developments to be balanced and repaired. New stainless steel split pin on fitting on castle nut.

4/ Drain carbs. On the engine undo the brass hex nut on each carb drain reservoir and inspect contents. Petrol and oil is fine. Any sediment, then carbs need stripping and cleaning.

5/ Remove thermostat and check water passage. Chances are there may be a sacrificial anode in there too. You can test thermostat in boiling water. New gasket required for refitting.

6/ Check sacrificial anodes (trim tab on anti cavitation plate, and under power trim unit). If serviceable, wire brush and refit, if like Swiss cheese, then replace. Don't use grease, dry contact required.

7/ New spark plugs, ensuring you don't just copy what's on the engine. Check with Yamaha for plug specification.

8/ Remove and clean fuel filter on engine.

9/ Check the electrical connections. Not unusual for bullet connectors to loosen or corrode. Especially 10mm nuts to starter motor live and earth points.

10/ Spray light coat of white grease on linkages to carbs ensuring safety R clips are in place.

11/ Grease gun with suitable marine grease on all grease points.

12/ Check battery condition with multimeter. If in doubt replace.

13/ Check fuel tank, hose and connectors (including 'o' rings and fuel primer bulb). If primer rubber pull feels hard to press then replace with genuine Yamaha or Quicksilver part.

14/ Check power trim fluid level and that it raises and lowers properly. Use ATR Dextron fluid, again check specification for Yamaha

15/ Check 2-stroke oil level, top up with Yamlube or Quicksilver

16/ Dismantle air box intake to inspect carbs and clean any oil residue. Also useful check of choke

There's still value in a Yamaha 75hp as its a mid-sized engine, and suspect that's where the value is, not in the boat or the trailer.
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Old 13 August 2020, 04:22   #3
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Country: UK - England
Town: PORTSMOUTH
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Engine: Yamaha 60FE -
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Brilliant advice above
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Old 13 August 2020, 04:36   #4
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Country: UK - England
Town: Winchester
Boat name: The Bandit
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Engine: Yamaha 90 2-Stroke
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Really useful service adice there Spartacus - many thanks.
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Old 13 August 2020, 09:29   #5
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That was an incredible response. You sold the boat to me that knowledge. Unfortunately, I was too slow to the post, the guy didnt reply to my second message yesterday and unfortunately he has now marked it as sold!....im not bitter in the slightest...!

Thanks again for the response and if anyone has a rib or speedboat for sale thats a decent size and fast arojnd £4k....let me know!!

Thanks again
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Old 14 August 2020, 06:12   #6
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Country: UK - England
Town: Godalming
Boat name: Bumblebee
Make: Avon
Length: 4m +
Engine: yamaha 40hp 2stroke
Join Date: Oct 2017
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I think a smoky start is the norm with these yammy 2 strokes. Only cold starts mind you. But that's fantastic advice. Going to follow it when I'm rebuilding my engine. Thanks a lot Spartacus
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Old 14 August 2020, 15:07   #7
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More important than any of the above is the condition of the gear shift rod and on pre 96 engines the gearbox casing.
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