reboring 2 strokes

dogboy · 26 August 2015, 08:18

I have been sibing for a few years now with my little zodiac futura and trusty yam 9.9 four, which feels like it will go on forever, but I am now feeling the need for a new experience. Probably in the form of a late 15HP two stroke of the yam/merc/mariner variety.

My question is, most of these are now getting on a bit at 10 years old, so how do they stand up mechanicaly and are many now in need of a rebore ?

As a teenager of the eighties I am used to owning hard ridden two stroke motorbikes, and their subsequent need for top end overhauls. So, are most of the 15hp outboards now soon to be needing this work.... or is it different with a boat engine ? These engines still command a fairly high price and a rebore on top of that makes them rather pricey I guess ! Any thoughts or experiences with this one ?

camelgas · 26 August 2015, 08:50

I too was around bikes during the 1980's RD & DT time and did my own maintenance

.

I have this year split my 90's 2 stroke suzuki OB, a decoke, de-salt of waterways and light hone of barrel was all mine needed.

I guess a compression test before purchase of motor might help to decide.

Working on one should not hold any terrors for you, if you were used to 80's bikes.

Good luck.

Fenlander · 26 August 2015, 10:03

I've owned a large selection of sub 25hp 2-stroke outboards over the past 20yrs. Late 70s Suzukis & Yamaha, mid 80s Mariners, late 90s Mercury, early-mid 2000s Tohatsu, Mariner & Mercury. Sizes including 2/3.5/4/8/9.8/9.9/15/20/25hp. About a dozen outboards in all.

All bar two have been bought privately, half of them with no demo before buying, and they have been between 6 and 25yrs old at time of ownership.

Not one has suffered any issues related to engine condition, just routine service work and the odd carb gasket kit, perished hose, seized tilt lock etc.

It's my opinion that in general smaller leisure use outboards get very little use so suffer minimal wear.

jeffstevens763@g · 26 August 2015, 12:01

last year i bought a 1999 Johnson 2st as a project not my best choice of engine but still, it had running problems which i new was down to a fuel pump issue got it home cleaned her up gear oil, £20 fuel pump re-firb kit new filter & plugs compression test thumb over holes blew it off put it on a zodiac 310 solid went like s--t off a shovel.
total cost £550.00.
as fenlander says private engines don't do a lot they usually suffer the lack of TLC and a good service once a year if used or not i always use wd 40 or similar to keep the salt away and a good quality grease.if buying secondhand see it running in and out of gear,pumping water ok and have a look at the gear oil, also if its tidy under the lid.
your right about the yam it will go on for ever.

cheers

dogboy · 26 August 2015, 20:40

Thanks folks for your thoughts. So it would seem its a fairly safe bet then. I.m glad they don't need the regular rebuilds like the old yam DT's did. It was fun at the time, but these days I'm a touch to busy for regular strip downs.

spartacus · 26 August 2015, 22:29

Unlike a motorbike engine, 2-stroke outboards are likely to suffer seized head-bolts, so the old adage, if it ain't broke, don't fix it certainly applies. In addition, outboard gasket sets can be rediciously expensive. As suggested, check the compression and maintain a rigorous service regime and there should be no need to strip it down.

uncle al · 27 August 2015, 20:10

If you do need a re-bore after all, find F,J,Payne eynsham Oxon. when I worked they did all our re-bores on OBMs, and I have used them on big engines as well, blind boring or just a straight re-bore.

Nightfisher · 27 August 2015, 21:07

Yes, a wet/dry compression test tells it all. Unlike most bikes, outboards are water-cooled above 3 HP. Before buying, even though the seller may say all cylinders are with 10 Lbs of each other never believe. In addition to doing both a wet/dry compression test, using a good light source look into each plug opening and inspect the cylinder head. If there's any sparkling particles on them don't buy it. It's been overheated somewhere along the line.

dogboy · 29 August 2015, 17:21

Lots of useful information. Thanks again to all offering their advice.

Nightfisher · 26 September 2015, 07:52

Sure a reboring's necessary? I mean there is a way to to do it cheap and write. But one who has not done it before needs to on how its done, i.e. skone-pressure, number of turns per minute, number of times to work the skones or stones as some call'm from one-end to the other per minute..so there's a lot of counting involved and all cylinders must be the same. Then there's the rental of a micrometer to ensure diameter even-ness and to know what size rings to purchase. I did it twice, both times successful just really need to read and understand the importance of exact counts per cylinder.