Tower of Power

[BigE]

Hey guys
looking for the low down on these old merc's. I have recently purchased a 2nd hand rig with a 115 hp inline 6 merc it has grey and red stripe on the cowl the engine serial number is OB380727 if that helps to identify the model. seems to be pretty well unmolstered old donk still running the autoblend oil mixing system and doesnt look butchered under the cowl.
she seems to have good compression and runs ok has a tonne of punch in the mid range and has the normal blue smoke of an old school 2 stroke at idle.
Well she is a bit before my time so for those with more experience "whats the low down of these oldies, the good the bad and the ugly" should i keep her or drop another 15G on a newie?

BigE

[BigE]

Nearly forgot I think it's an 89 model

[finga]

The good:
They've got heaps of grunt courtesy of the inline 6.
They're fairly basic so not too much goes wrong
Reasonably fuel efficient if handled with respect...other wise you might as well shove a funnel on top of it.
Strong gearbox

The bad:
Corrosion in the water jackets. If they haven't been flushed well corrosion in the water jackets can kill them
Old...means parts and seals (especially) are starting to let go
Old school...some people just like new things
If something goes wrong with the carbi's balancing the 3 carbi's is an art form.
The wires to the black box seem to have let go of their insulation by now if they've been sprayed with WD40 all their live.
A complete rewire is normal at this age.
If you get a good one it's a good one. if you get a bad one it's scrap.

Other then that I would not part with mine and it's older.
A lot of people would scrap it and out a newer, lighter motor on though.

Has that one got hydraulic trim/tilt or just tilt?

[Steeler]

All good points by Finga, do away with the mixer as the model you have was mercs first crack.

Good idea to replace the bottom crank seal every 500hrs or so if you have an engine crane not such a big job, just don't damage the bearing carrier they can be hard and expensive to locate.

Have the timing backed off a couple of degrees as these thing had a habit of detonating pistons.

Always found they ran better with Champion plugs L76's rather than NGK in them.

Finga if its the last of the inline sixes it will have the internal t/t not the external pump mounted in the boat.

As for replacing i would get a compression test done and these things will still run strong down as low as 95psi per cylinder as long as all are withing approx 7% off each other.

Seen a lot of these things buggered on the driveshaft spline so be sure to be liberal with the nickel anti seize if ever you have the gearbox off.

Like Finga said get a good one and your loughing but get a neglected one and well drop me a PM if you choose to dispose of it.

[BigE]

Finga
She' a trim & Tilt job the TT is internal. what is respectable fuel use on one of these babies?? I comming from a yamie 60 four stroke so i know i'm in for a shock.

Steeler
Thanks for the plug advice ( they look pretty old so i will change em)

What the best oil to use in them and if i pre mix is the ratio 50-1 ??

Thanks guys ( kinda like old school had a couple guys comment on the old girl whe they seen her )

[finga]

At around the 3000-3,500rpm mark we get about 36 km per 25l in the ocean with our 90hp.
We don't push it outside because decrepit old me is the limiting factor/weakest link.
Full throttle dragging a couple of biscuits complete with a couple of young 'astronauts' wanting to be launched you can hear the tank go down.

Any pictures??

[BigE]

Finga
just for you Pic's

signature 1750L and 115 merc.

[finga]

What a nice boat. You must be happy with that

[Steeler]

I'm almost betting that motor was the original fitted to that " Real Haines ".A good friend of mine had the 1550R with a brownband 115hp and it handled like it was on rails.

Thats a top boat ya got there.

[BM]

BigE,

You will be pleased to know that the last of the inline 6 Merc 115's were actually putting out 138hp at the prop!! So if she feels very punchy, you now know why..

50:1 fuel oil ratio if premixing. Premium unleaded fuel and never ever use stale fuel.

Knock the timing back a couple of degrees as mentioned and also fit one size larger main jets in the carbs. This will run you a little richer at high rpm and help prevent detonation.

These weren't issues back in that engines day as the fuel quality was far superior to todays fuels.

Enjoy!, they are a very good engine.

[BigE]

Yep
she was a "find" hull is sweet as. Just ordered a new multi rolla trailer to keep her on. Bloke at the shop said they have a side plate and main seal issue other than that there not bad donks just a tad thirsty.

Big E

[BigE]

another pic.

[BM]

Bottom seals can be an issue for any outboard really. When you do replace the 2 bottom main seals you can actually fit a third seal in there also which gives just a tad more protection from water ingress.

The inner sideplate is the main area of concern for the inlines. If you intend keeping the boat and motor for sometime and given its a healthy looking and sounding motor by your admission, it would pay to whip the powerhead off and remove the outer and inner sideplates. The plates should be reuseable, if not they are still available new from memory. Must be well sealed upon installation (including the bolts) as a water leak here puts seawater straight into the exhaust ports. And whilst the powerhead is off slip in 3 new bottom seals. New powerhead base gasket and you are back in business with only routine annual servicing to worry about.

Speaking of clean inline Mercs, I recently picked up an immacualte 115 Merc, 1982 model. Never seen an inline without corrosion on the trim rams or without corrosion on the tiller arm. Absolutely remarkably clean engine! Just ordered a used crank for it from the US ($500 landed). 1 piston and a few seals and bearings and she will be good to roll again. Bottom seal had obviously let go on this one causing it to fail when laid up. Apparently its lucky to have done 20hrs!!!!

Cheers

[finga]

When you do the top and bottom seal do the cooling plates.
Doing the water jackets is a a bugger of a job if the motor is in.

Gees eh...the old trailer looks pretty spiffy as she sits.
Are you getting a new with brakes or is there rust in the old one?

[BigE]

Thanks for the seal info. are there any warning signs of seal failure i should be aware off? or is a roll of the dice.
The trailer had a rust issue in one rail wear a tie down was left on when wet and the gal has lifted probably a 1-2 foot sectin that needs attention rest of the trailer is pretty good. (new drop axle & Hyd brakes and single gal spring 1400kg) I'll on sell it to some one with time and skills to rebuild, good cheap project for someone.

BigE