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PostPosted: Wed Aug 01, 2012 8:34 am 
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Am restoring an outboard engine at the moment, an Eaton's Viking made in Southend on Sea and I get from various dates on it, it was built in 1955, it's a two stroke so requires and oil/petrol mix, but at what proportion ?

Way back two strokes ran on various ratios of petrol and oil, I have seen 16:1, 25:1, 32:1 and 40 parts petrol to one part oil, but with those other engines I have been able to find documentation, but this Viking, I am finding nothing about it, yet I know the current mix that is being used is the reason I am repairing the machine, too much oil.

Now I understand since these ancient machines were first designed and used lots has changed, octanes of petrol and performances of oil and I have in the past stuck to the Stihl mix of 50:1 for everything two stroke using Stihl two stroke oil with bog standard supermarket 95 RON and never heard of engines failing, but maybe I just was never told. So what to do about this Viking, I know the reason I am repairing/restoring it is because of too much oil, in that the heavier molecules of oil have blocked the action of the Zenith 13T carb and lowered the octane of the petrol but the question, should old oil mixes be used today, I understand the owner of the machine has been using his standard 20:1, not information from any manual, but what he has always used on the rest of his two cycle machines not as old as this one.

I am thinking modern fuel has got worse, too many not so nice additives in it ethanol and other nasties in some cases and octanes have been lowered, in the case of a two stroke, the adding of oil reduces the octane further, but modern two stroke oil is far better than oil in the 1950's, so is an elder fuel /oil mix really necessary.

What do people think, use a modern mix of say 50:1 using high grade two stroke oil like say Stihl or use a mix from the past with modern ingredients ?.

I understand in marine environments it is common to use 100:1 now because of what water exhausts might be doing to what lives in it.

After I have sorted this Viking, I have a 1950's Clinton and a Seagull of unknown vintage to sort out, this guy likes his old engines.


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PostPosted: Wed Aug 01, 2012 11:14 am 
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Based on my experience tuning older 2-strokes for mopeds (mainly the Honda MB/MT/MBX/MTX models), I'd suggest staying away from anything synthetic or semi-synthetic.
These oils tend to require higher temperatures and more modern engine materials and tolerances to work properly. On an older engine, those synthetic-based oils simply wouldn't lubricate the piston and cylinder enough.

As for percentages : for regular engines I always used 2% oil (50:1). Tuned street engines used 3% (33:1) and racing engines used 4% (25:1).

To clean the engine, I would occasionally ride until the tank was nearly empty, then put in a liter of a special mixture (96% regular fuel, 2% oil, 2% nitromethane). Once that was mostly used, I'd fill the tank with its regular 2-stroke mixture again. My engines would usually last 20K miles before needing a rebuild, which is way more than the 10K miles that Honda claimed they'd do.


Of course your engine may require more or less oil than what I normally built. RC 2-stroke engines tend to need 20+% of oil, but then again those are really tiny, have an extremely high power/displacement ratio and run on methanol-based fuel rather than petrol-based.


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PostPosted: Wed Aug 01, 2012 12:06 pm 
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Start at 25:1 and if this is too rich and fouls the plug try 40:1, if not leave at 25:1 :wink:

Oh and don't use the cheaper supermarket fuel as it's crap for 2 strokes :wink:


Just had a look at what ratio a BSA Bantam(1948-1970) and the experts say 25:1 with any reasonable 2 stroke oil :)


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PostPosted: Wed Aug 01, 2012 12:47 pm 
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Storing and cleaning the fuel circuit I have always used STABIL a fuel stabiliser from the US, it treats 40 gallons and keeps it usable for 24 months as well as stopping varnishing, gumming etc. There is a very STABIL like smell to the exhaust gas when an engine has it in.

I think from what you have both said and the fact that this motor is 1950's i.e. pre unleaded fuel which (burns hotter), I will be going for 25:1. But it is not so much the plug fouling as too much oil stuffs up the carburation due to bigger oil molecules slowing or even blocking the drillings and jets in the carb, which then leads to incorrect mixture in the combustion chamber, but fouling on old engines I have always found to be down to incorrect tuning. Also when the octane rating is lowered which the presence of oil does, this can lead to fouling, so getting the right ratio is pretty crucial.

But the lowing of the octane rating by oil is an interesting one, as one could read a specification of fuel as being one number, then add oil and effectively lower the octane rating so the engine is not performing at it's best. I read elsewhere, trials were down by Husqvarna I think and they found what was considered an acceptable fuel/oil mix lowered the octane of the petrol by about 15 to 20 %, which on motor required for performance, is a real issue as an under performing engine can be a pita, and not only poor performance, but starting the thing can be erratic leading to issues of flooding.

As to supermarket fuel, yes, I know it's crap, with trials on my '94 clio 1.4, I get better mpg and a smoother running motor by using Shell, but recent trials on supermarket crud, I got 54mpg urban driving using my vac gauge.

It is only when one goes into what makes up petrol, one wonders, as some outfits are blending chemicals that actually harm engines in them, therefore it can be false economy buying bargain basement supermarket fuel, as what savings made could add up in repair bills and premature failure.

Oh and one final point, garages have seen an increase in repairs involving the induction on engines since the introduction of unleaded fuel, that being the lead in the fuel was a lubricant and it reduced is a problem and unleaded is not lead free, just seriously reduced lead and other additives combined to make up the short fall, but there is nothing like lead as a lubricant it seems.


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PostPosted: Wed Aug 01, 2012 6:24 pm 
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I know that the more oil you put in the lower the octane level.

We run 150 Ktm's @ 75:1 with 102 octane race fuel and have rebuild them very 5 to 10 hours it's the only way to make them go, bit expensive though :shock: :wink:


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PostPosted: Wed Aug 01, 2012 9:07 pm 
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modern fuels have a high percentage of benzine in them , this rots injectors/ carbs and associated plumbing so god knows what it will do to an old motor
as for oil castor based oils would be kinder to them ,but semi syn seems good for my old strokers lc yams ,non plated bore motors

what actually failed on this motor silverclaws ? did it seize or hole a piston ?

might just need a size up on the main jet


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PostPosted: Thu Aug 02, 2012 1:38 pm 
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The motor like all the motors in the place I work are dump finds, a whole plethora of mid twentieth century stationary engines and outboards the blacksmith seems to collect with the idea of getting them going but is vague as to what purpose they will be put beyond just having a collection of old stationary engines with no application.

But this motor being an extreme rarity is of particular interest in that no one has heard nor seen one and even the American's with their vintage Easton's Vikings deny they were ever built in the UK let alone Southend on Sea and it's appearance does not match anything they know of, yet it us a Viking outboard made out of aluminium which would fit post war UK production constraints ( the same reason why Land Rover went with aluminium, lots of it about post war, but steel was rationed).

This thing is traditionally British in design, an over engineered lump with a water jacket uptake pump that can be run dry as it is not a rubber vaned affair particular to nearly every other outboard, but an archimedean screw, the same principle of operation as the archimedean screws used for irrigation, and the gear box on this thing has an inspection port requiring EP-90, it has more in common with a land based machine than a machine used for marine use and all that powered by a piddly little two stroke.

But my effort which was more interest than anything else, I got the thing to fire and run for about half a minute, the longest it has run beyond a few puffs of smoke, but concluded the reason why it would not run properly was because of the fact that compression was being lost through worn crankshaft bearings, it was audible and in water, bubbles coming out of the exhaust spelled the same. I am confident the carb now works, I had to do a gen up on the principle of operation of a Zenith carb which did me good, but found the carb flanges to be warped, so these were flatted and new gaskets made. The ignition is fab what a spark so no problem there and the cylinder bore is unmarked, so the correct lubrication has been used in it's former life, whatever that lubrication ratio was. The induction I am confident now performs, leaving only the crank to sort out and last night at about seven pm I left a report for the blacksmith giving my findings. Piston rings, well it will surely come to that as well, but they might be a bit more difficult given we can find no data on this thing, but I will have a go.

If he is really interested, I will rebuild it, my labour is free, but he can buy the bearings and seals and with crank bearings replaced I am confident it will perform, it is an impressive little machine and as far as I can ascertain unique. It just happens the Blacksmith has an old boat that needs an old engine, the boat a Fairey something or other built with what was WW2 Motor torpedo boat hull technology and the fact that outside the smithy is an old WW2 gun boat is testimony to his interest in these things, it would be nice to get an odd engine working for an odd boat owned by an odd person who now has another odd person working in his smithy.

As it is the Blacksmith has offered me an apprenticeship to train as a Blacksmith, he says he needs to pass on his trade as is traditional with Blacksmiths but so far of all the helpers he has had no one aside from myself has shown any aptitude for the job, but then I have a metallurgy grounding in that I have been an amateur silversmith and jewellery maker for twenty odd years, blacksmithing to me is the heavy metal side of metal smithing and heavy metal and now death metal pumps out of the smithy speakers, bashing hot metal to Ramstein and now Haggard.

As to the engine repair thing that blacksmiths are asked to do from time to time, I was a plant and small tools repairman for ten years prior to my falling apart five years ago, so being apprenticed my machine repair skills will undoubtedly enhance the business.


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PostPosted: Thu Aug 02, 2012 2:51 pm 
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What a refreshingly positive and interesting post from SC! I have little real knowledge of what you are talking about, but it's definitely one of the brighter things I've seen you put on here. Great news about the apprenticeship too. Like you say, something to get your silver claws into :D


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PostPosted: Thu Aug 02, 2012 10:11 pm 
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if you get stuck with the piston rings you could get sleeves fitted down the bores an use slightly smaller pistons
as you would be using new pistons you would then have a better idea of the oil fuel ratio


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PostPosted: Thu Aug 02, 2012 11:32 pm 
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dan28 wrote:
if you get stuck with the piston rings you could get sleeves fitted down the bores an use slightly smaller pistons
as you would be using new pistons you would then have a better idea of the oil fuel ratio


True, but putting sleeves and smaller pistons in a 2-stroke engine is a bit more difficult as opposed to a 4-stroke. The latter don't have ports to worry about.
With sleeves you'll either change the port timing or disturb the airflow at the top and bottom of the ports.


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