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Old 29 June 2022, 07:52   #1
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Yamaha 6EO FOUR stroke!!!?

Hi,
I recently had an interesting 'buying adventure' on Facebook Marketplace.
My brother said, "you should stick it on the forums, the old men will s@@t themselves." So here it is.
Last night I bought a very clean looking early 80s 6EO (4 hp two stroke) Yamaha short shaft. The conversation at purchase went as follows:

Me: nice looking engine, what oil mix have you been using in it?
Vendor: What what mix?
Me: Two stroke oil mix, you know, in the fuel tank?
Vendor: It's a four stroke, I've been using it for the last Ten years and never put any two stroke oil in it. I bought it BECAUSE it's a 4 stroke and nice and quiet. The guy at work who I bought it from had it from NEARLY NEW and 'ran it as a 4 stroke' too.
('Work', additionally amusingly is a very well known UK builder of luxury motor yachts.)
Me: Do you see that sticker
Vendor: What sticker?
Me: the one on the front of the engine that says 100:1 with a graphic of a drop of oil next to it.
Vendor: It CAN'T be a 2 stroke. I've used it for the last Ten years, mostly flat out with no oil in it. It would have blown up.

A long discussion then took place with me showing where the reed plate was, suggesting that there might be somewhere to put 4 stroke oil in it if he was correct etc. Eventually, he realised and reluctantly admitted the error and a large re-negotiation on price took place. Perhaps I should have walked away, but I bought it, just out of interest to see if it has actually survived the experience.

Compression test and recommissioning today if I get time. I've bought it at parts value, but it seems to be running absolutely fine in a bucket, although I didn't let it run for long once the penny dropped.

I read a long discussion on either here or ybw, perhaps both about how these engines really must be run at 50:1 etc. Puts those sort of worries into perspective I think!

I wonder if I should ease it into premix? Maybe 800:1 for the first couple of weeks? (Not a serious suggestion)

Perhaps there might actually be something in the general consensus that 2 stroke Yamahas are bulletproof?
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Old 29 June 2022, 08:24   #2
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WTF! 135psi
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Old 29 June 2022, 08:34   #3
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We've got to get some fluids into this one, nurse!
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Old 29 June 2022, 09:51   #4
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Not sure who's doing the wind up here.

We all know that motor wouldn't have lasted five mins without oil never mind ten years.
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Old 29 June 2022, 11:46   #5
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To be honest that doesnt look like its done much as all through its life, I doubt the seller ran it much if at all. Maybe he did the odd short run where it never warmed up enough to come to harm, the crank bearings are ball & roller bearings which can run a very long time without oil. If its got good compression & runs & sounds ok I think you won a watch.
Even 4 stroke engines ran without oil rarely seize on the bores its always the cam or crank that nips up first
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Old 29 June 2022, 11:50   #6
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>>>Maybe he did the odd short run where it never warmed up enough to come to harm

I can only say that's contrary to my experience with 2-stroke motorcycles seizing very quickly with no oil.
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Old 29 June 2022, 11:55   #7
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Quote:
Originally Posted by Fenlander View Post
>>>Maybe he did the odd short run where it never warmed up enough to come to harm

I can only say that's contrary to my experience with 2-stroke motorcycles seizing very quickly with no oil.
Motorcycle engines are far more highly strung than an outboard, often turning 10k rpm + with limited cooling available its friction that causes the heat & heat that causes the sieze if this has 135psi compression its unlikely its been siezed
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Old 29 June 2022, 12:54   #8
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>>> its unlikely its been siezed

And that's why I think the whole back story is rubbish. Re-reading the OP it seems the claim is this 40yr old outboard has always been run without a sniff of oil virtually from new.
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Old 29 June 2022, 15:32   #9
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>>> its unlikely its been siezed

And that's why I think the whole back story is rubbish. Re-reading the OP it seems the claim is this 40yr old outboard has always been run without a sniff of oil virtually from new.
It possibly is all rubbish, my guess is the seller got caught out saying a two stroke was a 4 not really knowing the difference & rather than admit his mistake tried to brazen it out by saying the previous owner thought it was a 4 stroke too. The engine looks next to new, little used & by the sound of things the seller probably has run it without oil for an unknown period but as the compression is good the likelihood is the crank & bearings will be good so the buyer probably won a watch.
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Old 29 June 2022, 16:59   #10
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I,m with FL on this one. If this is a 6EO it is a 2t. Having owned 2t motorcycles for 50 odd years (still have two) there is absolutely no way that could have run without oil for more than a minute or two before siezing. I would not even start a 2t without oil even just to check that it would start.
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Old 29 June 2022, 19:23   #11
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Years ago my mate had a 55HP Yam 2 stroke premix, he forgot to add the oil into the 25 litre tank, ran it for a couple of hours before he realised, no damage was done and the engine ran fine afterwards
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Old 29 June 2022, 19:36   #12
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Quote:
Originally Posted by FoxZulu View Post
I,m with FL on this one. If this is a 6EO it is a 2t. Having owned 2t motorcycles for 50 odd years (still have two) there is absolutely no way that could have run without oil for more than a minute or two before siezing. I would not even start a 2t without oil even just to check that it would start.
Two stroke bikes can sieze with lots of oil never mind no oil, totaly different kettle of fish to a water cooled low po outboard.
Years ago we tried to deliberately seize a car engine, dropped the oil sat a brick on the accelerator pedal and waited for it to stop. 3 times we did that & each time it restarted once cooled & ran quiet untill the third time when it started to knock. Every car engine ive seen thats been run with no oil has siezed the crank ir cam first I'm not saying that its ran hard for 10 years but it does sound like it has at least been test run with no oil & survived
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Old 29 June 2022, 22:51   #13
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If I can be bothered tomorrow, I will write a diatribe on this subject as I do have a lot of experience.

For now though, I will just say that all engines need lubrication regardless of cooling or power output. Metal against metal will fail without lubrication, end of.
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Old 30 June 2022, 06:08   #14
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Only way to to verify is to go and run that engine without oil and report back.

Ultimately, that would be a waste of what looks to be a good engine and in reality, the chap has either sniffed too much boat glue, his mum always filled up the outboard for him or he stole it.

If his mate had run it for years without oil and he had also run it for years without oil then why bottle a sale and sell as scrap just because someone some random punter turns up and highlights something that isn't relevant to you? It seems more likely that the motor was new to him one recent evening and he was very keen to move it along for any cash reward?
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Old 30 June 2022, 07:06   #15
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Essentially nobody knows the history of this motor, only what you've been told which might be true or might be not (highly implausible in my view but then every day's a school day!).
What is true is that it's got good compression - which indicates it's probably OK. Doesn't confirm bearing condition but it's a good indication. Looks in visually good nick too which suggests it's been looked after.
Fill it with 100.1 mix and run it in a tank for half an hour. If it runs well and doesn't knock then it's a goodun. Then give it a good service and use it!
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Old 30 June 2022, 12:19   #16
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One possibility is that the seller was confusing it with some other engine he'd had. Although I did ask him if this was a possibility but he swore blind he'd had no other engine of that size during the time.

It was regularly serviced. I wonder if the place servicing it chucked premix fuel in it each time, and that meant there was some oil in there, just increasingly very diluted. The guy I bought it off used it ten hours total in about ten years, he says. So if the servicing people were putting a dash of fuel in it every couple of years, it might have primarily been running on that?

I ran it up to temperature yesterday. It's fine.
Not sure why the seller would make up lies about it that immediately cost him £200- the difference between what he was asking and what he got for it.

I will add that Evinrude once ran an Etec 2 stroke at WOT under load on a test rig with NO OIL. I can't remember the exact figures but I think it was 10 or 12 hours it ran for before it went bang. And that's flat out and a bigger multi cylinder much more powerful engine. But they had/ have some sort of very special metallurgy going on in the bearings that somehow 'absorbs' oil and can then be run with very low oil ratios. Maybe Yamaha played with such technologies too back in the day? They were certainly interested in reducing oil mix as much as they could, especially with this engine which was 100:1 when all it's competitors were still 50:1.

Additionally, the seller had it on a small inflatable that planed one up, and that was how he used it, he says he used to have fun races in it against other friends tenders. It has the 7 inch pitch propeller on it- this engine also came with an 8 inch pitch option. So I guess it has been running at very high revs too!
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Old 30 June 2022, 13:03   #17
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By the way,
I somewhat resent the comments above that this is lies on my part, the seller's part or that it is a stolen engine!
1) I actually suggested to the seller that he could either sell it to me at half price because of what we'd uncovered, or just keep quiet, put premix in it and sell it to the next buyer at full price because it appeared to be running fine. An honest, proper guy! He CHOSE to sell it to me. Would that, realistically, be the behaviour of someone who had just nicked a motor??!
2) He and the guy he bought it off work in a very well known company in the marine industry. He was genuinely shocked and surprised and not making stuff up! I could trace him in 5 minutes if I wanted to.
3) I am a marine journalist who has just spent the last 3 months as Features Editor of the best selling boating magazine in the UK and before that edited the highest circulation commercial marine magazine in Europe. Neither would it be in my interests to deal in lies, potentially stolen engines or any combination of these!
4) I have been around boats and boat engines for the last 40 years. I talked extensively with the seller about everything he had done with this motor., And we talked a lot about boats in general. Neither he, nor I could understand how it was still running. I can also guarantee the seller was who he said he was, and I am who I say I am!
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