Yamaha 8hp 2 stroke oil 'leak'

[bluetooth]

Doing fresh water run up before taking to boat. Noticed quite a bit of oil in the bin water and on removing noticed an oil covering above the anti cavitation plate. Now I had been running 50-1 but changed to 100-1 end of last season so is this just some, well a lot, excess oil build up. Had noticed not running as well with the petrol change and chaging to E5. Had full service last summer so all the internals etc have been cleaned. It also splutters a bit at times and on initial start up was quite smokey but has settled. Any thoughts?

 

[bluetooth]

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[SC35]

Oooerrr, that is a lot of oil.
Many two strokes had 100-1 stickers plastered on them for Eco reasons, but were in fact designed to run on 50-1.
Did you give the tank a REALLY good shake before starting it?

If so, and the fuel is fresh, then it could be something internal that is messed up, e.g. crankcase seal, piston rings, reed valves etc.

 

[colhel]

Could it just be oil sat on top of the water? Was it running for long in the tank?

 

[bluetooth]

Could it just be oil sat on top of the water? Was it running for long in the tank?

Yeah it was in tank for 30 mins or so. Lots if stopping and starting

 

[Macka1706]

I had 15hp Yammie for yrs for dinghy. Are you sure it's the fuel mix. oil.
The drive shaft has 2 oil seals inside leg (back to back. $27 the set here) When older they can go. Check the gear oil. is it low or water clouded???. Just a thort. That will float to top and rim the same if shaft turning..
PS ALWAYS run engine/Carby to stall point when finished. Otherwise oil in mix. IN CARBY. will solidify over time,and interupt fuel flow.

 

[Portofino]

Its either splunge *or possibly a gearbox crank seals gone .Assuming it had a rudimentary g box ( F- N -R ) ? .
Give it an Italian tune up to bow it out for now .

For g box ck replace the oil with clear ish fresh ( carefully measure the vol ) and after a few runs drain it to ck the colour .If its appreciably darker AND the vol a lot less then it’s the crank seal .

* Splunge is excess 2 T oil building up the exhaust and leads to a black slimy excrement. It wasn’t hot enough to burn properly - too long running at low rpms ? , or it’s vol ( the mix too great ) or oil entering on part of the 2T cycle from the bottom end crank seal that’s gone …usually the gear box side .

Its not a show stopper but do check the g box oil level periodically and top up if necessary if it’s the crank seal .= A winter rebuild beckons .

 

[colhel]

I'd be surprised if gear oil would be as black as that bearing in mind too, the engines service history

 

[Portofino]

I'd be surprised if gear oil would be as black as that bearing in mind too, the engines service history

Sucks it through the duff crank seal one part of the 2T ( the lower end ) cycle …..then it’s transferred to the upper end and semi burnt off .Results ( despite the 100/1 fuel mix ratio ) of excess semi burnt” splunge “ in the exhaust.

Part of the lower case 2 T cycle a fraction of a sec there might even be positive pressure ….momentarily some gases or unburnt products of the upper case combustion gets down below , depending on porting efficiency and just might go the other way through the seal , hence my suggestion of checking the g box oil colour ……as it could rapidly darken .

If it’s been sat about unused the resultant excess oily contents of the crank case separate out .Hence at restart the oily mess in the exhaust, and my suggestion of a good Italian tune up to get some fuel + heat through it to clear it .


As I said ck the g box levels , ck the g box oil colour .If not only to eliminate , reassure it’s not a crank seal .

The oils come from somewhere and @ 100/1 or even 50 /1 , the fuel or carburettor mix is unlikely. Unlikely as the op reports the thing starts OK ish and runs ok ish .

Needless the plug will be black FWIW .

You could argue 2T crank seals go on a spectrum , ie it’s not binary…..they all end up leaky to one degree or other .
You call time on them declare rebuild when it s diff to start , excess plug fouling, poor running ( as the fuel oil mix in increasing ) or the mess the splunge makes .The throttle response becomes erratic as it won’t quite get up the rev range .

Pot pot pootling around at low rpms masks this ^ .But exaggerates the splunge build up as it’s not blown out , nor hot enough to burn fully away .

 

[bluetooth]

Thx for comments peeps. Have dropped off with engineer as I just want to make sure all is fine for the season. He thinks its just a build up of previous excess oil but will check in next few days. I'll report back. Cheers