Worn rings on ysm8 yanmar?

[Compass790]

The proper cure for excessive oil pump rotor to cover plate clearance wear is to skim the face with a milling machine where the oil ring/cover plate sits. Or if you are underfunded/cheap like me you can file or oilstone it down. Dont rush in to replacing rotor assembly as that usually isnt the problem.
CORRECTION: Proper cure according to Yanmar mafia is to replace PTO case. The price was about US $500 here. I laughed & said "I can buy a whole used engine for that"


I'm surprised your oil pressure alarm squeaks at 25 psi. Are you sure your pressure gauge is working properly? Ours doesnt squeak at 10 psi but it certainly goes off at< 5 psi roughly. However it just could be/likely to be just sensitive to the pulses from oil pump at low idle. I set idle at about 850 as it's a lot smoother than the factory setting of 650 so maybe the alarm doesnt get time to react?
Doubt that spinning the oil filter handle is vital every time but should be done often.


Re converting to remote oil filter is not necessary as the engines last nigh on 40 years before rebuild, I did it because you get finer filtration & it gives me the warm fuzzies making an improvement for very small cost as a buddy gave me all the hose & fittings.

I would definitely check your oil pump clearances as its easy to do, well as easy an anything can be on a little boat engine no room. Obviously the oil pump is vital to engine care/longevity.


As for oil don't sweat it too much IMO, I'm running 20w-50 CF4 currently but used 15w-40 CH4+ in the past. IIRC changing from 15w-40 to 20w-50 the hot oil pressure went up by 5 psi.
I run 20w-50 as one main bearing has excessive clearance due to machinst error Dont ask who the machinist was


trust you to find something I missed Wottie! good call adding leaving on compression stroke

[Wotname]

I concur with Compass790 on all points above. The low pressure switch should only operate <5psi. 25psi at warm/hot idle is fine (assuming gauge is correct?).
Heck, I have 50 year old tractor that drops to almost 0psi at idle after working hard for a few hours but goes right back to 25psi above 1000 rpm and 35psi above 1500 rpm. Solution - I don't idle it when its really hot.

I also agree that the oil pump rotors won't be the problem, the alloy casing wears faster than the steel rotors. A new alloy casing (front cover in Yanmar talk) is unlikely to be available but if it was, you could buy a new boat for less!

Referring to the pictures - the shaft hole (red circle) wears and becomes it becomes a sloppy fit with the shaft. This allows the rotors to unevenly wear the bottom surface (yellow arrow). Also causes wear to the top cover (not shown).

I had the hole reamed out so it was circular again; the wall thickness is too thin to bush it (IMO). Then made a new rotor shaft to fit the new hole. Then had the bottom surface (yellow arrow) machined so it was smooth and square again to the wall. This necessitated the top surface (green arrow) to be machined in order to maintain correct rotor end clearance. The end clearance is critical for the rotors to maintain pressure. This meant depth on the O'ring groove was smaller but rather than try to machine it, I fitted a skinny O'ring. I also made a new top cover out of some 6mm aluminium stock but this wasn't really necessary.

Final rotor and end cover measurements were all good.

But I concede it was more expensive than the Compass790 method!!!

[Wotname]

You should occasionally (say every couple of years or 500 hours) pull the oil filter out and clean off the accumulated gunk on the filter and inside the housing. It can be surprising what ends up in there!

Shown is a cleaned filter and some of the worst debris I have seen in the filter housing. I have no idea how this stuff managed to get inside the engine and passed through the pump but it was there!!!!

[Atcowboy]

Originally Posted by Wotname

You should occasionally (say every couple of years or 500 hours) pull the oil filter out and clean off the accumulated gunk on the filter and inside the housing. It can be surprising what ends up in there!

Shown is a cleaned filter and some of the worst debris I have seen in the filter housing. I have no idea how this stuff managed to get inside the engine and passed through the pump but it was there!!!!

So far I've changed the oil twice, and each time I have cleaned the filter out. I change a spin on every time, this isn't much more work than that and gives one an idea of things happening in the engine.

So I did a nice long motor out to aquapalooza today. 2.5 hours or so at ~3.5kts. The head and near the thermostat/water out was about 35°c. The accessory case on the front was about 55°c. The very top of the engine where the oil I believe exits to go to the head was 63°-65°c.

-AT

[Compass790]

terrific posts Wottie
You said in earlier post I know all the oil pump tricks but more accurately I knew all the oil pump tricks.
Dunno how I forgot the nightmare of the egg shaped rotor shaft hole caused by a bit of big- end bearing shell chewing it out.
Anyway you have armed Atcowboy with all the necessary info. now.
My guess his rotor shaft hole could be ok.


Atcowboy another tip for you is if you chuck some new rings in you should replace big-end bearing at the same time as yours is old, or you can at least plastigauge it.

[Compass790]

I'd be checking your thermostat, havent checked the cylinder head temp but I certainly cant leave my hand on it after a 2 hr run.
Oil temp sounds about right. I've measured it at the remote oil filter at about 60oC
You definitely have a problem with prop, motor or gearbox going that slow.
Hard to diagnose without a tach tho.

[Wotname]

Yep, the 35C is too low IMO, should be more like 45 to 50; time to check the thermostat!

You can use your smartphone as a tach if you use the StrobeLight Tachometer app. Paint a white stripe on the PTO shaft pulley and go at it with the app.

[Atcowboy]

Originally Posted by Wotname

Yep, the 35C is too low IMO, should be more like 45 to 50; time to check the thermostat!

You can use your smartphone as a tach if you use the StrobeLight Tachometer app. Paint a white stripe on the PTO shaft pulley and go at it with the app.

I didn't know there was an app for that! I was planning on a slow motion video and manually counting revolutions.

3.5kts was average over the whole time, and not WOT. I guess it's nice to know there may be more speed there but that's about all I could muster last year after haulout/clean bum.

- AT

[Compass790]

Given yr sailing speed is 6 knots ( very close to ours ) you should be able to get 5 knts at a bare minimum with a clean bum & flat water. We get 5 knts ( overpropped) when motor is only putting out 5hp according to factory power curve. Anyway when you get your app up & running we'll see what sorta revs you are achieving.

[Compass790]

Atcowboy I ran our ysm8 today at the dock & the head didnt get as hot as I thought
I usually touch the injector or the rocker cover & they are lot hotter than the actual head. Not as hot as front PTO case either.
This was only a 25 min run so dunno if its long enough to get a true pic but it was under load.
To cut a long story short I'm not as sure as I was that your thermostat is faulty but it still should be checked as it could be a contributing factor to your white smoke problem.'
You dont have any water in the fuel do you? Fuel fill cap o-ring ok?
Water in fuel can cause white 'smoke' too.

[Halifax Sailor]

Sorry to bring up an old post, but ran into an issue I am confused about. Pics attached. When I put my ysb 8 away last year I has developed an oil leak. Let me go back......I overfilled the il, had a small run on condition. I stopped it quickly but have developed a small leak. When I put it away for the season, had a good look and I see a small white ring, on the governer shaft? when I run the engine at more than 1200 rpm's I get quite a leak. I am wondering: 1) did I fill the hose that runs from the breather to the intake and now fumes cannot pass so pressure in the crankshaft? 2) I have checked the valve spacing since, no issues 3) is the white ring out of place? I have never noticed it before, according to schematic it says a dust cover.

Looking for any info as the weather is improving and I am going to tackle it.

[Wotname]

Originally Posted by Halifax Sailor

Sorry to bring up an old post, but ran into an issue I am confused about. Pics attached. When I put my ysb 8 away last year I has developed an oil leak. Let me go back......I overfilled the il, had a small run on condition. I stopped it quickly but have developed a small leak. When I put it away for the season, had a good look and I see a small white ring, on the governer shaft? when I run the engine at more than 1200 rpm's I get quite a leak. I am wondering: 1) did I fill the hose that runs from the breather to the intake and now fumes cannot pass so pressure in the crankshaft? 2) I have checked the valve spacing since, no issues 3) is the white ring out of place? I have never noticed it before, according to schematic it says a dust cover.

Looking for any info as the weather is improving and I am going to tackle it.

HS, as you have correctly identified, the small white ring you can see is a dust cap designed to keep stuff from getting into the roller bearings inside the case. See attached diagram which is from the YSM service manual. The YSB has the same arrangement.

Oil shouldn't be coming out of there but I speculate the crankcase was over filled sometime in the recent past and a 'sufficient' amount of oil found its way into the two roller bearings and spacer. While gravity would cause the bulk of the oil to drain back, the inherent pulsing of the crankcase pressure in a single cylinder engine could be forcing the residual up past the dust cap.

The crankcase vent hose could be blocked but that is easy enough to check.

I would be tempted to run the engine at higher revs (say 2500 plus) for a few hours and see if the leak 'disappears'. Also try running it with the crankcase vent hose removed and note any changes.

Note, if you ever need to remove the governor arm, the securing pin is tapered - it only comes out one way!

[Halifax Sailor]

Thx for the advice. It didnt seem like the leak was under pressure so I figured it was my fault for being over exuberent with the oil. Learned that lesson!! It has had all winter to drain so maybe there won't be much left in there and I did remove that hose and it appears clear (ran a brush thru it), so does the nipple to the intake and the nipple from the crankcase vent. Thx again and I will let you know.

[Wotname]

There is always some pulsing crankcase pressure in a single cylinder engine unless the crankcase vent is HUGE. If you open the oil fill and put your hand over it, you will feel the pulsing pressure. While the average pressure should be relatively zero or close to it, the single piston moving in and out does create a pulse of pressure on each revolution.