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Old 07-05-2021, 15:32   #1
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Yanmar YSB 8 hard starting

Launched this week. Before launching tested the engine, started immediately as usual even after sitting all winter. After the run up I checked the valves (which may never have been done) engine is a 1978. When I launched motor was hard starting, almost catching then nothing, then finally starting. Once warm starts immediately. Have started twice since, same issue. Starts hard after cranking, but will start immediatelt when warm. Haven't changed filetrs yet, next on my list. Here's what I am thinking.
1) Last year first of the season I was given some "red" diesel about 2 gallons that I topped off my tank. Have since used at least 2 gallons new diesel. Could there have something wrong with that fuel although ran engine quite a bit after getting that fuel and no issues
2) when i checked valve clearances, they were quite wide, set them to .002 as per manual, about half of what they were. Could this have upset easy starting?
3) have checked all fuel lines, can see no issues with cracks but they are at least 8 years old. Maybe time to change?
4) engine runs so much quieter, runs smooth, can get 3500 rpm easy at full throttle, runs smooth at 2250, much better than last year so maybe the valve adjustment helped?

I am thinking maybe filters first then fuel lines. Then maybe the fuel? Or did I screw it up by adjusting the valves?
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Old 07-05-2021, 15:51   #2
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Re: Yanmar YSB 8 hard starting

I think you have read the manual incorrectly, a valve clearance of .002 (assuming ") is way too small.

The correct figure is 0.2 mm which is about .008".

My suggestion is to reset the valve clearance and try some more cold starting.
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Old 07-05-2021, 16:10   #3
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Re: Yanmar YSB 8 hard starting

Do you use a fair bit of throttle when starting from cold?
I find that helps. I would suspect a bit of air in the system for the hard starting if its different than last year. 8 years doesnt sound that bad if the fuel lines are good quality ones but check all the hose clamps. Filters last a long time if you dont have the dinky yanmar engine mounted one as they have tiny fuel consumption.
Also ditto for what Wotname said about valve clearances, its 8 thou in yr system both inlet & exh.
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Old 07-05-2021, 16:15   #4
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Re: Yanmar YSB 8 hard starting

1/2-3/4 throttle when cold starting really helps on those things.

Also your valve clearances are too tight (covered above)
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Old 07-05-2021, 20:03   #5
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Re: Yanmar YSB 8 hard starting

Thanks all. I just checked the manual I have for the engine and ......." it says .2mm" clearance!! Thx to all, I must have read it wrong / used the wrong size gauge. Will reset them tomorrow and let you know. I do use 1/2 throttle to start and usually it kicks over within 10 secs so the hard start was quite a surprise to me, especially when I was in the camber hanging waiting to launch. Red-faced because it had started easy when tested even after sitting all winter (prior of course to the valve reset). Again thx to all, love this forum!!
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Old 07-05-2021, 20:17   #6
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Re: Yanmar YSB 8 hard starting

OK, I will be keen to hear how it cold starts after valve re-adjustment!

However when you says it 'normally' cold starts within 10 secs, that seems quite long to me. Of course it depends on the ambient temperature and when I checked the current temps at Halifax (~ <50F), the 10 secs might be normal (?).

Otherwise you oil maybe too thick or you are slowly losing compression. Maybe pulling the head and doing a valve job at the next layup is on the cards.
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Old 07-05-2021, 20:41   #7
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Re: Yanmar YSB 8 hard starting

The other thing you can try for faster start is spinning it up decompressed & then pushing in the decompression knob as it makes it spin faster.
But agree with Wotname, seems slow starter but not much experience in that ambient. I would suspect compression getting lower as our YSM8 will start virtually immediately in 40oF using decomp lever to spin it up & 1/2 throttle.It has been recond. so has factory compression.

They are not tolerant to any air in the system though.
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Old 07-05-2021, 21:57   #8
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Re: Yanmar YSB 8 hard starting

If it starts easy warm and hard to start cold, everything else equal, a block heater, pan heater,or even a hair dryer blowing hot air into the intake will help starts. A diesel needs to reach 500°F+ to reach the ignition temp of diesel. That is accomplished by the engine compressing the air in the cylinder. Compressing air raises the temp. The warmer the engine is, makes it easier to reach 500°. As an engine wares it doesn't compress the air as much and becomes harder to start in cold weather.
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Old 08-05-2021, 14:54   #9
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Re: Yanmar YSB 8 hard starting

Quote:
Originally Posted by Wotname View Post
I think you have read the manual incorrectly, a valve clearance of .002 (assuming ") is way too small.

The correct figure is 0.2 mm which is about .008".

My suggestion is to reset the valve clearance and try some more cold starting.
Valve Clearance of 0.002 is very small for ANY engine. I agree
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Old 08-05-2021, 16:21   #10
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Re: Yanmar YSB 8 hard starting

If "red diesel" in Canada is the same as "red diesel" in the US it shouldn't make a difference. Red diesel is the same as regular diesel but is dyed red for off-road use; the price doesn't include road taxes (in the US).

If valve readjustment doesn't work, you might try joining the Yanmar diesel group on Facebook. The members their seem pretty knowledgeable. (Not to say the members here aren't )
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Old 10-05-2021, 11:36   #11
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Re: Yanmar YSB 8 hard starting

So, did the re-adjustment of the valves this morning. Used the gauge marked " .2 mm - .008". The engine started a little easier/quicker but still not like it used to before I screwed it up. Used the next one up ".237mm " and it seemed to make a little differnece but thwn again the motor was warm, even after an oil change. So, wondering, is there such a thing as too big a gap? My thinking says yes,no compression, won't start etc. Am I thinking right that maybe a little bigger gap than manual might be the cure? Tightened all the fuel hoses, no leaks, fuel filters full of fuel. Last time had issues with filters the smaller one was empty as large one plugged solid.

So cold start, hard to start.

Once warmed, easy to start, runs fine.

Difficult for me to understand is start from cold is difficult, then after small run time, motor will start easy in seconds. Can't be fuel? works the same with air filter on or off, cant be air? Motor will rev up to max.......very puzzled. And this only started after I first screwed up/adjusted the valves.

Only thing just occured, I am using the gap at the adjustment screw, seems like the manual shows that. Is there a difference ti use gap at the other end? seems like it wouldn't matter but I am not a diesel mechanic.

I have attached the manual I am using, page 26 shows the page I am referring to. Looking at it now shows using the gap at the other side, not the screw adjustment side. Does that make a difference?

Any suggestions?
Attached Files
File Type: pdf OPM_YSB8_12_E.pdf (1.39 MB, 10 views)
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Old 10-05-2021, 12:55   #12
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Re: Yanmar YSB 8 hard starting

Again, I would try joining the Yanmar diesel group on Facebook and pose your question(s) to them.
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Old 10-05-2021, 13:54   #13
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Re: Yanmar YSB 8 hard starting

Quote:
Originally Posted by Halifax Sailor View Post
So, did the re-adjustment of the valves this morning. Used the gauge marked " .2 mm - .008". The engine started a little easier/quicker but still not like it used to before I screwed it up. Used the next one up ".237mm " and it seemed to make a little differnece but thwn again the motor was warm, even after an oil change. So, wondering, is there such a thing as too big a gap? My thinking says yes,no compression, won't start etc. Am I thinking right that maybe a little bigger gap than manual might be the cure? Tightened all the fuel hoses, no leaks, fuel filters full of fuel. Last time had issues with filters the smaller one was empty as large one plugged solid.

So cold start, hard to start.

Once warmed, easy to start, runs fine.

Difficult for me to understand is start from cold is difficult, then after small run time, motor will start easy in seconds. Can't be fuel? works the same with air filter on or off, cant be air? Motor will rev up to max.......very puzzled. And this only started after I first screwed up/adjusted the valves.

Only thing just occured, I am using the gap at the adjustment screw, seems like the manual shows that. Is there a difference ti use gap at the other end? seems like it wouldn't matter but I am not a diesel mechanic.

I have attached the manual I am using, page 26 shows the page I am referring to. Looking at it now shows using the gap at the other side, not the screw adjustment side. Does that make a difference?

Any suggestions?

You use the gap on top of the valve stem cap to adjust gap. I.e. the other end of the rocker arm from adjustment screw.
Do not change the factory setting.


If you are absolutely sure there is no air in the system or fuel restriction your next point to check( assuming battery, starter & cables are all good ) is the compression. The first sign of compression dropping ( apart from smoke maybe) is increasing cold start difficulty but its a slow progression normally unless you have a catastrophic failure. If it comes on suddenly its more likely air ingress or fuel restriction.


If you can borrow a compression tester its pretty easy to check. Should be 397 -454 psi @ 200rpm. Minimum is 355psi.
There should be a service manual in the CF library but if you need a free PDF, PM me with yr email & i can give you one. Its good to have the YSM series service manual too as it's more detailed & there isnt many differences.
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Old 10-05-2021, 14:10   #14
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Re: Yanmar YSB 8 hard starting

Quote:
Originally Posted by Halifax Sailor View Post
So, did the re-adjustment of the valves this morning. Used the gauge marked " .2 mm - .008". The engine started a little easier/quicker but still not like it used to before I screwed it up. Used the next one up ".237mm " and it seemed to make a little differnece but thwn again the motor was warm, even after an oil change. So, wondering, is there such a thing as too big a gap? My thinking says yes,no compression, won't start etc. Am I thinking right that maybe a little bigger gap than manual might be the cure? Tightened all the fuel hoses, no leaks, fuel filters full of fuel. Last time had issues with filters the smaller one was empty as large one plugged solid.

So cold start, hard to start.

Once warmed, easy to start, runs fine.

Difficult for me to understand is start from cold is difficult, then after small run time, motor will start easy in seconds. Can't be fuel? works the same with air filter on or off, cant be air? Motor will rev up to max.......very puzzled. And this only started after I first screwed up/adjusted the valves.

Only thing just occured, I am using the gap at the adjustment screw, seems like the manual shows that. Is there a difference ti use gap at the other end? seems like it wouldn't matter but I am not a diesel mechanic.

I have attached the manual I am using, page 26 shows the page I am referring to. Looking at it now shows using the gap at the other side, not the screw adjustment side. Does that make a difference?

Any suggestions?
Valve Clearance is always measured at the top of the valve (valve stem).

As a quick check, go back and re-adjust the valve clearances to the halfway point from where they are set today (after you adjusted them) and where they were set before you adjusted them.

If the cold starting now improves, you have your answer.
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