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Old 07-01-2015, 12:37   #1
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Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

Hi all, I've had some great advice here in the past and read many other posts which have proved helpful and here I am again with my reluctant Yanmar, its a 3GM30, im unsure of its age but I can hazard a guess at mid 90s:

What I've done:
Top end rebuild, valve lapping, new head gasket, adjusted valve timing, changed oil filter and fuel filter, brand new fuel tank with new lines and lovely fresh diesel. I also added RedX diesel additive.

Problem:
So at first the engine would almost, but not quite fire so I took the injectors for pop testing at my local Yanmar specialist. In no uncertain terms he said these were knackered so I bought 3 new ones. After trying for quite a while I did finally get the little bugger to run (hallelujah!) but it is very ropey and I'm almost certain Piston 3 is not firing. and There is fuel at injector number 3 so I doubt its a supply problem.

I suspect 3 or 4 different things but I know some of you guys can diagnose a problem just by listening to an engine. I was thinking maybe I adjusted the timing wrong, maybe there is water in the cylinder (it is the lowest cylinder as the engine is tilted), maybe the new injector is faulty, maybe the injection pump timing is off, or (please no) the piston is holed/there is no compression.

Any tips on making it start easier as well?

All help, big or small, greatly appreciated.
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Old 07-01-2015, 13:40   #2
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

I would suggest you take a compression test. It sounded like under cranking there wasn't much compression.
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Old 07-01-2015, 13:55   #3
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

Thanks Zai

I have been considering doing this all along but I'm worried that low compression is a death sentence for the engine and a new one is big bucks.

Is it possible to get an engine with low compression back to a good standard?
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Old 07-01-2015, 14:29   #4
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

if it ran better than that before the head work, I'd check your valve timing.
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Old 07-01-2015, 14:34   #5
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

It ran about the same before the head rebuild, although all cylinders fired.

I took the head off in the hopes that lapping the valves would increase compression more easily/cheaper than changing piston rings.
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Old 07-01-2015, 15:06   #6
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

First up, recheck your valve clearances. A riding valve will produce your symptoms.

Regards,
Richard.
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Old 07-01-2015, 15:31   #7
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

Remove injectors put a tea spoon of engine oil in all cylinders then turn engine over not decompressed a couple of times by hand to check clearance.Engine mus tbe cold 1st start for the day.This test will indicate bore and ring condition if engine starts straight up you have poor compression under normal conditions.Do the easiest things first ie Valve timing, push rod to rocker gear placement and lift cam may be u/s, move an injector see if cyl miss moves.
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Old 07-01-2015, 20:31   #8
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

Thanks for all the suggestions, im first going to switch injectors 2 and 3 over and see if problems persist, if they do ill whip the bonnet and starter motor off and re-check my valve clearences. If that still doesn't work ill try the teaspoon of lube oil in the piston method suggested by shakey doug. I might have to ask for a bit more of a step by step instruction on that method if possible:

1 remove injectors, add lube oil to piston, re-install injectors
2 with compression on, turn engine over by hand (Normally I cant do this, too much resistance)
3 This will allow me to check clearence and bore condition.

I'm still reasonably amateur so forgive my lack of understanding, it sounds like a great suggestion I just don't fully understand the process shakey doug.

Also what is the general feeling toward starter fluid? Is a short spray of WD-40 in the naked air intake going to help it get that first pop or should I try a different product?
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Old 08-01-2015, 03:36   #9
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

When your doing all this cranking make sure you're not flooding your cylinders with water from over filling the wet lift. The motor has to be running to clear it. you may want to create a bypass to the exhaust elbow until it starts.

Another thing to check is the condition of the cam lobes. If the lobes edges are rounded off it would be suspect.

And ditto on swapping the injectors. If still the same, a compression check would be in order.
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Old 08-01-2015, 04:24   #10
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

I don't know much but I do know about hydrolock! I can undo the bolt on my water pump so it is not turning whilst I am cranking, once the engine is turning over I can tighten it again and it engages the belt.

Its about 2C here so overheating is not an issue whilst the engine is warming up. That's yet another reason why starting is difficult.
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Old 08-01-2015, 04:26   #11
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

Hey Delmarry, where are these Cam lobes? are they directly beneath the injection pump? What's the best way to tell if they are rounded off?

Thanks for your help
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Old 08-01-2015, 05:08   #12
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

What engine does Sailor Chic have? Didn't it have a broken piston?
I'd check cam wear with a dial indicator on the rocker arms myself, but what you have sounds an awful lot like timing of either cam and or fuel pump or a too tight valve etc.

Might want to PM Sailor Chic
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Old 08-01-2015, 05:10   #13
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

A compression test would rule just about everything except fuel pump timing out, broken / worn rings, broken piston, worn cylinders, valve timing and adjustment all would lead to low compression
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Old 08-01-2015, 05:17   #14
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

Ether is fine as long as they are no glow plugs, if there are glow plugs and you still want to use ether, be sure to dis-able the plugs.
WD-40 is sort of a low grade starting fluid, it works some what, but not nearly as well as ether. It is possible to get a small fire in the intake manifold with ether if you use a lot, if that happens usually best thing to do is continue to spin the motor as the motor will ingest the fire.
I like to spray ether directly into the intake manifold when the engine is turning over.
I've used ether most of my life on farm and Earth moving equipment, never a boat yet.
Ether may be heavier than air also, if so another reason to shoot it directly in the intake with the engine spinning.
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Old 08-01-2015, 05:36   #15
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Re: Yanmar difficult to start after rebuild and only firing on 2/3 cylinders

Quote:
Originally Posted by dtlx11 View Post
Hey Delmarry, where are these Cam lobes? are they directly beneath the injection pump? What's the best way to tell if they are rounded off?

Thanks for your help
Sorry, I guess the cam is inside the block. But like 64pilot says, you can measure the stroke with an indicator. Just make sure the lifter arm is not too tight. The intake and exhaust might have a different stroke so don't mix them up. They should be within a few thousands (.000") of each other.

Here is a manual for the 3GM30. goto page 455. Boatinfo - Yanmar Service Manual for 1GM10, 2GM20, 3GM30, 3HM35
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