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Calling Yanmar gurus . . .

11K views 25 replies 14 participants last post by  Capt Len 
#1 · (Edited)
My engine is a Yanmar 4JH2E (I think) non turbo 4 cylinder I think 49hp, it has done abou 3900 hours.

I will try and put this into clear perspective and the first description of a problem is not the subject - be patient :) this is a long post.

For a while now I have been having some issues with the engine losing power shortly after being started, sometimes it waits about 10 minutes before it manifests itself. The engine RPM falls off, stutters and won't rev up. I go down below and pump the fuel bulb in the line, the stutter clears and from then on it doesn't happen again until the boat has been left for a week or more. This has been happening for several months BUT like I said that is not my problem. I'm just setting the stage.

This weekend we were motoring out of our anchorage and the engine sounded sweet - the loss of power never happened on its normal schedule. Then, probably 45 minutes into the motoring session, the engine lost power.

At the same time there was a brief smell of hot oil. I checked the instruments and saw nothing unusual. The power loss lasted about 15 seconds and then cleared on it's own and the engine started running sweetly again, totally against the norm. I went down below to check the cause of the hot oil smell and saw nothing that scared me.

I went back on deck, couldn't have been away more than a minute and then the alarm buzzer went off. I checked the instruments and saw no oil pressure. I immediately killed the engine. There was no noise, no misfire, no abnormal activity of any sort. Even the hot oil smell was gone.

I went back down below and had another look and what I found beggars belief. The entire contents of the sump was lying in the bilge. Let me make that clear - ALL of the oil in the engine was now in the bilge. :eek: I know this because I later scooped it all up and recovered just short of 6 litres.

But the uncanny part is that I can't find any source of a leak. And I mean nothing. I have checked all around the engine with a strong lamp and there is no sign of where the oil could have come from. The only part that I can't visually check without removing the engine is the actual bottom surface of the sump and the rear of the engine inside the bellhousing.

So two things spring to mind. Either a sump plug has fallen out or there is a hole in the sump. Firstly I don't think there is a second sump plug - the first one is the dipstick connection to the sump but that is secure and dry. And in any case, if there is another sump plug it has been secure for three years at least, why would it come loose now?

I can't see under but I ran my hand over as much of the sump as I could reach and could feel nothing like a hole or a crack. My hand came away with a smear of oil but it was light enough to be just a smear, no droplets. With no ominous noises I find it hard to believe that anything inside the engine would have impacted the sump. With the kill cable pulled the engine still cranks normally with nothing out of the ordinary.

I've thought about the rear main oil seal popping out but I can't believe that that would completely empty the sump in a few minutes. I have checke the workshop manual I have and there is no reference to any external oil pipes that may have fractured.

Obviously I have missed something because the above tale sounds and probably is highly implausable. I have wracked my brains and can't think of a logical scenario that would cause this. Any useful thoughts members may have on this would be of considerable value since hauling the engine out of my boat is a nightmare job and if I can avoid it I would really like to try.
 
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#2 ·
Unknown Oil Loss...

As the general location of the leak isn't identifiable at this time, the first and simplest thing I would do is to spin off the oil filter and make sure the o'ring hasn't blown out.
I hope the solution is something as simple as this.....Good luck....
 
#3 ·
As the general location of the leak isn't identifiable at this time, the first and simplest thing I would do is to spin off the oil filter and make sure the o'ring hasn't blown out.
I hope the solution is something as simple as this.....Good luck....
The above is probably the most common source of air leaks.

The second probable most common source is ALL the 'compression fittings' that connect all the tubing, etc. in the fuel delivery system. Compression fittings are essentially a ONE-TIME-TIGHTEN ONLY devices and easily suck air. The copper tubing end thats inside the compression fitting eventually 'relaxes' (strain relief) thus allowing aiar to be sucked in. Boat manufacturers use compression fittings because they are cheap and require no tools to assemble.
Better is double flared connections on stainless steel tubing.
To find air leak on a system with compression fittings - PRESSURIZE the system, then look for the leaker. Pressurization will also uncover a lift pump diaphragm that has developed a pin hole.

If you cant pressurize, then tighten each and every compression fitting with a 'fitting wrench' (wrench face comes in contact with 5 sides of the compression nut --- unlike a standard wrench which only comes in contact with 2 side of a nut.)
 
#4 ·
Two separate problems for sure.

First as described above is an air leak into the fuel system most likely between the bulb and the fuel pump.

The loss of all oil quickly could be a broken pressure pipe after the oil pump. I would follow the lines from the pump to the oil filter and in that area.

Gene
 
#9 ·
Two separate problems for sure.

First as described above is an air leak into the fuel system most likely between the bulb and the fuel pump.

The loss of all oil quickly could be a broken pressure pipe after the oil pump. I would follow the lines from the pump to the oil filter and in that area.

Gene
The oil filter screws directly onto the engine block and I think the oil pump is internal. I can't see any pressure line externally but it had occurred to me that there may be something like that under the engine where I can't see or reach.

I'm hoping some Yanmar specialist will enlighten me.

Thanks for your input.
 
#10 ·
I can find a transmission cooler but not an engine one. If there is/was one that would be the most likely point of failure but I would have hoped it would be where it could be seen. Is it possible it may be under the engine? I sure hope so.
 
#6 ·
Just happen to be reading through a 4JH2E Yanmar Service Manual for another unrelated problem. I'd replicate your situation. Pour a litre or two of oil into the sump. Have some one else turn the engine over or start it up while you keep your eyes down near the bottom, so you can see which part of the engine the leak comes from. Don't forget to turn the engine off quickly though to avoid further damage. Once you see the oil spewing from a general location you can search more specifically for the source. I suspect that plug at the bottom of the dipstick tubing and also the oil pump which bolts onto the front of the block. Good Luck!
 
#11 ·
Just happen to be reading through a 4JH2E Yanmar Service Manual for another unrelated problem. I'd replicate your situation. Pour a litre or two of oil into the sump. Have some one else turn the engine over or start it up while you keep your eyes down near the bottom, so you can see which part of the engine the leak comes from. Don't forget to turn the engine off quickly though to avoid further damage. Once you see the oil spewing from a general location you can search more specifically for the source. I suspect that plug at the bottom of the dipstick tubing and also the oil pump which bolts onto the front of the block. Good Luck!
Yes I thought that would be the best solution even if it included just cranking the engine. The problem is that with the side bearers onto which the engine mounts and another beam that runs across the front of them, it is almost impossible to see under the engine. I had already dribbled some fresh oil in from the top and heard it trickling somewhere but it sounded like it was landing on an empty sump. It could have been coming out of the bottom of the engine :eek: but I couldn't see anything.

So for all the kind responders, here's what I plan to do. Whilst getting the engine out of the boat is a nightmare, I have figured out a way to at least lift it by about 400mm. I plan on removing the steering binnacle. That will leave a hole that is sort of above the crank pulley. Then I have two cockpit drains at the stern end of the cockpit floor that sort of align with the join between engine and gearbox. I will remove these.

I have bought three small chain blocks that will collectively be able to lift the engine so I will put two beams across the cockpit and drop a chain down each of these apertures and lift the engine off it's mountings. That way I will not only be able to see under the engine, I will be able to remove the sump if that becomes the reality.

Hopefully this will happen this weekend - I'll post the result here on Monday.
 
#12 ·
I'm pretty sure my 4JH2E has an oil cooler and it's by far the most likely suspect. I'd remove and inspect it. I don't have my manuals with me, but from memory, the water line exists the heat exchanger at the transmission (aft) end then forms a sideways V to starboard. I believe there are oil lines running to the V shaped cooler.

You should double check the part numbers, but I think this is what you will need to replace....

Yanmar 129470-33000 Ships Store Torresen

There should be no need to lift the motor.
 
#14 ·
I agree with BL, use mirrors and lights to see the bottom of the oil pan. Most likely it has a hole in it from rust/corrosion. If the oil had come from any pressurized spot there would be oil everywhere. The lack of any visible oil, or spray pattern means it's probably a hole or fitting in the sump unfortunately. Good luck.
 
#15 ·
He will need to raise the engine if the pan is holed in order to remove the pan to repair the hole or replace it. Ouch!

The oil cooler on the 4JH2-E is described in Section 5 of the Service Manual. It is a V shaped structure bolted on the rear of the engine on top of the Flywheel Housing. It has two oil lines, one input and one output connecting to the pump on the side of the engine block where the oil filter screws on. Check both ends of both lines. All this can be viewed in the 1991 Parts Catalog Figure 21 as well.
 
#16 ·
Two questions.. were you heeling while motoring? I seen some engines dump their oil reservoir out the dip tube if excessively heeled, sometime on only one tack..

Crankcase vent OK? Some blow-by and a plugged PCV valve could pressurize the crankcase and force the oil out, again through the dipstick tube.

I imagine you'd have seen it running down the tube so probably not??? - anyhow another $.02.....
 
#17 ·
I spent a few hours yesterday and discovered that the leak is coming from between the engine block and the transmission. The only thing that I can think of is there must be a welch plug in the back of the main oil gallery that has rusted through/blown out.

The service manual doesn't show that sort of detail so today I will be making an assault on the south face as it were - I'm going to pull the transmission, flywheel and flywheel housing off the engine to see what is what.

Will post the result for interest.
 
#18 ·
As with all things boat, the job has escalated into something that is really character-building.

I undid all the bolts on the bell housing, undid the prop coupling, cut the cockpit drains, undid the aft engine mounts, dropped some cables from the cockpit into the engine room and lifted the engine forwards to clear the prop flange and guess what? Yup, the gearbox ain't coming off the engine.

It is loose around the housing because I can stick a thin screw driver into the gap but the gearbox ain't going nowhere. A check in the manual shows that the only thing restricting it is the input shaft on the gearbox that must be rusted into the splined boss on the drive plate that bolts to the flywheel.

Since there is no way of getting into that area to do something about the stuck shaft, here is what I am planning:

The bolts that hold the drive plate on are shown by the red arrow and there are six of them.

The back view looks like this with the red dot being the spot behind which the bolt will be/pass.

So if I put a 25mm hole saw through the housing at this spot, by rotating the engine and exposing each bolt, I can undo the plate and pull the gearbox with the plate in place on the input shaft.

This operation is planned for this weekend so if anybody has a wise idea about how else this can be done, I would be pleased to get that info before the weekend.

Thanks
 
#19 ·
do you have the yanmar mechanic's service manual (not the abbreviated free 'owner manual' )and the parts manual for this engine ? sure makes putting it back together easier.

(spoken by one who spent the weekend tracing a coolant leak coming from the freshwater pump on a 40hp yan 3JHE...without the parts manual it never would have gone back together..)
 
#20 · (Edited)
I haven't got a parts manual but I have the full Yanmar service manual which is reasonably detailed.

I have actually found the problem after three days of stripping off parts and struggling with siezed bolts and other delaying tactics. The engine seemed to take on a beligerent life of its own placing every kind of obstacle in my path.

The problem is in the exact spot that I expected - I expected to find a rusted frost plug or whatever other members choose to call it. I was right about the plug - I was wrong about the rust. The problem is way more sinister than that and the engineering principle behind it is so obviously flawed that one starts to wonder if it is designed-in redundancy to get more engines sold.

The plug covering the back of the camshaft is less cup-like than one would expect, more like a shallow dome. And the aperture into which it is pressed is only about 2mm deep rather than the 5 to 10mm that one would expect from a cooling jacket frost plug aperture.

The gap between the back end of the camshaft is almost non-existent. So when the part at the front of the engine that restricts end float on the camshaft gets a little wear, the cam moves back and rubs against the plug. So the plug gets really hot and WELDS itself to the back of the camshaft. And that is what I found. I have to use a chisel to get the plug off the camshaft.

So, since the camshaft is not going to be stopped, something else has to move and the only other part that can move is the plug. Which then rotates in the aperture. Which causes it to neatly re-size the hole. Which means that the new plug ain't gonna fit.

So where to now? Well, at this time I don't have the answer to that question.

Oh yes, and what about the concept of incorporating the sump gasket into the rear bellhousing? Who still makes engines like that? Why the hell can't the sump be a seperate entity with its own gasket? Now I have to remove the sump as well just to refit the bellhousing properly. Another example of mindless engineering. Or is it?? Now I have to buy a sump gasket.

What I do know is that my earlier undying respect for the excellence of Yanmar engineering is now decidedly ailing and could actually expire. So if I have to replace the engine, I will be looking on this board for recommendations but I have to say, the prospects are bleak for finding another manufacturer that makes a decent engine.
 
#21 ·
Yanmar solution (photo heavy)

So here's how we fix the poor design I discussed earlier. The area on the back of the engine has a gap between the flywheel housing and the plug that closes off the end of the camshaft. You may remember that the plug got screwed and was the source of the leak.

So the first step is to mill the housing flat in that space.



Then cut a cardboard template of the space



Then cut a block of 20mm aluminium plate that fits into the space that has been milled out (the piece shown has already been pre-heated for welding)



The block is then welded in place



And finally milled back to the same level as the rest of the engine facing area and the bolts holes machined back to standard



The full area that is now faced to the back of the engine is installed with a gasket and the newly inserted piece covers the area where the camshaft is leaking oil. And the good part is that there is now a gap of 2mm between the cam and the back cover so it is very unlikely to ever cause a similar problem. The engine will actually stop running before then.

This whole setup will be assembled onto the engine this weekend and I will report back when it's running.
 
#23 ·
Just to round off the report on this fix, I assembled the whole thing up, put a gasket between the "new" back housing and the hole at the back end of the camshaft.

I ran the engine for a little over an hour and there is no sign of any oil leak.

So the fix seems to work well.
 
#24 ·
good to hear.
 
#26 · (Edited)
General thoughts .Removing the trannie is easy or not if it holds the rear mounts. May have to jack up rear of engine and carefully block.Don't punch in the oil pan.Seals are straight forward but if you are a beginner, take it to a shop. Bet you have to pull the prop to bits and insure the numbers and letters match and the blades connect at the right tooth. If the shaft sticks out proud past the shaft nut ,it needs cutting back,. (common when retro fitting) and improper installation of wrong cap zinc can jam a blade. Based on my experience. Yours may vary.
 
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