A modern mystery (Yanmar injectors)

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A modern mystery (Yanmar injectors)

This topic has 24 replies, 7 voices, and was last updated 14 June 2025 at 22:42 by Fulmen.

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31 May 2024 at 09:04 #733470
Fulmen
Participant
@fulmen
So I’m like servicing the injectors on my boat, one of those ubiquitous (I actually spelled that right on the first go) 3 cylinder Yanmars. The nozzles look fine, so not much to do except removing some rust, dirt and carbon build up. But after 40 years I’m sure the pressure needs adjustment. My local mechanic can test them, but he doesn’t have a lot of shims so I figured I would buy some just in case. But nobody sells them.

Now the nozzles I can get everywhere, best deal I could find was 6 for 30EUR. So why are the shims unobtainium?
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31 May 2024 at 12:43 #733514
David Jupp
Participant
@davidjupp51506
These ?

https://www.dam-marine.com/gb/injector/527-set-of-yanmar-injector-shims-110250-53150.html
31 May 2024 at 13:34 #733518
Fulmen
Participant
@fulmen
Idunno, they don’t list what engine it’s for.
31 May 2024 at 15:33 #733534
Clive Brown 1
Participant
@clivebrown1
French Marine of Colchester deal with Yanmars ancient and modern. You don’t say what engine you have, but, for example, they list “plate assembly adjust” for the GM series injectors. Is this the type of thing you need. Might save money of course if you test the injector pressur before splashing out.
31 May 2024 at 16:22 #733543
Fulmen
Participant
@fulmen
I might have overstated how hard they are to find somewhat 🙂

Using the yanmar parts number I’ve found several vendors, but there is still a weird mismatch here. The nozzles are sold by the crate like eggs, in fact I can buy them for the same price as a set of shims. It’s as if everybody swap these nozzles out at the drop of a hat without ever checking the pressure.

As far as I can tell mine are fine after 40 years of light duty, but the spring is appr 0,5mm shorter than factory specs. According to the manual we’re talking appr 10 bars per 0,1mm, this could explain the drop in power at full throttle (3-400 rpm).
31 May 2024 at 22:06 #733584
Howard Lewis
Participant
@howardlewis46836
Since you are looking for shims, presumably your local mechanic has found the breaking pressures to be out of spec?

If within spec, and spraying satisfactorily, my advice is to leave well alone. (And that includes not trying nto decarbonise the spray holes in the nozzles; you are talking just a few thou here, probably less than 0.020″ if the engine is direct binjection.

If the spray quality is poor, that will reduce power, and mean that the nozzles and needles need either attention (Lapping or replacement)

If the breaking pressure is lower than spec, I would expect fuel delivery to have increased (Although you will have no means of checking this, withouit a test machine)

The loss of power MIGHT be due to other things, such the fact that a lower breaking presure will effectively over advance the injection timing, or if the spray quality has reduced, that might decrease power, at the expense of slightly increased smoke levels.

If the injection pump is feeling the effects of old age (Plunger/barrel or delivery valve wear) that might well reduce fuel delivery and power. Have you had the pump checked ?

Also, valve sealing may be worse. A compression test might show this.(Assumes that the air filter, or exhaust system, is not restrictive)

Howard
1 June 2024 at 08:55 #733605
Fulmen
Participant
@fulmen
No, I just assume they will need adjustment after 40 years. Might as well have the shims ready, they’re not that expensive.

Haven’t checked the pump or compression, that’s a bit too much work for now. If the injectors are fine I’ll just have to live with what I’ve got.
2 June 2024 at 16:36 #733801
Howard Lewis
Participant
@howardlewis46836
Very wise!

Just check the injectors, if the breaking pressure is within spec, and they spray ok, just brefit.

“If it ain’t broke, don’t fix it”

Sleckeming an injector retaining nut could shearb the stud and that makes anotherv problem, that ndidn’t exist before. Sod’s law says that the stud will shear off level (IF you are lucky) or below flush and then that has to be removed.

Howard
4 June 2024 at 12:45 #734058
Andy_G
Participant
@andy_g
On 31 May 2024 at 16:22 Fulmen Said:

this could explain the drop in power at full throttle (3-400 rpm).

My first suspicion would be some restriction in the fuel supply – a clogged filter or something. If you’ve picked up the dreaded “diesel bug” it can clog the tank pickup pipe as well as any filter(s) in the line.

Second suspicion would be a clogged exhaust elbow.

(Ex 2GM owner).
4 June 2024 at 15:19 #734077
Fulmen
Participant
@fulmen
I discovered the diesel bug last year, so the fuel system has been thoroughly cleaned including a fresh filter. That’s also part of the reason for this service, I did find some crud in the nozzles (the filter body had a rust hole).

Never thought about the exhaust though. It’s a fairly large pipe so a clog seems unlikely, but it’s simple enough to check…
4 June 2025 at 19:06 #801338
Fulmen
Participant
@fulmen
I got the engine running again last year, but it ran rough and smoky at low RPM. So I ended up buying this tester:

https://www.hbm-machines.com/nl/p/hbm-diesel-verstuiver-tester-600-bar

Pulled the first injector today. It was leaky, full of dirt (far worse than when I cleaned them last year) and had a opening pressure of 60 bars, a whole 100 bars low. No wonder it didn’t run right…

It took a 1mm shim to get it back into spec, and it already runs better and cleaner. Now I just need to do the other two and I should be good for another 40 years 🙂
5 June 2025 at 01:07 #801392
howardb
Participant
@howardb
If you have had the diesel bug you need to add a biocide additive to the fuel in your tank to prevent it reoccuring, even if you have cleaned out the fuel system.

https://www.google.com/search?q=diesel+biocide+additive&rlz=1C1CHBF_enFR1036FR1036&oq=diesel+biocide+additive&gs_lcrp=EgZjaHJvbWUyBggAEEUYOdIBCTEyMDU4ajBqN6gCALACAA&sourceid=chrome&ie=UTF-8

Take your pick !!
5 June 2025 at 06:08 #801393
Fulmen
Participant
@fulmen
I know, and I already do. Don’t want to do that job again if I can help it.
9 June 2025 at 10:26 #802169
Fulmen
Participant
@fulmen
Finished the last two injectors, the worst was at 60 bar and the best of the lot was just shy of 100. And it really did a difference, engine starts as if new and runs smooth and quiet.

I did not get any top end power back, which actually makes sense. These engines has a governor, and after 40 years the springs are bound to have lost some of their springiness. So that will be next.
9 June 2025 at 11:19 #802171
noel shelley
Participant
@noelshelley55608
Hi Fulmen, thats a neat injector tester, for your job, if I had one handy I might be tempted to fit a 0 – 250 bar gauge. The man to talk to here is Howard. Does it reach max revs ? I take it it did. Noel.
9 June 2025 at 19:49 #802219
Fulmen
Participant
@fulmen
No change in revs, but I suspect it’s an issue with the governor. It’s not very accessible, so it’s probably a job for the winter. According to the manual there is a rev limiting set screw somewhere.
11 June 2025 at 17:27 #802509
Howard Lewis
Participant
@howardlewis46836
If the governor springs have weakened, the idle and max speeds would increase, and max no load speed might become unstable.

The max speed screw should be somewhere on the injection pump. There will be two screws, one for low idle, and the other for high idle.

You need to check that the throttle linkage is actually pushing the lever onto the idle and max speed stops.

Sometimes manufacturers have an additional speed screw on a lever in the linkage between the throttle lever and the speed lever on the pump, so that the lever is held about 0.010″ clear of the stop on the fuel injection pump, to avoid overloading the throttle shaft in the pump.

Presumably it is a small flange mounted in line pump, mounted above a camshaft on the side of the timing case.

(Diesel Kiki?)

What speed are you looking for?

Probably the engine, assuming that it is a small indirect injection unit of about 2 litres or less, would normally be limited to about 2500 or 3000 rpm, no load.

Are the inlet or exhaust ducts obstructed in any way? An obstructed inlet would show as smoke as well as low speed and power. (Not unknown for long rubber hoses to delaminate internally, or to be sucked flat as speed increases!)

HTH

Howard
11 June 2025 at 17:47 #802517
Howard Lewis
Participant
@howardlewis46836
Am assuming that it is a marine engine.

Presumably the engine is being run up with the gearbox in neutral? The prop would impose a load which increases nearly as the cube of speed (2.8 factor probably)

So any drag imposed by the transmission imposes a load, which means that the engine will not reach the proper no load speed

Max power will only be available when the speed decreases down the governor curve back to Rated Speed.

So an engine with a 2,750 rpm No load Speed, will only deliver maximum, power when the speed is dragged own to about 2500 rpm by the load.

If in gear, and the prop pitch is too coarse, the engine might be dragged down below rated speed, since it is overloaded.

Howard
12 June 2025 at 09:00 #802619
Fulmen
Participant
@fulmen
On 11 June 2025 at 17:27 Howard Lewis Said:

If the governor springs have weakened, the idle and max speeds would increase, and max no load speed might become unstable.

Wait what? I believe it will be the other way around, the governor should act as a rev limiter with the weights working against the spring.

The engine is a Yanmar 3HM35, it has a no-load max rpm of 3600-3650. And when new it did do almost that at full load. Now the full load max rpm is a little shy of 3200. I would like to get it up to 3400 which is the 1 hour max rpm.
13 June 2025 at 20:08 #802842
howardb
Participant
@howardb
3HM35 IDLE RPM 850
FULL THROTTLE RPM (NO LOAD) SPEED 3625
https://www.manualslib.com/manual/1017139/Yanmar-1gm10.html?page=6#manual

3HM35 30 HP @ 3200 RPM ( in gear with boat under way)
https://www.manualslib.com/manual/1017139/Yanmar-1gm10.html?page=7#manual

Panel tachs are not that accurate – VDO instruments were only guaranteed + or – 50 rpm when new.

Use this,
TOPWAY Digital Tachometer, Handheld Non-Contact Digital Photo Tachometer RPM Tester,
I’ve got one and I seem to remember it includes some self adhesive reflective tape, clean the crank pulley off with some solvent stick tape on and do the rpm checks with the hand held tach . Useful for lathe and mill speed checks too.

https://shorturl.at/4eQrZ
13 June 2025 at 21:33 #802855
Fulmen
Participant
@fulmen
On 13 June 2025 at 20:08 howardb Said:

Panel tachs are not that accurate – VDO instruments were only guaranteed + or – 50 rpm when new.

Fair enough, I’m assuming the instrument hasn’t changed in 40 years.

I should probably scope the raw sensor signal for a better reading before doing anything drastic. But from memory the top speed is a bit lower than when new (GPS so should be reliable). Then again neither the hull or the propeller is pristine anymore, so I’m not putting too much faith in those numbers either.

It’s not a huge priority, I’m just curious. I’ve never had any reason to work on it before, it’s just always worked.
13 June 2025 at 22:07 #802858
Howard Lewis
Participant
@howardlewis46836
The governor DOES act as as a speed limiter. That is why it is there!

In this context, we are talking of mechanical governing, particularly with a forty year old engine.

Electronic speed control is completely different.

If the engine is running slowly, and the throttle lever is moved against the Max Speed stop, the spring force will exceed that provided by the governor weights, and the fuel delivery will increase to increase engine power and speed.

The engine speed will increase until the force provided by the governor weights equals that exerted by the governor spring

When the engine is fully loaded, at rated speed, the force exerted by the governor weights is equalled by that applied by the governor spring.

If the load decreases, the engine speed will increase and the governor weights will exert more force than the governor spring, and begin to decrease the fuel supplied. The engine is now going down the governor curve, and when all the load is removed , the engine will have the fuel delivery reduced until the engine runs at Max No load speed.

The gradient of the curve (Run out – change between FLRS and Max No Load Speed (High idle)) will depend on the spring rate of the governor spring, and levers within the governor system.

An engine driving an alternator will have a low % run out (Tight governing) to control closely the supply frequency. So would an engine for a combine harvester, to control reel speed. Probably 5 %

50 Hz – 1500 rpm, 1570 No Load, 60 Hz – 1800, 1880 No Load

A vehicle , or marine propulsion engine does not need close governing, so the run out could be 10 – 15%

3200 FLRS, 3625 High Idle means a run out of 13% What would be called “Slack Governing”, so being marine propulsion, precision is not called for.

This would merely limit engine speed if the prop came out of the water, or the drive shaft disconnected or broke.

As the governing gets tighter, for any reason, stable speed control becomes more difficult, but with special damping, isochronous governing (Zero run out) becomes possible.

Tight governing on a vehicle can be unpleasant, Run a Series 2 Land Rover upto No Load speed in the gears. When the governor cuts, the change in power feels like someone has killed the engine

Gardner powered vehicles can feel the same (1700 rated speed, 1770 max engine speed)

Hope that this gives a better understanding of how a governor operates on an engine.

Howard
13 June 2025 at 23:35 #802866
Howard Lewis
Participant
@howardlewis46836
Sadly, marine life is not simple!

As always, the devil is in the detail, and we are assuming that the refurbished injectors are as good as they were originally.

Dirt in the nozzles may have worn the needle and nozzle body, increasing back leakage, which will adversely affect delivery. Was the back leakage checked, as well as breaking pressure? Or were new nozzles fitted?

Changing the thickness of the washers under the Injectors will affect nozzle protrusion and engine performance

We are unlikely to be able to prove that the calorific value of the fuel has decreased, or the viscosity increased, over the years, and we are assuming that nothing has happened to increase fuel inlet temperature, or restrict fuel delivery to the injection pump (Feed pump /pipework/ filters)

Changing the bore or length of the injector pipes can have an enormous effect on engine performance. And a 2 mm bore pipe will not be better than an original 1.5 mm! So stick to the original bore and length of pipes.

Are the delivery valves in the injection pump still sealing properly?

If dirt has passed through the injection pump, the barrels and plungers might be worn, and leaky, increasing leakage and decreasing fuel delivery. Only a check on a rig can show that.

Flexible “rubber” pipes can delaminate internally, whilst looking good externally.

I have witnessed a change of filter supplier causing enormous problems!

You might get a different engine speed when doing a bollard pull, as the supply of water might be different from that when on open water.

A fouled hull or deeper than designed draft will increase drag, so the hull will not reach design speed, the engine could be overloaded, and fail to reach rated speed.

An even slightly damaged propeller will not be as efficient as when new and clean.

Since the prop law is that the power required increases by almost a cube factor (About 2.8), a small change of speed brings about a far larger change in power requirement.

Ideally, the pitch of the propeller should be such that it absorbs the engine power at rated speed, without any cavitation.

Howard
14 June 2025 at 04:02 #802867
Howard Lewis
Participant
@howardlewis46836
If you have the speed but not the power, the problem is not with the governor, but in the quantity of fuel delivered to the engine, or the engine itself.

Start checking the fuel system, starting with the cap to the tank, is the vent obstructed? Then check the low pressure feed lines, (Correct, CLEAN filter element, and the air bleed system clear back to tank?) Then when it comes to the injection system, it can get expensive since checking and possibly refurbishing / resetting the injection pump needs specialised equipment and knowledge. Then check the H P pipes, are they correct bore and length? Bores not closed up by over tightening the nuts.

Then the injectors need to be checked and set as well checking backleak. Are they atomising correctly, and are the sealing washers the correct thickness?

It might be that the engine itself has deteriorated, valves not sealing as well as they did previously.

Any obstructions in the intake or exhaust system? Hoses not delaminating or being sucked flat?

Plenty to check and possibly rectify, to restore original power.

Howard
14 June 2025 at 22:42 #802945
Fulmen
Participant
@fulmen
I did not check back leak, other than noting that it was not excessive. I ran all injectors for a good while without any noticeable filling of the spring cavity. I’ll try to remember that next time. Other than the shims in the injectors the engine is of factory specs, not modified or wrenched in any way or form. We’ve had the boat from new and it has never needed any servicing before now.

I just did a check and I get 3400rpm with no load according to the original tacho. The electrical specs are 1v or more AC, so a multimeter should be able to read that, though I might have to use a small transformer to get the voltage into a more suitable range. I can even borrow a proper digital oscilloscope if needed.
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