Yanmar 3GM hard starting after injector service

Theoretically if your IP was underperforming, PO may have altered timing with shims to try to compensate. If a new Barrel and plunger is now fitted in IP, the spill timing may be different now. I would look at that. Get a pack of shims or make them and have a go. the shims are shape of the bottom of pump and various thicknesses 0.02mm et IIRC.
All this being said, your builder should have done that and maybe has. The compression he is speaking about is probably in the IP. If that compression is not up to scratch, then just like low comp in engine, cold starts are very difficult.

Tillana said:

My old md11c was a pain to start with lots of turning her over. Ended up being small holes in filter housing letting air in and caused the fuel to drain back toward the tank. Found out by doing as suggesting with priming with lift pump and it started loads quicker. Replaced filter housing and all was well.

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Did you bleed it at the injectors, or just prime the system via the lift pump? Would using the integrated Racor pump in the primary filter do the job (it’s a much easier pump to use than the lift pump), or would only the lift pump work? How long did you have to pump the lift pump?

lexi said:

Theoretically if your IP was underperforming, PO may have altered timing with shims to try to compensate. If a new Barrel and plunger is now fitted in IP, the spill timing may be different now. I would look at that. Get a pack of shims or make them and have a go. the shims are shape of the bottom of pump and various thicknesses 0.02mm et IIRC.
All this being said, your builder should have done that and maybe has. The compression he is speaking about is probably in the IP. If that compression is not up to scratch, then just like low comp in engine, cold starts are very difficult.

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The compression the shop measured were the engine cylinders. They measured cold compression of 160, 170, 160. I understand a warm engine would result in higher numbers. Not sure why they would measure compression cold if warm provides more accurate info.

The IP was rebuilt “to spec”, so I assume the compression in the IP is the appropriate range.

The shop that performed work said they used the same shims as were there before. If you’re correct, and the PO adjusted timing shims to compensate for a failing IP, then adjusting the timing shims now would be the way to go.

Ah gotcha. Can't recall what guys have got when compression testing and I don't think Yanmar give figures. They could have done a wet test to see if the figure jumped up, indicating piston ring wear. Maybe they thought those figures were up to scratch as per their experience? They are near enough each other but whether 160 psi is in ballpark, others may know. If IP is in spec then they must have pressure tested it as that is only way to know and get the book figure, less you just renew all parts inside it £ouch! Get into your manual and after you have rechecked your system for air ingress, and other possibles. check your spill timing. The compression test is done cold. That is the reading you need. You can start a warm engine if it has worn rings, as the heat expands everything. You measure all the engine parts when cool. That figure is calculated to deal with the expansion on heat cycles.
If you cannot get fuel from lift pump to IP bleed screw, turn engine Crank at pulley, as the lever of lift pump may not be on the cam inside......it makes a big difference.

Skunther said:

The compression the shop measured were the engine cylinders. They measured cold compression of 160, 170, 160. I understand a warm engine would result in higher numbers. Not sure why they would measure compression cold if warm provides more accurate info.

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Those 3 figures are closely similar, but assuming they are psi, overall they seem low to me. I'd expect considerably higher, 250+?, for a diesel engine of around 20:1 compression ratio.
Either the cranking is very slow or the piston / valve sealing is poor. Either would make for poor starting.

The workshop manual has a procedure for measuring TDC gap to cylinder head, or "top clearance" as it is called, through an injector port. It involves using fuse wire, crushing the wire at TDC and then measuring the thickness. The 3GM30F is 0.68 to 0.88 mm. If outside these tolerances it suggests further investigation. If the head has not been off, then no reason why it would have changed from when the injectors were serviced.

It is correct about putting solder wire into cylinder, but you are measuring for bent Con Rods or massive piston top erosion. That is a possible, but could be another rabbit hole.

Skunther said:

Not sure why they would measure compression cold if warm provides more accurate info.

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Low compression would make for hard starting. 340 psi is around what it should be.
I recently had a no compression 1gm. Bad valve seal. Fixed that and got 110 psi. Next i honed it and put in new rings, 220 psi. Absolute dog to start but once going it ran fine.

Skunther said:

Did you bleed it at the injectors, or just prime the system via the lift pump? Would using the integrated Racor pump in the primary filter do the job (it’s a much easier pump to use than the lift pump), or would only the lift pump work? How long did you have to pump the lift pump?

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Just a few pumps of the lift pump. I went on a canal and River trust engine maintenance course and the guy running the course suggested looking for air getting in. Want enough to drip, just let air on when left for a few weeks

Bleeding required is a possibility.
The key to starting a Yanmar GM is usually cranking it fast enough.
Battery, Wiring, Starter Motor could all affect that.

I would try spinning it decompressed and release the decompressors, see if that does it.
If it's a matter of bleeding, it should sort itself out, unless air is leaking in somewhere.

I have a primer bulb at the fuel tank, if that went soft while the engine wasn't running, that would imply air getting in/fuel running back?

earlybird said:

Those 3 figures are closely similar, but assuming they are psi, overall they seem low to me. I'd expect considerably higher, 250+?, for a diesel engine of around 20:1 compression ratio.
Either the cranking is very slow or the piston / valve sealing is poor. Either would make for poor starting.

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It started fine (within 5-7 seconds) before IP and injector work was performed. Now it won’t start after a full 30 seconds of cranking.

B27 said:

Bleeding required is a possibility.
The key to starting a Yanmar GM is usually cranking it fast enough.
Battery, Wiring, Starter Motor could all affect that.

I would try spinning it decompressed and release the decompressors, see if that does it.
If it's a matter of bleeding, it should sort itself out, unless air is leaking in somewhere.

I have a primer bulb at the fuel tank, if that went soft while the engine wasn't running, that would imply air getting in/fuel running back?

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Would more cranking amps potentially address it? I currently have a new group 24 starter battery with 550CCA and 700MCA. How would I test the system to ensure it is currently cranking adequately?

Surely you can add all the power in the world but if the compression is barely half of what it should be more current is not going to fix the compression issue ?

What you find with these engines is that many things can be worn on them, but they plod on. Then one day even though you have fixed one issue, the other crows come home to Roost. If the compression figure really is 345psi then your readings if correct, will not cut it. Rings/bore or valves. Stuck rings is a slight possibility. It is always in for a penny, in for a pound with these old things, and a 3 pot is expensive.

Skunther said:

Would more cranking amps potentially address it? I currently have a new group 24 starter battery with 550CCA and 700MCA. How would I test the system to ensure it is currently cranking adequately?

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There should be a figure for the cranking RPM in the manual?

If you can measure the voltage at the starter motor during cranking, and also the voltage at the battery, you can see whether a better battery might help or maybe you have voltage drop in the cables and isolators etc? Personally, I'd try using the house battery paralleled with the engine battery. Ensure all batteries are fully charged!
I might us e a clamp ammeter to check the current too.
It's possible to have a partly failed starter motor, one or two coils burned out maybe, this can draw a lot of current while not delivering much torque or speed.

When the engine starts after 30s of cranking, do you get signs that fuel has been injected all this time? You might notice the exhaust water looking distinctly oily just after starting? If not then the fuel system may be the issue.

Double check the 'throttle' and fuel stop controls are properly connected and adjusted.

The compression test figures sound very low to me, either they were taken while the engine was not turning fast enough, they're in strange units, or the engine is pretty tired, If the engine is that worn, I'd expect lots of blow-by when running, take the oil filler cap off and I'd expect to see lots of fumes.

There is a sheen in the water once it starts, as well as some grey smoke (unburnt fuel, no?). If air were in the system due to a leak somewhere, could symptoms be the same and could that be the cause of hard starting compared to how it started easily before work was performed?

Normally air in system, it won't start, or will die after starting. The elephant in the room is your compression ratio. Once you have satisfied yourself on air issues and timing, You could get someone out to do a leakdown test. Only thing after that is head off for a look at valves, then sump off to check rings and pistons. Engine out. Make sure you have eliminated all else before diving in of course.

If an engine runs and starts well, has some work done and then immediately afterwards doesn't start properly it must be almost 100% certain the problem lies with the work that was done or something closely connected with it, not some vanishingly unlikely coincidence of all cylinders mysteriously losing compression equally and simultaneously for instance.
For a start compression is seldom lost equally across cylinders, there is almost invariably a fairly wide sperad of pressures between the cylinders, unlike the closely grouped figures the OP has quoted. This is the reason Yanmar and most engine makers don't specify figures for this.
Additionally all the advice I have had on compression is that absolute numbers are a completely unreliable guide to compression health as there are so many variables in the (uncalibrated) measuring process. It can only ever be a comparative indication, either instantly between cylinders or long-term as a trend over several tests over months or years by the same mechanic with the same test kit. (When I rebuilt the top-end of my 3GM) my comp tester showed about 175psi with a 5psi spread and it started on the first compression.)

The only rider I'd add to that is to ensure that the battery, connections and wiring really are sound. That is easily addressed by starting it direct from a known good battery with a set of decent quality jump leads applied direct to the starter motor terminals.
You can easily check for poor wiring by cranking the engine for several seconds then feeling each starter wiring connection with a finger. A hot connection (and maybe a yell of "Ow!") easily identifies a problem
But I'd bet good money that compression is almost certainly not the culprit.

Didn't even know you had glow plugs. If you have, that is a must check first item on relay, wiring and plugs.

Slowboat35 said:

For a start compression is seldom lost equally across cylinders

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My 60 year old bmc measures within 10 psi on all 4 cylinders ! I'm down to 260. It should be 340 for me. Saving grace is that it has glow plugs so still starts.
30 years ago i could do 7.5knts, now only 6.5knts.