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Old 03-07-2022, 07:35   #1
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Yanmar injection timing

The injection pump and all 3 injectors on my 3GM30F were rebuilt and are now installed. I checked the timing and cylinders 1 & 2 are spot on. 3 is a bit off - as you can see in the pic it's about 1/2 a tooth off. Is this enough to worry about?

The engine now starts much better than it did, but it also seems to be knocking alot worse. Wondering if this is because of the timing on cylinder 3.
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Old 03-07-2022, 15:44   #2
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Yanmar injection timing

My initial thought was that itís not possible to have one element out of phase on a cassette injector pump but after a cup of coffee I realized that it can happen in at least 3 ways.
1. The pump tech got the phasing shims wrong on the test rig...... unlikely.
2. Your injector pump camshaft has a worn lobe..... also unlikely but definitely possible.
3. Your timing technique is different to what we normally do.
If you time using the pop pressure of the delivery valve as injection point and the (non adjustable) delivery valve spring is weak the fuel will appear early at the delivery valve outlet. The timing may be correct in reality but the indication will be misleading. This is normally ok to roughly time a pump but the preferred way is to spill time the pump by removing the valve , spring etc and re fit the empty valve holder THEN rotate the engine gently toward the timing mark while operating the lift pump lever. Fuel will flow freely until ď Spill cutoffĒ which is as close to injection as possible (extremely close). Now observe the timing mark alignment and add or remove pump base shims according to the late or early alignment of the flywheel mark at the pointer.
Itís sometimes easier to simply ease off the injector pump securing bolts and slip a few bits of shimstock to test time the spill without pulling out the whole darned pump and re installing it.
Iím not sure if thereís anything to be gained by checking timing on all 3 cylinders. Oh, the cylinder closest to the flywheel is #1Click image for larger version

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Old 03-07-2022, 15:51   #3
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Re: Yanmar injection timing

Oh one more thing, be extremely careful if you remove shims from under the pump , itís possible for the pump plungers to bottom out if too many shims come out
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Old 03-07-2022, 17:38   #4
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Re: Yanmar injection timing

I agree with Skipperpete.

Additionally a half a tooth difference is less than 1 degree of rotation. I can't remember the number of teeth on the 3GM30 flywheel but IIRC, it is more than 180.

If the timing on one cylinder is really <1 degree out compared to the other two cylinders, it would not be noticeable on old style IDI mechanically injected engine like the 3GM30.

From the manual, timing is 18 +/- 1 degrees before TDC.
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