How many degrees....

[Doug]

Can injector timing be off on a yanmar 2gm20f and still start and run effectively?By our readings we are off by 130 degrees or so. Isn't that impossible? We followed the manuals to the letter and checked 6 times. What are we doing wrong? The fuel starts bubbling up from pump (with high pressure lines removed) no where near the timing marks on flywheel as viewed from starter motor access hole. This is making us crazy. The two dealer/service centers in our area told me, and I quote: "don't worry about it, just put it back together". One told me (and this from the head mechanic at an authorized yanmar dealer) "I haven't checked injector timing on a yanmar in over 10 years, they are always fine unless something breaks". Why then, does the yanmar owners manual show this as a standard maintanence item to be checked and if needed, adjusted every 500 hours??? Somebody out there has to know what we are doing wrong.Thanks.dougps. I posted an illustration of what are readings are in the photo forum under "injector timing". Sorry for reduntancy of multiple posts but I have to get this dialed in.

 

[Bob England]

Injector timing

Well, I don't know much about adjusting injector timing (so, why am I writing this, you ask) but one thought is that the injectors probably don't release their fuel charge (i.e. "fire") as soon as the fuel starts coming out of the pump. They let the pressure build up until a critical pressure is reached, and then some sort of valve-equivalent function in the injector tip releases the whole fuel charge suddenly, under the high pressure. It could be that the 130 degres of crankcase rotation you mention are required before the pump produces that critical pressure threshold. If I were adjusting injector timing, I'd connect the injectors to the high pressure line upside down, and watch the spray. That's the point at which the cylinder "sees" the fuel. Just a thought.Bob.

 

[Gordon Torresen]

Injection timing

You ask what you are doing wrong. I might suggest that your biggest error is getting in over your heads. As indicated by the two mechanics that you have consulted, injection timing is something that seldom goes wrong and making a correction is feared by most. Will the engine run with the injection 130 degrees off? Definately not! Plus or minus 5 degrees makes a radical difference in the running of the engine. The timing is adjusted by adding or removing shims under the pump. Remove too many and you are in for major pump repair. Taking the pump out and in is a king-sized undertaking in itself. You mention the fuel is "bubbling up" when you are checking the timing. Even one bubble indicates that the air has not been properly bled from the system. Seeing the start of the fuel movement is very difficult. I have taken a thermometer tube and opened it at both ends. I place this in a hose attached to the delivery valve and check the movement of the fuel in this tiny tube. The only time we check injection timing is if we have changed components within the fuel pump or done a major engine overhaul. Unfortunately, the Yanmar engines are so well constructed that we don't get the opportunity to go inside often enough. We refer to this as the Maytag syndrome. My advice to you is to put the engine back together and go sailing. It ain't broke. YET.