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-   -   Full throttle needed to start Yanmar 2GM20F (https://www.sailnet.com/forums/diesel/94998-full-throttle-needed-start-yanmar-2gm20f.html)

73Morgan 12-15-2012 10:53 PM

Full throttle needed to start Yanmar 2GM20F
 
I need some help here. While I have a fairly good shade tree mechanic experience with gasoline engines, this is my first diesel engine.

My starting problem has been getting progressively worst over the years, to the point where now I have to give it full throttle to start the engine. In an effort to resolve this problem the head was rebuilt by a reputable machine shop, and the injectors were rebuilt by my local boat yard.

To start the engine I have to crank it for a while and give it full throttle. When it does start it seems to start on one cylinder, while keeping it in the higher RPM range so it does not stall, after a while the second cylinder kicks in.

While cranking at startup I get occasional kick back. During the start up and until it warms up a little there is a lot of suttee black smoke. During startup and after the engine fully warms up under way there is what the mechanic tells me is a fuel knock. When under way I am able to reach full RPM's.

Now I am being told that the compression is low, and that it might be as simple as frozen piston rings.

At this pint my main question is, if the compression is low why would I be getting fuel knock. As I understand it fuel knock and kick back is a result of early combustion of fuel, and it seems to me that if you had low compression the fuel would ignite later rather than early.

Any help is appreciated.

overbored 12-16-2012 02:18 AM

Re: Full throttle needed to start Yanmar 2GM20F
 
I had the same type problem on my 1GM10, the single cylinder model of the 2GM and it was the injector timing. also I don't rebuild the injectors as they are only $100 each and the cost to rebuild is $125. did your mechanic set the timing to 15 or 25 degrees yours should be 15 and some mechanics don't know that there is a difference in the models of the 2GM series engines
low compression can be valve setting. make sure that the two end valve rockers are held in towards the center of the engine as they will slip outward during setting with the valve cover off and the valve clearance will be to tight when you reinstall the valve cover.

Minnewaska 12-16-2012 07:41 AM

Re: Full throttle needed to start Yanmar 2GM20F
 
When you push the throttle to full open, you are both introducing more air to accommodate ignition and flooding the cylinder at the same time. The chugging you are referring to as starting on one cylinder sounds like a symptom of poor atomization of the fuel/air mixture. That's how a flooded engine runs at first.

As you said in your other thread, you had the injectors rebuilt, but haven't clarified what that means. All signals are to a fuel/air problem and injectors are usually at the heart of that. They simply wear out. Other causes could be a blockage or poor fuel pump pressure, but less likely. Although, some get ridiculous with the fuel filters they use and assume that lower microns are always better. Not always true, as your system may clog too fast or overwhelm your pump. Have you checked them? What microns do you use? Also, as I mentioned in your other thread, the rebuilt injectors may have been reinstalled incorrectly, with the wrong seats, so the spray pattern would be affected.

Personally, I've had smoking issues and oil burn from low compression, but until its very low, I've not noticed this kind of starting trouble.

Faster 12-16-2012 01:00 PM

Re: Full throttle needed to start Yanmar 2GM20F
 
I think OB and Minne are on the right track.. while 350 compression may be on the low side I don't think it's low enough to make starting problematic with good fuel delivery. And that means timing and proper atomization.

If you're cranking for excessive time periods try to remember to leave your RW intake closed until the engine catches. Flooding the exhaust system with RWC is never a good thing.

Having to use wide open throttle during starting seems to be SOP for some of these older Yanmars..

73Morgan 12-16-2012 01:44 PM

Re: Full throttle needed to start Yanmar 2GM20F
 
Quote:

Originally Posted by overbored (Post 962359)
did your mechanic set the timing to 15 or 25 degrees yours should be 15 and some mechanics don't know that there is a difference in the models of the 2GM series engines
low compression can be valve setting. make sure that the two end valve rockers are held in towards the center of the engine as they will slip outward during setting with the valve cover off and the valve clearance will be to tight when you reinstall the valve cover.

Quote:

Originally Posted by Minnewaska (Post 962390)
As you said in your other thread, you had the injectors rebuilt, but haven't clarified what that means. All signals are to a fuel/air problem and injectors are usually at the heart of that. They simply wear out. Other causes could be a blockage or poor fuel pump pressure, but less likely. Although, some get ridiculous with the fuel filters they use and assume that lower microns are always better. Not always true, as your system may clog too fast or overwhelm your pump. Have you checked them? What microns do you use? Also, as I mentioned in your other thread, the rebuilt injectors may have been reinstalled incorrectly, with the wrong seats, so the spray pattern would be affected.
.

There were 3 different mechanics who worked on the engine over the years. Each time I ask around and try to find someone who really knows what they are doing. The last one (No. 4) I had look at it and took the compression, he works exclusively on diesels. But, he said he works on larger engines and he did not sound that familiar with this engine, he also said the timing is fixed at the factory. The injectors were actually rebuilt 4 seasons ago and again this last season. Unfortunately I don't know what that means since i relied on others. No improvements either time. This is why I have to take matters into my own hands. There are to meny people out there who call themselves mechanicks.

The fuel filters I have always changed myself. There is a water separator mounted up stream of the engine, and the filter on the engine. Even though I don't have the numbers on hand I don't believe that is the problem since I get the same numbers every year to replace them, and the engine used to run better.

I will check the valve adjustments, mixing tube, and I will get a brand new set of injectors and seats, worst case scenario I end up with a spare set. Also, it has been suggested in my other thread to change out all the fuel components.
The Fuel Feed Pomp works fine. Personally, I am leaning towards the Fuel Injection Pump or timing.

I don't know how to trouble shoot the Injection Pump. The Yanmar manual is not very helpful when it comes to trouble shooting.

Rockter 12-18-2012 10:55 AM

Re: Full throttle needed to start Yanmar 2GM20F
 
Full throttle at start-up is normal for my Volvo diesel motor.
Remember though guys, there is no throttle (per se) in a diesel motor in contrast to the throttle gates of a gasoline engine.
For a diesel, full throttle just helps enrich the first few firing strokes.... it squirts more fuel in.
Throttle back the moment it starts.

MarkSF 12-18-2012 11:22 AM

Re: Full throttle needed to start Yanmar 2GM20F
 
Am I correct in thinking that the Yanmar doesn't have glow plugs? I'd expect this to result in difficult starting and having to use full throttle to start. Can't understand why they thought it would be OK to not install them.

Minnewaska 12-18-2012 11:57 AM

Re: Full throttle needed to start Yanmar 2GM20F
 
Quote:

Originally Posted by MarkSF (Post 963533)
Am I correct in thinking that the Yanmar doesn't have glow plugs? I'd expect this to result in difficult starting and having to use full throttle to start. Can't understand why they thought it would be OK to not install them.

I have no glow plugs on my Volvo and it starts right up, in idle, every time. Knock on wood! I had to move it a couple of years back on a 30 deg day in March and it fired up normally after sitting on the hard for months.

The bloody turbo, however, gives me fits.

L124C 12-18-2012 05:59 PM

Re: Full throttle needed to start Yanmar 2GM20F
 
Quote:

Originally Posted by MarkSF (Post 963533)
Am I correct in thinking that the Yanmar doesn't have glow plugs? I'd expect this to result in difficult starting and having to use full throttle to start. Can't understand why they thought it would be OK to not install them.

I have the same motor as the OP. I always do a cold start at 3/4 throttle, throttling back to idle immediately after start, as directed in the manual. It's over 20 years old, does not have glow plugs, and has never had a starting problem (in the moderate SF Bay Area climate). Kicks on the first crank every time! Once warm, it starts immediately from idle position.
Sounds like a good Yanmar mechanic is in order for the OP. If he is in the Bay Area, List Marine will sort it out in short order. I'll bet they will also tell him to cruise at 3000 RPM when it is running properly. Makes for a happy 2GM20!

73Morgan 12-18-2012 08:44 PM

Re: Full throttle needed to start Yanmar 2GM20F
 
Quote:

Originally Posted by MarkSF (Post 963533)
Am I correct in thinking that the Yanmar doesn't have glow plugs? I'd expect this to result in difficult starting and having to use full throttle to start. Can't understand why they thought it would be OK to not install them.

Agreed, it does not have glow plugs, and it probably should, it would help if it did. But, about 8 years ago it used to start with almost no throttle. Whatever is going on is not normal.


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