Decompression Lever
- Thread starter GMaurer
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- decompression lever
First, re-check the diagram in your manual. As I remember, this is shown in my Universal manual, which covers all the small diesels in the line (circa 1988). FWIW, you should see a lever on back side of the valve cover. This is true on my model M25XP engine and on a two cylinder Volvo owned by a friend of mine.
Another option is to buy the parts manual for your specific engine, from Universal. There is a wealth of detail there, even if we never plan to personally rebuild our motors.
I would look it up but my manual is down at the boat -- I am going to be away from the YC most of this week, so I cannot easily check on this for ya.
Loren
Another option is to buy the parts manual for your specific engine, from Universal. There is a wealth of detail there, even if we never plan to personally rebuild our motors.
I would look it up but my manual is down at the boat -- I am going to be away from the YC most of this week, so I cannot easily check on this for ya.
Loren
You can view the Operator's Manual on line at www.marinedieseldirect.com.
Robert Mann
Member I
My Universal 12 manual also shows the decompression lever. There is no provision on the engine for it. I have a Kubota parts manual that also does not show the parts. I wonder if it was an option that didn't make it as late as 1988.
Geoff Johnson
Fellow Ericson Owner
Interesting. I had assumed the stop lever was the same as the decompression lever on my M25 engine. Maybe someone can explain the difference.
Robert Mann
Member I
GMaurer is correct the shut off lever moves the injection pump rack to a zero fuel position, shuting off the fuel supply to the pump plungers and hence the injectors. A decompression device operates on one of the valves and opens it slightly relieving compression in the cylinder. If this is not adjusted correctly (and sometimes even when correctly adjusted) and the decompression device is used to stop the engine, at high speed, a valve can touch the piston. Repairs get expensive sometimes. Traditionally the decompresion release is/was used on hand cranked engines. Sometimes it can be used to coax enough speed out of a less than sufficient battery to get the engine started although I doubt the Universal with IDI would show much cooperation as the flywheel is quite light and also glow plugs need battery.
Geoff Johnson
Fellow Ericson Owner
I gather, therefore, that if one ever experiences a runaway diesel, the solution is not to open the decompression lever, but to put a board or something solid over the air intake.
Geoff Johnson
Fellow Ericson Owner
Well no, because as I understand the phenomenon (which I hope never to experience) is that the engine starts to run off the crankcase oil because of overfilling, worn piston rings and maybe some other causes. Therefore, shutting off the fuel has no effect. I believe the proper procedure is to keep the engine in gear so that the engine does not rev too high and to then shut off the air supply somehow (without using your hand or you will lose the skin). Of course, this means climbing around an out-of-control engine - not a pleasant prospect.
Robert Mann
Member I
Strictly speaking, if the engine runs away in the true sense, ie it ingests fuel through the air intake, such as some type of combustable gas or the fuel rack should stick in the wide open position or something in the governor jams, (all of which are possible), stopping it with the compression release is preferable to a rod launched through the block (working on the principal of contained damage)! If panic allows, and this is usually directly proportional to the engine size, blocking the air intake is preferable. Interestingly, engines in oil and gas field applications usually employ air intake shutdown valves by regulation. I would hesitate to open the fuel system, as fuel will go a long way and under high pressure can be very dangerous, although i have seen this done as a last resort. Fortunately I think run aways are rare, just as well in close confines (someone in the engine industry once said, "operators run away, engines overspeed").
What's the correct position for this, then?
I apparently have one of these on my M25 diesel - the level is smallish, located at the back of the valve cover, and has a spring attached to it (it's a spring level).
Given the spring, it appears it can really only be left in one position - but is there a 'correct' position that it should be in to avoid ruining the engine?
//sse
I apparently have one of these on my M25 diesel - the level is smallish, located at the back of the valve cover, and has a spring attached to it (it's a spring level).
Given the spring, it appears it can really only be left in one position - but is there a 'correct' position that it should be in to avoid ruining the engine?
//sse
Robert Mann
Member I
If it's spring loaded one would like to presume the decompression release is not engaged when it the natural position. This is the case with all such devices I have seen. The mechanism should operate on the exhaust valve. If the valve is all the way closed then you ought to be able to feel the valve as the decompression release opens it, with the engine stationary. If the release is actuated when the engine is running, such as stuck open, then the engine is not firing on the decompressed cylinder, runs rough and will generally sound ugly when accelerated. Also the exhaust will contain unburnt fuel and there will probably be evidence in the water. After the last string on this i looked at my U12 and there are 2 spots on the cylinder head cover, non machined that I believe would be the spots for the decompression release.