Decompression lever

John-Paul · Post by **John-Paul** » Sat Sep 26, 2009 5:13 pm

Hi folks

I seem to remember reading somewhere that using the decompression lever to assist with starting the Major is bad for the engine. Could someone explain why this is please?

Many thanks,

J-P (who is off to hunt for the battery charger so he won't have to resort to this trick anyway)

Post by **Brian** » Sat Sep 26, 2009 7:20 pm

It was only to be used to turn a cold engine by hand rather than a starting aid, if used in that way, valves and pushrods can be damaged.

John-Paul · Post by **John-Paul** » Sun Sep 27, 2009 12:14 pm

OK, thanks!

Tiger · Post by **Tiger** » Thu Dec 03, 2009 2:58 pm

could someone please point out where this leaver is so i don't touch it, Thanks

MAXPOWER · Post by **MAXPOWER** » Wed Jan 06, 2010 7:29 pm

front of the engine, near the valve cover.

danger will robinson danger.

Post by **Brian** » Thu Jan 07, 2010 8:35 am

As Maxpower says but earlier tractors up to 1957 had the lever coming out of the rear of the cylinder head near the leak off pipe fitting.

TOH · Post by **TOH** » Thu Jan 07, 2010 9:49 am

Brian wrote:As Maxpower says but earlier tractors up to 1957 had the lever coming out of the rear of the cylinder head near the leak off pipe fitting.

On my 1955 FMD it is in the front of the valve cover. It is an export model, though.

Tiger · Post by **Tiger** » Sun Jan 31, 2010 10:09 pm

Hi, My new engine has a decompresion lever on the front of the rocker cover. should it be up or down. It dosn't appear to make any difference ??
Thanks

henk · Post by **henk** » Sun Jan 31, 2010 10:17 pm

Tiger,

it should be down.
If it make no difference the lever is not taking the rod with it I think.
Normally the tractor won't run with the lever up, because there's no pressure in the cylinders.

rok25 · Post by **rok25** » Thu Feb 04, 2010 4:13 am

Hi,
maybe I don't understand very well what Brian means but in my opinion,a decompressor is always a starting aid.Although I agree that it should be used whith caution and certainlly not engaged when the engine is running by itself.I have made a copy of the starting instructions whith decompressor from an instruction book for the (Ford) industrial engines but it is the same on a tractor.Note that use of decompressor is allowed either by electric starter cranking or by hand cranking.Obviously it is a two man operation unless you have a very long arm.

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MAXPOWER · Post by **MAXPOWER** » Thu Feb 04, 2010 4:20 am

now if i can only find a hand crank, been looking for one for five years!

Post by **Brian** » Thu Feb 04, 2010 8:54 am

If you read the text it is the same as I said but instead of using the crank, they are using the starter. It is just to allow the engine to be turned, not for starting.

A number of diesel engines use a decompressor to allow the engine to get up speed before dropping back to full compression "on a roll". Field Marshal tractors did this and so did a number of stationary engines in cement mixers and dumpers. Swing like mad and when you have momentum, drop the decompressor and the speed helps the engine over compression and she starts.

Not so with the Major. You use the crank or short bursts on the starter to enable the engine to turn over slowly. Then reset it and start the tractor. This is what the manual and the instruction books say. And so do the bent pushrods and smashed rocker gear if it is not done in this way.