I recently put a new hydraulic pump on SMTA that I purchased from this site. It has a plug in the top, rear with a light spring and steel ball under it. Tractor started fine but if I shut it off and restarted it the engine turned hard, as if there was pressure on the pump. If I let it sit a while it was ok. I checked hydraulic valves but they were in neutral position. Finally backed out plug in pump and that seemed to solve problem. The spring under the plug is so light I couldn't believe it was keeping that much pressure in pump. Has anyone else run into this with new pumps? There was no paperwork with pump mentioning the plug.
- Thread starter Hayfarmer
- Start date
Janicholson
Well-known Member
Sometimes the M, SM, SMTA tractors display that starting issue. The port you discuss would flow 1/10 the output of the pump, so I see no way for that to be a factor. If it persists in cranking slow when warmed up, and you think it is hydraulics. Remember it is an open center system that has no pressure until a valve is closed. If in doubt, hook a loop in the ports, or operate a cylinder when cranking.
thanks for the reply. My thought was that maybe there was internal pressure in the pump and that port allowed it to bleed off as it only seems to happen when I restart a short time after running it. I have moved valves including power steering but didn't seem to helpp. Is it possible for pump to have internal pressure?
Janicholson
Well-known Member
Not unless it is trying to lift or push a cylinder and the valve is closed pushing fluid to do something. Open center no pressure. The tractors need Battery cables that are sized for over the road trucks. 2-O gauge. If smaller it will be tough to start after running. Be sure the timing is at TDC when static timed, and that the advance is correct. A Battery with 650 Crank amps is actually required to make reliable starting after running. I have fixed this issue on Ms SMs SMTAs and 400/450s until they had 12 volt systems. Jim
the tractor vet
Well-known Member
Here is one more thing to check , if you are having a hard time tryen to turn over once warm then best look at ing timing . If you are to far advanced then this is your problem . Max advance at wide open throttle is no more then 27 degrees and better at 23-24 BTDC . also take a look at you mechanical advance and make sure it is not stuck in full advance or have broken springs.
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