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300sd can't start changed motor, please help.

Group,

I hope some one can help me with a very frustrating problem I am having with starting up a recently purchased 126 motor. I blew up my motor in my 1982 300sd last January. After studying option's for months I decided to buy a low mileage (78K) motor complete. I did not want to deal with all the hassles of rebuild. The new motor is now in the car and won't start though it was a running motor three months ago. I have a 5 gallon can of fresh fuel on the fender with clear hose to the pre filter and clear hose from the bypass back to the can. No air in hoses. Glow plugs have been pulled, tested, and they draw current and get hot. The engine was cranked over with the glow plugs removed and all cylinders discharge a violent fume of fuel vapor on each stroke, so I know that the injectors are working ok. The engine has good compression. I have purchased a new 950 amp battery and have had the starter rebuilt so the engine for at least the first 15 seconds cranks at a good clip. No vacuum lines are hooked to the injector pump. The engine tries to fire now and then but not enough repetition of firing to start the motor. After much frustration I shot small quantity of ether into the turbo and got the motor to start. It ran with my foot on the excellerator if I kept speed up to 2500 RPMs the sound was normal and all 5 cylinders were hitting ok, but when I let it drop below 2000 RPMs it faltered and died. I have not been able to get it started again. Can any one suggest what I am missing on this I really need to get this thing out of my garage and am clueless what the problem is.

Thanks. Bruce Buchanan

Najurb key

Reply to
Bruce Buchanan
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Need more information. Did the motor come complete? With IP installed on motor? or was this a stripped down motor where you installed all your old parts?

Reply to
Nobody

This is sure a puzzler!

You've done some good diagnosis; the problem is obviously not fuel or glow plug related.

It's time to check the valve and injection timing, also the valves' gap.

Remove the valve cover. Turn the engine (a wrench on the nut of the power steering pulley should do it) in the correct direction until the notch in the thrust collar immediately behind the cam's chain sprocket is aligned with the groove cut into the left side of the front most cam support tower. That's TDC for #1 on the cam, now read the crankshaft angle off the harmonic balancer - it should be between 0 and 5 degrees, especially if the engine has be run only 78 K miles.

If the angle is significantly different from (0 to 5 degrees) then the chain has jumped and the cam needs to be reset to be correct with the crank. That's a possibility but not probable.

The next is to check some of the valves' gap. .004 INCH for the INtakes and .015 INCH for each EXhaust. Check each valve with its cam lobe pointing 180 degrees away from its rocker. WRITE DOWN each that you check to avoid duplicating your work. Adjust the CAP nut and lock the adjustment with the lower nut. 14 MM straight wrenches can be used if you're patient.

If the cam is correct and the valve adjustment reasonably OK then the injection timing is suspect - probably badly retarded, beyond adjustment range. That means someone removed the injection pump and installed it, probably 24 degrees retarded. Again, #1 cylinder is the reference point. There are various methods of checking the fuel delivery - drip tube, water bubbles etc.

Or you can turn the engine to 24 degrees BTDC (be sure its for #1 - that both cam lobes are away from its rockers) and remove the injection pump. Its drive gear has an intentionally mission tooth - that should be aligned with a groove cut into the collar immediately behind the gear. Reinstall the pump and check the fuel delivery. Turning the top of the IP toward the engine will advance the injection timing, turning the top of the IP away from the engine will retard the timing. The timing isn't too critical if its basically OK, you can adjust it later - easy starting but poor power indicated retarded injection, preignition too far advanced timing.

You have your work cut out. Hope this helps you.

Tom

Reply to
T.G. Lambach

Or you can turn the engine to 24 degrees BTDC (be sure its for #1 - that

Reply to
Bruce Buchanan

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