400i starting problems

How long has it been since it last started and ran? Was it running okay when it was last shut down?

 

You did the right thing to remove the plugs (just in case a cylinder had filled up with coolant). Next step would be to see if you can manually rotate the crankshaft by driving the big nut at the snout -- if not, remove the starter (which I know is a beyotch on a 400) and try again -- if still no go, a very bad sign.

 

Not being sure of what the fastening torque is on the crank bolt and keeping "Lefty loosey, righty tighty" in mind I'd turn it clockwise as you face the motor so as not to loosen it. With the plugs out it should turn pretty easy.
From what you have described it sounds as though the starter has died, perhaps just the solenoid.
It doesn't matter what gear you're in if an automatic, put it in neutral if a manual box.

 

A few months back I had exactly the same syndrome with my 1980 400i..It turned out to be two things at the same time in my case(so what else is new),,,the starter ($900 very old technology) needed to be rebuilt..the parts as I found out were available at Algar..at that time only two sets were in captivity in the U.S...so they're probably gone by now..I found a WODERFUL shop locally that was able to fabricate the parts for $90..dig it... third generation shop..Also..to remove the starter..You MUST remove the exhaust manifold in two pieces..amazingly easy one you accept the fact that starter is way too large to squeeze out..you must put it on a high lift..it takes one hour and a very stubby 18mm and 19mm wrench to get in there..use plently of rust buster and let it work for a while gloves help ...next..the positve lead on my car was green with corrosion.impeding voltage to the starter solenoid.. made new one with marine 2guage.. easy..If it were me in this situation I would opt for the new high torque British Starter for $450 U.S. made specifically for the job..they're up in Massachusetts..British Starters.com. Had I known of them at the time, I would have gone this route be because these old Marelli starters just destroy your battery charge...also.. the 412's went to a Bosch starter quite available but again still slow cranking..Sorry to rattle on, but 10 years of ownership has shown me a few things...Jacques..I just hope this helps you.

 

This is actually quasi-good news -- tilts the odds towards the starter itself.

Clockwise. See the timing chain figure in your 400i OM -- item 16 is the driving gear on the crankshaft.

Yes, Neutral (not Park) with the emergency brake "on" or appropriate wheel chocks.
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My starter went in the summer (similar symptoms to yours) and I had it replaced with one from British Starters - it spins the motor very fast, way better than the original. As Jacques says, the manifold must be removed, which I think entails removal of the injection unit.

Good luck!

Aidan

 

This is a straight forward operation..these manifolds must be removed from the bottom..they are in 2 pieces of 3 ports each..also..and this is imperative..unbolt them from the collector BEFORE you attempt to unbolt them from the block or you will create a severe torque situation on the bolts going into the engine block and you will break the flanges or strip the bolts... as I mentioned previously these bolts are usually quite rusty so use plenty of rust buster of your choice let them sit for at least 30-45 minutes minimum so that you don't round of the bolt he-heads..if you get in a hurry your 2-3 hour labor charge will pale by comparison from there on out..no fuel inection or gas lines are involved..I watch with amazement the senseless troubles people on this f-chat forum cause themselves by being impacient and sometimes too frugal (spelled cheap) to do things the proper way..I hope this helps...Jacques..remember that self-bonage is the worst bonage of all...