engine turns over backwards on cold starts!

[Nutsnbolts]

Whitedog:

I loved the versatility of those engines. Even loved the noise. Just not the piddling. And its associated slimy mess. I never understood why those engines would just not seal- although I never had a comback on the two that I worked on, so I don't know if they're still out there somewhere... Absolutely disgusting in a truck/bus with more than 10 miles on it. At least with the EMDs (locomotives) the grime was reduced because the engines are in ROOMS that can keep the road nastyness out.

Do you play with those?

Many people collect cars. Some people also collect other stuff. I'd love to add a fully restored and operational 12V71 on a stand to my collection of junk someday. I'd try for a 16V, but I don't think I could find a floor to carry the weight!

The day is coming, and I don't think it's far away, when these engine will be out of operation, and more people will talk about them than use them.

-Rich

 

[whitedog]

I have only played with a few of them. One was a replacement for the original engine and it was the wrong configuration. The head was on backwards and it didn't have a turbo and maybe one other thing. I also like that with just a few small tools, you can rebuild the entire fuel system.

 

[supton]

I thought so, made sense given your background and a good guess. I've heard elsewhere they leak alot too. Poor cylinder sealing, high crankcase pressure maybe? IIRC, it's a ported design, in that the intake is ported at the bottom of the cylinder, while the exhaust is out the cylinder head via convential valves. The famous Roots blower is mounted sideways I think, on the motor, not quite the way it's used on gas motors as a supercharger; but I've never seen a pic of these motors, in person or on the web, so I could be wrong. Anyhow, I wonder if the ports weaken the wall a bit, allowing either flex or wear or egg shaping, so that ultimately they tend to have alot of blowby.

Or could it be even simpler: when the piston at at TDC, intake pressure (from the supercharger) tends to leak into the crankcase? I have no idea how the piston is done, must have a low(est) ring on it it seal the intake port for this reason.

Head on backwards? I guess the head studs are symetric in design, maybe not the coolant passages, but I'd tend to think that the mistake would be obvious rather quickly ("Hey, how come these fuel lines are too short all of a sudden?").

 

[whitedog]

Head on backwards? I guess the head studs are symetric in design, maybe not the coolant passages, but I'd tend to think that the mistake would be obvious rather quickly ("Hey, how come these fuel lines are too short all of a sudden?").

It is by design. Part of the portability of the engine.

Part of the reason for the leaking is that there is no head gasket, but rather fire rings and rubber seals.

 

[supton]

Ah, ok, makes sense--flip around the head based upon the application, to move the exhaust manifold around. Injector lines follow. Interesting motors, they are distinctive in sound.

 

[whitedog]

No injector lines. It's unit injectors so there is just a fuel line to the transfer pump and from the head to tank.

 

[supton]

Learn something new every day. Thanks whitedog.

 

[Nutsnbolts]

...And any end of the crankcase can be used as the front/back! You can mount the bell housing flange at either end, so the blower is on the side you need it on. Very versatile.

-Rich

 

[guntherfrank]

I just have been reluctant to work on the issue since I have been back in washington where the weather hasn't been favorable for working on a car outdoors. I did however try out a couple of things the other day when It cleared up. With a fully charged battery I tested the voltage to the main power of my ecu and it was 12.5v but while cranking the starter it dropped significantly to 7 or 8 volts. I also tried hooking up jumper cables directly to the starter bypassing any possible bad connections or battery cables. The starter still cranked the engine over slowly like it was struggling. This is a IMI high torque starter which should have no trouble cranking over my engine. this has led me to believe that my starter motor is fried or something and is drawing way too many amps so It is robbing power from the rest of the electrical system. I think I will have to come up with a new starter before I can really test this theory so It might take me a month or more to come up with the extra cash. I will keep you all posted and post some pictures soon. thanks for the help everyone.

 

[chrisfiat]

does your friends turn over faster??? check all grounds from the battery to the engine and body you should have a ground wire direcitaly to the block ?? if youy don't currant will be trying to find another path through cables mounts fuel lines etc and do a voltage drop test on the starter cables and the two ground cables( from the battery to block and block to body). voltage drop should be no more than .3 to .4 volts either way

 

[guntherfrank]

yeah my friends did turn over faster. he modified a starter from a diesel vanagon to fit his conversion. The IMI starter should have more cranking power. I did hook up a ground strap from the bolt on the starter directly to the body hoping to solve a grounding problem but it made no difference. I will try the voltage drop test on the starter cables and the ground cables next time I have a chance. Wouldn't hooking up jumper cables directly to the starter bypass any bad battery connections?

 

[guntherfrank]

case closed

I finally picked up a new starter. just like the one I had. an IMI high torque starter, hooked it up and blam! it started right up perfectly smooth. even on cold starts it starts right up first try every time. so I guess the theory about the old starter being partially burned out drawing too many amps, robbing voltage from the ECM and not turning the engine over fast enough was the case. I will post some pic's soon.

 

[EddyKilowatt]

Chrisfiat's right... starter motors are series-connected commutator motors; if you reverse the external (battery) polarity, they'll still turn the same direction.

You'd have to reverse the current flow thru either the armature or the field coil, by fundamentally rewiring the internal wiring in the starter, in order to reverse its direction of rotation.


Eddy

 

[Dick_Larimore]

Starter Motor Design

Virtually all light duty starting motors today have permanent magnet fields. All present day TDI's are of this design. If you reverse the battery connections to these starters, they do run backwards. However, since starter drives have a one-way overruning clutch, if they run backwards they won't provide any torque to the vehicle ring gear.

 

[mijbo11]

The only way it would be turning over backwards is if the starter motor was running backwards. The only way for the starter motor to run backwards is for it to be wired backwards. Or the battery to be hooked up backwards. But the solnoid might be not engaging all the way. I, too, would pull the starter apart first to check things out.

And then it could be the adapter like David says,

dc power will not turn a starter backwards only ac power

 

[guntherfrank]

we actually went over this already and it had nothing to do with the starter going backwards. chrisfiat mentioned something about if the starter wasn't turning the engine over fast enough (250 rpm) there wouldn't be enough momentum to complete the revolution when it initially fires and the engine would fire backwards. I forget why the engine can't actually run backwards but I know it would always stall immediately if I kept trying it would eventually fire the right way and run fine. the loud grinding noise was from the flywheel trying to go the opposite direction as the starter. crisfiat also mentioned something about the ecu preventing the engine from firing if the the rpms are below 250. I am thinking this function was inhibited because there wasn't enough voltage going to the ecu because the starter motor was partially fried and drawing too many amps. new starter=engine turns over faster and starts right up.

 

[EddyKilowatt]

My old British motorcycle will run backwards for one revolution when you're kickstarting it, if there isn't enough momentum and the spark timing is a little advanced. The loud grinding noises come from your ankle and knee in that case, though...

Eddy

 

[redmondjp]

dc power will not turn a starter backwards only ac power

Um, not true. Most DC motors will actually run on AC just fine. The brushed-type of small electric motors typically used in everything from drills to kitchen mixers to vacuum cleaners were originally developed as the so-called 'universal motor' which would run on both DC or AC. This was very helpful in the early days of the 20th century when there were still Edison-type 120VDC electrical systems in use (some of them in NYC buildings with their own power plant in the basement) as well as the Tesla/Westinghouse 60hz AC system which has become the standard today. You could sell an appliance to anybody without worrying about whether it would work at their home.

Some quick clarification on DC motors. If one wants to change the direction of rotation, the polarity of either the field (the stationary windings around the outside) OR the armature (rotating field inside) must be changed. Changing the polarity of both will have no effect at all on the rotation.

In a DC motor with field windings (as opposed to permanent magnets, as used on the starter motors of older vehicles), there is no way to change the direction of rotation without rewiring the motor. Changing the external polarity doesn't change the relationship between the field and armature so the motor will run in the same direction no matter what the polarity of the applied power is.

In a permanent magnet (PM) motor (as many starter motors are now), however, the polarity of the field magnets is fixed. In this case, changing the polarity of the applied power will cause the direction of rotation to change, as the relationship between the polarity of the field and armature is affected by the external polarity.

Thought you'd like to know! In one of my former jobs, I was the EE for battery-powered lifts for a major industrial equipment manufacturer, and I dealt with DC electric motors of all types (series and shunt-wound-field types, PM, and seperately-excited or 'sepex'). So I guess you could call me a motorhead

 

[mijbo11]

i didnt say they wont run on ac just that reversing polarity wont reverse rotation of the starter.