Smoking & Hard Starting

[rims421]

I have a Cub Cadet 7275.
The tractor belches blue smoke when running.
It is also hard to start when warmed up.
When I start the machine when cold after heating it up with the glow plugs for a good long time it starts right up.
After it has been running and up to temp. it does not want to start unless I engage the glow plugs again for a very long time. When I got the machine it would start up when warm without using the glow plugs at all. I have changed the air filter, pulled the injectors and had them pop tested ( they were good) and changed the oil.
I suspect that the valve seals may be leaking allowing oil to drip into the cylinders. By engaging the glow plugs for a good long time it heats up the oil/ fuel mix enough to ignite it.I noticed that when i changed the oil last time I got a very large puff of smoke upon start up.
Anyone have any other ideas? The level of the oil on the dipstick does not seem to be lower between oil changes.
The machine runs fine otherwise.
If it is the valve seals can they be replaced without removing the head? /forums/images/graemlins/confused.gif

 

[KennyV]

If this engine has a lot of hours it may need more than valve seals /forums/images/graemlins/shocked.gif… check the compression. Good luck KennyV.

 

[slowrev]

Sounds like more than valve seals to me. Maybe worn/broken/collapsed rings....I think a compression test would be in order.

Ben

 

[normde2001]

"The level of the oil on the dipstick does not seem to be lower between oil changes."

Seems to me if oil was the problem, you should surely be losing/using oil. Since the average guy doesn't have the equipment to do a compression test on diesels, my next step would be to check/adjust valves, check for plugged muffler and crankcase vent.

 

[KennyV]

Sorry I just noticed I didn’t address your guest ion about changing valve guide seals without removing the head.

You should be able to /forums/images/graemlins/ooo.gif...

With each piston at TDC valves closed, you can rig up a continuous air supply into the injector or glow plug, this will hold the valves closed while removing the valve springs.

But R&R of the head is not a big deal /forums/images/graemlins/grin.gif. You will not save any time not removing the head, and you may get a chance to look at other things while your’ in there /forums/images/graemlins/tongue.gif. KennyV.

 

[rims421]

I think the smoking and hard starting are seperate issues.
I discovered last night that the tractor will not start due to lack of fuel. I cracked open the injector supply tube, turned the machine over and found no fuel was leaking out. Next I checked the voltage at the fuel selenoid. The hold side has 12 volts. The pull side has just 5-6 volts. Next I checked the voltage at the starter. The supply side has 12 volts. The feed from the starter selenoid to the starter motor is where the pull side of the fuel selenoid is fed from. When I engage the starter the voltage drops to 5-6 volts. I have pulled the starter and will drop it off at the rebuild shop. It must be heating up causing the resistance to go up. The lower voltage is not enough to open the fuel valve. I will let you know how this thing turns out.

 

[Soundguy]

How is the system voltage during starting? If the batt voltage drops to 5-6 volts you may have a severly discharged battery. Also, a short in the starter, lowering the resistance, drawing more current, or a dragging starter due to a bad bearing/bushing might also account for such a voltage drop.

Heck.. could be a bad solenoid..

Either way the rebuild should fix that..

let us know what you find.

Soundguy

 

[rims421]

Let me backup for a minute. I first had a problem starting the tractor during the summer. When I would turn the key to engage the starter I would get just a click, and the engine would not turn over. I removed the starter and dropped it off at the rebuild shop. The solenoid was replaced and I think a bearing. After the repair it never seemed to start the tractor well. I mean it would start but not turn over as fast as it used to. Also i found it required engaging the glow plug to start it.( I never had to before unless it was very cold out) I was so busy using the machine that I figured it would have to wait till the winter to get figured out. Eventually it got much harder to start after it was warmed up. I have to believe it is somthing to do with the starter. The strange thing about it is that it would somtime not start for several try's. Then i would engage the key and it would fire right up. By removing the wire from the fuel solenoid and still not having the voltage it would appear that the rest of the wiring could be ruled out.
I got he starter back from the repair shop again this weekend. It is doing the exact same thing. The guy went through the whole thing and could find nothing wrong.
I returned the starter again and he is trying to figure out what to do next with it. Anyone out there with any ideas?

 

[normde2001]

Maybe it's not the starter. Have you tried running jumper cables directly to the starter?

 

[Soundguy]

I agree.. the battery.. or cables may simply not be carrying the load needed for the starter.

Assuming your rebuilder has properly rebuilt it.. it should be almost as good as new if the comutator was dressed and mica undercut.. brushes repalced.. good bearings and good bushings that are not siezing.

Never know.. cables may be bad..or a bad ground connection to the frame.

I'd try a spare battery and some beefy jumper cables as a test.

Soundguy

 

[rims421]

Problem solved at last.
It was lack of voltage going to the starter solenoid.
The wire from the key switch to activate the solenoid was only putting out about 10 volts. I thought that would be enough to pull in the plunger in the solenoid and engage the starter. I had checked the voltage on that wire at the start of this mess with the wire removed from the solenoid. When applying a load on the wire by attaching it to the solenoid the voltage dropped a couple more volts. 8 volts is not enough to pull in the solenoid all the way. The result was that the starter was not getting full voltage across to the terminal that drives the starter motor and pulls in the fuel solenoid. I ran a new wire from the key switch to the solenoid and it fired right up.
I will need to trace out the problem with the old wire at some point because it is wired through all the safety switches, But at least I can use the tractor for the first time in a couple of weeks. Thanks guys for all your input.

 

[Soundguy]

Wow.. a static voltage drop of 2 volts on the solenoid wire.. that would have been a red flag for sure.. especially since as you observed that when loaded the votlage dropped even lower.

Soundguy