Hey folks, got a question about diesel knock

[General Lee]

I just got this new to me 1978 B7100. Today I changed the oil, fuel filter and air filter. Changing the fuel filter caused the fuel system to loose prime. Took me a while to figure out where the bleeds were. I first cracked the bolts for the injector lines and turned the motor over for a while trying to bleed the system. That didn't work. It wasn't until I bled the system at the fuel assembly and injector pump that the motor finally started. When it started I noticed a pronounced knocking that wasn't there last night (when I first brought it home)
I ran the tractor for a bit and seemed to be a little better but had to cut it short because a storm rolled in. I also noticed a little smoke from the exhaust when I throttled up at times. This wasn't happening yesterday either.

So in short, these issues started after I change the oil and fuel filter. Could the knocking be from an overload of fuel from me turning the motor over numerous times with the injector lines cracked while trying to bleed the system? And whats up with the motor smoking after a fresh oil change?

 

[DiezNutz]

Could the knocking be from an overload of fuel from me turning the motor over numerous times with the injector lines cracked while trying to bleed the system? And whats up with the motor smoking after a fresh oil change?

No, the injectors won't even open below a minimum pressure, so with the lines cracked no fuel was being injected... any excess fuel would be running out the connections you cracked. That's why you turn it over until you see fuel appear at the injector unions, then you tighten them and try to start it. You can't "flood" a Diesel (except with leaky injectors). Did you crack the connections at the injectors or at the pump?

What color smoke... blue (oil) or black (fuel)?

Do these injectors not have return ports and a return line? Pulling a vacuum on the return is sometimes preferred vs. cracking unions loose.

 

[General Lee]

Smoke color - Hmmmm, seems more on the white side maybe with a hint of blue, not black unless its during start up. The injectors do not have return lines that I know of or if there are I don't know what I'm looking at. If I knew about the bleed on the injector pump before hand I wouldn't of had to crack the lines, lol. I really don't have much experience on diesel engines. I'm in the learning stage with my tractors.

 

[kuboman]

Quite normal to have excess knock after air is introduced. It will take a while to work the air out.

 

[General Lee]

Quite normal to have excess knock after air is introduced. It will take a while to work the air out.

Hmmm, interesting. Makes feel a bit better. I know it just doesn't sound right now.

 

[kuboman]

Air compresses, diesel does not so when you get air in the injector lines you get inconsistent spray patterns which causes the knock plus the fact that you are not getting the full charge of fuel or in some cases overfueling. Air can give all kinds of symptoms. Quite often the air will clear out faster if you put the engine under some load.

 

[aczlan]

White smoke after the engine is warmed up can be a bad thing, it is a common indicator of coolant in the combustion chamber (frequently caused by a leaking headgasket)


Aaron Z

 

[Giles]

How long have you owned the tractor
This is by no means, a diagnosis, but something to thank about.
When rod or crank bearings start to wear, it is most noticable when a cold engine is first started. The engine has cooled down and the thin oil has escaped the bearing surface and returned to the sump. This is accelerated with worn bearings and more of the residual oil is lost. After warming up, the engine will quieten down and may not be noticable.
I have seen many engines, both gas and diesel, behave like this and lasted a long time---and some didn't
I would do an oil pressure check with a known good mechanical gauge if the symptoms last and I would not work the machine hard for a few hours.

 

[kuboman]

I really would not worry about anything really bad going on here until you get the air out of the system.:thumbsup: I have had it take up to an hour on some engines before everything was right again. White,black,blue smoke means nothing until the air is gone.

 

[E/S]

I really would not worry about anything really bad going on here until you get the air out of the system.:thumbsup: I have had it take up to an hour on some engines before everything was right again. White,black,blue smoke means nothing until the air is gone.

X2
Take it out and work it.

You guys are scaring him.

E/S