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Why is My C-123 Engine Smoking?

N

NawlensGator

Member
Copious blue grey blue smoke comes from the exhaust of my 1971 140. It's a real fogger, lightens a little after few minutes under load, but fogging resumes when idling.
It uses about 1/2 quart oil every couple hours and the plugs are wet with oil and grime. It runs really well mowing with a 6 ft woods mower going up and down hills with plenty of power. Oil pressure runs at the second mark left of 75 on the original gauge, which is the 1st mark right of vertical. I'm guessing at least 40 psig.
A Compression test shows all cylinders between 155 and 160 psig.
There is no water in the oil and the radiator water level stays constant.
I bought the tractor in 2004 in great shape and have put less than 500 hrs on it (<30 hrs/yr).
I would like to fix the oil burning problem and continue using this tractor, but I don't have a clue what to fix or look for. Any advice is greatly appreciated.
I was considering sending it to the local shop for an engine rebuild but maybe that's overkill.
 
A overkill, maybe, but maybe not, it's definitely going to need rings,so whats a little more money when you got it apart,do you want a partial overhaul or would u like it rebuilt. My brother 400 gas used 2-3 quarts of oil to,@day, i took it apart, it looked very nice from the top down,but the last over haul was a cheaper kit, it lasted about 20 years, on light work, put new set Hastings rings in, i had to honed cylinders, but that fixed the oil burning !! Get a new kit from this website, you will be fine!!!
 
Thank you very much Fast. I suspected the compression readings at 155+ psig meant the rings/cylinders were good. I guess that was incorrect.
 
Well that's good compression, but that's not the total package,you're mechanic can tell you more when he gets it apart, but chance's are there cant be that much oil coming down thru the valve guides!
 
Well it's like this IF you are sucking thru a half qt. of oil every couple hours then this is a no brainer . She is sucking oil past the guides and past the oil rings . Probably because the rings are glazeds along with the sleeves , You still can have good compression but still have and oil drinker . So to stop tis the head needs to come off and get rebuilt and the pan needs dropped and pull the pistons and dig out the mic's and bore gauge and see how much ware and out of round then IF your lucky and it is still round and not egg shaped a bottle brush hone job and new rings .
 
Agree,it needs an overhaul. the rings are probably glazed,the result of too much prolonged idleing,or 'poopin' around.Go ahead,bite the bullet and overhaul. Do the head too.Then work it or dyno it to break in. then pull the snot out of it from time to time. Get it good and warm.
 
Try some hotter plugs and change oil so it uses some oil but runs just fine Oil is pretty cheap compared to a new engine. Unless you can do all the work a new engine can run 1000 easy and that buys a lot of oil.
 
What is the weight of oil? When was it changed last? I would try a heavy oil like 20w50 with a dose of STP & if it still drinks it up, it is tear down time.
 
Has anyone checked the valve train and make sure the oil drains back down. I am not sure but maybe umbrella seals could be put on the intakes.
 
I really appreciate the great feedback from this forums' experts. Thank you all very much!

I understand the good cylinder compression and oil pressure readings don't negate the need for an engine rebuild if I intend to operate this tractor long term. The local tractor shop suggests sending the head to a machine shop for a rebuild, replacing gaskets, pistons, sleeves, rod bearings, and feeling the crank shaft play by hand to see if main bearings (& crank turning) need replacing. Replacing main bearings and main seals is a more expensive option which I'm not sure is worth it. Does the shops suggestions sound like a good plan?
 
30 hours a year - 15 quarts total at $3 a quart - the oil is $45 for annual operating cost to the tractor. With a rebuild it will probably still burn a quart every 8 to 15 hours of use so a complete rebuild will save about $39 a year. That't if the cylinders don't get glazed by the light use making another rebuild necessary.


I'd just keep adding the oil and look for an opportunity to put a full load on the tractor and run it hard for 8 hours - that MIGHT clean up the glazing.
 
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