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Putnamd17 
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 Topic: D17 leaking oil from spark plug
Posted: 14 Sep 2026 at 9:24pm |
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My d17 series 4 gas, has some oil leaking from the spark plug closest to the fuel tank, I checked the compression and it was about 157, there is some smoke coming from the exhaust as well, I am thinking this is a valve seal issue. Anyone run into a similar problem before?
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DrAllis
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Posted: 14 Sep 2026 at 9:31pm |
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There are no valve seals or valve stem umbrellas. The valve guides and valve stems are probably worn out. The piston ring grooves are loose top to bottom, the sleeves have a heavy ring edge at the top and the ring gaps are too wide. In short, everything wears out at the same time. A 98% chance it is time for an overhaul.
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DrAllis
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Posted: 15 Sep 2026 at 6:21am |
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How do you use or intend to use the tractor?? As long as you aren't fouling a spark plug all the time, you could run it for a long time with this condition, using it for light jobs/short run times. If you intend to grind feed weekly and expect to operate it mowing, raking and baling hay, then your days are probably numbered.
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Putnamd17
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Posted: 15 Sep 2026 at 6:41am |
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I was hoping to use it for some light plowing with a 2 bottom and bailing about 5 acres of hay.
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Putnamd17
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Posted: 15 Sep 2026 at 6:42am |
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I had a mechanic go through the engine and look over everything he said he wouldn’t be concerned with anything at the time he went through I asked him about my cylinders and he said they had a lot of life left yet.
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DrAllis
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Posted: 15 Sep 2026 at 11:06am |
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"Go thru the engine"..?? what does that mean exactly ??? He had it apart and looked at the cylinders?? and now it smokes blue out the exhaust ??
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DrAllis
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Posted: 15 Sep 2026 at 11:08am |
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Your oil leak isn't as simple as a valve cover gasket leaking ?????????
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Putnamd17
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Posted: 15 Sep 2026 at 12:29pm |
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I do not see any oil coming from the valve cover, he went through and mainly replaced all the seals and such said the cylinders looked good he had the engine out and completely apart on an engine stand, I do not see much blue smoke there was some white smoke but only for a little bit
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Dirt Farmer
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Posted: 15 Sep 2026 at 12:40pm |
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What are the chances that the crush washer is missing on the spark plug and what you are seeing is seeping past the threads
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DrAllis
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Posted: 15 Sep 2026 at 1:16pm |
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A fairly typical result of an "oil burning" AC engine is engine oil leakage around a spark plug. That's just a fact on these engines. So, does it use oil or not?? and you just bought the tractor so you don't really know ?? If he didn't have the cylinder head removed, he only saw the cylinders from the bottom side, which is kind of meaningless.
Edited by DrAllis - 15 Sep 2026 at 1:18pm
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Putnamd17
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Posted: 15 Sep 2026 at 1:38pm |
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I know he had the head removed, it uses some oil but there is a small rear main leak so I’m not sure where most of it goes but it seems like I’m loosing more oil than what’s coming out of the rear main. It is not a very large leak, it has a new head gasket should I be running different spark plugs in it? Hotter ones? It has the 3/4 ones recommended in the book in it
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DrAllis
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Posted: 15 Sep 2026 at 2:14pm |
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If you aren't fouling a spark plug, there is zero reason to go to a hotter heat range plug.
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Putnamd17
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Posted: 15 Sep 2026 at 2:22pm |
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The spark plug is completely covered in carbon very black.
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8070nc
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Posted: 15 Sep 2026 at 4:33pm |
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Id put a new set of plugs in it and run it some and see what happens and figure it out from there
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1984 80780
1957 D14
DES 300 with 25000 engine
616 tractor
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DrAllis
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Posted: 15 Sep 2026 at 6:45pm |
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It's sad to think that he had the engine out and in a stand?? and the rear seal wasn't replaced?? or he replaced it and it still leaks?? Could be either one......
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Putnamd17
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Posted: 15 Sep 2026 at 7:42pm |
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It was replaced and still leaks
Edited by Putnamd17 - 15 hours 57 minutes ago at 9:04am
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DrAllis
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Posted: 15 Sep 2026 at 8:35pm |
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He doesn't know how to install a D-17 gas rear seal correctly. You haven't said how long you've owned this tractor.
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Putnamd17
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Posted: 16 Sep 2026 at 4:14am |
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Maybe 2 years but the first year it sat around didn’t work at all only was ran to move it, and he just went through the engine a few months ago so was hoping to start using it
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Putnamd17
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Posted: 16 Sep 2026 at 4:15am |
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Work as in pull anything only moved from on shed to another
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DrAllis
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Posted: 16 Sep 2026 at 5:49am |
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He had to remove and reinstall the oil pan to do the rear crankshaft seal. If one isn't proficient at those tasks with this engine, it could be leaking at either or both areas.
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SteveM C/IL
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Posted: 16 Sep 2026 at 9:51pm |
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Wow! Had the head off and didn't give it a simple ring job?
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Clay
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Posted: 18 hours 4 minutes ago at 6:57am |
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Was this the first time the mechanic worked on an engine without supervision?
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DrAllis
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Posted: 16 hours 16 minutes ago at 8:45am |
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That might be a little harsh. Each brand and model of engines has its own quirks. I never knew that some small block Chevy engines needed to have Permatex or some sort of sealer on the head bolt threads or you would probably wind up with leaks when completed. I don't work on small block Chevy's, so why would I know that. Likewise, rear crankshaft seals, pan and arch gaskets take some expertise on these AC engines to keep things dry. If he didn't use some sort of sealer on the head gasket, that might be next. But, taking on jobs that one knows nothing about is a risk to the Tech doing the work and the owner of the machine.
Edited by DrAllis - 16 hours 15 minutes ago at 8:46am
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Putnamd17
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Posted: 16 hours 5 minutes ago at 8:56am |
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He’s a good mechanic he’s just a case guy not many ac guys in my area that I know of
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Putnamd17
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Posted: 16 hours 3 minutes ago at 8:58am |
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What’s this about sealant on the head gasket? I’m going to have the head removed again so wanna make sure it gets the new one installed right
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DrAllis
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Posted: 15 hours 36 minutes ago at 9:25am |
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Get it apart and tell me what type of head gasket material it is made of.
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DaveKamp
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Posted: 2 hours 6 minutes ago at 10:55pm |
I can't imagine a guy pulling an engine out, removing the head, removing the pan, changing a main seal, and still having this result from the scenario... something simply doesn't add up here.
The Allis D17 engine is a replaceable wet sleeve engine... with the head off, and pan off, you can literally pop the rod caps, push the rods, pistons, sleeves right out of the block, swap in new pistons, rings, and sleeves in one work shift... in-frame rebuild kits are available from at LEAST 20 suppliers, they're usually under a grand. If someone goes through the trouble of opening one up 'for a look', it's silly to not already have an in-frame kit in consideration, as the resources one invests to get IN THERE is significantly higher than getting the kit on-hand.
But let's go back to the original complaint- Oil leaking out of the spark plug.
Is that oil coming from around the threads, from the junction between the steel housing and the ceramic insulator, or from the cylinder head/valve cover above?
If it's coming from the junction between the steel housing and ceramic insulator, the crimp and seal have failed- you have Champion plugs, remove and replace them with Autolite AC252's.
(when the crimp/gasket fails, the plug's ceramic insulator will fracture and drop a chunk of very hard stuff, along with a piece of the electrode, into your cylinder, which will dig a huge gash up your cylinder wall, and ram it into the head, punching a hole into the casting. If you're lucky, it won't bend the rod and break the crank, but you'll be investing in an in-frame kit AND a cylinder head, and Champion simply doesn't care- Don't ask how I know how badly this goes, and how costly this becomes...) 
Edited by DaveKamp - 2 hours 4 minutes ago at 10:57pm
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Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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DaveKamp
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Posted: 1 hour 52 minutes ago at 11:09pm |
And I hate to have to bring this up, but my daughter called me one day about her car 'making some strange noises'. She took it to three different mechanics, who all drove it, and said 'nothing wrong'. She said they looked underneath, all around, and found NOTHING.
She drove it 4hrs home on the interstate, and when she turned into the driveway, the problem was not only audible from 60ft, it was VISIBLE. The transmission tailshaft was visible, when it SHOULD have been tucked up into the hump in the floor. The transmission support crossmember had rusted, such that the tailshaft support and mount isolator dropped 4", with the tailshaft housing riding directly on the FRONT of the crossmember, and the rear driveshaft (it's 4wd) rubbing on the remains of the REAR side of the crossmember.
How it is that ANY shop can have ANY individual with an ASE patch on their shirt, and NOT notice this, is totally beyond me, but the answer is very clear: What one identifies as a 'qualified' or 'good' or 'trusted' is meaningless, when an obvious problem gets dismissed. IF the guy is a CASE guy, then he's probably had his hands in an SC, or a VAC, or a DC, or RC, or L... mebbie a 350, 530, or a 910? They're all in the same technical realm and operating principle of the Allis... if he was seeing oil leaking out of the spark plug of a 530, would he think that normal? I wouldn't... a leaking spark plug isn't part of the suck, squeeze, bang, blow process. This just doesn't pass the simple scrutiny test.
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Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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