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D17 leaking oil from spark plug

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Putnamd17 View Drop Down
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Joined: 19 Aug 2024
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Putnamd17 Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2026 at 11:29am
Measured the inside of the cylinders and they match what the book says they’re supposed to be
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DaveKamp View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DaveKamp Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2026 at 1:33pm
So one thing you CAN do...
Git a big-arse magnet, and stick it to the combustion chamber side of the head.

Go over to your bench grinder/vise area, and gather up all the iron/steel filings from when you were hand-filing that one thing a while back... 

Get 'em gathered up (I use a piece of paper...)  and sprinkle them onto the cylinder head where you THINK there's a crack.

The filings will present a very visible TRACK where a crack exists.

Note-  If you see the filings showing a track, but you don't SEE a crack, that means the crack is under the surface, where you cannot SEE it. 

You can also expose hidden  cracks in machined surfaces by scrubbing them clean, then take a Sharpie marker and 'paint' the surface thoroughly...  then pour acetone on the surface, let it run across... then stop, and let the acetone evaporate.

After the acetone evaps, you'll see that the permanent marker ink will migrate to reveal surface imperfections, particularly cracks. 

BOTH of these techniques work in realm similar to 'magnafluxing'...  but on a poor-man's budget.

My bet is that, if you move that spark plug to a different cylinder, it will leak there, too, which is a bad plug.  Believe me- failed crimps on spark plugs is NOT uncommon... and on Champion plugs, it is VERY COMMON.  

When the crimp seal fails, two things happen-
1) Compression drops... and it has greater effect at low RPM than high RPM (it has longer to leak)

2) The ceramic insulator no longer cools properly... so it overheats, which means:
Preignition occurs... (even if the engine is turning slow, and under a light load, it does!)
Electrode erodes
Ceramic becomes brittle
core fractures and drops parts into the hole....
remains of core spits out into your very dry bean field (or in my case, a boat engine compartment)... starting a fire...

Damage to all those expensive internal parts... and the heartache that ensues.




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 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DaveKamp Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2026 at 1:59pm
Bore gauge and micrometer.  To 0.0001", measure:

Diameter of bore 3/8" down from deck:
Parallel with crank
Perpendicular to crank.

Diameter of bore 3" down from deck:
Parallel to crank
Perpendicular to crank

You SHOULD find (on a well-worn engine) that the cylinder bore is wider perpendicular to crank, than parallel.  This is a result of thrust-side wear. 

You MIGHT find that the cylinder bore is JUST SLIGHTLY wider PARALLEL to crank... this is usually result of the piston warming faster than the cylinder wall under load change.

Lightly clean and measure ridge at top of cylinder liner in both planes.  It SHOULD be same measurement, but slightly smaller than diameter of the bore above.  

Apply a precision straightedge to the top of the cylinder liners.  They'll be the same height... unless there's something fishy afoot.

Bring a piston to about a half inch from TDC.  put a rubber hammer handle on the top of the piston, hold the hammer head in one hand, put your other hand on the hammer handle, and push the piston fore and aft, and right-left.  Does the piston move around in the cylinder?  That's the actuality of slop-  a combination of cylinder liner wear, and piston wear.   If the engine was run with ineffective air filtration, you're gonna find plenty of slop... because dirty soil farm air is very abrasive to engine internals.  That same wear winds up in piston rings, wearing the groove lands and ring surfaces.

You will PROBABLY find a hairline fracture in the block deck between the two center cylinders.  This is not a problem.

Fortunately, the Allis wet-sleeve engine is REALLY easy to refresh... it was a beautifully thought-out exercise in industrial engineering both in production, and in future maintenance.   If you have the engine out of the tractor, giving the castings a little touch-up, and reassembling it with the overhaul kit gets it back into service for another three decades swiftly and economically.  It's almost like the Allis Chalmers engineers had been building industrial-grade stuff for over a half-a-century already...
Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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DrAllis View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DrAllis Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2026 at 3:15pm
This tractor needs to be diagnosed properly. By that I mean filled with motor oil to the full mark and used until it is at the add mark, which is one quart. If the rear main seal is leaking, hang or wire a catch pan under that area to be able to account for how much actually has leaked instead of guessing. Move/swap the leaky spark plug to a different cylinder and see if the leak stays with the cylinder or follows the spark plug. At this point there's no accurate information as to whether we are leaking all the oil or leaking and burning oil. If you think about it, there shouldn't be any oil in any cylinder.....only gasoline mist and air and exhaust gasses. So, if there's oil.....prob not good.
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steve(ill) View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2026 at 3:32pm
i agree with DR.... not much Complete info at this time... Mechanic might have done a very good job, or maybe missed something minor... Engine had 157 psi compression, so dont sound like piston rings are leaking... Cyliner liners look good, no ridge, so the mechanic decided not to go any further into it..... Now has an oil leak "somewhere"... Could be the rear seal was damaged, could be not proper  pan gasket install, could be spark plug compression ring......... could be  BASICALLY NOTHING wrong... Let your new mechanic check out the head, then reinstall... check pan gaskets !
Like them all, but love the "B"s.
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HudCo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote HudCo Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 2026 at 9:38pm
dint read all the posts but did the valve cover gasket get replaced or checked 
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Putnamd17 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Putnamd17 Quote  Post ReplyReply Direct Link To This Post Posted: 1 hour 6 minutes ago at 1:39pm
Tore it all apart Dr was right it’s getting the head redone and I’m putting in new sleeves and rings and etc, what’s the best place to buy this stuff? Am I correct in thinking the overbored kits will drop my HP?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DrAllis Quote  Post ReplyReply Direct Link To This Post Posted: 1 hour 3 minutes ago at 1:42pm
You'll lose or not gain ANY HP if the compression ratio is spec'd at less than 7.25 to 1. Many of those after-market overbore kits are 6.5 to 1 compression ratio, if they will even admit to that.  There are some out there that are 8.0 to 1 and that would be GOOOOD!!
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steve(ill) View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote steve(ill) Quote  Post ReplyReply Direct Link To This Post Posted: 38 minutes ago at 2:07pm
you can still buy the higher compression kits, but they cost 4 TIMES as much $$$


Like them all, but love the "B"s.
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