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Spark plug location(non Allis question)

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Hillmann View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hillmann Quote  Post ReplyReply Direct Link To This Post Topic: Spark plug location(non Allis question)
    Posted: 03 Dec 2022 at 9:57am
I know this is an Allis forum, but there are a lot of smart people here who know a lot about engines so I figured I would ask here since I am already signed up instead of trying to find a forum that would be better suited. 

I have an old kohler engine K321 AQS the spark plughole is helicoiled and the helicoile is stripped.  I ordered a replacement head that fits but the spark plug hole is in a different location.  Originally the plug was between the valves, now it is over the center of the exhaust valve.(the plug doesn't protrude through fully through the head so hitting the valve won't be a problem)

Will the spark plug being in a different location cause a problem with the way the engine runs?
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jaybmiller View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jaybmiller Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2022 at 10:41am
Would really need the Kohler part numbers, but is it the right(correct ) head ??
 As long as the plug don't get hit by the piston, it might not matter 'where' it is.. pretty sure fuel economy isn't a consideration....
3 D-14s,A-C forklift, B-112
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tractorboy Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2022 at 10:55am
Not a small engine guy, I would think it would be ok since both valves should be closed when it fires.  keith so. va.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hillmann Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2022 at 11:09am
Originally posted by jaybmiller jaybmiller wrote:

Would really need the Kohler part numbers, but is it the right(correct ) head ??
 As long as the plug don't get hit by the piston, it might not matter 'where' it is.. pretty sure fuel economy isn't a consideration....


I don't know if either of the heads (replacement or the one that was on there) is correct.  They stopped making this engine in the 70's so the only way to get big parts is to buy them second hand. 

I don't have a clue how important plug placement is.  Is a plug in there anywhere good enough?  Or will the mixture not ignite reliably if the plug is way out of place.  If location is just an issue with fuel economy trying to squeeze out as much power as possible, then I don't care. 

Normally I would just throw the head on and find out but I did a lot of other changes to the engine and making a bunch of changes all at once makes it hard to troubleshoot if it has problems once I put it back together.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jaybmiller Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2022 at 11:37am
found this...

YIKES, the price of the head make MY head spin !!! Sad thing is I probably have 2-3 here (12-14-16 hp used same heads I think....
3 D-14s,A-C forklift, B-112
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Hillmann View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hillmann Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2022 at 12:36pm
That link to jacks small engine sovled my issue.  Once I searched for "Center spark plug location" along with k321 I found all sorts of information that I wasn't finding before. 

It looks like the only issue is I will have to drill a hole in the engine sheet metal for the plug to fit though.  The head I received is designed for easier cold weather starting.  By not fouling the plug with cold unburned gas when cold starting.

And it produces more power by keeping the plug warmer by being directly over the hot exhaust valve.

Both are good for my needs, now that I know, if I were given the choice when I ordered it this is the one I would have ordered.

I bought mine on ebay for $60 and I felt that was kind of expensive for a used part.


Edited by Hillmann - 03 Dec 2022 at 12:38pm
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modirt View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote modirt Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2022 at 12:55pm
More of a comment than a reply of any value, but on occasion I take stuff to a small engine guy. A week or so back, I was out behind his shop for the first time. There was a windrow of dead mowers, tillers, etc......looked to be about 8 feet wide, piled 5 foot high and ran maybe 100 feet down the fence row. Wasn't sure if that was just an eyesore and potential landfill stuffer, or mountain of used parts galore worth who knows how much.

Potentially the latter, but how does one put buyer and part seller together on same page? Probably biggest issue is the parts he has to salvage are not the one's that go bad that turned a potentially good mower into junk.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DaveKamp Quote  Post ReplyReply Direct Link To This Post Posted: 03 Dec 2022 at 5:19pm
I've rebuilt several K-series, I have a beastly little K201 in my Cub Cadet plow/puller tractor... and it is REALLY happy to work hard.

The K-series Kohler went through lots of little improvements over time.  The location of spark plug was ONE of those improvements.  As you noted, the burn efficiency is better with the ignition source located over the exhaust valve... that's because, being an L-head, the valves exist in a 'pocket' off the side of the chamber.

L-head engines naturally don't develop much compression easily, and trying to increase compression by decreasing the head-to-piston clearance puts the chamber in a 'shrouded room', so expanding chamber pressure builds up in that pocket, but the piston is 'over there' and doesn't rapidly receive combustion pressure as it would in an overhead-valve design.

What they found, is that the central-location design would present good ignition in the cylinder, but there would be a significant amount of unburned fuel (carbon deposits) building up on the exhaust stem and port interior... and this was caused by the flame of the centrally-located spark spreading out to the edges of the CYLINDER, but not continuing into the VALVE POCKET.  Effectively, the exhaust gases of the flame front would effectively 'isolate' the pocket, preventing any fuel in that area from getting  enough oxygen to burn, so instead, it just sent it out the valve to become black goo.

By moving the plug to above the exhaust valve, IT was the first area to burn, and the flame propogated from there, into the chamber. 

The downside, is that starting 'in the pocket', would be slowed because it was stuck travelling through a 'tunnel' into the chamber, but this doesn't become a serious impedance to power output until the engine's speed is significantly higher than it's intended powerband... which L-head engines naturally suffer anyway.

Basically, moving that plug brought up the horsepower a LITTLE, but reduced the fuel consumption very noticeably, and eliminated a significant amount of carbon fouling of the exhaust valve.

There's also an LP-gas head for the Kohler K-series... difference being interior volume.  Gaseous setups require higher compression ratio, so they simply made it in reduced head volume.  Competing guys will look for the LP head specifically for this reason... and then they'll go to steel crank and flywheel, forged aluminum rod and piston...
Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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