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Discussion Starter · #1 ·
Well folks after 40 years the stock Koehler k321 went out, and not exactly in a pretty manor. Finally got time to open it up last night and come to find out I had a blowout in the head. Have a couple of pictures to show ya what in dealing with. Was wondering 1. What everyone’s thoughts were on used heads and 2. If my cylinder wall looks clean enough to go back in with std size piston. Anything helps, thanks!
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Dumb question,

How was it running prior to blowing the head? It would also seem,by the soot marks, that it had been leaking for,looks to be for a whiles,,

No hit marks visible on the head, that I can see,,, can you see any?
 

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Discussion Starter · #3 ·
Dumb question,

How was it running prior to blowing the head? It would also seem,by the soot marks, that it had been leaking for,looks to be for a whiles,,

No hit marks visible on the head, that I can see,,, can you see any?
No sir, piston head looks fine, just pretty rough carbon buildup, to be honest with ya when I bought it I brought it back to life after what I assume was 15+ years, (the battery that came with it was dated from 03’). So long story short I personally don’t think it had ran all that great in general, I just gave it a good ole lube tech fluid changeout and hoped it lasted til fall, I planned on rebuilding it this fall/winter, just fell short by about a month.
also yes seems that time sitting did not help the gaskets, as I located two leaking points after pulling the head.
 

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Most used heads are not flat. You can put yours on a flat surface and check with feeler gages how much "warp" you have. For a stock build anymore than 0.003" requires resurfacing. I use a fly cutter on the mill. However you can tape sandpaper to your flat surface and hand sand the head flat. It takes time but works fine. Also use a Kohler head gasket. The cheap ones are garbage in my opinion.

Your cylinder walls don't look too bad but the bore straightness is another critical measurement on these engines. The bottom of the bore wears out of round over time. Another thing is you don't know if the engine was bored oversize before you got it. My advise is tear the engine down, measure everything, compare your measurements to Kohlers rebuild spec's, and then purchase all the parts you need at one time.

If you need to use the tractor until winter, true up the head and throw a new head gasket on it. Then you can do the full rebuild over winter.
 

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Discussion Starter · #7 ·
Most used heads are not flat. You can put yours on a flat surface and check with feeler gages how much "warp" you have. For a stock build anymore than 0.003" requires resurfacing. I use a fly cutter on the mill. However you can tape sandpaper to your flat surface and hand sand the head flat. It takes time but works fine. Also use a Kohler head gasket. The cheap ones are garbage in my opinion.

Your cylinder walls don't look too bad but the bore straightness is another critical measurement on these engines. The bottom of the bore wears out of round over time. Another thing is you don't know if the engine was bored oversize before you got it. My advise is tear the engine down, measure everything, compare your measurements to Kohlers rebuild spec's, and then purchase all the parts you need at one time.

If you need to use the tractor until winter, true up the head and throw a new head gasket on it. Then you can do the full rebuild over winter.
Appreciate the insight, only reason I say std Is because the current piston head is a marked std
 

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Hello
std is standard, put a good Kohler head gasket on and run it
Sometimes the head bolts stretch
bigman
----------------------------------------------------------
How Much Does a Bolt Stretch? – Security Locknut
How Much Does a Bolt Stretch?
Answer: a very small but important amount.

In previous posts we discussed how a bolted joint works, how clamp force is calculated, and how to determine torque required to achieve the clamp force. This month we’ll present more details about the workings of a bolted joint and why bolt stretch is important to understand.

To get clamp force on a bolted joint assembly, the bolt is stretched just a small amount. The solid steel shaft of the bolt acts like a very strong tension spring as illustrated below. The spring tension created when the nut is rotated, and the bolt is stretched, creates the clamp force.


It is important to understand this because, if this small amount of stretch is lost, the joint will fail.

For example, a 3/4″ UNC grade 5 bolt with a 3” clamp distance, fully tightened, only stretches the bolt approximately 0.006”. This stretch creates 21,300 lbs clamping force.

In most components that are bolted together, after tightening, the components settle in or embed in each other, and the clamp distance along with the bolt stretch distance is reduced. This is especially an issue if the bolted components have rough finished surfaces, softer materials, or flex under load.

In the example above, if just 0.006” of clamp distance is lost due to these issues, the clamp force is reduced to zero and the joint will begin to fail.

To calculate the amount of stretch for any bolting situation, the following formulas are commonly used:

 

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Appreciate the insight, only reason I say std Is because the current piston head is a marked std
I didn't see where you identified the piston as standard before this. It is good that the bore is original. That means there is plenty of meat to bore it out if required. It's possible the engine ran poorly due to the head gasket leak which got progressively worse.

I feel your options are to put a head gasket in it and see what happens. I would check the flatness of the head to prevent any premature failure. Option #2 would be a tear down, full inspection/measuring session, and rebuild as required.
 

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Discussion Starter · #12 ·
I didn't see where you identified the piston as standard before this. It is good that the bore is original. That means there is plenty of meat to bore it out if required. It's possible the engine ran poorly due to the head gasket leak which got progressively worse.

I feel your options are to put a head gasket in it and see what happens. I would check the flatness of the head to prevent any premature failure. Option #2 would be a tear down, full inspection/measuring session, and rebuild as required.
Little late on the update, but luckily for me our local small engine repair had a brand new kohler oem head
 

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Discussion Starter · #15 ·
Good deal. I haven't seen a new OEM head available for many years.

Don't toss the old head. There are people who would buy it for reconditioning.
Thank ya, I suppose if anyone wants a head with a hole/crack in it I have what ya need.
Thanks everyone, will keep you all updated with how it goes as I get further down the line
 
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