Head Gasket Replacement and Head Planing

[benjiboo 174]

So on my K91 Kohler that came on my Suburban 400 I had noticed a little bit of oil bubbling between the head and block. Yummy....this means a head gasket/head work needed. So I pulled the head off and the head gasket actually looked like new without any burn through or anything like that. But....the head obviously hadn't been planed prior to replacing the gasket so...here are a few pictures of my process from beginning to the end result. 

[benjiboo 174]

This picture shows just how "out of flat" a head can get and the need to plane or "reflatten" the head when replacing the head gasket.

[benjiboo 174]

A few pictures of the condition of the block deck and cylinder bore. 

[benjiboo 174]

Here are the rest of the pictures of planning the head and the end result. 

[benjiboo 174]

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Edited December 19, 2022 by benjiboo
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[Jeff-C175 7,203]

And don't forget to retorque after a few heat/cool cycles!

 

[benjiboo 174]

5 minutes ago, Jeff-C175 said:

And don't forget to retorque after a few heat/cool cycles!

 

Yes, this is absolutely correct. 🙂

[ri702bill 8,990]

1 hour ago, Jeff-C175 said:

And don't forget to retorque after a few heat/cool cycles!

BUT - before that - you still need to do the tried and true fine sandpaper on a FLAT surface, done in a figure 8 motion. This is needed to remove the milling cutter swirl marks, and it leaves a suitable sealing surface that has random micro scratches. If you were to dust a light coat of black primer on the milled surface - one pass on the sandpaper would show that more work is needed.

 

And yes - retorque it before working it too hard....

Bill

[WHX?? 50,758]

I hate glassing  heads... requires patience which I have none of. I do mist them abit with paint and when the paint is gone good to go. 

Not worried about raising the compression Ben? 

[benjiboo 174]

8 minutes ago, WHX?? said:

I hate glassing  heads... requires patience which I have none of. I do mist them abit with paint and when the paint is gone good to go. 

Not worried about raising the compression Ben? 

Not enough to be an issue. I'm not sure exactly what the compression ratio of a K91 is supposed to be after doing a quick search, but skimming a few .001" off isn't going to hurt anything. If anything it'd probably give this old engine a little more spring in it's step. The manufacturer calls for 86 octane or higher so it's definitely not a high compression engine from the beginning. Some may want to go on about timing issues and such blah blah blah but on this engine it's not going to make any real notable difference. If one was to really mill the head down then yes eventually you'd run into issues with high compression...but what I've done is no different than the sand paper and piece of glass technique, I've just done it how it's done at the factory with a mill.

[benjiboo 174]

26 minutes ago, ri702bill said:

BUT - before that - you still need to do the tried and true fine sandpaper on a FLAT surface, done in a figure 8 motion. This is needed to remove the milling cutter swirl marks, and it leaves a suitable sealing surface that has random micro scratches. If you were to dust a light coat of black primer on the milled surface - one pass on the sandpaper would show that more work is needed.

 

And yes - retorque it before working it too hard....

Bill

Not really...I'm pretty sure the heads are milled flat after casting when they're new. The sand paper trick wouldn't hurt anything but it's really not necessary, it'll seal up just fine after milling. 

[WHX?? 50,758]

4 minutes ago, benjiboo said:

The sand paper trick wouldn't hurt anything but it's really not necessary, it'll seal up just fine after milling. 

I would guess so if the mill tool is right and speed right. 

[953 nut 57,965]

12 hours ago, benjiboo said:

I'm not sure exactly what the compression ratio of a K91 is supposed to be after doing a quick search, but skimming a few .001" off isn't going to hurt anything.

It was 6.6 to 1 coming off the assembly line, bet you have kicked it up to 6.600001 to 1.                 

12 hours ago, benjiboo said:

Some may want to go on about timing issues and such blah blah blah but on this engine it's not going to make any real notable difference.

Probably not too much of a high performance issue but the timing needs to be spot on if you want it to start well.

[ri702bill 8,990]

13 hours ago, benjiboo said:

Not really...I'm pretty sure the heads are milled flat after casting when they're new. The sand paper trick wouldn't hurt anything but it's really not necessary, it'll seal up just fine after milling. 

Curious on this one - please continue the post after there are quite a few hours of use - be nice to know it the step I recommended is, or is not necessary for a longterm repair....

Bill

[benjiboo 174]

2 hours ago, ri702bill said:

Curious on this one - please continue the post after there are quite a few hours of use - be nice to know it the step I recommended is, or is not necessary for a longterm repair....

Bill

 

2 hours ago, ri702bill said:

Curious on this one - please continue the post after there are quite a few hours of use - be nice to know it the step I recommended is, or is not necessary for a longterm repair....

So basically my point about this part was that they don't have people in the factory with glass and sandpaper planing out heads...they're mass produced and after casting are probably either milled or knocked flat on a belt sander and slapped together. Lol. I'm not saying your method is wrong or doesn't yield excellent results, as I've done it myself that way in the past and it worked great. If we were working on really high compression, high revving race engines then I'd agree a little more attention to detail would probably be in order. My thought process was do it as close to the manufacturing process and it should be sufficient since they, by in large, operate trouble free that way for years from the factory. When we tighten down these heads they deform and deflect a little anyway so as soon as you torque the bolts down, it's no longer perfectly flat anyway. So at some point we end up unnecessarily chasing our own tails if we over complicate it. Lol. I would say most head gasket replacement failures are a result of an improper torque process if the head is satisfactorily flat. As for the heat cycling and then retorque....well...not a bad idea one would think, but is that a recommendation from Kohler on a new engine? I don't have a definite answer for that but one wouldn't think so either however I definitely could be wrong on that part...🙂

[Jeff-C175 7,203]

1 minute ago, benjiboo said:

is that a recommendation from Kohler on a new engine? I don't have a definite answer for that but one wouldn't think so either

 

Run it a few times, then put the torque wrench on it and check it.  You will be surprised at how loose the head bolts have become!  That should be the answer right there I think?

 

 

[benjiboo 174]

2 minutes ago, Jeff-C175 said:

 

Run it a few times, then put the torque wrench on it and check it.  You will be surprised at how loose the head bolts have become!  That should be the answer right there I think?

 

 

Yeah probably not a bad idea one would think. 🙂

[Snoopy11 5,717]

2 minutes ago, Jeff-C175 said:

 

Run it a few times, then put the torque wrench on it and check it.  You will be surprised at how loose the head bolts have become!  That should be the answer right there I think?

 

 

Most of the time I torque mine when the engine is warm, as well.  NOT HOT... just warm.

 

Don

[Jeff-C175 7,203]

4 hours ago, Snoopy11 said:

Most of the time I torque mine when the engine is warm, as well.  NOT HOT... just warm.

 

Don

 

I usually wait till it cools again.  But 'warm' is a relative term!  I don't usually torque heads when the wind chill is -25 !  

[Wheelhorse#1 1,761]

Doesn't hurt to replace head bolts either.Although Some may say....relax, its a lawn mower not the Space shuttle! 

[RED-Z06 2,479]

31 minutes ago, Wheelhorse#1 said:

Doesn't hurt to replace head bolts either.Although Some may say....relax, its a lawn mower not the Space shuttle! 

Depends on the bolt, I really like to try and find Grade 8 serrated flange head bolts when I can find the right length, but as long as they haven't been over torqued, older head bolts don't "wear".

[Jeff-C175 7,203]

2 hours ago, RED-Z06 said:

serrated

 

I think serrated is a mistake Tom.

 

 

 

 

 

 

Edited December 21, 2022 by Jeff-C175

[RED-Z06 2,479]

25 minutes ago, Jeff-C175 said:

 

I think serrated is a mistake Tom.

 

 

 

 

 

 

Not a fan of serrated?  I like how they really bite the head.  Head really shouldnt be something you remove often, 500 hours or so.  Haven't noticed any problems with the torque wrench on them, but i don't use them often...maybe a dozen engines that kept having loose head bolts with new oem hardware torqued to spec.

[Jeff-C175 7,203]

20 minutes ago, RED-Z06 said:

Not a fan of serrated?

 

No... I'd be afraid they would chew up the aluminum head.

 

But the K series have a steel washer under them so that shouldn't be an issue.

 

Wouldn't use them without a washer on aluminum though.

 

 

[WHX?? 50,758]

10 hours ago, RED-Z06 said:

 head bolts don't "wear".

They say they can "stretch". 

While we're on the subject lube or anti-sieze them?