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ri702bill

The Importance of retorquing a cylinder head

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ri702bill

One of the reasons I like old Tecumseh H60 engines is that all 8 of the head bolt are accessable once the engine is reassembled unlike a Kohler K161'

I installed a new Stens gasket after I did a valve job and decarboned the combustion chamber. Sanded the head surface with 400 grit paper on a flat surface.

I followed the manual for the torque sequence - first 50 in/lbs, then 100, then 150, finally 200 at room temp and a validation sequence at 200. Engine sat a day before I fired it, so I figured I should check it to see if all was good. ALL were down 25 in/lbs, now 175. Retorqed all 8 to 200 in/lbs.

Fired the engine, ran it for 10 or so minutes. Checked the torque as it cooled - Surprise! ALL were now down to 150 in/lbs. Retorqued to 175 and to 200, with a third go round to verify. 

Engine cooled to room temp, rechecked today - all 8 are at 200 in/lbs.

Is this type of loss in torque normal - a day later cold and more loss after heated??

Bill

Edited by ri702bill
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ri702bill

Ran it for another short time today - all 8 check in at 200 in/lbs......

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squonk

Pretty normal. Aluminum head steel bolts and iron head. different expansion rates. Even they aren't torque to yield bolts I install new ones when feasible. After 50 years why not and they are fairly cheap.

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ebinmaine
1 hour ago, squonk said:

Pretty normal. Aluminum head steel bolts and iron head. different expansion rates. Even they aren't torque to yield bolts I install new ones when feasible. After 50 years why not and they are fairly cheap.

 

Agreed.  

 

Absolutely normal.   

 

I install new grade 8 bolts for every one I take apart unless

~ I KNOW ~ 

it was me that had it apart and less than 3  times.  

 

When I did the remove clean plane reinstall on Cinnamon Horse K341 it took 3 torque sequences over a couple (?) hours run time to set right.  

 

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ri702bill

Just wondering if they had some Torque Jockey at either Tecumseh or Kohler making the dialy rounds ..??

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ebinmaine
21 minutes ago, ri702bill said:

Just wondering if they had some Torque Jockey at either Tecumseh or Kohler making the dialy rounds ..??

My gut reaction would be... Maybe??

 

IIFF they were run tested at the factory for a bit then they could retorque with that in mind.  

 

Maybe they assumed/expected/required the buyer to retorque?

 

Interesting question.   

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Wheelhorse#1

Same here.Normal .Over time they loosen up.Constant Hot and cold cycles expand and contract  + vibration  it just makes sense.

I replace the bolts too.If they are original its prolly time for a new set.

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953 nut

Kohler service manual calls for retorque of head bolts, That is good enough for me.

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ri702bill
11 hours ago, Wheelhorse#1 said:

Constant Hot and cold cycles expand and contract  + vibration  it just makes sense.

Back in my Mfg days, we used thermal chambers and vibration tables to qualify our OEM products. My favorite was a device with the two combined - "Shake and Bake"

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lynnmor
14 hours ago, ri702bill said:

Just wondering if they had some Torque Jockey at either Tecumseh or Kohler making the dialy rounds ..??

 

I very much doubt that any head bolts are re-torqued by the factory, the selling dealer or the consumer.  It is a good thing to do it, but I can't imagine it happens very often.

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Handy Don
2 hours ago, lynnmor said:

 

I very much doubt that any head bolts are re-torqued by the factory, the selling dealer or the consumer.  It is a good thing to do it, but I can't imagine it happens very often.

Agreed. I’ve always assumed that the manufacturing/assembly process accounted for getting them out the door reasonably torqued. Possibly by assembling with heated components and/or bolts?

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lynnmor

Today I had lunch with an old friend that owns a small equipment dealership.  Over roughly 40 years he sold everything from weed whackers to 4WD small tractors.  So I asked him his position on the head bolt torquing question.  He said that one model of an ATV had a requirement of having the head bolts re-torqued during the 500 mile service and that requirement was dropped after a few years.  He also said that head gasket failures don't happen unless there is some reason other than head bolt torque.

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