Farm Equipment - plaining 426 head

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plaining 426 head - clearances

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Category: Allis Chalmers
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=45930
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Topic: plaining 426 head - clearances

Posted By: wekracer
Subject: plaining 426 head - clearances
Date Posted: 20 Feb 2012 at 8:39pm

Dad and i are doing an in frame rebuild on our 8050. the machine shop that we use called and said that the head had 3 thousandths warpage and needed to take 8 thousandths off to make it right. but their book said that it would be 3-4 thousandths out of speck when they do. they said they could recess the valves to they wouldn't be a problem but thought they had the specs for a reason.

The allis dealer that we use said they don't worry about it , they plain them 2 and 3 times as long as the valves are recessed. does anyone know anything that we should be concerned about. if they plain it and something goes wrong its' on us now.

PS the injector will clear as well.

thanks,

Derek

Replies:

Posted By: MACK
Date Posted: 20 Feb 2012 at 9:51pm

I don't have the recess at hand but can look tomorrow. If they are not recessed enough the valve will hit the piston. MACK

Posted By: wekracer
Date Posted: 21 Feb 2012 at 6:39am

Thanks Mack but they said the valves would not be a problem, they would recess them. just wondering if there is another reason that we're not thinking of.

thanks,

Posted By: MACK
Date Posted: 21 Feb 2012 at 6:52am

If they recess them to the proper depth every thing should be ok. MACK

Posted By: Dave in il
Date Posted: 21 Feb 2012 at 9:13am

So lets see if I understand this. To recess the valves, they grind the seat so the valve sets deeper in the head and then shorten the stem a corresponding amount. So as the valve opens the relationship is same at the valve face to the seat and the head of the valve and the top of the piston?

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AGCO My Allis Gleaner Company

Posted By: wekracer
Date Posted: 21 Feb 2012 at 3:49pm

That's pretty close Dave, but i don't think they change the valve stems. just adjust the clearance on the rocker arm.

Posted By: MACK
Date Posted: 21 Feb 2012 at 9:32pm

NO Dave. If the valve moved down .500 then when you recess it .020 deeper, it still moves .500 but it starts out .020 further away from piston.

By the way these modern Allis Chalmers engines have adjustable rockers so no need to shorten the stem. MACK