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jdanefellows

Milling heads

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How much is too much material removed when milling heads?  The machine shop had to remove 8 thousandths on one head and removed none from the other because the surface was good.  Will this cause me problems he didn't seem to want to machine the other one and said it wouldn't cause any problems on a street engine.

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Well, I am not a machinist but that is only .2mm. I suspect there is a spec somewhere that provides guidance on your question. I deal with machine shops that I "blindly" trust for the most part, and if I have a question, such as the one you ask, I inquire of them. Hopefully someone who has been there (milling heads, specifically our Duratec's) will respond in kind.

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I am sure Terry will "chime in". His vast knowledge in this area will benefit all of us.

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Yes I posted this and a PM to get your attention. Thanks for the info.  I posted here first because the forums seem to be slowing down a bit and I didn't find any posts that gave info on this.  No if someone has a question like this there's a record.  I didn't mean to double post, I just wanted to immortalize good info :). Do you know the maximum that you can take from one of these heads before you have messed up when milling?  I think that would be a good piece of information for those who follow ?  Thanks

 

Jameson

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A number of things can be done incorrectly to a head to cause it to be "messed up". I won't elaborate just point to the source that has done me well with the VW aircooled engines and occasional Ford cast iron head inline 6 whose head I had on a Roland - http://www.enginebuildermag.com/2007/06/common-mistakes-to-avoid-when-resurfacing-cylinder-heads-blocks/

 

There are many variables to consider when milling a head or block. .2mm is nothing more than "cleaning up" the surface, as Terry pointed out.

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That's a good link to post mondeoman. I had read it several times before making this post its what lead me to the shop I ended up getting to resurface my heads as they had the best looking machines and smoothest finish on heads of anyone I had visited.  It doesn't however tell you what the maximum that you can remove from your heads without causing a problem.

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I have searched high and low for this specification - min/max milling of the Duratec 25 heads, w/o success. Somebody have a Factory Shop manual that might give this spec? Agree w/you, maximum removal is not spelled out in the linked article. I see we are having no success on the CEG site as well.

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I just looked at my CD - says that the 2.5 is not to be resurfaced at all!  (Referring to both head and cyl block faces I suppose)  Which surprises me, sounds excessively strict, but that's what it says and may explain lack of a spec.  I'd certainly take Terry's word re this instance being OK though.

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My son, a very recently SAE Certified Mechanic, tells me that they don't mill any aluminum heads - these are viewed as "disposable". He reiterated what Terry has already stated - .2mm is nothing but a "cleaning up" of the head surface in order to remove minor imperfections.

I suppose you could email Cosworth and base your decision on their response. Not like they haven't modified their share of aluminum heads - I owned a '75 Coswrth Vega, and I regret to this day selling it after 17 yrs of mostly trouble free ownership. I did correspond with them, via email, once in the 17 years and they got right back to me.

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Don't panic, I can't believe .008" is going to make any real difference, you should be fine.  The manufacturers tend to be ultra cautious - understandably so - on repair specs.  They may have been as worried about surface finish as they were re dimensions.  Terry is an experienced engineer and knows these engines well, follow his lead.

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lol thanks.  I just decided to hold a bit until I got a bit more information.  I will probably continue with my build this weekend.  and I agree.  You cant even see .008 between the heads literally.

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lol thanks.  I just decided to hold a bit until I got a bit more information.  I will probably continue with my build this weekend.  and I agree.  You cant even see .008 between the heads literally.

PM sent.

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OK, found this info - Cylinder head warpage limit 0.006 overall, as per http://mechdb.com/index.php/Ford_Contour_specifications

 

Doesn't tell us how much material can be removed, but would indicate that .006 is the max in order to eliminate warpage.

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Right on!! Good job and thanks for getting back to us. I would think you would know something one way or the other within the next few weeks/500 or so miles.

 

Waiting to hear your report/update!

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Hello I just wanted to check in I got the engine running this Saturday and everything seems to be working well.  There appear to be no adverse affects of having the extra .008" removed from the head.  The engine runs as well as can be expected for being unturned and running 24# injectors in place of 17#.  Thanks for the all the help.  I will check back in at 500 miles and let you know if its still going strong.

 

Jameson

 

https://www.youtube.com/watch?v=C-wqETJFXoU&Feature=youtu.be

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