Author Topic: Stock heads what's too much milled off?  (Read 593 times)

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Offline ReapersWG

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Stock heads what's too much milled off?
« on: September 15, 2020, 01:56:15 PM »
Found a set of heads that were ported but the guy that has them for sale says they measure 70cc now I know 83cc is stock. He ran KB flat tops. He said the KB pistons even though flat top were .8cc? Thought most flat tops were -1.5cc? Even with flat tops at 70cc I would think there would be a risk of piston to valve clearance especially running a .030 HG. He also said his build had a .028 squish. Thought .030 was the lowest most would wanna go with a street carbed evolution. Thanks

Offline thumper 823

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Re: Stock heads what's too much milled off?
« Reply #1 on: September 15, 2020, 02:23:25 PM »
I know nothing most the time but my guess is you are way way safe
Unless you are running all sorts of lift/overlap.

Measure and you will know.
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Offline ReapersWG

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Re: Stock heads what's too much milled off?
« Reply #2 on: September 15, 2020, 02:33:04 PM »
I'll be running a Woods W6H cam. Have Jim's rollers new tappers from Larry and brand new S&S tappet blocks. I am milling the pistons a little to achieve zero deck height with a 030 HG. With my current heads which are 73cc I'd be in the 9.8 to 1 range but I know the 6H likes 10.2 so if I used these heads I'd be much closer. I'm also wondering about the Keith Black flat tops. Online says they are +.8cc but then they list their domed pistons - vs everyone else lists their domed + example 12.9cc on a Weisco and a KB domed lists -9.9cc for a domed piston. Just want a little clarification I'm not engine builder thanks

Offline HD Street Performance

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Re: Stock heads what's too much milled off?
« Reply #3 on: September 15, 2020, 02:43:19 PM »
Sounds like a candidate for compression releases

Offline ReapersWG

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Re: Stock heads what's too much milled off?
« Reply #4 on: September 15, 2020, 07:13:12 PM »
Ok let me ask this my heads measure 74cc can I have them milled to 70cc without any issues? I already have releases

Offline Hillside Motorcycle

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Re: Stock heads what's too much milled off?
« Reply #5 on: September 16, 2020, 04:03:26 AM »
Ok let me ask this my heads measure 74cc can I have them milled to 70cc without any issues? I already have releases

May need to surface intake manifold pads, and increase valve reliefs in the pistons.
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Offline HD Street Performance

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Re: Stock heads what's too much milled off?
« Reply #6 on: September 16, 2020, 05:44:11 AM »
What is the measurement,  top to bottom?

Offline aswracing

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Re: Stock heads what's too much milled off?
« Reply #7 on: September 18, 2020, 03:37:20 AM »
What is the measurement,  top to bottom?

This.

Stock is 3.750.

Offline Hillside Motorcycle

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Re: Stock heads what's too much milled off?
« Reply #8 on: September 22, 2020, 04:16:10 AM »
3.750" is the O/A dimension for the thickness of OE Evo, and T/C heads.
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Offline Hillside Motorcycle

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Re: Stock heads what's too much milled off?
« Reply #10 on: September 23, 2020, 04:38:36 AM »
I disagree.
I have measured them more times than I can ever remember.
That dimension is in fact 3.750", unless a mis-machined from HD.
A Screaming Seagull performance head will usually measure 3.690". (minus .060"), and the intake pads are also cut deeper. :smile:
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Offline Buglet

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Re: Stock heads what's too much milled off?
« Reply #11 on: September 23, 2020, 05:39:46 AM »
   Have a set on a bike that measures 3.590 no problem fitting. being running for ten years plus. All the stock ones seam to measure 3.750, had a couple old ball ones that measure bigger.