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Heads CC’d

Started by Sunny Jim, June 22, 2020, 07:12:31 AM

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Sunny Jim

June 22, 2020, 07:12:31 AM Last Edit: June 22, 2020, 07:35:28 AM by Sunny Jim
So I had a pair of 107 heads tidied up. The engineering shop measured the chambers at 85cc each after they faced them.  They tell me they faced the heads at .010 .
I am curious as to whether the chamber numbers stack up to only taking .010 off.
I would appreciate your input.

OldMike

Do you know what the stock CC is supposed to be for reference?

Hillside Motorcycle

Depends on what was done inside the chamber ie blending, radius top cut, etc, and if the valves had reversed tulips on them, etc, etc.
Many variables.
Otto Knowbetter sez, "Even a fish wouldn't get caught if he kept his mouth shut"

Sunny Jim

The heads were standard 107 heads that had been faced. No chamber work or valve work.
The original fly cut marks were as deep as .003 - .004 thou.
The original measurement was 89cc.
After the heads were faced they measures 85cc.
I guess I am trying to equate how many thou removed would give me 85cc.

Don D

What is the head thickness?

Sunny Jim


Don D

That is the fast way to tell what was milled off. So what is the number for the M8? I would have to check a set, 3.750" on most other big twins with OEM heads

KiwiRob

Quote from: HD Street Performance on June 26, 2020, 08:52:11 AM
That is the fast way to tell what was milled off. So what is the number for the M8? I would have to check a set, 3.750" on most other big twins with OEM heads

I get 2.450" ish with verniers on the heads I have here. - Rob

Jmd897

Mine measured 89cc too.  With my FM kit the compression comes out to 10:75:1.  If i bring it down to 86-87cc I can get a 11:1 but decided that later on I will upgrade the valve springs when I get it milled.

Don D

I have a nice set of springs that are 70lb seat at 1.57 and good for. 600 lift.

Sunny Jim

Quote from: KiwiRob on August 19, 2020, 02:22:58 PM
Quote from: HD Street Performance on June 26, 2020, 08:52:11 AM
That is the fast way to tell what was milled off. So what is the number for the M8? I would have to check a set, 3.750" on most other big twins with OEM heads

I get 2.450" ish with verniers on the heads I have here. - Rob

Just consider the heat when you
Raise that compression.

mike jesse

As a side ?, what are the stock base and head gasket thickness?

KiwiRob

Used set of 107 head gaskets I get 0.043" and base comes in at 0.013". - Rob

mike jesse

Thanks for the info Rob.