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Thread: 45 head work

  1. #1

    Default 45 head work

    I was told the no.6 45 heads are higher compression. so what can I mill off of a no5 head? or are there more changes to be done or is it worth the trouble? will make my 69 servi a little faster along with the 30 tooth motor sprocket?

  2. #2
    Join Date
    Jan 2006
    Menomonie, WI


    Before you ruin a nice set of heads why don't you buy a really cheap set from me to play with. I have a whole box of heads that have mainly fin issues that I would sell for $20 apiece + shipping Jerry
    Last edited by Jerry Wieland; 07-17-2018 at 08:31 AM.

  3. #3


    Jerry, what other 45 parts do you have?

  4. #4


    Consider shortening the cylinders by about .050" (from the top is easier but removes part of your current valve job, doesn't affect manifold or exhaust position; from the flange is more difficult, leaves valve job alone, moves manifold down and closer to nipples). This gives you much better piston to head quench @ TDC, .035" min.
    No, milling the head doesn't do this.

  5. #5


    ok guys, we got tops milled off to get to .035 quench as talked about before. now I cant find any posts that tell how much to take off of the no. 5 heads that will help also. I am using k valve springs larger intakes, cleaned out the ports, will be running a mikuni 34mm carb, copper head gaskets. anything else you guys can offer that is not to costly let me know. thanks for all the help.

  6. #6


    IIRC it takes about .100" mill to get the chamber down to #6 size, the new gasket surface will be only slightly taller than the bottom of the last fin in the casting.
    When you mill the heads, you begin to reduce the clearance between the intake valve head and its relief pocket. The offending area is typically the corner radius, which can be Dremeled out to give at least 1/16" minimum clearance to the valve when fully open. This will be worse with more lift (duh), or a larger intake valve such as the KNS Cycle. Ideally, the roof of the intake valve pocket should be deepened to the lift + .090" at right angles to the valve stem (not horizontal) of 4.5 degrees in the front-to-rear axis.

  7. #7


    Kitabel, with going to these dimensions what will the c r be? I think I have seen some where that flatheads maybe should not go to more than 7 to1. That right?

  8. #8


    All flathead engines have a "breathing vs. static CR problem", as the CR goes up it restricts gas flow across the deck to the bore, but there is no fixed number. The Ford V8 ran numbers as high as 10:1, following the old rule "if you can't get much charge in there, compress the %@(:{+$ out of it!". Engines with low VE (a KR is far better than the Ford) don't need much transfer area because there isn't much charge.
    The major factors:
    1. bore and stroke (longer stroke can be higher)
    2. negative or flush deck vs. pop-up (allows higher)
    3. distance from the bore edge to the outer edge of the farthest valve seat (closer allows higher)
    4. valve seat reliefs (allow higher CR by improving gas flow)
    There are significant differences between H-D models (W vs. WR), and between H-D an Indian.
    The numbers mentioned will not create problems.
    I suggest light reliefs on all 4 seats.

  9. #9


    30 tooth is really tall, you may not like it. Many people found a 27 easier to live with. I hope you don't have N50-15 rear tires?
    Downside of high CR:
    1. more knock sensitive
    2. fixed spark not a good idea, your auto-advance is probably OK for now
    3. after break-in go to a colder plug to test
    4. add .002" to valve lash until the seats break in

  10. #10


    Running 30 tooth was rough on clutch on a sick engine. Had broken rings on rear cylinder and scored. New style .020 pistons sure to help. Running 195/70r14 tires and hoping the rebuild will be the answer. May have to look into clutch improvements with that gearing.

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