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  1. #1

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    Milled heads on a 750

    Was wondering if I put a set of milled heads on my slt750 with stock cylinders and pistons will it work correctly or do I need to bore out the cylinders and get larger pistons??


  2. #2
    bowsniper's Avatar
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    I'm not sure. wait till others chime in. I believe if you mill the head, you made the dome smaller and hense the piston wont travel up there and may hit the ridge of the smaller dome. Unless you had the dome opened (bigger dia.) up to accomadate the piston. You'll need to check SQUISH too. But, thats another subject.

  3. #3

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    Ok yeah I found a set cheap and was just wondering what had to be changed and I figured the pistons and the cylinders would probably need to be bored.

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    bowsniper's Avatar
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    Let the others guide you on this one. I don't have experience with this.


    The guys will ask what kind of head? what kind of gasket thickness, compression numbers, type of pistons and rings, length of rod to be used, How much was it milled? ,who did the work?,was this the second time on milling? was the dome messed with?,type of piston, dome or flat, ring gap, among other variables that I have no clue about.lol

  5. #5

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    Thanks for the help and heres the details for the others..

    They have had .020 milled off of the heads and I don't really know much else about the heads..They would be going on a stock 750 engine with stock cylinders and stock pistons.

  6. #6
    Hayabusa's Avatar
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    Quote Originally Posted by roscofisher11 View Post
    Ok yeah I found a set cheap and was just wondering what had to be changed and I figured the pistons and the cylinders would probably need to be bored.
    I take it that you are referring to the set on ebay. Milled 750 heads on a stock 750 bore engine should in theory, work fine or should I say "bolt on" with no modifications to the engine. However, you could end up with too much compression and other issues if something like squish, was not cut correctly. They might work out fine but there are some things to consider.

  7. #7

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    Yeah I figured that they might have some other issues with them if im using stock pistons and cylinders.

  8. #8
    Hayabusa's Avatar
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    Quote Originally Posted by roscofisher11 View Post
    Yeah I figured that they might have some other issues with them if im using stock pistons and cylinders.
    Using stock pistons is not the issue. It's not unusual to raise the compression using milled stock heads or aftermarket ones. They just have to be cut correctly so that you end up with an engine that can be run on pump gas if that's your objective.

    If you are just trying to raise the compression a little on you 750, I would suggest that you try using only 1 of the 2 layers of the stock 750 head gasket. It's kind of hard to explain but if you look at a stock head gasket, it's actually 2 layers sandwiched together. Split them apart, spray some copper coat sealer on it and bolt it back together. It works great and is basically free. After that, be sure to check that your compression is no greater than about 150 PSI and you should be good to go using 93 octane fuel.

  9. #9

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    So instead of milling the heads I just use one layer of the head gaskets and I will be able to get about 150PSI out of the cylinders and run 93 octane?

  10. #10
    Hayabusa's Avatar
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    Quote Originally Posted by roscofisher11 View Post
    So instead of milling the heads I just use one layer of the head gaskets and I will be able to get about 150PSI out of the cylinders and run 93 octane?
    Yes and no. It depends on how much compression your engine currently has, but it will raise it for sure. A stock fairly "fresh" engine will normally be in the 120 - 130 PSI range. Removing a layer will bring it up roughly 10 -15 PSI. Add that number to your current compression and it will give you a rough idea of where you will end up.

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