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  1. #1
    CB750 Member justafarmer's Avatar
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    Is bigger better

    Thoughts. Thinking about giving cyclex a stack if money. Send them a 78 lower end 73 cylinder and head. They send me back a complete mill sporting 970ccs 12.5:1 comp. Running hard weld rockers beehive springs .4 lift cam 263 deg duration. Enlarged intake ports with 34mm carbs. I hardly see any streets. Nearest city 60 mile away so it be rode on highway mainly

  2. #2
    Moderator dirtdigger's Avatar
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    If it is just highway riding and no drag strip or anything like that then there is no reason to go that big. Your build would be a drag race engine. 836cc w/ 10:1 or maybe the 915 at the very most with mild port job and a higher lift short duration cam, stock or bored stock carbs. I guess a more definitive use of the bike would help determine what you would want. Really big bores make cost go way up, and produce more heat not really something you want or need for just a highway runner. With 970 you will need aftermarket rods, heavy duty chains, cylinders need welding and then boring for big sleeves or it will seep oil. 836 is just a stock sleeve bore job and is 100% dead reliable. Why the 73 head?

    Now you can send Kenny as much money as you want and I am sure he will build you what you want but why that big? More info needed on your desired purpose of the engine you are building.

  3. #3
    CB750 Member justafarmer's Avatar
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    Thanks for your insight. The reason for that big is i ride with 113hd bike n wanna easily keep up. The 73 head to keep compression up. Since you are familiar with cyclex the cam in question was their hellcat1 cam. In your opinion an 836 with the 78 head be a better cchoice.Which cam?

  4. #4
    CB750 Member justafarmer's Avatar
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    It will be a highway "runner"

  5. #5
    CB750 Member justafarmer's Avatar
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    The bike would be run in the 70 to 90 range. With the desire for a 140 plus rip to put the hd in its place

  6. #6
    Moderator dirtdigger's Avatar
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    Here are my thoughts. A stock displacement 750 that is fresh and tuned keeps up with most HD's. I know because I like to give HD's fits during the Sturgis Rally every year when they invade my neck of the woods lol. Anyway. I have run and built many 836 970's and 1030 motors. 836 has been around since the 750 came out. Dead reliable and with a good head and cam and tune up with run with all but the biggest HD's around. I run a 970 with ported F2 head in the bike you see as my profile pic. It doesnt get many miles just playing around and beating up the HD's. It has an oil seep on the cylinder which is common with the big sleeves when they are not welded before boring for the sleeves. The big motor makes a lot of heat for which I also run an oil cooler to help keep it in check. In my opinion the 836 is the best for a reliable highway runner. They make the F2 specific pistons to keep the compression up in the F2 head. This head is far better then the early heads as it has larger intake and exhaust valves and the ports are larger as well. Get a little porting done and you have a good flowing head without tons of porting. Although you need to have cycle x do the steel guides and upgraded valve train. In my opinion 12.5:1 is far too high for modern fuel unless you plan on running a blend with race fuel. 10.5:1 is about as high as i run on an old air cooled engine to run on premium pump fuel. People always get into the bigger is better when coming to camshaft selection. The hellcat would be to big for a cruising camshaft...far too much duration. I like the high lift lower duration camshafts as that as well keeps you cylinder pressures up. I would be looking more at the cx3 or even the cx7 if you want to push the limit for a street 836 build. If you insist on going bigger bore then you obviously can run more camshaft. But I would let kenny make a final decision on it if you are going to let him build it. Hardwelded rockers are a must with a new cam....heavy duty cylinder studs must. Bottom end you need to balance the crank, maybe a slight lightening but not too much. To me anything over stock bore in the sohc requires upgraded connecting rods...the cycle x rods are good for 836 and bigger if rpms are regulated. I have them in my 970 and so far so good. Heavy duty cam and primary chains are a must as well as upgraded tensioners. Tranny stock is ok but undercut if you want to make sure it wont pop out. Now for carbs....stock will run ok. I like the Keihin CR carbs but Kenny likes the mikunis. But to me the Mikunis are to large for 836 but Kenny runs them. I would do Keihin 29s but my opinion. Also run at least a Dyna ignition. Exhaust system very important to how it runs and what power you end up making. A good Cycle X 4 into 1 is probably the best for power.

    The bigger bore stuff gets more complicated and far more expensive as there is much more machine work and parts that need to be upgraded. The bigger you go the more you impact durability and reliability especially if you want a highway cruiser. Obviously a bar hopper or a more town and free spirited riding type bike you can get away with a motor that is built more on the edge as it doesnt have to put up with constant highway speeds and engine loads and temperatures.

  7. #7
    Moderator dirtdigger's Avatar
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    kenny is a good dude and a straight shooter. He will tell you exactly what he thinks even if you might not like it. I would call him, tell him what you want and he can build you a motor that will do what you want.

  8. #8
    CB750 Member justafarmer's Avatar
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    Thanks again for your time in replying Dirtdigger.
    I agree a fresh mill would give most hds a fit but once we shift into fourth and there is another 10 mile of straight lightly traveled road in front. With my untouched 78ss after 3rd buddy would leave me. Cams. i know the joys of running over duration cams on street. But with bike motor i had no real clue as to how much is too much. Thanks for giving me a range to play in. So in your experienced opinion my dream motor would be great for the mileage i would get to put on it but not for the way i would put them on. In my limited experience my bike is no fun to ride when she not running right. In that she doesn't handle the same either. Part of the reason for the 970 was cost well if i am going to spend that much whats a third more of the cost. The reason for choosing cyclex for the build was because they have the stuff there for the whole thing ie tranny parts hd prim and cam chains. i had no intentions of cheaping out. Been there Gee this double roller cam chain half of speed shop chain price. Duh me.

  9. #9
    Moderator dirtdigger's Avatar
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    Cycle x is definitely my go to for parts. you will probably be paying 2x the money going with 970...there is a lot more machine work that gets done when going that big. I am glad you want to do it right and know its going to cost some good money to do it. Honestly if money isnt much of an object I would go directly to Kenny at cycle x and talk with him. He knows 100% what works and what wont. Me personally for you purpose of a highway machine I wouldnt go more than the 836, maybe the 915 but thats just me. Keep us posted on what you do and how the project progresses!

  10. #10
    CB750 Member justafarmer's Avatar
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    You mentioned lightening crankshaft. I kinda on the fence keep the rotating mass for little lower end or lighten for better top end . was considering first level lightening offered by cyclex, But i think i would stay with standard weight rotor. Also you said regulated rpm for the rods. As cyclex says rev to the moon. Not speaking of their rods but of certain valve train components

  11. #11
    Moderator dirtdigger's Avatar
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    I would do stock or slight weight reduction but balanced. Stock rotor but also balanced. Regulate the rpms meaning nothing more then stock rpm especially with big bore with the cycle x rods. If you want to rev a big bore and not worry then step up to the big boy carillo rods.

  12. #12
    Moderator dirtdigger's Avatar
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    I if you look at the pictures in my photo albums most of the parts I have talked about I have used and you can see in some of my builds.

  13. #13
    CB750 Member justafarmer's Avatar
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    Yes my dream motor borrowed more than few pieces from your bikes lol. Stock rpm well that's no fun haha

  14. #14
    Moderator dirtdigger's Avatar
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    Well honestly the sohc doesnt really make any more power above the stock redline. Its been shown that the head just wont support it without massive modifications.

  15. #15
    CB750 Member justafarmer's Avatar
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    You mean massive amounts of money. Thanks for your views and advice. Don't want this to be a should have done this instead of, type motor like most of my sbcs.

  16. #16
    Moderator dirtdigger's Avatar
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    I think best bet would be tell Kenny what you looking to do, he will get you set up.

  17. #17
    Moderator dirtdigger's Avatar
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    Curious as to what direction you are going with your engine?

  18. #18
    CB750 Member Justafarmer2's Avatar
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    Hi there dirtdigger. Weather n life conspired. Finally got pieces down there. Find out tomorrow what we build.
    Kenny not feelin too great but still pluggin away. A bit behind they are.
    I am leaning towards 915 running a cx11 cam. 34mm mikunis. I think 31mm keihins would be better until it gets over 3/4 throttle.

  19. #19
    CB750 Member Justafarmer2's Avatar
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    But the keihins about 450 more though

  20. #20
    CB750 Member Justafarmer2's Avatar
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    Hey there dirtdigger. Motor is getting built as an 890 sporting an f head cyclex cx11 cam . Rotor lightened. crank balanced stock weight. Cyclex rods, just as strong as carrilos but a touch heavier,
    Ken said so. All the related goodies. Hardweld rockers second level springs. Undercut tranny. Thermal barrier on head n pistons. Ken is most excellent to deal with.

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