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Thread: Best components to build a 1000CC engine for a /5 bike

  1. #1

    Best components to build a 1000CC engine for a /5 bike

    I like to build a low cost 70 HP 1000CC motor with bits I have or easily can buy.
    1. If I would buy all major motor components used from what models should I get parts for reliability and power?
    2.What are the benefits or limitations of using a /7 verses /6 verses a /5 block. I have a /5 bock that matches the frame number but would use later block if advantages are significant.
    1.Is this true that the R60/6 cam from 1974 and up is the most aggressive production cam for Airheads?

  2. #2
    Registered User AntonLargiader's Avatar
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    Jul 2004
    Charlottesville, VA
    There is no /5 block which will accept an R100 cylinder. The block you want was introduced for the '76 model year and then upgraded in '77.
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  3. #3
    You can have a /5 or /6 case bored to accept 1000cc cylinders, but it's certainly easier to use a /7 on case. The R60 camshaft has always been the least aggressive cam in the range. It's running duration is 20 degrees shorter than the bigger bikes.

  4. #4
    Quote Originally Posted by boxerotto View Post
    I like to build a low cost 70 HP 1000CC motor with bits I have or easily can buy.
    The Euro spec R100/7 engine was a 70 hp engine. Shouldn't be too hard to find or reproduce. FWIW, I'm keepin' mine.

  5. #5
    Probably best to just get a complete motor and transmission. I don't believe that the /5 Trans. will bolt up to the R100 engine block properly.

  6. #6
    there were some 78' RS heads on ebay two days ago:

    not a bad price, but those are the heads you're looking for anyway along with the other stuff suggested here. i almost bought these myself.

  7. #7
    The four-speed will bolt up, as long as you retain the '70-'80 clutch.

  8. #8
    Me? I'm in the middle of building/rebuilding my R-90 motor and my advice would be for you to simply buy a ratty R-100 with a good motor and swap the thing into your bike.

    The best choice? The latest model engine that you can find but skip the idea of basing your build on a /5.... Too many issues, starting with a comparatively weak block, the earliest oiling system and virtualy no HP parts availability.

    There were a lot of changes made to the Airhead mills over the years and in general, they all made the bikes and engines better, including better oiling, better clutches and clutch actuation, electronic ignition etc.

    Just a couple of days ago, I ordered a complete hi-comp Nickasil top end and it cost me exactly what a really good engine would cost! After adding in the costs of rebuilding my top end, adding a lightened flywheel, a 336 cam, some machining, some parts, etc, etc... Well, you get the picture! The only advantage for me is that my engine is in very good shape with new bearings and I want to preserve the "dated" appearance of my "76" R-90. What I'll end up with is a wolf in sheeps clothing but thats my personal sickness!

    If you buy an early 80's 1000cc engine and swap to hi-comp pistons and slugs you'll get about 70 HP. Add in a set of used/rebuilt Delortos, a 336 cam and a late model clutch and transmission and youre about where you need to be, without spending a fortune or having an engine that you spend more time fixing than riding.

    Good luck!

    PS: Contact Motoren Isreal and order a catalog. Parts prices from Germany are screemingly expensive but since you asked...
    Last edited by mymindsok; 04-06-2009 at 07:43 PM.

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