Engine swap question ('81 CM400E)
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  1. #1
    Junior Member Brynomite's Avatar
    Join Date
    Nov 2015

    Engine swap question ('81 CM400E)

    Hey guys!

    I recently purchased a 1981 Hondamatic CM400E with a blown motor, was looking into buying a replacement and came across one locally.

    its from a 1981 Honda CB450A, from my understanding this would drop right into my frame correct?

    Just wanted some confirmation before I pulled the trigger.

    Also I was a bit confused, I thought the CM400A was the Automatic transmission, Did the CM400E come with an automatic option? My title definitely says CM400E

    Last edited by Brynomite; 11-20-2015 at 12:15 PM.

  2. #2
    Super Moderator J-T's Avatar
    Join Date
    Jun 2009
    Tea, South Dakota
    The CM400E is a manual transmission model, kickstart only, spoked wheels, and drum front brake. The CM400 and 450 A models have the automatic transmission, disk front brakes, electric start, and comstar wheels. Swapping an automatic engine into a manual frame is somewhat more than a simple bolt in operation.

    I would suggest that you start by comparing the serial number on your title with that stamped on the identification plate on the frame neck below the handlebars.

    Welcome to the group.

    Got pictures?
    81 CM400T

  3. #3
    Junior Member Brynomite's Avatar
    Join Date
    Nov 2015
    Yeah I only paid $75 for it so I didnt really look too much into what it was before handing over the money, I'm pretty sure he advertised it as a Hondamatic but its definitely a manual. VIN Numbers match, its a CM400E. It was pretty stripped down when he dropped it off (no handlebars) so I guess I took it for granted that it was an automatic haha. I guess that changes what I'm looking for!

    Im excited to rebuild it regardless, so as far as motor replacements what am I able to use as a replacement aside from the obvious CM400E engine? I'm assuming any 80-81 CB/CM 400/450 manual transmission engine will be compatible?

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  5. #4
    Senior Member dtsmjr8dan's Avatar
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    Oct 2011
    Windsor, Ontario, Canada
    You can use CM400/450 engines from 78 to 85 at least. Although , there is some changes to make it completely compatible wiring wise. For the most part direct swap.
    1977 CB750 (acquired project)
    1979 CM400T (rider),
    1979 CM400T (resting)
    1980 CM400T (just picked up in pieces)
    1981 CM400T (in surgery receiving transplant)
    1982 CM450 (donor engine for 81)
    1982 CB450 (parts bike)
    1985 VT1100C (rider)

    Past rides: Vincents, Triumph, BSA's, Suzuki's, Twingle, Corgy, others.

    Remember, today is the tomorrow we worried about yesterday.
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  6. #5
    Junior Member Scott92's Avatar
    Join Date
    Sep 2019

    1981 cm400a

    Was wondering since I seen that someone said the engines are swappable from 78 to 85 I have a 81 cm400a and was wondering if I could swap the engine out for a 78 cm750a and without having issues?

  7. #6
    Sensei 66Sprint's Avatar
    Join Date
    Sep 2008
    Roanoke, Virginia
    NO...... That would be 400/450 engines, NOT 750's....
    I'm only familiar with the CB750A in '78......Where did you come across a CM version?...Or was that a Typo?
    Last edited by 66Sprint; 09-17-2019 at 06:01 AM.
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