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Thread: Differences between the B series engine used in the Marina and the MGB?

  1. #1 Differences between the B series engine used in the Marina and the MGB? 
    club member Club Member
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    The engine in the car I am rebuilding is pretty tired having done over 130k miles without any major work as far as I can tell. Rather than do a full rebuild, which can be pretty expensive nowadays, I am considering replacing it with a second hand MGB engine of which there are many availaible. The MGB engine is possibly more desirable anyway as it's camshaft is (alledgedly) more suited to a sports car than a saloon. However, are there any other differences I need to be aware of?
    So far I have identified a couple of wrinkles....

    1. The spigot bearing in the end of the crankshaft would need changing to that for a Marina as the Marina gearbox input shaft is a different diameter.
    2. I guess the backplate would also need changing
    3. And probably the flywheel

    Anything else to be aware of?

    Cheers, Robin
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  2. #2 Re: Differences between the B series engine used in the Marina and the MGB? 
    Club Member lil_red_roadster's Avatar
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    In addition to the flywheel, backplate, starter motor & spigot bush (which you may need to get made, as the hole in the MGB crank is way larger than the Marina), depending on the age of the MGB engine you may also need the later chrome bumper front plate (same as Marina) and you will need to reuse the engine mounting brackets from the original Marina block. Sumps and dipsticks can differ too.
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  3. #3 Re: Differences between the B series engine used in the Marina and the MGB? 
    frequent forum contributor Club Member stevejgreen's Avatar
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    To add to the list there are a variety of cylinder heads that were fitted to an MGB, including changes on valve diameters.

    this is the best document that I have found http://www.flowspeed.com/cylinder-ident.htm
    MOC member since 05/97
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  4. #4 Re: Differences between the B series engine used in the Marina and the MGB? 
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    Thanks all.
    Robin
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  5. #5 Re: Differences between the B series engine used in the Marina and the MGB? 
    frequent forum contributor Club Member stevejgreen's Avatar
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    Quote Originally Posted by martinclan56 View Post
    Thanks all.
    Robin
    I think that the take home message should be that after the best part of 50 years and enthusiastic adaptation, it’s increasingly problematic to expect that any second or third user engines are still in their original form.

    My gut feel would be to rebuild what you have got to suit your needs. Following Peter Burgess’s guide would be a great start. At least that way you can be certain of what you end up with.
    MOC member since 05/97
    1984 Marlin Roadster SWB.
    1800TC, Unleaded ported head, stage 2 cam. Ford Type 9 gearbox, Dolomite Sprint rear axle fitted with MGF disc brakes.
    Three core radiator, Renault Clio vented front discs.
    The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.

    Loads of Marlin Reference can be found documents here or there.
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