>On Monday, November 18, 1996 9:21 AM Gerry wrote:
>>Over the next couple of months I shall be rebuilding an
>>MGB engine. However I have not decided yet if to
>>rebuild a 5-main or a 3-main engine. I have several 3
>>and 5 main blocks so I can use either. The engine will
>>be going in a MKI ('62) MGB and I want to use the
>>3-synchro gearbox, because I do not want to make any
>>modifications to the body to get the 4-synchro to fit.
>
The 'purist' in me says ... "Go with a 3 main engine"
... IMHO, only reasons for making the coversion are
1) a 3 main block is not available 2) you plan on making
some serious mods that are not possible with or will
stress the 3 main engine ... like oveboring ... or radical
cam that delivers power at very high high rpm band.
The 5 main engine was developed due to crank failure
in 3 main racing engines ... IOW, the benefits of the
5 main engine are not really that great unless you are
preparing a 'modified' engine ... of course this is just
my opinion and YMMV.
>>Has anybody successfully fitted a 5-main engine to a
>>3-synchro gearbox ?
>
Personally ... no ... but this is a common conversion.
>
>>I know that the gearbox input shaft is small on the
>>3-synchro 'box and therefore I shall have to machine a
>>spigot bush to fit the 5-main crank and the 3-synchro
>>'input shaft.
>
The spigot bush required for the conversion is available
from Moss ... part no 330-570.
>>But apart from that is there any reason I can NOT mate
>>the two parts together ?
>
No problem ... just use an early 5 main (18GB) backplate
and flywheel. To my knowledge an early 5 main (18GB)
flywheel will boltup to a late 5 main (18V) crank ... can
someone please confirm this?
>>I will probably have to use the 3-main starter and therefore
>the 3-main flywheel/clutch, ....
>
The 3 main flywheel will *not* bolt-up up to a 5 main crank
... you need to use the early 5 main flywheel. The clutch
is the same for both 3 and 5 main engines. I don't recall
if the the starter changed with the introduction of the 5 main
engine and all my reference material is at home ... the ring
gear is the same on the 3 and early 5 main flywheels ... if
the 3 main starter is different I'm not sure if it will boltup to
the early 5 main backplate ... regardless the early 5 main
starter will work.
>>although I could change the bell housing and use the later
>>starter/flywheel.
>
I'm not sure, but I don't think you can swap the front castings
between the two ... can anyone confirm if this is possible?
>>Any body done this before ?
>
I have not ... but that never stopped me from posting ;^)
>
>>PS - the lack of synchro in 1st gear does not bother
>>me in the least. I have never found a need for synchro
>>on 1st - comes from plenty of practice double-declutching.
>
Amen ... "I don't need no stinkin' synchro"
Don't forget that the 5 main engine is not machined for the
mechanical tach drive ... I've been told that the block can
be machined to accept the drive but I've not tried this ... most
folks just fit a later model electronic tach.
Safety Fast ... larry.g.unger@lmco.com
> MGA 1600 MkII
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