Classic Motorcycle Mechanics – September 2019

cmm

Allen

Award-winning motorcyc

I

feel thatowningandridingaclassic

bikegives meaproper ‘seatofthe

pants’ riding experience without the

needforABS, tractioncontrol,electronic

throttlesoramulti-coloured LCDdash.

WhenIridemy1970s two-strokesthey

feel crispandraw; theyrespondto my

input directly, without the need fora

computer. There is rarelyaboring

momentbecauseIamconstantly

connected to thebikelistening to the

engine...‘Wasthat noisethereearlier? Is

thattick gettinglouder?’,and when I

parkupIlook fordrips andleaks.Iget

the same feeling when working on and

maintaining my classic bikes. I’vealways

liked gettingmy hands dirty andfixing

things, making replacement parts rather

thanjustbuyin gparts. I’ve reallyenjoyed

working onmy ol dVelocetteMac engine.

Olde rbikes were quite oftenover-

engineeredwiththicker castings and

larger, heavier components, and in most

casesapart only hasonefunction,

making iteasi er to repair or adapt.

Afte rweeks of trialbuilds, making and

adaptingparts,Iwas looking forwardto

thefinal buildofmyV-twin engine.With

allparts forthe bottom-endcleane dand

checked,the first thing to do was to lower

thecrankshaftinto the right-hand

crankcase, thenapplyathin bead of

jointing compoundtothe mati ng

surfaces.Iuse Permatex ultra-grey.Itis

similartot he grey-coloured gasket

sealant that Kawasaki useto assemble

their engines. Theleft-hand crankcase

was then lowered over thecrank shaft,

makingsurethe connecting rodswere in

their correctorientation, then the

securingboltswere tightened.Iwiped off

any exce ss jointingcompound then

placedthe crankcaseassemblyontomy

engine stand.The stand was made from

some scrap anglesteel cut and welded

togethe r, butcould just as easily have

been made by boltingthe jointsif you

don’t have access toawelder.

With th eenginenow heldsecureinan

upright position Icouldget on with the

assembly of the timing side. Firstlythe

crankshaftgear,bronzeoil pump helical

gear andspecial anti-rotationwasher

were fitted, then the left-handthreaded

nutwas tightened. Thecrankcasewas

then heated withablowtorchlocally

wheretheoil pump fits, andthe oi lpump

tappedinto placewith ahidemallet,

taking caretoengag ethe drive gearwith

thebronzehelic al gear,thenthe four

securingscrews weretightenedholdingit

firmlyin pl ace. Thenext jo bwas tofit the

two camshafts, cam followers and

intermediategear, lining up themarks I

hadpreviouslyetched toensure correct

camshafttiming for each cylinder.The

stee lsupport platewasthen boltedin

place.Ihad bought newoversize piston

kits andvalve guides for theengine, so

thenextthing Ihad todo wasre-bore

each cylinder to accept thenew pistons. I

use my 1958 Minibore boring machine to

re-boremy cylinders. Itsagreat little

machine and will machinebores from

45mm to 90mm, so it’sperfe ct formost

classic motorcycles.

The first thing todo isclean upthe

barrel seating surface, thenclampit in

place under theboring machine table.

Then theboringbar is centralise dusing

threepins thatexpandinto the cylinder

bore until itscentral, then theboring

The finalbuild

Allen revealsthe final thingstodotoc ompletehis Velocette V-twin engine.

Crankcase assembled in engine stand, barrels looselyfitted.

Re-boring the cylinder on my

Minibore machine

68 / classic motorcyclemechanics