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E: Engine Flywheel Fit


Well Known and Active Website User
VOC Member
Could I ask for opinions please on the following problem.
The fit of the crankpin into the flywheel should be , Pin at 1.002 and hole in wheel at 1.000 - giving a fitting pressure of approx 6 tons.
As can be seen from the photo`s the test bar at 1.001 is " not right "!!
The Go - No Go gauge in Brass ( smoother surface ) has various diameters of 1.001 , 1.003 and 1.006. As can be seen at 1.006 the gauge disappears. The Timing side is correct at 1.000 ( and a bit )
Several solutions come to mind one being to bore out the hole in the wheel and weld in a insert as per the Drawing. There is probably another 1/16 inch to be had on the outside Diameter of the insert. Using the large Diameter of the Nut recess as a register this can then be bored out to 1.000.
Solution two is to weld " strips " across from front to back ,finishing with a circular run front and back. Face off and bore out.
If you are not already asleep these next points are important
!. I / We will not buy a new oversize pin at 1.125 since we already have a perfectly good ,new Vincent Big End assembly
2 I / We will not buy a new wheel since - in the words of Mr Dunn " unless its a pile of ash everything is salvageable " This oversized hole is just an engineering challenge.
3 I / We have access to ( in order of priority ) Single malt , Coffee and Cake , A Bridgeport Milling Machine , a BIG Colchester Lathe , MIG , TIIG , Gas and arc welders
And a bucket of inspiration ( empty ).
Comments please . Thanks.IMG_2031.JPGIMG_2028.JPGIMG_2033.JPGIMG_2035.JPGIMG_2031.JPGIMG_2028.JPGIMG_2033.JPGIMG_2035.JPGIMG_2031.JPGIMG_2028.JPGIMG_2033.JPGIMG_2035.JPG

roy the mechanic

Well Known and Active Website User
VOC Member
Metal spraying can work on exterior surfaces. I used to do it in an engine overhaul shop. I can't see it on interior (in a hole) jobs. Spark eroding can still be a life saver. Crank pins are available in several oversizes. I have one in stock at 1,250".


Well Known and Active Website User
VOC Member
Hi Roy
Best reply yet - thanks . What is the Crank Pin large diameter please. ?
Is your pin a Alpha or a Vincent ? since they have different inner diameters for the cage.

Thanks Alan.

Martyn Goodwin

Well Known and Active Website User
VOC Member
The bore of the flywheel looks to be in poor condition with lots of pitting and potential distortion. Given this connection is relying on friction, you should consider resizing this bore to the correct surface finish and making an oversize pin.
It might be more cost effective to buy a new crank assembly from Terry Prince?
I understand that Terry is no longer supplying ANY items, has sold off all he could and retired.

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