High mileage

mdt-son said:

Is the threaded section serving as bearing in the cradle?? Wow. What a bummer by NV. Thanks for raising awareness. A new cradle will be fitted to my Mk3 build, and I will certainly follow your example.
May I ask what size you chose for the g/b bolts? How did you ascertain tensile strength requirments specified by N-V were met?

- Knut

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I turned the studs from larger (12mm dia x180mm long) 8.8 metric bolts to make sure i used the right material. Make up 4 off short expanding dowels to locate the cradle to the cases as accurately as possible so you are reaming out the least material. Ream the middle hole first, turn/grind the stud to suit the hole, fit and tighten then remove one pair of the dowels and ream that hole. The studs I made I used 3/8 UNF on the ends to keep with the original look. Note that you will be reaming through the hollow dowel in the top engine bolt position. The g/box bolts/studs did the same trick, used a bigger bolt for the material. I started with the top g/box bolt as that has the most load on it. Measured the holes, , ream out the smaller hole/s (either in the cradle or g/box) then made a close fitting stud.
fitted and tightened, then set about the bottom stud and do the same. Quite a bit of work for no visible gain but well worth doing as it keeps the g/box mainshaft centered in the primary case (I've seen these way off center on some bikes I've worked on).

I just use Grade 8 bolts and hard washers... 4 x 3/8" and 1 x 5/16". No machining or drilling required. Then tighten them up really good.

I am also a big fan of routinely inspecting my bikes and I "nut & bolt" everything. They are old and British - stuff comes loose...

dobba99 said:

Note that you will be reaming through the hollow dowel in the top engine bolt position.

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Why is that necessary when you have two close fitting bolts in situ preventing rotation of the individual parts?

dobba99 said:

The g/box bolts/studs did the same trick, used a bigger bolt for the material. I started with the top g/box bolt as that has the most load on it. Measured the holes, reamed out the smaller hole/s (either in the cradle or g/box), then made a close fitting stud,
fitted and tightened, then set about the bottom stud and did the same.

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I guess you centered and secured the lower position lug to the cradle by dowels while working on the g/box upper lug/cradle holes. As there is no rotational restraint by centering one bore, one or two hollow dowel(s) would be needed in the top bolt bore while reaming the very same bore.
It's hard to understand how this process can be accomplished accurately, and how to guide the reamer if it's a stepwise process. I think some kind of drilling jig for line boring operations is called for. If used consecutively for the g/b casing and the cradle, the bore alignment will be constrained.

Does anyone know the blueprint dimension between the gearbox lug bores?

- Knut

mdt-son said:

Why is that necessary when you have two close fitting bolts in situ preventing rotation of the individual parts?

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The note about the hollow dowel in the engine cases is to alert you to the fact that reaming the holes out slightly bigger can and, probably will, take out some material from the hollow dowel (that dowels the crankcases together) i.e. that hole will ream differently than the other two.

mdt-son said:

I guess you centered and secured the lower position lug to the cradle by dowels while working on the g/box upper lug/cradle holes. As there is no rotational restraint by centering one bore, one or two hollow dowel(s) would be needed in the top bolt bore while reaming the very same bore.
It's hard to understand how this process can be accomplished accurately, and how to guide the reamer if it's a stepwise process. I think some kind of drilling jig for line boring operations is called for. If used consecutively for the g/b casing and the cradle, the bore alignment will be constrained.

Click to expand...

You are over thinking the process, G/box wise. Measure the top g/box hole, and the cradle holes. They will be 9/16" clearance. One part will be bigger (no two holes will be the same) make the stud to the bigger dimension and ream either the g/box or cradle to get the holes the same size. Fit the top stud.
Bottom hole is 1/2" clearance, make up a couple of expanding dowels again (to drag the box and cradle into alignment) these can be made from short lengths of scrap and can be inserted from either side. Clamp the box into the cradle so it won't move, using toolmakers clamps etc, remove the dowels and ream the hole, make stud to suit. Job done

mdt-son said:

Does anyone know the blueprint dimension between the gearbox lug bores?

- Knut

Click to expand...