crank pulley/keyway engagement.
Turbo Mini Forums

I have been looking into some of the practicalities of supercharging, particularly with the 16v head.

Looking at the engagement of the crank pulley there is only about 13mm of engagement. With a 5 port head obviously the pulley can to some extent rely on the friction between the it and timing chain pulley, and the end of the main bearing journal from where they are squeezed together by the bolt.

This will obviously be the same for the 16v, but with the cam drive pulley being made from aluminium this will presumably want to wear with the addition of the load from the 20-25 odd horsepower the charger will consume.

Would it be possible to extend the keyway or maybe drill and tap the crank/pulley to pin the two together?

A lot of supercharger drives use a steel boss, onto which any drive pulley bolts.

That should resolve some of the engagement/strength issues.

Keyways can be extended, but key machining isnt an easy process.

What the LS guys do with their crank pulleys which are steel, non keyed and an interference fit is they axially pin the crank.
A small jig is made up and you drill 1 or two holes axially at the crank-pulley interface effectively creating a round key hole into which a snug fitting pin is inserted.

Easy to DIY.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Not sure if this is of any use or approved by better informed people than I, but here goes.

From experience with worn gearchange shafts on bikes I have used the following technique to secure a lever to the shaft, which will also serve for the above.

I drill an axial hole on the edge of the gearlever (read pulley) half in the shaft and half in the lever i.e. half in the pulley and half in the end of the crank.
It doesn,t need to be very deep, say 10/12mm . I then put a drill shank in the hole and tighten up.This prevents any movement as long as the drill shank (or roll pin, maybe ?) is a reasonably snug fit.
Sorry if this offends any proper engineers on here but I am a founder member of Bodgers Anonymous.

Infact I've just had another idea.

Drill and tap through opposite sides of the pulley, spot through onto the face of the crank to a depth of 4mm tighten up bolts. Pulley positively located in addition to keyway/friction holding it firm - Easy, cheap, strong.

Being 16v there is no gasket/timing chain cover to interfere with.

Edited by minimole23 on 7th Jul, 2012.

If the above post is suggesting radially pinning, this is not as strong as axially.
Although I cant picture what you're describing.

The other issue to consider with blower drives, is the side loading from belt tension. You really want the main pulley as close to the crankshaft as possible so there is less leverage acting on it. Also, the more the pulley engages on the crank, the stronger it will be.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Or you could machine a much longer keyway 180 degrees round as I did with my old crank which was chewing woodruff keys!

On 5th Sep, 2011 Vegard said:
I stand corrected. You should know

Not sure which 16 kit you intend to use, but I know of none that use aluminium on the crank sprocket.