16-01-2021, 11:20 PM
(This post was last modified: 16-01-2021, 11:22 PM by Stuart Giles.
Edit Reason: typo
)
If you're looking at making a crank, it ,might be worth taking a look at a Reliant SV crank which has the same bore pitch as an A7 but has thicker centre webs by virtue of increasing the big end offset whilst using the same big end width as the A7.
If I was going to go down this route, as a start as well as increasing the big end offset, I would look at increasing the diameter of the centre main and making it narrower which would allow yet thicker centre webs on the crank. SV Reliant cranks in common with many other three bearing motors tend to fail on the centre web. In fact, while you're making a crank, why not increase the big end diameter too?
Some time ago I engineered and did trackside for a blown 3 bearing car. This used a Reliant SV crank and rods and had all 4 big ends lubed via the centre main, our experience was that at high revs an overbored A7 oil pump simply wasn't supplying enough volume/pressure to the bottom end. Centrifugal force is not helping the lubrication of numbers 1 and 4 big ends at high revs.
If I did this job again with a Reliant crank, I would seriously consider keeping the front and rear main shell style bearings and keep conventional big end lubrication with only big ends 2 and 3 being fed from the centre main. This is what Chris Gould (who pioneered the Reliant crank conversion) did for the 10,000 mile record attempt. AFAIK, Chris's (now road going Ulster Replica/special) still uses this setup. The only giveaway of the rather special bottom end is the complete lack of ball and roller bearing noise when the car is running.
If I was going to go down this route, as a start as well as increasing the big end offset, I would look at increasing the diameter of the centre main and making it narrower which would allow yet thicker centre webs on the crank. SV Reliant cranks in common with many other three bearing motors tend to fail on the centre web. In fact, while you're making a crank, why not increase the big end diameter too?
Some time ago I engineered and did trackside for a blown 3 bearing car. This used a Reliant SV crank and rods and had all 4 big ends lubed via the centre main, our experience was that at high revs an overbored A7 oil pump simply wasn't supplying enough volume/pressure to the bottom end. Centrifugal force is not helping the lubrication of numbers 1 and 4 big ends at high revs.
If I did this job again with a Reliant crank, I would seriously consider keeping the front and rear main shell style bearings and keep conventional big end lubrication with only big ends 2 and 3 being fed from the centre main. This is what Chris Gould (who pioneered the Reliant crank conversion) did for the 10,000 mile record attempt. AFAIK, Chris's (now road going Ulster Replica/special) still uses this setup. The only giveaway of the rather special bottom end is the complete lack of ball and roller bearing noise when the car is running.