Carb bolt

[stonedrive]

Hi all, does the bolt that holds the carbs on the inlet manifold just unscrew out. Many thanks Steve

[Lingen]

Stonedrive. The factory arrangement is a stud that screws in to the inlet manifold, and a nut + sealing washer on the other end to hold the pedestal in place. If your has been replaced by a bolt, it should still unscrew.
Mike.

[stonedrive]

Hi Mike, many thanks for that. Cheers Steve

[jbuckl]

If the seal groove gets over-filled with swollen o ring (epdm instead of nitrile) and or additional sealant, the 3/8” unc thread can strip in the manifold….its often got porosity in the boss too.

the upper end of the stud is 3/8 unf originally.

[Philip Wardle]

I inherited an inlet manifold with a stripped thread as Julian describes. The attempted repair had involved making a larger stud, boring out and tapping a larger thread in the manifold, boring out a larger hole in the pedestal, and fitting a larger ID fibre washer, flat washer and nut at the top end. This didn’t go well because the larger nut left very little access to the vacuum pipe to carb adaptor, and geometry of the pedestal limited the OD of the washers so that the that contact area was now too small to achieve a reliable airtight seal. We wasted a lot of time chasing this leak till we realised the problem - to prove the point in the short term we applied PU sealant, but this isn’t a viable solution as it was now difficult to get the pedestal + carbs assembly on and off easily.

The inherited manifold had other issues, e.g. a UNF bolt forced into lower UNC thread for the thermostat housing, and there was a dribble from the two front joints with the heads - over a 20-minute interval we measured a pressure drop from 20 psi to 10 psi. So we sourced a good used manifold and pedestal, and took the opportunity to resolve several issues in one go.

Dimensions of the fibre and flat washers seem quite critical to getting a good seal. For the original stud and later manifolds the parts book specifies fibre washer WF509 and flat washer WP20, which are both 5/8 inch OD. On earlier manifolds flat washer WP45 is specified, which is 3/4 inch OD – I don’t know why there’s a difference, although the larger diameter seems like a good idea.