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Re: Additional cylinder block studs

May I add my own ideas to this thread?

In the pursuit of strengthening the block to crankcase fitting I modify the crankcase to take 5/16 BSF cap screws fitted from the underside. The idea being that the stress is taken more on the cap screw shoulder rather than the limited thread in the crankcase face.

This is possible in five positions. I have a special counter-bore tool as shown in the picture. This works by screwing the brass guide into the stud hole and the fitting the cutter from the underside. Then an electric drill is attached to the outer part of the shaft and using a slow, reverse speed the cutter is pulled outwards until a clear shoulder is produced.

The crude part of the operation is that the 5/16 BSW tapped hole has to be re-tapped as 5/16 BSF to take the cap screw. It may prove necessary to chamfer the cap of the screw to allow clearance of the cam lobes etc (as shown in the picture). In extremis I have used a 3/8 BSF or BSW cap screw and turned down the outer part to be 5/16 BSF. This required a larger counter bore cutter and guide.

If I remember correctly the original idea came from 750 MC Special Builders Guide or Companion.

If anyone would like more details of the tool or even borrow it please let me know.
 photo 20170212_110411_zpslsrl9phk.jpg

Location: Beautiful North Hampshire

Re: Additional cylinder block studs

Martin, as far as I can see both BSF and BSW cap screws are available, at least according to Google. If true, might avoid some angst next time?

Regards,
Stuart

Re: Additional cylinder block studs

Stuart

Depends if you want to use a BSW thread for the pull down nuts.

Another plus I forgot to mention is that cap screws are made of a much higher spec steel than normal studs.

Location: Beautiful North Hampshire

Re: Additional cylinder block studs

Hello Gents

Thank you for all of your valuable inputs, the various suggestions are all greatly appreciated.

We're currently busy with modifying the crankcase and block to take 5 cap screws from underneath. We're also making a pair of little blocks to bolt down either end of the block

The Phoenix crank is in and we've now got to align the double oil jet mod with the crank pockets and pump paraffin through them to double-check the squirt. Credit must go to Mike Forrest for this way back in the '60's I believe.

The oil pump has been bored out and hopefully we have decent pressure, I've got around 6 to 8psi hot with the Green Job and that's only running the conventional 2 jets.

I've got a bit more welding to do on the tube frame, then it's off to get clad in ally and then a lick of paint. I'm almost done with the supercharger mounting plate, it incorporates the front shock mounts - the plan is to lock one and use the alloy shock link on the other two eliminate axle movement sideways while still allowing axle movement.

We're really having fun building this little single seater, I'll try post some pictures for you.

Makes a change from rebuilding the 750/101 Giulietta's

Cheers
Greig

Location: Sunny South Africa