From: STEVE JONES - PWA7C - [email protected]
Date: 08 Apr 2002
Time: 21:49:23
Remote Name: 195.93.50.186
Whilst it must be nice to achieve an oil tight block/crankcase joint using the original set up, for many, the level of work detailed in the site recommended by Bill will be a route they do not want to go down. Sealing the joint with some form of sealer does work well and, done properly, achieves a good joint without the need for much skilled work.
The sealer to use is automotive silicone, readily available but note for maximum flexibility it should be low modus, not high modus.
The method I use (and I know many who do also) is:
Remove the crankcase studs. Lightly countersink the stud holes so as to remove any thread that has pulled up. Also, remove any obvious high spots on the case upper face. Ensure the crankcase threads are in good condition. If in any doubt, helicoil or similar. Refit studs (or use new ones) using loctite or similar (I have a friend who araldites them in but I have never found this was required). If you use oil baffles, snip them so that the baffle can be bent back so as to permit the big end part of the rod to pass through. Fit baffles in crankcase. Apply a bead of silicone sealer to the crankcase mating face and lower the block onto the studs. Fit & tighten the stud nuts to within a quarter of a turn from final tightened position. Remove all excess silicone both internally and externally. Leave to cure overnight. Next day, tighten the stud nuts the final quarter turn. Rods and pistons can now be passed down the bores and fitted to the crank in the normal way. When rods/end caps fitted, carefully bend the oil baffles back into position from either with a finger or screwdriver.
No doubt the purists and 'engineering excellence is all' Sevenists have now thrown their hands up in horror. So be it but many, many have found this to be an easy and reliable solution to a problem that has existed with Sevens from the beginning and I would ask them to remember (a) moderns are pretty much glued together with silicone nowadays and (b) given his desire for cost savings, be assured, that if silicone sealants had been available in the 1920's/1930's, Herbert would have used the stuff everywhere he could.
The tip to do away with one of the engine holding down bolts so as to reduce flexing of the crankcase is also valid. An extension to this, particularly for cars used in competitions or driven in a sporting manner, is to omit one of the front bolts and to replace the rear bolt diagonally opposite with a longer bolt than normal with a strong spring (7 clutch spring works well) between the underside of the chassis rail and the nut/washer. I shall now sit back and wait for the bolts of lightning to hit me!!! STEVE