26-12-2018, 07:46 PM
When we built the blown motor for the blue single seater we increased the size of the block hold down studs from 5/16ths to 3/8th... except we went 10mm & used HT cap screws which Dad machined down in the lathe. We drilled the block out the same size. I made a jig to tap the crank case squarely.
We made up a little threaded brass tool to screw into the new 10mm threaded holes in the crank case and this allowed me to insert an ordinary wood router bit from underneath and catch the same in the chuck of my big battery drill. Running this in reverse effectively shaved down the aluminium of the block to form a flat seating surface for the now machined down head of the cap screws - that & Locktite took care of the studs.
The weak points on the original block-to-crankcase-joint are the ends of the valve chest as there is nothing holding them down. We devised a neat hold down using aluminium square bar which was machined to take two 6mm allen head cap screws in from the side and then one 8mm Allen head cap screw from the top at the rear. The same block was used at the front but a longer high tensile cap screw was machined to become a cam bearing locator peg. This was given a screwdriver slot at the top and a lock nut with a washer and a wipe of sealer. A separate hole was drilled into the crankcase next to the rear cam bearing and threaded to take the 8mm cap screw.
The 6mm cap screws fixing the aluminium hold down to the side of the engine block were drilled and tapped into the block - BUT they were not drilled through into the valve chest, so no potential for leaks. To provide positive tension I mounted the hold down on a thick piece of gasket / Vellumoid before drilling, but fitted it using only a special anerobic gasket sealer so that the crank case hold down bolt is always pulling the corner ever so slightly onto the crank case. All the cap screws are held in with lock washers & Locktite.
Thus far it's all holding together - further testing will be done at the Simola Hillclimb in May
Aye
Greig
Sunny South Africa.... Port Elizabeth, a tropical climate.... what is this 'snow' stuff y'all keep mentioning
We made up a little threaded brass tool to screw into the new 10mm threaded holes in the crank case and this allowed me to insert an ordinary wood router bit from underneath and catch the same in the chuck of my big battery drill. Running this in reverse effectively shaved down the aluminium of the block to form a flat seating surface for the now machined down head of the cap screws - that & Locktite took care of the studs.
The weak points on the original block-to-crankcase-joint are the ends of the valve chest as there is nothing holding them down. We devised a neat hold down using aluminium square bar which was machined to take two 6mm allen head cap screws in from the side and then one 8mm Allen head cap screw from the top at the rear. The same block was used at the front but a longer high tensile cap screw was machined to become a cam bearing locator peg. This was given a screwdriver slot at the top and a lock nut with a washer and a wipe of sealer. A separate hole was drilled into the crankcase next to the rear cam bearing and threaded to take the 8mm cap screw.
The 6mm cap screws fixing the aluminium hold down to the side of the engine block were drilled and tapped into the block - BUT they were not drilled through into the valve chest, so no potential for leaks. To provide positive tension I mounted the hold down on a thick piece of gasket / Vellumoid before drilling, but fitted it using only a special anerobic gasket sealer so that the crank case hold down bolt is always pulling the corner ever so slightly onto the crank case. All the cap screws are held in with lock washers & Locktite.
Thus far it's all holding together - further testing will be done at the Simola Hillclimb in May
Aye
Greig
Sunny South Africa.... Port Elizabeth, a tropical climate.... what is this 'snow' stuff y'all keep mentioning