1098 box onto 948 engine

[philthehill]

Rob
You are correct in that the Minor 948 camshaft has 0.280" valve lift with standard rockers.

Again correct in that the 998cc Metro camshaft has 0.318"/0.300" valve lift with standard rockers.

Can you please clarify - are you going to use a 12G295 head or 940 head?

If you use the 12G295 head there will be no problem with using the 998cc Metro camshaft (or any other camshaft for that matter).

The 998cc Metro camshaft has a lift of 0.250"/0.230". The Minor 948 camshaft has a lift of 0.200"/0.220.

With a quick mental calculation - using the Minor 948cc camshaft and 940 head should work - But clearances will be tight.

I would recommend that you fit and torque down the top end of the engine i.e. head, rocker etc with a used head gasket. Before fitting the head place a piece of plasticine on the top of one of the pistons. Turn the engine over. Remove the head and see what deformation to the plasticine has occurred. I had to use this procedure when building my 1380cc as clearances were very tight and the block had been decked to suit the pistons.

If not too much deformation has occurred you may be able to get away with the 948cc camshaft and 940 head. That 0.050" difference in valve lift may make all the difference between go and no go.

I would try it but on the face of it the 998cc Metro camshaft may be a step too far.

Phil

[RobThomas]

Thanks. Good plan.

A quick re-calc brings up 9.1:1 ratio with a 12G940. If I sink the valves upwards then I might be able to do away with the Shorrocks (and sell it). What about using double gaskets? Disaster waiting to happen?

[philthehill]

I would not recommend the use of double head gaskets. Disaster waiting to happen.

You should get a good price for that Shorrocks supercharger especially if you have all the bits including the triple crankshaft pulley.

Phil

[RobThomas]

Yes, It's all here. I sat a pile of heads together in the garage. 0.280 is the max gap for the 12g940s so I think the smartest move is to get the 12g295 skimmed either for the Shorrocks or to skim it a lot more and to get a far more entertaining camshaft. Either way, I'll need the head skimmed and both of the options would allow for a better cam. Maybe a 2-ring one from the late Midget 10CC here? Does anyone have a decent different camshaft without too much overlap? I pulled a Kent 286 (288?) off the shelf but it has worn right through one of the lobes. So lumpy that I didn't notice until it came apart.

Sorry for cluttering up with such random questions. Grateful for the chance to bounce ideas around.

Rob

[RobThomas]

Another alternative. Anyone got a good 1275 they'd like to swop for a £1200 alloy 12G940, brand new in the box?