Morris Minor Owners Club

I'm going to mate a 12G940 head off a MG1300 onto Sophie’s 948 block.
I've decided to pocket the block rather than recess the valves.

1) I wanted to work out how wide the pockets should be so while I have the engine stripped right down with the pistons and crank out I popped the valves in the head and bolted it onto the block without a gasket
a) I checked that the inlet valves clear the block - no problem.
b) I turned the assembly upside down and pushed the exhaust valves up so that they hit the block. Then I sprayed some silver paint into the bores so that the vales were painted, this shows me how big wide the pockets need to be.





2) I need to know how deep to make the pockets so I measured the length of the exposed vale stems with the valves up and down - this isn't very accurate but I measured about 6.5mm of movement.

The 1098 cam I'm going to use has 0.250 inch lift and the rocker ratio is 1.25 so that gives me nearly 7.94 mm when I covert back to metric.
So the pockets need to be at least 1.5mm deep. I haven't allowed for the head gasket but I think that will give me some room for error.

I'm thinking of 2mm pockets what do people think?

Sounds well thought about. There was apicture on another thread the other day, that showed a pocketed block.
I'll try and look that up

I have done mine, it is not hard. There are threads on this here, they can be found using the search " pocket and block " so I wont repeat what is already there. Before you commit to a final depth, do a final check using blu-tak or similar on the valve face and carefully wind the engine over. The down side for you might be getting a practice assembly of your engine. The depth is dependant on a lot of variables and this method will take them all into account. Mine ended up being 4mm which was less than calculations suggested. Have fun

) I need to know how deep to make the pockets so I measured the length of the exposed vale stems with the valves up and down - this isn't very accurate but I measured about 6.5mm of movement.

How do you mean - 'valve up and down' ?
I'm guessing that you mean the valve face flush with the head (gasket) face compared t the valve fully into its seat.
If so, that's a fair way to measure it.

If you make thew pockets a bit more generous on width and depth, then this will help the gas flowing, and also give a bit more margin in case the head is changed for another one in future!

You could try this link;-

http://www.minifinity.com/modules.php?o ... d_to_a_998

Thanks folks I have seen the other threads. This is just an update on the actual method for the job.

I hope that the photos and calculations are of interest.

Roger.

It's whole lot easier to just sink the exhaust valves into the head by 40 thou!! But I have done the pocket route several times in the past - first time almost 40 years ago! The rocker ratio is almost 1.3 / 1 - you would be better to use that in your calcs. The 40 thou sinking of the exhausts is plenty - so 40 thou deep pockets are also plenty provided you don't go to a high lift cam like the SW5 or the 544. But for the AEA 630 cam (ex 1098) 40 thou is plenty. You don't want to go too deep - because you will be getting close to the top ring, which won't do it any good at all. If you study your 940 head - you will see the exhaust port is VERY restrictive where it turns the corner - just at the valve guide. Even if you do nothing else to the head (and there is much that can be done in the inlet throat - but for your 948 engine the flow will be fine) -ease this corner with a grindstone in a drill - it makes quite a difference.