Pockets for Sophies block

Post by **RogerRust** » Sat Dec 16, 2006 7:50 pm

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?

Post by **Onne** » Sat Dec 16, 2006 8:42 pm

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

Post by **Roni** » Sat Dec 16, 2006 9:06 pm

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

Post by **rayofleamington** » Sat Dec 16, 2006 9:12 pm

) 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!

Post by **wanderinstar** » Sat Dec 16, 2006 9:28 pm

You could try this link;-

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

Post by **RogerRust** » Sat Dec 16, 2006 11:47 pm

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.

Post by **bmcecosse** » Sun Dec 17, 2006 3:50 pm

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.