16 replies to this topic

[matt large]

As title guys, any recommendations for measuring the extra cc in the block once pocketed, cheers matt

[bmcecosse]

Best plan - don't pocket the block! It doesn't do the top ring any favours...... Why are you doing this ?

[Wil_h]

Depends on how big you make them, typically around 0.5 to 1cc

Not sure what the issue with the top ring is?

[matt large]

block is already pocketed for a 12g940 head, engine currently has 731 cam in but looking at a 544 for something a little more torquey, top ring should be far enough away from the area pocketed id have thought to not cause any issues,
cheers matt

[Sam Walters]

I guess what BMC is on about is that sometime people are tools and make the pockets too deep. Past the top ring.

It would be hard to do to be honest.

[bmcecosse]

Any pocket exposes the top ring to hot gases - best to sink the valves rather than ruin the block with pockets. However - it's done already I gather - so how deep are they and how wide at the narrow edge?

[matt large]

not sure on specifics, is one old man done bout 10 years ago, never had any issues with it, survived 3 hard years racing so must have done something right.

[Dan]

Squeeze a lump of Blutac into the pocket, make it flush with the deck and shape it to the bore. Shape it as accurately as you can and be sure to fill the pocket properly. Pull it out and drop it into a small finely graduated measuring jug with a known amount of water in. If the jug scale isn't fine enough you can use a syringe to draw the level back down to where it started.

[matt large]

that is a very clever solution to a simple problem, simple displacement, cheers

[Dan]

Thought it might be nice if someone actually answered the question.

[matt large]

appreciated : )

[Cooperman]

I was going to say to bring a piston to TDC, fill the piston top and the pocket with a fluid and measure with a shrynge as you put the fluid in. Bring it up to deck level, then you have the piston to deck volume including the pocket volume.

[Dan]

That's a great plan but you'd probably have to do it with alcohol due to the surface tension of water. You don't want to use a more aggressive solvant like thinners because what ever you use it will run down into the guts. I don't think a little spirit or meths will do much damage.

[Wil_h]

Any pocket exposes the top ring to hot gases - best to sink the valves rather than ruin the block with pockets.

Why does it expose the top ring to hotter gasses? How are they hotter at the pockets?

I run pockets on possibly the most powerful 998 cc A-series engine in the world (please correct me if I'm wrong). And there is no evidence of any ring damage. Or, as the rings constantly rotate, you're really looking for piston heat damage, never seen any caused by the addition of pockets.

[Cooperman]

White spirit is a good fluid to use or, as you say, meths (no sniffing now!).