Pocketing the block

Post by **Onne** » Fri Oct 13, 2006 10:06 pm

What is actually involved in this?
Does anyone have any pictures of it?

Onne

Post by **JimK** » Fri Oct 13, 2006 10:10 pm

You need big pockets. Really big pockets.

Sorry

Post by **Onne** » Fri Oct 13, 2006 10:11 pm

Now that is usefull

:D:D

Post by **Roni** » Fri Oct 13, 2006 10:18 pm

I have some photos of when I did mine. I put them up soon as now I have to go and pick up my car from the painter after a looooooooong paint job. It will be like having a new car again.

Post by **RogerRust** » Sat Oct 14, 2006 6:16 am

Onne, I found a really usefull thread on this subject from 2003 read right through it. I'm going to pocket the block on my 948 and fit 12g940.
http://www.morrisminoroc.co.uk/index.ph ... highlight=

Post by **zippy500** » Sat Oct 14, 2006 7:34 am

take a look at this its in the mini forum ,but the same applies. I started looking too because I think its the route I will take.

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

Post by **Onne** » Sat Oct 14, 2006 7:51 am

Thanks Zippy, finally a picture of the pockets

Looks quite scary though

Post by **ian-s** » Sat Oct 14, 2006 11:20 am

Those pockets look quite deep suitable for a race cam/hi lift rockers,/ highly skimmed head to give 12:1 + compression ratio. you only need about .040 I think for standard valve gear. Of course it all depends how much you machine of the head to get the compression ratio correct.

Post by **bmcecosse** » Sat Oct 14, 2006 5:23 pm

You only need to do this pocketing if you are fitting a high lift cam - anything up to an Mg metro cam will be fine with the exhaust valves simply sunk into the head by 40 thou - and no pockets. It only takes about 10 mins in a machine shop ! It works.

Post by **Roni** » Sat Oct 14, 2006 9:40 pm

The pockets on mine were borderline for being necessary. The motor is standard except for the machining of the head and block, done at different times. I didn't want to mess with the head again. The pockets are not very deep, as you can see, but do give the required clearance as found out with the blu-tak test. They were not hard to do, Dremel + stone + time. Maybe not machine shop quality but smooth and no sharp edges and they work.

Post by **bmcecosse** » Sat Oct 14, 2006 9:55 pm

Nice job Roni! I first did this some 40 years ago when I ran a full Cooper S head on my 998 Mini engine, Since I was using a full race (649) cam in the engine the pockets had to be very deep - and very large since the S exhaust valves are bigger than the (now common) 940 head valves. No matter how deep I made the pockets - and tested them with plasticine - whenever i took the head off there would be signs the valves had again been touching the block. Valve 'float' - probably because i was using ~ 9000 rpm for short bursts. If using a normal lift cam ( AEA 630/731/MG Metro) then there is no need for pockets - sinking the exhaust valves by 40 thou is so much easier - and doesn't spoil the block. Keith Calver recently published an article on this - in which he shows an improvement in air flow through the 'sunk' valves. Mind you - he also makes some daft claims for the power gain which are frankly unbelievable - but the idea is definitely shown to work very well ! If anyone is interested i can point them to the article - just don't believe the power figures quoted!!

Post by **Alec** » Sun Oct 15, 2006 7:18 am

Hello BMCE,

we have talked about this before and I don't believe sinking the valves is good for power. Neither do I believe that it increases airflow unless you relieve the chamber also which will decrease compression. The other thing it does is upset the rocker geometry.

I have no doubt that it will work but it is a bodge.

I ground pockets in our 1098 block by using a spare head as a jig, after making up a mandrel to take a small grind stone. I found this quite easy and quick. If anyone is interested in what is required I will explain in greater depth.

Alec

Post by **bmcecosse** » Sun Oct 15, 2006 12:22 pm

Yes - i did open up the chamber slightly around the 'sunk' valves - and KC 's article shows that it seemingly actually improves the flow through the valves - he flow tested before and after. However I would take with a pinch of salt - and just be happy with the 'same' flow. The 940 head is SO much better than the original 202 head (and even the 295) that a tiny loss in power from exhaust valve flow is totally swamped by all the other gains. I actually wanted the CR to be dropped slightly - I felt with 21.4cc 940 head on the 1098 - which normally has 26.4cc 202 head - the CR would be too high - and so the slight drop by sinking the valves was fine for me. My compressions on an engine that has done ~ 70,000 miles are all around 180 psi with the 940 head on - and it pulls very well indeed. The head I used cost me £5 - the exhausts had started to recess slightly anyway - and so this seemed a good way to do the job for very little cost. Yes the valves do stick through another 40 thou (and 40 thou washers are needed under the springs to keep them right) - if I was worried i could have ground 40 thou off the ends of the valves stems - i decided not to bother - but I agree for the very last half bhp the geometry is no longer perfect and if it's a worry for you then simply shorten the valve stems - there's plenty sticking through the collets. I have done pockets several times in the past - but it does spoil the block. At least doing it the head way means I can swap back to standard simply by swapping the head over.

Post by **Alec** » Sun Oct 15, 2006 12:37 pm

Hello BMCE,

Ok, by the way I had a car that the valve clearances were adjusted (when the range of tappets was not enough to get the correct clearance) by grinding the valve stem tips. The manufacturer specified no more than 10 thou as then the hardening would be gone.

Alec

Post by **bmcecosse** » Sun Oct 15, 2006 12:45 pm

Could be - but I think these valves are hard through and through - there's no sign of a heated zone. When I looked at mine after fitting the head there was still plenty adjustment on the rocker screws - so I left well alone !