13 replies to this topic

[ministe]

I've finally found a unmolested 12g295 head from a 1968 cooper. The head comes with the original rocker gear that was on the car, so i'm wondering what type these would have been? Any improvement over my standard 998 ones?

Also, if I were to buy these pistons (http://www.minispare...=...8611&title=), would the head still need skimming to get the compression down?

[ministe]

Any help with this please?

[mk1leg]

Hi..Tried replying last night BUT server would'nt let me the rockers are a standard item on all modles accept the cooper 'S' wich had these..........

http://www.minisport...fo_12G1221.html

then came the roller rockers in the 80s..........

http://www.minispares.com/Search.aspx

................hope this helps

[BoboGib]

I have just fitted on to my 998, measured the combustion chamber at 28cc so again is pretty much untouched. Had to fit it as my standard one cracked.

No body seemed to give me an answer as to whether it would run or not but did a bit of research and a lot of cars in the 60/70's had compression rations ans low as 7.5:1

I took the plunge and fitted it as I wanted to use the car for the Riv Run.

As I thought, it runs, quite well when its revving but is quite flat and lumpy when at low revs and cold.

Going to play around with the ignition timing and advance it a little but I think a rolling road session would sort this out as they can do the fueling at the same time.

So to answer your question, it will run. How well nobody can tell till you fit it.

[miniobsessed]

The Cooper rockers are pretty standard but if they are the pressed steel type they will (more than likely) give you the best and most consistant lift of any of the 'standard' rocker types. If you're in any doubt get a good set of 1.3 roller rockers for it (1.5's are not the go here as they will most likely give you a smaller peak torque figure).

With your head... The only way to set everything up is to actually check all of your values by measuring them.

The 60 thou flat tops are a good start (or even better go for the 80 thou). +60 will give you about 1046cc while +80 will be about 1061cc.

Once the block is bored to the size of your choosing you need to 'dry build' the short motor. This involves fitting the crankshaft and con-rods/pistons to the block without the rings fitted but everything very clean, lubricated and torqued up. You then need to measure the distance between the top of the piston and the face of the block with each piston at TDC (hopefully they will all be within 1 or 2 thou of each other), disassemble the engine again and have this figure machined off the top of the block.

With all your block machining done (plus other things you'd probably be best doing while everything is apart... Cam bearings, etc...) you can now pop your oil gallery plugs and core plugs and clean everything (block, crank, cam, rods, everything!) until you'd be happy eating off it then assemble your short engine re-checking that your pistons are dead flush with the top of the block.

If you go for +80 thou pistons and your head is in fact standard (about 28cc) if you bolt everything up you should have a compression ratio of about 9.2:1 which for a road going motor with a road going cam in it is about on the money. But just make sure you measure everything and get it right

Hope this helps...
Cheers

[bmcecosse]

Use the rockers - don't use fancy high-lift rockers. If flat top pistons you 'could' just use the head as it is- but for best result it will want 60 thou off.

[logan]

ive just done two builds one with a 295 head with the combustion chambers at 22.5cc to give higher compresion and the other one with a 295 head with the combustion chambers at 27.5cc,both running the same cams and gearing, and the one with the high compresion is a lot quicker on the top end but i did not find a lot of diffrence on the bottom end.

[ministe]

Just got the head, it looks great! Heres a quick picture of the rockers, any ideas which ones they are?

Edited by ministe, 09 May 2010 - 06:49 PM.

[mk1leg]

there bog standard items pressed steel................

[ministe]

Thought as much! Thanks for all the help guys, got a lot to think about and a lot of measuring to do.

[liirge]

i quite like those style of rockers, they are a consistent (or the best bmc managed) ratio between sets, and they are lighter than the later rockers.

Edited by liirge, 09 May 2010 - 07:15 PM.

[bmcecosse]

And much more reliable - and stronger. Unfortunately - these ones look a bit rusty.............

[mk1leg]

The 'S' forged rockers are the best for most jobs but Roller rockers are for hi.lift cams...............

Edited by mk1leg, 09 May 2010 - 10:57 PM.

[Cooperman]

Those rockers are quite light in weight and are good for high performance engines. However, the two faces which sit touching can 'spread' slightly when used with heavy springs and high revs, the cure being to run a line of weld along the top and grind it back. Then you have a set of really good rockers.