26 replies to this topic

[babsbrown]

Hi guys,

I know it can be hit and miss as to whether blocks need pocketing or valves sinking for the 12g940 head

has anyone fitted one to a 1098 with standard cam?

I'm thinking the 1098 cam is actually pretty good for Stock and if the 12g940 head will fit without the need to sink the valves or modify the block I might do so.


Thank you babs

[nicklouse]

The only way to know is to measure your set up.

 

how do you know if yours has never had a skim?

[babsbrown]

The only way to know is to measure your set up.

how do you know if yours has never had a skim?

Ah yes absolutely, to fit it to my 998 I had to pocket the block even though it measures 2.75" and 21.5cc in the chambers, so I assume no skim.

I wasn't sure whether it was an absolute dead cert that it required work to fit, with the extra cam lift on the 1098 cam.

Cheers nick

Edited by babsbrown, 09 December 2024 - 06:23 PM.

[Spider]

As Nick suggested, check it, but with a stock cam and stock rockers, the block shouldn't need pocketing.

[babsbrown]

Thanks I'll just put it all together and measure up.

To be honest I'm in 2 minds because it seems a shame to not fit something sportier. But research tells me the stock 1098 cam is pretty good.

[Spider]

,,,,, But research tells me the stock 1098 cam is pretty good.

 

It's the same profile as fitted to the 998 Cooper Engines as well as most 1275's, including the MKI Cooper S..

It's a better profile than given credit for and one I use.
 

[babsbrown]

,,,,, But research tells me the stock 1098 cam is pretty good.

It's the same profile as fitted to the 998 Cooper Engines as well as most 1275's, including the MKI Cooper S..

It's a better profile than given credit for and one I use.

Ahh brilliant thanks Spider as always I never knew it was in the cooper S
The engines been bored to 1132cc too. So with the 12g940 head and 21.5cc chambers. I'll be seeing a compression ratio of 9.4:1 with dished pistons I'd be happy with.
So it sounds like the 1098 stock cam may be perfect as It won't be high revving.

[timmy850]

You *may* find with an overbored small bore engine that the 12G940 valves don’t hit the top of the cylinder walls, especially if it’s one of the bigger overbore pistons. Always worth double checking

[babsbrown]

You *may* find with an overbored small bore engine that the 12G940 valves don’t hit the top of the cylinder walls, especially if it’s one of the bigger overbore pistons. Always worth double checking

Great shout there. I didn't even think of that. Unfortunately I just checked it out and the valves hits the block.

[panky]

I fitted a 12G940 to my 1098 Morris Minor. Everything was standard but the exhaust valve clearance to block was about .010" a little tight I thought, so I skimmed another .020" off the valve face and all was well. The head was off a '91 Cooper so chunkier exhaust valve faces. With an 1 1/2" carb on an alloy inlet manifold and a 1 1/2" exhaust it went well - until I fitted a 3:7 final drive which dulled the performance but gave it nice long legs. 

[babsbrown]

I fitted a 12G940 to my 1098 Morris Minor. Everything was standard but the exhaust valve clearance to block was about .010" a little tight I thought, so I skimmed another .020" off the valve face and all was well. The head was off a '91 Cooper so chunkier exhaust valve faces. With an 1 1/2" carb on an alloy inlet manifold and a 1 1/2" exhaust it went well - until I fitted a 3:7 final drive which dulled the performance but gave it nice long legs.

Thanks panky that sounds great. How did you manage to skim the valves? Just in a a lathe? Mines the older head with the non unleaded seats.

[Shooter63]

You can turn the valve in a lathe, but they are very hard, remember to grind the radius back on.

Shooter

[babsbrown]

Thanks shooter.

So I've just measured the lift on my block without the head fitted. Just from the pushrod and the pushrod is moving up by 7.1mm

The depth of my chambers is 7.3 on average, so as much as they won't hit I don't want to run such small tolerances in case of valve bounce. So inevitably they'll definitely need sinking.

I called around today to different machine shops but nobody seems willing to want to do it.

[babsbrown]

To confirm the measurement I will dummy build the engine and put some plastigauge in between to get a more accurate figure.



But I can still be cracking on with other engine bits in the meantime.

[Shooter63]

Thanks shooter.

So I've just measured the lift on my block without the head fitted. Just from the pushrod and the pushrod is moving up by 7.1mm

The depth of my chambers is 7.3 on average, so as much as they won't hit I don't want to run such small tolerances in case of valve bounce. So inevitably they'll definitely need sinking.

I called around today to different machine shops but nobody seems willing to want to do it.

Have you taken into account the rocker ratio? which will be a minimum of 1.23 if you are using the A+ type rockers upto around 1.27 if you are using the big pad pre A+ big bore version. This whole set up is what I call fighting you, as in you are getting problem on problem. Keith Calver recommends the head gasket thickness as your safety barrier in these situations.

Shooter