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Anyone Fit A 12G940 1275 Head To A Stock 1098?


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#16 Spider

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Posted 11 December 2024 - 07:37 AM

 

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

 

 

There's also circa 0.040" (1 mm) to be 'gained' in the head gasket thickness, moving the valve further away from the block.



#17 babsbrown

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Posted 11 December 2024 - 07:46 AM

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

Thanks shooter,

To be honest the whole build Is giving Me problems. I had a 12g202 head that I ported and flowed which then cracked at the machine shop.

Then I have a 12g295 but the valves are too far recessed into the head that I'd need to throw a lot of money at for oversized valves and unleaded seats and finding someone to do it. Then my 12g940 is an option but then these valves will need sinking too.

Par for the course I guess.
I'm half tempted to just buy an already done head at this rate haha

#18 panky

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Posted 11 December 2024 - 02:30 PM

 

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.

 

 

I was a bit agricultural as I didn't have a lathe or tools to cut the surface tools. So a trip to a friends with a lathe and me wielding an angle grinder on the face of the valve spinning in the lathe did the trick, I did practice on an old valve first to get the feel for it. I know I'm an animal.



#19 Shooter63

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Posted 13 December 2024 - 07:42 AM

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.


Are you sure you are getting 7.1mm lift at the pushrod? That equates to around 280 thou of lift while most all STD BMC/BL camshafts lifted 250 thou (6.35mm ). If I was you I would degree and lift the cam to see what you have exactly. Also I thought the only small bore engines to get the Cooper S cam was the Cooper 998 and the MG1100.

Shooter

#20 babsbrown

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Posted 13 December 2024 - 10:38 AM

Thanks gents. To be honest, after a bit of deliberation I'm going to fit an evo001 cam. The reason being is that on closer inspection one of the exhaust lobes Is looking quite worn. It seems a Shame, but to put a worn cam in a new engine seems wrong.

Thanks shooter, I will buy a cam disc over the weekend, as I'll need to time the new cam in and allow for chain stretch etc...
Really appreciate your help

#21 Shooter63

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Posted 13 December 2024 - 03:02 PM

The Evo1 cam has a fair amount of duration, are you sure you wouldn't be better off with a SW5?

Shooter

#22 babsbrown

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Posted 13 December 2024 - 09:09 PM

The Evo1 cam has a fair amount of duration, are you sure you wouldn't be better off with a SW5?

Shooter

Yes absolutely, I feel as though the Sw5 is the better cam, but I'm trying to work to a budget build, so will compromise with the evo001 one.

Edited by babsbrown, 13 December 2024 - 10:46 PM.


#23 babsbrown

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Posted 13 December 2024 - 10:00 PM

.

Edited by babsbrown, 13 December 2024 - 10:47 PM.


#24 Shooter63

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Posted 15 December 2024 - 10:32 PM

The Evo1 cam has a fair amount of duration, are you sure you wouldn't be better off with a SW5?

Shooter

Yes absolutely, I feel as though the Sw5 is the better cam, but I'm trying to work to a budget build, so will compromise with the evo001 one.

A quick set of calcs tells me you will be at least 80 thou in the block with that cam so I presume you have decided to pocket the block.

Shooter

#25 babsbrown

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Posted 15 December 2024 - 10:47 PM

The Evo1 cam has a fair amount of duration, are you sure you wouldn't be better off with a SW5?

Shooter

Yes absolutely, I feel as though the Sw5 is the better cam, but I'm trying to work to a budget build, so will compromise with the evo001 one.
A quick set of calcs tells me you will be at least 80 thou in the block with that cam so I presume you have decided to pocket the block.

Shooter

Ah no I opted to go for the 12g202 head instead. I'm really struggling to get machine shops to do that sort of work. I will have to get it skimmed by about 60 thou to get the compression up. But everything was seemingly an up hill battle so settled for an easier option

#26 Shooter63

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Posted 16 December 2024 - 06:34 AM

The Evo1 cam has a fair amount of duration, are you sure you wouldn't be better off with a SW5?

Shooter

Yes absolutely, I feel as though the Sw5 is the better cam, but I'm trying to work to a budget build, so will compromise with the evo001 one.
A quick set of calcs tells me you will be at least 80 thou in the block with that cam so I presume you have decided to pocket the block.

Shooter

Excellent option, no more fighting you, fit and forget.

Shooter

Ah no I opted to go for the 12g202 head instead. I'm really struggling to get machine shops to do that sort of work. I will have to get it skimmed by about 60 thou to get the compression up. But everything was seemingly an up hill battle so settled for an easier option


#27 babsbrown

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Posted 16 December 2024 - 01:12 PM

The Evo1 cam has a fair amount of duration, are you sure you wouldn't be better off with a SW5?

Shooter

Yes absolutely, I feel as though the Sw5 is the better cam, but I'm trying to work to a budget build, so will compromise with the evo001 one.
A quick set of calcs tells me you will be at least 80 thou in the block with that cam so I presume you have decided to pocket the block.

Shooter
Excellent option, no more fighting you, fit and forget.

Shooter

Ah no I opted to go for the 12g202 head instead. I'm really struggling to get machine shops to do that sort of work. I will have to get it skimmed by about 60 thou to get the compression up. But everything was seemingly an up hill battle so settled for an easier option


Absolutely! Thanks shooter. Just gotta get that compression ratio up after a good skim then should be good!!




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