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| Cylinder Head 12G940/12G938 11 Stud https://ausmini.com/forums/viewtopic.php?f=2&t=97677 |
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| Author: | cooperess [ Wed Aug 22, 2018 12:04 pm ] |
| Post subject: | Cylinder Head 12G940/12G938 11 Stud |
I have the head stated above. The stange thing is that four of the valve spring seats are deeper than the other four seats. Is it still ok to use with double valves spring or should all the seats be the same depth. Attachment: Mini Head Sand Blasted 001.jpg
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| Author: | simon k [ Wed Aug 22, 2018 2:11 pm ] |
| Post subject: | Re: Cylinder Head 12G940/12G938 11 Stud |
that's not the valve seat, the seat is on the other side - I forget the correct name for it, but if you call it a seat you'll confuse people. It might be called a 'land'... Are they actually different heights (and therefore have been machined), or are the valve guides just pressed in to different heights? |
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| Author: | cooperess [ Wed Aug 22, 2018 4:35 pm ] |
| Post subject: | Re: Cylinder Head 12G940/12G938 11 Stud |
Fixed the wording to Spring seats. The guides are also different lengths. Attachment: Mini Head Sand Blasted 004.jpg
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| Author: | Karcraft [ Wed Aug 22, 2018 8:58 pm ] |
| Post subject: | Re: Cylinder Head 12G940/12G938 11 Stud |
It would appear that the exhaust valve spring pad has been machined. This is normally done when Mk1 exhaust valves are fitted to a Mk2 head. Measure the head diameter of the exhaust valve. Mk1 = 1.219" or 31mm. Mk2 = 1.156" or 29mm. Mk1 overall length is 3.520" Mk2 overall length is 3.570" To fit the shorter Mk1 exhaust valve into a Mk2 head your machine the spring pad area. Hope this helps. |
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| Author: | Scoop [ Wed Aug 22, 2018 9:00 pm ] |
| Post subject: | Re: Cylinder Head 12G940/12G938 11 Stud |
Like simon said, did you measure from the rocker pedestal pad height or the valve guide? How much difference is the measurement? |
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| Author: | cooperess [ Wed Aug 22, 2018 9:06 pm ] |
| Post subject: | Re: Cylinder Head 12G940/12G938 11 Stud |
Here is a picture from the other side. Attachment: Mini Head Sand Blasted 005.jpg
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| Author: | drmini in aust [ Thu Aug 23, 2018 7:16 am ] |
| Post subject: | Re: Cylinder Head 12G940/12G938 11 Stud |
You can fit a spring seat washer to restore the depth then use oversize 31mm MK2 S exhaust valves like I did. You want all the valve stems the same height. Bin the old valve guides and fit new to the correct height. |
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| Author: | cooperess [ Thu Aug 23, 2018 3:34 pm ] |
| Post subject: | Re: Cylinder Head 12G940/12G938 11 Stud |
Is there a correct position for the valve guides in the head as the inlets are deeper than the exhausts. |
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| Author: | drmini in aust [ Thu Aug 23, 2018 6:27 pm ] |
| Post subject: | Re: Cylinder Head 12G940/12G938 11 Stud |
I have a tool for setting the depth I will confirm the dimension in the morning but I think it's around 1.5mm above the top face of head. Edit: confirmed top of guide is 1.5-2.0mm above top face of head. Fit exhaust valve stem seals, as oil level can get above guides sometimes with 1100S style blocks due to restricted drainage. I recommend Viton seals on the inlets as they don't harden like stock Mini/Metro ones. |
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| Author: | low n blown [ Sat Aug 25, 2018 8:25 am ] |
| Post subject: | Re: Cylinder Head 12G940/12G938 11 Stud |
In my experience you may need to machine the inlet Spring Seats down as well. When fitting new springs you need to know the installed height (don't just use the height supplied by the spring manufacturer) You need to know the height of the spring at say 80lb pressure installed and to achieve this more often than not the spring seat is too high meaning your installed height is also too high as the spring is compressed a little too much. Using a spring tester you can mix and match your inner and outer springs to get them all as even as possible before installation and ascertain your desired height to achieve say 80lb. You will need to temporarily install the valves with a retainer (after the valve seats and spring seats have been machined) to ascertain how much room you have there for a spring to fit. Based on this calculation you can then add shims to achieve your desired seat pressure. I like to install a bottom cup directly under the spring which prevents spring shuffle and then the shims are underneath this. Sounds like a fair bit of work and ....... yes it is. But if you want to do it properly thats how. If I have confused you and you want more info call me. 0402214066 |
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