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| Rebuilding 12g295 head - 27mm exhausts. https://www.ausmini.com/forums/viewtopic.php?f=2&t=88387 |
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| Author: | Irish Yobbo [ Wed Jan 21, 2015 8:20 pm ] |
| Post subject: | Rebuilding 12g295 head - 27mm exhausts. |
I have a 295 head that I am building up for a fast small bore. When I bought the head, I thought it was standard, and bought some new exhaust valves - that are too small. It appears to have 33mm inlets and 27mm exhaust valves. Stupid of me to not measure first :/ The inlets seem fine, and I'm going to reuse them if I can. Two of the exhaust had some scoring on the stem (the reason I bought the new ones). The question is, which valves do I now use for the exhaust? The ones I have measure 27mm across and are about 88mm from end to end woth a large collet groove. The inlets are 33mm across and about 92mm from end to end with a small collet groove. Is it unusual to have inlets and exhausts a different length? |
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| Author: | Scoop [ Wed Jan 21, 2015 8:59 pm ] |
| Post subject: | Re: Rebuilding 12g295 head - 27mm exhausts. |
I believe 1275 valves are a bit longer so you could have standard 1275 valves as inlets. |
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| Author: | Irish Yobbo [ Wed Jan 21, 2015 9:39 pm ] |
| Post subject: | Re: Rebuilding 12g295 head - 27mm exhausts. |
I'm sure the doc just replied and replied back - but they're gone! Doc, you said you had 27mm exhausts for a small bore, but are 33mm inlets available? I was under the impression that the 295 valves were longer anyway? |
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| Author: | drmini in aust [ Thu Jan 22, 2015 7:06 am ] |
| Post subject: | Re: Rebuilding 12g295 head - 27mm exhausts. |
Here I am again, the info I gave wasn't quite right. The valves should all be the same length. If you fit machined down 1275 ones, the rockers need packing up a bit to match. I have a set of new 27mm smallbore exhaust valves if any help. You can buy oversized (1.125"?) smallbore inlets from Minis Plus http://www.minis.com.au/minis/catalog/p ... cts_id=869 |
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| Author: | Irish Yobbo [ Thu Jan 22, 2015 8:12 am ] |
| Post subject: | Re: Rebuilding 12g295 head - 27mm exhausts. |
drmini in aust wrote: Here I am again, the info I gave wasn't quite right. The valves should all be the same length. If you fit machined down 1275 ones, the rockers need packing up a bit to match. I have a set of new 27mm smallbore exhaust valves if any help. You can buy oversized (1.125"?) smallbore inlets from Minis Plus http://www.minis.com.au/minis/catalog/p ... cts_id=869 I think those oversized smallbore inlets are just a little on the samll side - mine are about 33mm (so I figure 1.312" like a lot of the 12G940 heads) whereas those are 1.26 (about 32mm). So I either need to get small bore 33mm inlets and small bore 27mm exhausts, or I can reuse my inlets, use big bore 27mm exhausts (if they exist?) and pack up the rockers? |
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| Author: | drmini in aust [ Thu Jan 22, 2015 11:43 am ] |
| Post subject: | Re: Rebuilding 12g295 head - 27mm exhausts. |
I'd put 33mm 1275 inlets in then and machine some 29.4mm 1275 exhausts down to 27mm. GR sells laser cut rocker packers, so does Minis Plus. |
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| Author: | Irish Yobbo [ Thu Jan 22, 2015 1:02 pm ] |
| Post subject: | Re: Rebuilding 12g295 head - 27mm exhausts. |
drmini in aust wrote: I'd put 33mm 1275 inlets in then and machine some 29.4mm 1275 exhausts down to 27mm. GR sells laser cut rocker packers, so does Minis Plus. I think that's probably the best too. I'll have another inspection of the head this evening to see if anything else is out of order. What's involved in machining the exhausts down to 27mm? Is it just a matter of turning it down in a lathe? Will most machine shops do that sort of thing? |
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| Author: | drmini in aust [ Thu Jan 22, 2015 1:09 pm ] |
| Post subject: | Re: Rebuilding 12g295 head - 27mm exhausts. |
Any decent machine shop in Tassie can do it, GR does them all the time. You want the valve's seat faces machined @ 45deg again after valve is turned down. |
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| Author: | Irish Yobbo [ Thu Jan 22, 2015 1:12 pm ] |
| Post subject: | Re: Rebuilding 12g295 head - 27mm exhausts. |
Sounds good, I'll ask around. |
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