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| 12g202 head mod machining review https://www.ausmini.com/forums/viewtopic.php?f=2&t=98155 |
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| Author: | simonw [ Sat Jan 12, 2019 11:24 am ] |
| Post subject: | 12g202 head mod machining review |
Hey lads some questions: -Guides don’t seem to be pressed all in -valve stem heights not all similar - porting seems to only have tickled the sides - chambers look ok , should they have told me cc amounts when returning head Just trying to work out fair value on the work done . I supplied everything except the hardened seats      Sent from my iPad using Tapatalk |
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| Author: | simon k [ Sat Jan 12, 2019 3:53 pm ] |
| Post subject: | Re: 12g202 head mod machining review |
I don't know much about small bore heads, but it's had a bit done in the chambers. Looks like plenty of de-shrouding and reshaping of the chamber, the beak is gone They probably machined the guides shorter before they pressed them in so they're out of the air path |
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| Author: | Scoop [ Sat Jan 12, 2019 8:51 pm ] |
| Post subject: | Re: 12g202 head mod machining review |
I would say not alot has been altered. About the only obvious bit is the combustion chamber has been altered. Doesn't look like the port has been altered much if any... |
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| Author: | Ian_B [ Sun Jan 13, 2019 2:57 pm ] |
| Post subject: | Re: 12g202 head mod machining review |
Read the small bore Russell Engineering stuff The Vizard book |
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| Author: | Ian_B [ Sun Jan 13, 2019 4:12 pm ] |
| Post subject: | Re: 12g202 head mod machining review |
Would expect double valve springs ?? If the valve tip heights arent equal then are all the springs fitted with correct load and shims used |
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| Author: | Goldbrocade_62 [ Sun Jan 13, 2019 6:07 pm ] |
| Post subject: | Re: 12g202 head mod machining review |
All 295's I have seen had double springs |
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| Author: | Ian_B [ Sun Jan 13, 2019 7:01 pm ] |
| Post subject: | Re: 12g202 head mod machining review |
Its a 202 Rob but every performance head ive seen had double springs |
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| Author: | simonw [ Mon Jan 14, 2019 4:33 pm ] |
| Post subject: | Re: 12g202 head mod machining review |
Previous advice has been that single springs on a road 1098 with standard rockers will be fine . I got the spring rates off the machinist and he did shim them . Apparently that why one will get differing heights on the valve stem tips. Following are his final calcs on the install. Am I right in assuming standard Steel rockers are 1.3 ?  Sent from my iPad using Tapatalk |
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| Author: | simon k [ Mon Jan 14, 2019 5:19 pm ] |
| Post subject: | Re: 12g202 head mod machining review |
simonw wrote: Am I right in assuming standard Steel rockers are 1.3 ? they're meant to be 1.25, Dr Mini says they vary from 1.2 up to 1.27 ish |
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| Author: | cooperess [ Mon Jan 14, 2019 6:17 pm ] |
| Post subject: | Re: 12g202 head mod machining review |
Surely it would not matter what springs or spacer are used, if all the valves are the same height before putting them in then that should be the end of it. The valve seats must be different. |
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| Author: | drmini in aust [ Mon Jan 14, 2019 6:30 pm ] |
| Post subject: | Re: 12g202 head mod machining review |
Cooper S forged rockers were about1.16, Pressed steel 850/998/1098 and sintered late 998 ones around 1.2. Pressed steel 1275 ones were around 1.25. I have the actual figures in a file somewhere. All lift ratios calculated with an RE13 cam (0.290" lobe lift). BTW, Putting offset bushes into stock pressed steel or forged rockers does NOT give you 1.5:1 ratio. Contrary to what some suppliers have claimed in the past. |
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| Author: | Ian_B [ Mon Jan 14, 2019 6:44 pm ] |
| Post subject: | Re: 12g202 head mod machining review |
They end up at different heights depending on the depth of the seat or insert . My mates 1100 should have exploded 7000 to 8000 revs regular .Waggot 544 copy and double springs |
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