12g940 head on 1028 engine

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12g940 head on 1028 engine

Postby morrison62 » Wed Jun 06, 2018 8:17 pm

hi hope someone can assist just fitted a spare head I had purchased in the past its a 12g940 unleaded head, took a day and put all back together no leaks and had to drill the block to accomidate water ways ,unfortunately the exhaust valves are hitting the block after reading up on the mod sink the exhaust valves into the head by 320 thou or skim the valves can someone explain how to do this? is this something that could be done at home or do the valves need to go to a shop ? I live remote with no car as moggys my daily driver in a bit of a bind any help would be awesome thanks :)
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Re: 12g940 head on 1028 engine

Postby Panky » Wed Jun 06, 2018 8:38 pm

Yes I've done the mod and got away with skimming the exhaust valve faces and it works well. The head I used hadn't been skimmed so I didn't need to take much off the valves(20 thou) as there was already some clearance, but the head you have may have been skimmed at some point and as the valves are touching you will need to take off around 350 thou to be safe. Check to see if the valves have enough meat on them before you go this rout.
I took the valve to a friends workshop and used his lathe but I found the valve material too hard for normal lathe tools. I ended up spinning the valves in the lathe and used an angle grinder carefully on the faces as they spun, maybe looked on as a bit of butchery but it worked and I got a great finish and got the measurement I wanted to within a couple of thou.
Sinking the seats can be done at home but you really need some seat cutters but If you've got hardened seats fitted then this wouldn't work. Just a thought - are you using a 1275 head gasket?
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Re: 12g940 head on 1028 engine

Postby morrison62 » Wed Jun 06, 2018 9:00 pm

thanks panky , I used a standard composite gasket as was a bit unsure about fitting it as the standard heads valves were burnt out proberly from the hs4 attached saved moggy from the crusher 2 years ago built all from scrap donars that were at the yard so many worn parts pistons look ok was ment to be the hobbie car but main car dies more than moggy so now just running on the moggie, normally go with the copper gaskets 2nd time ever doing a head , should I use the 1275 gasket ? for this mod is it thicker? I can believe the power difference coming from the exhaust I restriped the head this eve the exhaust valves are coperish color with circle within circle not too sure if that's hardenes , is sinking when you use grinding paste my father in law normally does anything valve related retired mech , when measuring the height on the head face to valve I got 7.7/8mm please find pick attached thanks
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Re: 12g940 head on 1028 engine

Postby Panky » Wed Jun 06, 2018 9:32 pm

You need to use a 1275 head gasket to clear the exhaust valves as the 1098 one will get in the way. copper is fine but you still need the 320 thou between valve face and head face to be safe.
Using grinding paste is to clean the valve and seat mating faces so they dont leak, it would take an awful lot of grinding in to sink the valves enough but looking at your measurements 7.7mm is approx 300 thou so a skim off the valve face (not the seating face)would be fine
Here's what mine looked like after a 20 thou skim, still loads of meat left

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And remember it's only the exhaust valve that need doing, the Inlets don't overhang the edge of the bore.
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Re: 12g940 head on 1028 engine

Postby Panky » Wed Jun 06, 2018 9:55 pm

I've sent you a PM
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Re: 12g940 head on 1028 engine

Postby BrianHawley » Fri Jun 08, 2018 10:47 am

Once done, you can check what clearances you have by putting plasticine balls on top of the piston, reassembling, and turning it by hand. It will be cold of course, but it will give a rough idea.
Brian

"Jodie". '67 Traveller, 1275, discs, van wheels, vert shocks, arb etc.
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Re: 12g940 head on 1028 engine

Postby Custard » Fri Jun 08, 2018 3:40 pm

Its not rough, it works very well.

http://plastigauge.co.uk/

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Re: 12g940 head on 1028 engine

Postby BrianHawley » Fri Jun 08, 2018 3:51 pm

Plastigauge is the posh way of doing it :)

I was thinking more of valve stems lengthening with the heat when running, but I guess it’s not by much.
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