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Minimum cossie head thickness????

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Old 04-03-2005, 10:22 AM   #121
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What I don't get though, is that if ferriday say they can machine the head to loose some compression ratio following too many skims, that would suggest they also do something with the valve seats (sink them further in the head), otherwise, as you say, their whole procedure would be pointless.

As much as I trust Karl implicitely, I would have thought a little machining would be less stressful to the head, but I am no specialist and could easily be talking out of my backside here.

Maybe I'll give ferriday a call after all and report back.
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Old 04-03-2005, 10:30 AM   #122
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whilst valve seats 'can' be removed and the pockets machined to refit them deeper, that is a fairly major operation, and not without risk of problems with the seats coming loose later...
Ferriday do seem very competent though, so well worth talking to them to see what they have to say.
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Old 04-03-2005, 01:09 PM   #123
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Quote:
Originally Posted by Stu @ M Developments
Brad,
Its a misconception that the head becomes "Too thin, or weak" and also that its about the altered "Compression Ratio"

The issue is the area around the valve seat becomes dangerously thin after 138.68mm. As a last resort the head can be diagonally skimmed if the damage is around the exhaust side, but a new casting is of course the proffessionals prefferred choice.

Stu is a 100% right
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Old 04-03-2005, 02:04 PM   #124
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Just ordered a new one (ouch), so that's my problem solved for now

I'd still like to know what the practical options are for reclaiming old heads as this will become a necessity in the near future for many of us who want to retain YB power
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Old 17-03-2005, 01:11 PM   #125
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Quote:
Originally Posted by dave cos4x4
Stu,

i had my head work done by a bloke called Adrian.

has a head shop called 'Impulse Developments' in Todmorden.


Dave.
He's moved to Rochdale now. Very nice bloke.


He's done some good work for me.
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Old 17-03-2005, 03:46 PM   #126
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Great thread.....
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Old 17-03-2005, 04:09 PM   #127
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Ive got a lot of stuff (fancy valve cutouts on ma pistons, modded combustion chambers, etc) related to this thread actually on my car...

Basicly, as mentioned, you want as small a squish area as poss, and whatever flat raised areas on the head, should match whats on the pistons, so it all as good as touches, thats good squish, lol.

And IF you have no real choice but to have a fairly big squish (its not the end of the world in turbo engines) get rid of all the flat surfaces, edges, lumps, etc, that includes these fookin razor sharp valve cutouts n piston dishes you see, as any flat spots or sharp edges heat up and promote det, by working like a fookin diesel glow plug!

Most standard cars have a squish area on the head that match the one on the pistons, which is good, but many aftermarket or modded pistons people use, dont, so it dont match, creating a flat area with sharp edges on the head and/or pistons, just asking to get hot n promote det, like i already mentioned.

If youve not got that squish on your pistons anymore, the one on the head could well be doing more harm than good.
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Old 17-03-2005, 11:03 PM   #128
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This is back up again I see!

Think this needs to go in the Tech Essay Archives with a different title.
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Old 19-05-2005, 10:02 PM   #129
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Quote:
Think this needs to go in the Tech Essay Archives with a different title.
Agreed quick, before it disappears again
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Old 26-01-2006, 09:29 PM   #130
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this is very relevant to me at the moment - without actually measureing mine as ist still on the car... does mine (before i refitted it last time) look to have any squish area left of has it all gone....?


this is it after it was run after being skimmed


and this is it before it was fitted after it had been skimmed(ignore eh red cirles
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Old 26-01-2006, 10:02 PM   #131
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Dave that head looks VERY thin.. the inlet valves look like they are hanging out over the edge beyond the face??
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Old 26-01-2006, 10:08 PM   #132
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the machinist had to rebate the valve seats 0.5mm when he did it as he did say it was v thin, he took the same deprth off the length of the valves at the top though... ill have to actually measue it next week when it come to bits i reckon...
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Old 26-01-2006, 10:12 PM   #133
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Quote:
Originally Posted by richm
Dave that head looks VERY thin.. the inlet valves look like they are hanging out over the edge beyond the face??
this is not quite minimum thickness.. you can see the clearance between the edge of the inlet seat and the machined head face.





the edge of your valves look like they overhang the headface, never mind the seat..
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Old 26-01-2006, 10:20 PM   #134
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bugger - so it may well be needni another head aswell

ca ching
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Old 26-01-2006, 10:38 PM   #135
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as i understand it Dave, the main issue with head thickness is the security of the valve seat inserts once the edge of the seat becomes exposed to the headface edge. There is a potential risk of the seat insert(s) coming loose with the obvious impending disaster. How serious that risk is, and under what conditions, I'm not too sure..
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Old 12-05-2013, 01:36 AM   #136
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http://www.coordsport.com/index.php/...head-and-block

This company re-manufactures Cosworth YB heads and blocks. Overskimmed heads and overbored blocks should not be problem because these engines are available as re-production though they cost alot? Anyone used these?
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