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runningrich
Big valves and odd rods
#1
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Does anyone know if an A15 rod is longer than an A12 rod? and is Big end bore size different? I wouldnt mind getting some larger valves for the A15 head, any ideas?

Posted on: 2009/11/25 10:17
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Gylezy
Re: Big valves and odd rods
#2
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l16 vaulves mate....
gotta be cut down tho and re sleved.
not to much work tho, i had some put in a head not long ago, the motor isnt going yet tho haha.
the inlet was about 1.6mm bigger and exhause was about 2.8mm? they fitt really nicely!
hope it helps.
cheers

Posted on: 2009/11/25 10:35
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b310gx
Re: Big valves and odd rods
#3
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the a15 conrod is definitely longer, the gudgeon pin bore is bigger but the big end bore is the same between the two engines. As for larger valves, cut down L16 valves work, but you need collets on the top, or the valve stem will wear away.

Posted on: 2009/11/25 10:37
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runningrich
Re: Big valves and odd rods
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thanks, what do you mean collets, aren't they made with collets? or do you mean valve stem caps? and would you know exactly how much longer the A15 rods are at all?

Posted on: 2009/11/25 10:43
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ddgonzal
Re: Big valves and odd rods
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When you cut the valve stems to shorter length, can you re-harden the tip, or do you need a stem cap?

I see a lot of A-type heads fitted with 7mm valves instead of the stock 8mm stems. Apparently you only need new guides to do this.

Valve collet (split-collet)
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Posted on: 2009/11/26 2:49
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A14force
Re: Big valves and odd rods
#6
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my local cam guru said it's better to leave your new valves a bit longer than stock ones. When you have a big lift camshaft, the rocker geometry goes out a bit at peak lift. And a longer valve helps this. He said he'd even cut down the rocker shaft pedestals in the past to aid rocker geometry.

Posted on: 2009/11/26 8:22
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MLS
Re: Big valves and odd rods
#7
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A12 rods are 121.5mm centre to centre
A14 / A15 rods are 133mm centre to centre.

Also you might be interested to know that the A14 / A15 block is 14mm taller than the A12 block.

Posted on: 2009/11/26 11:24
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D
Re: Big valves and odd rods
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DD can you put the engine deck heights up on the Tech Wiki? (or are they already up there as I couldnt find them)
Inst it 189.1mm a12 and 204.1mm a14/15??? therefore 15mm difference?
MLS your speedway blocks running Meth must have 1mm skimmed off for comp?

Posted on: 2009/11/26 11:35
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ddgonzal
Re: Big valves and odd rods
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I do not know. The factory service manual doesn't list the block height, probably because shaving the block deck is not a typical rebuild procedure.

Posted on: 2009/11/26 22:19
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D
Re: Big valves and odd rods
#10
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After all these years its still a mystery for many seasoned Dattoccentrics :)

Posted on: 2009/11/26 23:24
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