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'66 A65 head #775092 05/29/19 9:01 pm
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Samsmc1 Online Content OP
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I've stepped into another puddle where I can't find the technical data I need to finish properly rebuilding an A65 head. I know the the correct spring height and seat pressure. What I'm not finding is the correct stem height so that I don't get the rocker arm ratio out of kilter.
This head had many previous valve jobs and the seats were a little recessed. After replacing the guides, I was able the blend the seats into the combustion chamber so that the valves aren't shrouded. I can shim the springs easily enough to get the proper seat pressure, but the valve stems must be shortened.
Can anyone tell me where I might find this length or better yet, have any of you engine builders ever measured a virgin head and discovered this information?
Thanks
Sam

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Re: '66 A65 head [Re: Samsmc1] #775131 05/30/19 9:27 am
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gavin eisler Online Content
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Valve tip to valve spring pocket, should be 1.730" - 1.750".

These dimensions work for my 71, not sure about earlier models.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
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Re: '66 A65 head [Re: Samsmc1] #775135 05/30/19 10:37 am
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gunner Online Content
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I'd be careful if you're shortening the stems, you might find that the springs become coil bound when closing.

If the seats are significantly pocketed, a better approach might be to get new seats installed.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: '66 A65 head [Re: Samsmc1] #775146 05/30/19 1:49 pm
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edunham Offline
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Can you use oversize valves to move the valve heads back to where they ought to be? I successfully did this on a Trident years back.

Ed from NJ

Re: '66 A65 head [Re: Samsmc1] #775148 05/30/19 2:33 pm
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Samsmc1 Online Content OP
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Gavin
I don't understand your terminology.
Is your measurement from the valve tip to the cup the spring sits in or to the aluminum base under the spring cup?

Gunner
You got by me on your suggestion - what does shortening the stem (grinding the end down) have to do with coil bind?

Ed
Just installing larger valves still wouldn't tell me what the correct spring height should be. The valve seats look really nice just as they are plus larger valves could cause tuning problems down the road.
Thanks
Sam

Re: '66 A65 head [Re: Samsmc1] #775150 05/30/19 2:48 pm
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bodine031 Offline
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www.kibblewhite.com
free length inner 1&7/16" outer 1&3/4"
fitted inner 1.277" outer 1.370" outer spring fitted with closed coil down in spring cup
clearance cold Int. .008 Ex. .010

Re: '66 A65 head [Re: Samsmc1] #775158 05/30/19 3:47 pm
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Allan Gill Offline
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Originally Posted by Samsmc1


Gunner
You got by me on your suggestion - what does shortening the stem (grinding the end down) have to do with coil bind?



Exactly, your not adjusting the position of the collet by grinding the top of the valve, just creating more clearance, my only concern would be that you have broken through the case hardening by grinding back.

The rocker geometry will only change though if you have changed the pushrod total length or overall height of barrel and/or cylinders. The adjustment otherwise is above the valve stem and they would have to be seriously out to not meet the adjuster.

The recession of your valve seats though will hurt flow and affect performance more than not checking spring pressure and coil/spring height. For a road bike my only concern there is coil bind. If you can turn the motor over and see a gap between the springs coils then worry over for a road bike. If it was a race bike then if he more concerned about those values


beerchug
Re: '66 A65 head [Re: Samsmc1] #775161 05/30/19 4:15 pm
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gavin eisler Online Content
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Is your measurement from the valve tip to the cup the spring sits in or to the aluminum base under the spring cup?


To the alloy , only valve and guide required. To be clear , from the extreme end of the valve to the alloy well around the guide top.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
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Re: '66 A65 head [Re: Samsmc1] #775183 05/30/19 6:29 pm
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gunner Online Content
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Quote
Gunner
You got by me on your suggestion - what does shortening the stem (grinding the end down) have to do with coil bind?


I see what you mean now, I thought you wanted to use a shorter valve with lower collet slots rather than grinding the top off the valve.

If you do grind down the head bear in mind any hardening which may be removed as Allen suggests.

Last edited by gunner; 05/30/19 6:30 pm.

1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: '66 A65 head [Re: Samsmc1] #775186 05/30/19 7:20 pm
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Gavin
Thanks for the info - that gives me something to work with.

Allan
you're right about the rocker position - that's not changing. Since I already had the specs on the valve springs, I should be able to shim them OK. Also I'm aware that BSA may have had some coil bind problems. I have both types of new springs to play with.
I blended the seats into the combustion chamber so that the valves aren't shrouded. I may loose one or two tenths of a point in compression - that won't bother me a bit. I want this old dog to be right, but it will never get hammered again.
What would be the purpose - most any modern 500cc bike would run away from this thing.
I should be able to find some ball end valve adjusters to compensate for the valve stem tips if I pull off to much of the hardening.
Thanks to all of you for your help.
Sam


Re: '66 A65 head [Re: Samsmc1] #775509 06/03/19 7:53 am
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NickL Online Content
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Fitting mushroom head adjusters is a good idea BUT really you should run lash caps if
you grind the valve stems enough to remove the stellite or hardening. PM do suitable caps.
Just my 2c.


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