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#709847 - 09/27/17 4:33 pm A 65 rocker ratio  
Joined: Aug 2001
Posts: 244
Phil in Germany Offline
BritBike Forum member
Phil in Germany  Offline
BritBike Forum member

Joined: Aug 2001
Posts: 244
Duesseldorf/Germany
Hi all,

I do have a possible issue. Together with a mate I have come across a '70 A 65 Lightning puzzle. We could not resist and bought it. grin

The cylinder head has already been refurbished with new Colsibro guides and new Nucleus valves.
What makes me feel slightly uncomfortable is a measurement I have taken on the guides. The valve stem ends do protrude through the guides only 22 mm, every other head I have in reach shows a measurement of 24 mm.

10 years ago I had my own Lightning head refurbed at the shop which did the current head as well and I ended up with too long guides. The collar had hit the guides with a hot engine. Of course this went along with nasty noises. eek

If I do assemble the top collar with the collets to a naked valve I measure around 11.5 mm from stem end to the collars bottom end. This leaves me with 10,5 mm available travel for the collar when the valve is opening.

The cam is a standard 68-0437 with .306" lift resp. 7.8 mm. If the rocker Ratio was 1:1.2 I I'd end up with 9.4 mm valve lift or about 1 mm clearance.
My gut feeling is that this will not suffice due to the dynamic behaviour of the valve train and thermal expansion.

Is my assumption regarding the rocker ratio reasonable? Unfortunately I could not find a figure with the search function on the forum.

I am inclined to get the guides shortened by 2 mm.

Can you help me out with any input regarding my issue?

Thanks in advance and best regards

Phil


Best regards
Phil
Duesseldorf/Germany
'62 A 65 Star (disassembled)
'69 A 65 Lightning
'71 A 65 Firebird
'75 T 160
'84 Yamaha SR 500
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#710647 - 10/05/17 10:14 pm Re: A 65 rocker ratio [Re: Phil in Germany]  
Joined: Jan 2014
Posts: 3,247
NickL Online content
BritBike Forum member
NickL  Online Content
BritBike Forum member

Joined: Jan 2014
Posts: 3,247
Aus
I have had similar experience with guides made to take seals (extra 1.5mm long)

If you run less than 12mm then make sure the springs are the correct weight or you will end up
with bent pushrods or worse.

This can also be the case when fitting large valves, either the stem length must be extended or the seat cut further back.
I think Gavin Eisler had this problem a while ago when fitting SRM big valves.
My own practice when racing was to set the springs (W+S) for 60 thou from coil bind by spacing the spring seats from the head.



#710648 - 10/05/17 10:25 pm Re: A 65 rocker ratio [Re: Phil in Germany]  
Joined: Aug 2001
Posts: 3,291
gavin eisler Online content
BritBike Forum member
gavin eisler  Online Content
BritBike Forum member

Joined: Aug 2001
Posts: 3,291
argyll. scotland, uk
Yes I had an issue, i had oversize inlet valves fitted, the new seat left the valve very proud in the combustion chamber, leading to piston clearance and valve binding issues, once the seat was cut 0.070" deeper normal service was restored, so not really a valve guide problem. Using the stock spit cam and valve springs from SRM , no issues 3K later, ( I dont push the rev ceiling very hard , its seen 6.5 k a couple of times.),
I dont know about rocker ratios, I believe Mark Parker has special rockers with offset buttons to get more travel.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#711244 - 10/11/17 9:15 pm Re: A 65 rocker ratio [Re: Phil in Germany]  
Joined: Aug 2001
Posts: 244
Phil in Germany Offline
BritBike Forum member
Phil in Germany  Offline
BritBike Forum member

Joined: Aug 2001
Posts: 244
Duesseldorf/Germany
Hi there,

I have now done some measurement on the rockers. The inlet ratio seems to be 1.11, the exhaust ratio 1.16.

Anyway, I have shortened the guides to give me peace of mind. With the valves pushed to the seat the valve stems now protrude 24 mm resp. 15/16" in your money through the guides.

FWIW

Cheers!

Ph.


Best regards
Phil
Duesseldorf/Germany
'62 A 65 Star (disassembled)
'69 A 65 Lightning
'71 A 65 Firebird
'75 T 160
'84 Yamaha SR 500

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