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#846017 04/13/21 8:28 pm
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knuckle head
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knuckle head
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I checked the cam timing on my A10 ....It's an 0357 cam and the engine is more or less a Super Road Rocket in a stripped down machine.
96.5 degrees, I think 100 degrees would be better and I can make an offset key for the cam wheel.....Be used for sporty riding on back roads...
Any opinions ?


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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Hmmm, Good exercise and it couldn't hurt. PRT

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Is the A10 engine breathing mechanically timed like on the A65 or does it have a different way of breathing? (I know the thickness of the cork discs are important but thats about it) If its mechanically timed like the A65 then you may need to install an aditional breather system. I found my A65 needed one when the cam was timed differently.

If your using this more for back roads, why don't you think of Advancing the cam instead of retarding it? you'll have the same spread of power but it will come onto cam more at lower revs, I doubt you'd loose anything at top end but it would make it feel like it has more pull lower down the rev range.


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68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (undergoing restoration)
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knuckle head
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Yes ,A10 has a timed breather on the cam gear...The engine has the stock breather arrangement but I redrilled the left side exit to face upward and add a small filter. Also added a breather pipe to the intake valve cover...I may just allow it to breath freely like my Triumphs...
Pushrod Tom says the stock timing is 100 degrees so 96.5 is somewhat advanced...


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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My take on timed breathers, or reed valve breathers, or even PCV valves on breathers, is if you use any of these, adding an open breather, like the valve cover cap breathers, will just make things worse. The timed breather attempts to create a slight vacuum when the pistons are moving upward in the barrels, as do the other ones I mentioned. If you add an open breather, the timed one can't work at all, as the open breather allows air to enter as the timed breather closes.

So go big on the open breather or stay home, as BSA B50 and later Triumphs do, which basically just lets the engine breath to the atmospheric pressure with very little restriction. As the late Stan Millard said when asked how big, "how ugly can you stand?" He used breathers on his flat track racers that looked to be about 1-1/2" hose!

Tom


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The timed breathers on old Brit bikes don’t work at high rpm.

An extra open or reed valve breather won’t do any harm.


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knuckle head
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My experience with open breathers is on the race Triumphs and T140's. the dual pre unit engine bike has one 3/4 id hose per engine off the timing case. The single engine bike has one 5/16 hose off the timing cover and a 7/16 hose off the front mount cavity. Zero oil blows out the hoses and no engine oil leaks so I assume they are doing the job .
I believe two free flow 3/8 hoses on the A10 will be ok for street use.and if not, I learned something from my own experiences wink


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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This thread made me dig out my notes, such as they are. The 357 is pretty much the same as the 473 in A-65s. Looks like I retarded the cam to I 102 E 104 and, yes, it was worth a bit on top. This will be a fun bike!

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knuckle head
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Tom, I think so....The R&R rods are based on Triumph 650 rods so they are about .040 longer than stock A10 rods. So the 7.4 compression flat pistons are .010 below the deck giving a 8-1 compression ratio. In the past .060 larger intake valves were installed in the alloy head. I don't know how that will affect the performance..Be using my Mikuni flatslide carbs as usual, one 32 mm. And a RGS style siamese exhaust...Doug Wood did a total rebuild on the Manual advance mag...


79 T140D, 96 900M Ducati ,61 A10 .On a bike you can out run the demons..
“But I don't want to go among mad people,” Alice remarked. “Oh, you can't help that,” said the Cat: “we're all mad here. I'm mad. You're mad.
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In the 1950s 8.0:1 compression ratio was the compression ratio for the sporty models.
The cooking models had a 7.25:1 compression ratio.
So at 8:1 I reckon you are set fair for a nice sporty bike that is still eminently road rideable.

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Originally Posted by Hillbilly bike
My experience with open breathers is on the race Triumphs and T140's. the dual pre unit engine bike has one 3/4 id hose per engine off the timing case. The single engine bike has one 5/16 hose off the timing cover and a 7/16 hose off the front mount cavity. Zero oil blows out the hoses and no engine oil leaks so I assume they are doing the job .
I believe two free flow 3/8 hoses on the A10 will be ok for street use.and if not, I learned something from my own experiences wink
I added a 1/2" ID hose to the timing cover on my A10, between this added breather and factory timed breather, I never had leaks out of the factory crankcase breather.


1955 BSA Bantam D1 Plunger
1956 BSA A10RR Street and LSR Bike
1961 BSA C15S
1966 BSA spitfire
1969 Triumph T100C
1970 Triumph TR6R
1970 Triumph TR6C
1972 BSA Lightning LSR Bike
1974 Triumph T150V

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