The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: A10Boy on 24.08. 2009 14:06
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In the Haynes Bible its got A10 Ex valve clearances at 16 thou for 1950 - 59 models and 10 thou for 1960 onwards.
I was wondering does anyone know the criteria for the change? I mean was it becuase of different valves, pushrods or what ?
My engine numbers are 1962, but its an early 60 bike, so it could be a 62 engine, or merely replacement cases with happen to be 1962 with the original pre 60 internals. It would be good to set the right clearances.
Ive got a 356 cam, alloy pushrods, cast head
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Ive got a 356 cam, alloy pushrods, cast head
Cast iron or cast alloy ?
Mike
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Iron
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According to S.S. 701, all A10's except Road Rockets and Super Rockets used .010" and .016". This would indicate that all iron head A10's should be set to these values.
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Just done tappets on my 1952 goldflash,service sheet 203 states A10 & A7 engines after engine number AA7-101 inlet .010in / exhaust .016in. A10 superflash .008in inlet / exhaust .008in. A10 road rocket 008in inlet / exhaust .008in .A10 & A10sr frame prefixed GA .008in inlet / 010in exhaust. There is also
a note for quite running clearances which are .008in lnlet & .010in exhaust which replaces .010in inlet & .016in exhaust which are full power clearances. I set my 52 flash to .008 in inlet & exhaust. I wouldnt take a lot of notice of haynes manuals but ok! for basic info. Dave...
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Agree with G/F DAVE, the owners book that came with my flash (in 61) specified two sets of clearances one for quiet running and the other for max power ( as G/F DAVE states)
Don't need to say what set of clearances I choose as a nineteenyear old, the local bobby had already had his steel rule out to test baffles so a bit of rocker clatter wasn't going to get noticed.
All the best - Bill
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The valve clearances are determined by the camshaft used.
67-334 .010/.016
67-356 .008/.008 Later changed to .008/.010
67-357 .008/.010, Max power - .010/.012
Trev.
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Thanks Guys.
I don't take a lot of notice of what the Haynes Manual states - at least I always double check it.
So if I'm reading this right, 59/60 Iron Flash with 356 cam should be set at .008/.010 which is what I have set them at - now I can sleep easy..
Cheers
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Cold clearances with alloy pushrods.
I know these should be set hot, but the first start is always cold, so what's about the right settings for the first cold start?
(Alloy head)
-Jools
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G'day all,
I can't get my head around the different settings. Less gap = quiet running OK but larger gap + more power if valves open later and close earlier = less duration and lift. What am I missing ?
Cheers
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67-357 .008/.010, Max power - .010/.012
haha i love it - max power.....thats funny
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Well, here's what I think as regards the larger clearances and power: Yes, smaller clearances give quieter running and (marginally) more power.... up to a point. My Flash has S-R pistons in it and I used to set it at .008 and .010. Unfortunately, when pushed hard (full throttle up a long hill, trying to hang with a T160 and an 850 Commando or extended runs at the Ton), the exhaust clearances closed up. Now, while it's entertaining to your mates to see 3 ft. flames shoot out yer tailpipe (picture the aftermath of of two Chuychangas with extra green chile sauce from Chuys, Mike) it doesn't do much for the go and I imagine the long-term consequences are also undesirable. Now, I haven't pushed her quite that hard since I opened up the exhaust clearance, but I'm guessing this is what they're referring to.
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Thanks Alex. That explains the run up Kangaroo Valley the other week. Pushing hard to keep up with a new Bonnie (only 5 seconds behind at the top) she seemed a little tired. I reset to .010 + .012 and had no problems.
Cheers
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picture the aftermath of of two Chuychangas with extra green chile sauce from Chuys, Mike
ouch - good one Alex, my roids grimaced in anger at the thought ! Thats why having good clearances in those critical areas will undoubtedly save you many embarrassing moments.....
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Please correct me if I am wrong, but, less clearance would equal longer open times and greater volume exchange, i.e more power, cooling and less noise ?.
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Not sure about that Josh, does longer open not also mean more overlap? gotta keep the suck away from the blow.
All the best - Bill
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Please correct me if I am wrong, but, less clearance would equal longer open times and greater volume exchange, i.e more power, cooling and less noise ?.
I don't see why it would mean more cooling, but one thing I do know is that more power=more heat, hence the problems with the clearance closing up when you're really flogging, 'em.
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Tighter clearences do reduce noise and aid hight speed running at the expense of low rev power.
Logic goes like this,
At low revs not enough time to properly fill the cylinders at the lower gas velocities and add to that losses from the fresh charge wafting out the exhaust valve do to longer and larger amount of over lap.
Also reduce the clearence between the valves & the piston.
The opposite applies to sloppier settings used fro high speed running