The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: A10Boy on 24.08. 2009 14:06

Title: A10 Valve clearances
Post by: A10Boy on 24.08. 2009 14:06
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
Title: Re: A10 Valve clearances
Post by: MikeN on 24.08. 2009 15:18

Ive got a 356 cam, alloy pushrods, cast head

Cast iron or cast alloy ?

Mike
Title: Re: A10 Valve clearances
Post by: A10Boy on 24.08. 2009 16:45
Iron
Title: Re: A10 Valve clearances
Post by: beezalex on 24.08. 2009 16:57
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.
Title: Re: A10 Valve clearances
Post by: G/F DAVE on 24.08. 2009 17:29
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...
Title: Re: A10 Valve clearances
Post by: bsa-bill on 24.08. 2009 17:50
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
Title: Re: A10 Valve clearances
Post by: trevinoz on 24.08. 2009 22:06
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.
Title: Re: A10 Valve clearances
Post by: A10Boy on 25.08. 2009 19:47
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
Title: Re: A10 Valve clearances
Post by: Joolstacho on 03.02. 2010 01:46
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
Title: Re: A10 Valve clearances
Post by: muskrat on 03.02. 2010 06:43
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
Title: Re: A10 Valve clearances
Post by: mike667 on 03.02. 2010 11:15

67-357   .008/.010,  Max power - .010/.012


haha i love it - max power.....thats funny
Title: Re: A10 Valve clearances
Post by: beezalex on 03.02. 2010 18:00
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.
Title: Re: A10 Valve clearances
Post by: muskrat on 03.02. 2010 18:57
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
Title: Re: A10 Valve clearances
Post by: mike667 on 03.02. 2010 19:03
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.....
Title: Re: A10 Valve clearances
Post by: Josh Cox on 04.02. 2010 22:23
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 ?.
Title: Re: A10 Valve clearances
Post by: bsa-bill on 05.02. 2010 10:35
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
Title: Re: A10 Valve clearances
Post by: beezalex on 05.02. 2010 16:41
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.
Title: Re: A10 Valve clearances
Post by: BSA_54A10 on 06.02. 2010 10:16
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