Author Topic: A10 barrel  (Read 1549 times)

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RESTORER

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A10 barrel
« on: 17 February, 2020, 17:20:00 »
I have an original 1954 A10 thin flange barrel 67-1074 which I took off my machine.  I am now having problems with the engine and looking at going back to my old barrel whilst the engine is down.  My old barrel obviously needs a rebore and a good clean outside, but is still at standard size and has all its flanges intact. There is however a problem:  There are two cracks at the bottom of the bore, starting from the two radiussed corners of one of the cut-outs, see pic.  One crack is about 27mm long and the other is about 20mm long, although these dims may be optimistic with a proper inspection.  Can these cracks be safely repaired?  Do these cracks prevent re-lining?  Thanks for reading.
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1954 A10 Golden Flash, Swinging Arm

Bess

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Re: A10 barrel
« Reply #1 on: 17 February, 2020, 19:04:39 »
Hi,
    It looks like one of the cracks has extended into the flange/finned area of the barrel and its location, drilling a small hole at the end of the crack to stop it progressing is near impossible. I wouldn't use it, I would say get someone like SRM to see if lining would be an option.

Best wishes...
« Last Edit: 17 February, 2020, 19:11:52 by Bess »

DAVE BRADY

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Re: A10 barrel
« Reply #2 on: 22 February, 2020, 11:11:12 »
Hi,

Looking closely at the first image is there also a crack on the cam follower block?  There is some thing running from between the two on the left diagonally down to the right.
These cylinders must have had a hell of a shock at some point.

Dave.

RESTORER

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Re: A10 barrel
« Reply #3 on: 22 February, 2020, 20:46:22 »
Thanks lads, I think I will stick with the barrel I have on at the moment, at least for now.  I have no history at all for the machine, it was a mess, so I have no idea about previous treatment.  Its just that the replacement I got hold of and fitted is at +060 already so I thought I would make some enquiries about a possible repair.  In the picture from Bess near the base of the LH cylinder, there is a distinct line running around, and I have a similar line.  On the first pic, mine runs about halfway round and then upwards vertically (downwards when fitted) to the edge on both sides, about on the L-R centre line.  It is not clear as it is out of focus but it has a similar look to that of a run of weld.  Any idea what this line is?  It is only present on one bore.
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1954 A10 Golden Flash, Swinging Arm

DAVE BRADY

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Re: A10 barrel
« Reply #4 on: 22 February, 2020, 21:13:44 »
Hi,

I do not know if they are still available but SRM had some +80 pistons.  I fitted some to my wife's '51 Flash and it all seems fine. In fact the extra few cubes make it hard to keep up with on my standard A65.
A re-line means boring out to +120 and as this takes several goes with the borer it can get a bit expensive. Then the fitted liner has to be bored to standard size and standard pistons bought.
If you can get the +80s then this is a cheaper option and you still have more of the original material.  I have it on good authority that +100 is possible but the pistons are probably not available.
Imagine an A10 with just about 700cc.  +80 gives 684cc and +100 gives a tad under 698cc.

Dave.
« Last Edit: 22 February, 2020, 21:39:25 by DAVE BRADY »

RESTORER

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Re: A10 barrel
« Reply #5 on: 23 February, 2020, 10:03:19 »
Thanks Dave, I will certainly go into that. +80s could well be the best option if I do have to strip down again.
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1954 A10 Golden Flash, Swinging Arm

Mike Farmer

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Re: A10 barrel
« Reply #6 on: 05 March, 2020, 20:35:17 »
 :) :) :)

I have a similar problem, so I spoke to SRM about +080" and they say not for A10.

Mike 8) 8) 8)

DAVE BRADY

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Re: A10 barrel
« Reply #7 on: 05 March, 2020, 21:43:24 »
Hi,

It is a pity that SRM do not do these pistons any more as they would be in demand.  I suspect that they used a 650 Triumph piston.
A +0.080 on an A10 increases the bore from 70mm to 72mm.  The 650 Triumph standard bore is 71mm so a +0.040 Triumph piston would be 72mm.   I do not know if the small ends are the same size or if the compression height is the same but if my numbers above are correct then the Triumph pistons could be used!!

Dave.

ChrisG

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Re: A10 barrel
« Reply #8 on: 06 March, 2020, 09:39:55 »
Hi Dave,
I could be wrong but I though all small ends and Gudgeon Pins  were 3/4" dia. so should be OK.
Chris

DAVE BRADY

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Re: A10 barrel
« Reply #9 on: 06 March, 2020, 09:53:56 »
Yes, I think they are and if the gudgeon pin is in the right place then we are in business.  Has anyone got a Triumph piston to compare with a a BSA one?

Dave.

JulianS

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Re: A10 barrel
« Reply #10 on: 06 March, 2020, 10:46:14 »
I recall some time ago hearing that you could use a piston from a Nissan Cherry.

Not seen it done.

https://www.fwthornton.co.uk/19690-std-piston-for-nissan-cherry-1200-218685

73mm standard bore. Concave crown.

(Not convinced there is enough metal in the barrel for this)

Smaller pin.

Lower comp height 32.6 mm than 7.25 comp A10 which is 34.5mm. The 6.5 comp A10 has comp height 33.3 mm.

Slightly longer overall.
« Last Edit: 06 March, 2020, 11:06:10 by JulianS »

Mike Farmer

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Re: A10 barrel
« Reply #11 on: 06 March, 2020, 12:39:19 »
 :) :) :)

About £150 to have it re-lined plus pistons.

Mike 8) 8) 8)

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Re: A10 barrel
« Reply #12 on: 06 March, 2020, 15:25:05 »
Thanks for all this information lads, I seem to have provoked a really interesting and much broader discussion than I expected.  Who else but Julian would come up with a Nissan Cherry piston?  I had searched the SRM website and not found any +080" pistons, but I hope to be back up and running shortly and will see if I have bottomed my problems.  If not then I can look at relining my +060, so thanks for the estimate Mike, at least I have an idea.  Can I assume that any change of piston size will need a re-balanced crankshaft, dynamically with a full assembly of rods, pistons rings etc for the smoothest performance?
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1954 A10 Golden Flash, Swinging Arm

DAVE BRADY

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Re: A10 barrel
« Reply #13 on: 06 March, 2020, 16:23:53 »
If you have had the crank dynamically balanced and you change the pistons you may be able to match the new ones to the existing ones.  If you re-line and go back to standard you will in theory be using slightly lighter pistons.  However, the weight varies between manufacturers.
When the time comes accurately weigh your existing pistons complete with rings and gudgeon pins.  Then when looking for new ones get the weight - it is usually in the specification.  You may find that there will be a standard piston (complete) that is the same weight or even a bit heavier than your -0.060 ones.  If a bit heavier then some material can be removed from the skirt of the piston below the gudgeon pin.  Obviously this is done very gradually with equal amounts being removed from each side of each piston and leaving a very smooth finish.

Dave.