The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: sean on 02.01. 2021 19:57
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just honing the cylinders to clean them up and noticed several deep pits near the top ...cylinders are at plus .060 and I am not sure going to plus .080 will clean these up , they are fairly deep and this side of the cylinder had a broken valve guide in the head .
the bike sat for 10 years and was seized when I got it striiped it down and rebuilt everything but just saw this .
my options are paying for a rebore that may or may not work ,cylinder liners or trying to find a used set of barrels ......be interested to hear opinions
1962 super rocket
thanks
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Here is a pic
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just honing the cylinders to clean them up and noticed several deep pits near the top ...cylinders are at plus .060 and I am not sure going to plus .080 will clean these up , they are fairly deep and this side of the cylinder had a broken valve guide in the head .
the bike sat for 10 years and was seized when I got it striiped it down and rebuilt everything but just saw this .
my options are paying for a rebore that may or may not work ,cylinder liners or trying to find a used set of barrels ......be interested to hear opinions
1962 super rocket
thanks
I would get liners fitted, my GF has them and no problems, you can rebore them once as well. The type with locating “ledge” at the top (to ensure they don’t move) are worth fitting for peace of mind.
You or engineer would have to get the grinder out to make slots for the rods.
Just my 2 cents worth.
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Hi sean,
I had a similar problem on my 1660 A10. i decided to put new standard stepped barrels in. The good thing with stepped barrels is you dont get any movement with them as the cylinder head traps them in position. Also you have nice thick walls so in future you will get at least three rebores out of them.
Cost wise mine only came out a few pounds less than having them bored to maximum and buying a new set of pistons.
ELLIS
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Yes, chiming in to agree with KiwiGF. I was also at +60 thou". The "flanged" liners (with the "ledge" at the top) weren't available anywhere. Then Adrian Wright, the proprietor of IMD pistons (which I have also been recommending) - came up with some. They just need to be cut off at the bottom..
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I found the liners on their web site and e bay but I dont see a flange on them ?
do they have to be honed or bored after fitting as I imagine they would be a press fit ?
seems they have a machine shop a couple of hours from me in Canada they deal with according to the web site .
thanks
Sean
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Do a quick fit up and check where he pits are with respect to the top of the top ring.
Most of the compression is done by the second ring in an case .
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was going to do that today .....found a set of barrels std size but I think they are from an Ariel huntmaster they have no casting numbers and the Bsa Ones have the part number [ 67- 1210 ] cast into them.
I belive the fins are different between the 2 types not sure how to identify the ariel one for sure and I think they are interchangable , but I am going to pass.
Sean .
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G'day Sean.
I'd be going for liners. Straight ones are OK if their given enough interference. 1 thou per inch is about right. The materials are very similar being spun ci in cast ci so thermal expansion is very similar and the liner will heat up more and faster than the barrels so will not move.
This will also give your grandkids a re-bore or two ;)
Cheers
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Sean, as a cheapskate those pits don't look too bad. To raise the ire of the precision engineers among us, is filling with braze and polishing back a reasonable solution to restore this small area of an otherwise good bore?
Swarfy.
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cylinders have about 100 klm on the according to previous owner they were rebored before he stored the bike
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Swarfy, I normally agree with all you say, but filling with braze? I'd rather leave alone.
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Do a quick fit up and check where he pits are with respect to the top of the top ring.
Most of the compression is done by the second ring in an case .
Practically all the compression sealing should be done by the top ring. The second plain ring does some useful oil scraping.
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Thanks for the replies
Going to go with liners got too much money in this to cheap out now just have to find a supplier hopefully in Canada but not looking good so far and no replies yet from Uk..........being on pension sucks .
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"Practically all the compression sealing should be done by the top ring." Especially those engines that only have one compression ring!
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"Practically all the compression sealing should be done by the top ring." Especially those engines that only have one compression ring!
Racers!
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Do a quick fit up and check where he pits are with respect to the top of the top ring.
Most of the compression is done by the second ring in an case .
Practically all the compression sealing should be done by the top ring. The second plain ring does some useful oil scraping.
The top ring is called he fire ring for good reason, it takes he brute force of the combustion
The first set of gapless rings I installed I fited the gapless one on the top and they failed myserably
Swapped them around, gapless 2nd ring, worked like a dream
According to some conversations with Total Seal, they suggest opening the gap on the top ring and closing the gap on the 2nd ring regardless of weather am using gapless or standard rings.
Too little gap on the top ring prevents suffcicient gas pressure getting behind the second ring fast enough to create a proper seal.
has been taught the top did all the work but apparently it should be the 2nd.
In use I have run more than one engine with pitting in the bore because new barrrels or liners were beyond my finances at the time
Unless the pit wa almost a full ring, the worst case was an engine that was a little more smokey than it should have been.
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One of my quick Norton engines exploded long ago and left a few dings in the upper end of the LH barrel. I rebuilt the engine without reboring the barrels as they were not worn out - except the dings. Ran a hone through and put used pistons in. No smoke as the dings cannot collect oil - they are all above the upper travel end of the oil scraper ring. So check location, if yours are as high up the barrel as they appear, I would use as is.
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Swarfy, I normally agree with all you say, but filling with braze? I'd rather leave alone.
S O P with large marine deisels
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Hi all
Just to revive this older post the question to my mind is that in order to fit the liner to the barrel, which already has a reputation for breaking above the base flange, is further weakened. I measured the casting above the flange which is 81/82mm I have seen liners for A10 advertised with an O.D. of between 73 and 80 mm. Surely this a has serious risk of failure when the wall thickness of the original casting is best case 4mm and worst case 0.5mm!
So much better if one of the piston suppliers made +0.080" pistons which gives a wall thickness of 4.5/5.0mm, I know Cake Street had a batch made, if only these were availiable again.
Cheers
Chris
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G'day Chris.
I just threw a set of +80's in the Cafe's barrels that had been previously sleeved (aprox 75mm od). Still plenty of meat. She'll be running 12:1 comp but the head is through bolted to the cases. *eek* *whistle*
If you could find a old bike or car shop, take a pin & piston to compare with another make of bike or even car. A mate has a diesel piston in a Yammie XT600
Cheers
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My sleeves-in-waiting are 73mm O.D.
Richard L.
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Yes Thanks Richard, Musky
My instinct runs against such a thin liner, and I think the 80mm O.D. liner advertised has been read from a "spec sheet" for a 70mm piston to give a 5mm wall thickness not realising the block is only 81mm. I am no expert so if the original casting is bored perfectly and the spun cast liner if perfect and with the correct interference.. then the font of the engine gets the cold air will a liner only 1 or 2mm thick be ok? I dunno.
Alternative pistons are, I think, the answer and the prime candidate must be 650 pre-unit Triumph, air cooled and with a standard bore of 71mm thus giving two rebores after the A10 +0.060 max, and leaving the original barrel 4.5/5mm thick. There is a problem though, the small end is 11/16" and the gudgeon pin hole is in a different position relative to the top of the piston which means the Triumph piston would come out the top of the block. So to do this you would need a new pair of special rods and a new pair of pistons and re-bore. That lot would set you back at a guess around £600 which is probably why people go for liners!
Love to try it, anyone felling ftush.
Cheers Chris
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Correction, its not that the piston comes out the top of the barrel, it's that it doesn't reach the top, by about 7mm I think. So a longer rod is required, still need special rods though.
Chris
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G'day Chris.
I think sleeving back to standard is your best option. Richards 73mm sleeves still gives one or two oversizes for the future.
Cheers
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Hi All
Just thinking about this??? what about B31 pistons which are also 71mm std
If I think of it I might compare them tomorrow, If I can find a B31 piston in the melee
John
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many years ago i fitted a +60 A10 piston into a B31 and it fitted, needed a spacer under the barrel as the piston came out, was not much think is was about 3mm so an alloy spacer was made, worked a treat rode to Holland on it.
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Hi All
Yes the B31 piston compression height is too low compared to the A10
John
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I don't have my 60's piston catalogues in front of me, but the B series had three different lengths of conrod (the ZB had the longest, the CB was shorter and the DB shorter still) so presumably gudgeon pin to crown height changed as well - ie there might be a more suitable version that would do.