The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: AndyDenmark on 07.07. 2014 17:46
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Hi all
I have a question on liners and pistons. It appears that my pride and joy requires some major work. I need a set of new liners and pistons among other things but need to know if the outside diameter of the liners varies before I order the wrong bits. The engine stamp tallies with a 1954 small journal motor with a cast head. Is there a standard O.D for the liners? and with regard to the pistons I am not looking for wild performancs so am thinking of putting standard pistons in. I can see on Draganfly there are several size pistons such as...20,40,60 Is this for different sized piston O.Ds due to rebores etc as I am a little unsure which ones to order. Sorry this is a bit of a long post but I am on a ship in the North sea ordering from the U.K for a mechanic in Copenhagen....:).
Thanks in advance...Andy
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Normally +060 is the last oversize on A10's but I have used some +080's supplied by SRM and they worked fine. STD is the standard manufactured original size which for A10's is 70mm diameter then each oversize is in increments of .020". It was possible to get +030's back in the day but I don't think they are available now. If your barrels are already on +060 and are worn out or scored you will probably need new liners and a set of STD pistons. Take the whole lot to a reputable, experienced engineering firm and leave the rest to them. However, they need to take a bit more material out of the bottom of the barrel than the top or, when fitting the new liners, there is a good chance that the original barrel skirt will split or crack. I would also recommend no less than .004" piston clearance which, assuming good quality pistons, should be sufficient to safeguard against potential seizure when running in (carefully!). Seizing new liners can be a real disaster, to be avoided at all costs!
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Hi all
I have a question on liners and pistons. It appears that my pride and joy requires some major work. I need a set of new liners and pistons among other things but need to know if the outside diameter of the liners varies before I order the wrong bits. The engine stamp tallies with a 1954 small journal motor with a cast head. Is there a standard O.D for the liners? and with regard to the pistons I am not looking for wild performancs so am thinking of putting standard pistons in. I can see on Draganfly there are several size pistons such as...20,40,60 Is this for different sized piston O.Ds due to rebores etc as I am a little unsure which ones to order. Sorry this is a bit of a long post but I am on a ship in the North sea ordering from the U.K for a mechanic in Copenhagen....:).
Thanks in advance...Andy
Is there a reason you want to resleeve the barrels? it would pay to identify what oversize the motor currently is first and also determine whether the bores have been previously resleeved. Obviously resleeving allows you to return to a standard piston bore, but also limits the viable oversizes that can be then fitted. Whereas an unsleeved A10 barrel will typically go out to +100 or +2.5mm safely
Living in the antipodes we take for granted getting supplies from the other hemisphere. Unless you have a damaged sleeve I would consider a resleeve a last resort option but be looking to carefully measure up first.
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Obviously resleeving allows you to return to a standard piston bore, but also limits the viable oversizes that can be then fitted. Whereas an unsleeved A10 barrel will typically go out to +100 or +2.5mm safely
Really useful knowledge there RR. Thanks. *smile*
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hi andy, my a10 barrel is sleeved back to std bore size and the liners are 1.6mm wall thickness. I am not sure if there is a standard wall thickness (hence outside diameter) but from what Ive heard and also the comments above about the bottom of the barrel splitting it would not be advisable to for a thicker wall liner.
Ive heard it is ok to rebore a sleeve at least once, maybe twice, but Im not sure I would do twice!
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Thanks for that guys. It was just that I read....or dreamt :) somewhere that there were different O.D liners and wanted to make sure I ordered the correct ones and have done so now.The reason I am replacing them is that the existing ones are borderline and thought while the motor is in four hundred pieces I may as well go the whole hog and get new liners and pistons in as well.Expensive at the moment but hopefully cheaper in the long run :)
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I relined with bores worn at +060. Couldn't get any +080 at that time but gather that they can be found. 2.5 mm over ... +.100 - really? where from?
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+.100 - really? where from?
yes that one surprised me also, I have heard advice against even +80s due to the lack of metal left on the barrel
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+100 sounds like thin ice to me! You might well get local hotspots with that thin a cylinder.
Dont forget that whilst a liner will restore cylinder rigidity, it wont help structural strength over the length of the cylinder. Wont help prevent blowing the topend off!
If it really needs lining, why not get whoever does the job to source the liners? No mistakes then.
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Living in the antipodes we take for granted getting supplies from the other hemisphere.
Interesting stuff about sleeves, and I think I will be back to this thread in my next rebuild, but I also found the "antipodes" reference amusing. Is that a common term used in NZ to describe remoteness from the U.K.? I looked up my own antipode when the Malaysia Air flight was lost (not shot down). It turned out I was about on the exact antipode from where they were searching off of Perth. You, RR, appear to be antipodal with Gibralter.
...and yes, I was bored and wanted to do something unrelated to work, so antipodes is as good as the next distraction.
Richard L.
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I relined with bores worn at +060. Couldn't get any +080 at that time but gather that they can be found. 2.5 mm over ... +.100 - really? where from?
When I was doing some fin repairs I was donated a scrap thin flange barrell that had blown off the flanges *eek* ,however it had a set of heavily shagged 10.5:1 +100's in it that had obviously done some very HARD work in their lifetime before she had lifted the barrells off. But I was not privy to that abuse personally.
It isnt a given for every barrel, but +100 can be done, I have been offered new 10.5:1 +100's, but dont have a requirement as yet. I havent come across them in lower compression, but havent looked.
I tend to measure up carefully and only rebore if I have to and resleeve only as a last resort.