Author Topic: rebored BSA a7  (Read 541 times)

Offline tim

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rebored BSA a7
« on: 23.06. 2018 21:30 »
Hi
I have recently re -sleeved and rebored my 1960 BSA a7. Seems to run ok except for a lot of smoke coming from the left hand exhaust pipe. - should I just leave this to hopefully settle down or should I investigate straight away?
Tim
(Northumberland)
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Online Greybeard

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Re: rebored BSA a7
« Reply #1 on: 23.06. 2018 23:22 »
A reconned engine will tend to smoke from both sides until the rings bed in. If you are seeing a lot of smoke from only one side, I'd suspect a ring may have been broken during the rebuild.
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Online berger

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Re: rebored BSA a7
« Reply #2 on: 24.06. 2018 00:34 »
i have been to the pub *countdown*, so I give myself license to talk loads more shite, tim did you check the ring gaps in each bore before you put it all together, did you do the boreing etc and did you hone the bores, check piston clearances . what make rings are they, I was sent some from a well known scouce that threw neat oil out the exhausts and found out they were shaped like a new pound coin after marking blue the bores, I went f&&kin mad at them *fight* *bash* *pull hair out* anyway is it a bit or a lot? give it 100miles and if still the same strip it / edit did you check valve gear when it was in bits.
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Online muskrat

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Re: rebored BSA a7
« Reply #3 on: 24.06. 2018 04:54 »
G'day Tim.
How many miles have you done since the work? As GB said a broken ring is first suspect. Can you get hold of an endoscope camera and have a look at the bore down the plug hole? The local bike shop may have one.
Cheers
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Offline tim

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Re: rebored BSA a7
« Reply #4 on: 24.06. 2018 06:40 »
Thanks everyone for your contributions. I have only done 10 miles since rebore.
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Online mugwump

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Re: rebored BSA a7
« Reply #5 on: 24.06. 2018 19:00 »
As mentioned above, if you can borrow an endoscope they are a great tool. I was given one as a present and wonder how I ever got by before. They are good for checking the bores and especially for checking the seating  of the push-rods when re-fitting. Also, when I bought new Hepolite, sorry I mean taiwanese made pistons I was advised to throw the rings and fit good ones. The rings supplied were very rough. Where abouts ( county will do ) in UK are you.
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Online bsa-bill

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Re: rebored BSA a7
« Reply #6 on: 24.06. 2018 20:26 »
Quote
Also, when I bought new Hepolite, sorry I mean taiwanese made pistons I was advised to throw the rings and fit good ones

Yes I've done that a few times but sometimes wonder if all rings fit all pistons (given size for size), will all grooves in the same size/bore pistons accept all rings for the same size piston ??
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Offline tim

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Re: rebored BSA a7
« Reply #7 on: 24.06. 2018 22:02 »
Northumberland
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Online Triton Thrasher

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Re: rebored BSA a7
« Reply #8 on: 25.06. 2018 06:36 »
First thing to try is make the engine pull hard in bursts, to over 4,000 rpm.

Obviously won’t fix a broken or upside-down ring, but might bed rings into the bore if you’ve been pussyfooting around on it so far.
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Online Greybeard

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Re: rebored BSA a7
« Reply #9 on: 25.06. 2018 08:55 »
First thing to try is make the engine pull hard in bursts, to over 4,000 rpm.
I've taken that comment on board!
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Online muskrat

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Re: rebored BSA a7
« Reply #10 on: 25.06. 2018 09:02 »
Good point TT. Most people baby a new bore.
In Tim's case a lot of smoke from one pot and not the other indicates something is not quite right. The left can smoke a bit more than the right due to the little hole in the rod throwing a bit more oil up that side, but shouldn't be lots.
Cheers
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'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7