The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: tim on 23.06. 2018 21:30
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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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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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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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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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Thanks everyone for your contributions. I have only done 10 miles since rebore.
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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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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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Northumberland
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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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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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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