Author Topic: pistons and rings  (Read 2309 times)

Offline Tumbleweed

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pistons and rings
« on: 16.04. 2012 20:32 »
hi everybody , i have just acquired a 10 engine , having removed the head and barrels i find it was very badly coked up, i took a ring from each piston and put it in the barrel and the gap is 0.045 " on the one , and 0.035" on the other. the problem  is there is no markings on the pistons, how do i find the size of the pistons and rings *conf*
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Offline wilko

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Re: pistons and rings
« Reply #1 on: 16.04. 2012 20:36 »
Der, measure it!

Online Triton Thrasher

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Re: pistons and rings
« Reply #2 on: 16.04. 2012 21:03 »
I expect you mean 0.045"  and 0.035". Those are big gaps and probably indicate worn bores, along with the oily carbon.

Do I guess right, that you don't own or habitually use an internal micrometer? I certainly don't and I'd get it examined and probably bored out by an expert in old bikes.

Offline Tumbleweed

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Re: pistons and rings
« Reply #3 on: 16.04. 2012 21:33 »
Thanks, the with  measuring tool i have , the bore is 70mm and the piston is  68mm,would this be standard or o/s. i know i have got to have work done to it, but it wont be for a while yet i would just like an opinion
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beezermacc

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Re: pistons and rings
« Reply #4 on: 17.04. 2012 00:29 »
If you're lucky you may only need rings. In the absense of an internal micrometer you might use the following method...... Measure the piston to bore clearance with some feeler gauges 10 mm from the top of the bore and at the bottom. When measuring at the top of the bore use the piston upside down and measure at the front of the bore between the front of the upside down piston and the bore. Then measure the skirt / bore clearance at the bottom. This is simply using the piston as a constant and will tell you how much extra wear there is at the top compared to the bottom. To further confirm your measurements check the ring gap at the top and bottom of the bore; a large variation indicates bore wear.

Offline muskrat

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Re: pistons and rings
« Reply #5 on: 17.04. 2012 08:08 »
"the bore is 70mm and the piston is  68mm,"
Std bore/ wrong piston. Would be like a c@ck in a sock *eek*
0.004" clearance between piston & bore measured at 90deg to piston pin and bottom of bore. If more than 0.008" at top of bore it'd due for re-bore.
Cheers
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Offline Tumbleweed

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Re: pistons and rings
« Reply #6 on: 17.04. 2012 11:41 »
thanks for the info,    the gap at the top of number  1cyl is 0.050" at the bottom its 0.047".  number 2 is 0.059"  top and 0.052"bottom , you mentioned that the piston was too small (or words to that effect) what would be the measurement of a standard piston and what size rings o/s  .   thoughts much appreciated   p/s there is no lip on the top of the barrels .      thanks again tw
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Online KiwiGF

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Re: pistons and rings
« Reply #7 on: 17.04. 2012 12:30 »
As per muscrats post standard bore is 70mm and a new standard piston would be around 004" less than the bore to allow for expansion

The pistons you have are far too small for the bore, I very much doubt they are worn small they might be pistons just installed to make the engine look more complete?

Are you sure they have such a big clearance 050" is over 1 mm!
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Offline Tumbleweed

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Re: pistons and rings
« Reply #8 on: 17.04. 2012 12:47 »
sorry kiwigf,  i didnt make myself very clear i meant i put a comp ring in the top of barrel , and in the bottom and that was the measurements of the gaps,   cheers tw
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beezermacc

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Re: pistons and rings
« Reply #9 on: 17.04. 2012 14:22 »
The ring gaps on the second cylinder suggest 0.007" wear which is too much.  0.050" ring gaps are too much as well. I dare say it would run but if you want some pleasure from the bike (i.e. a reasonably quiet engine) I would be going down the rebore and pistons route. As per previous comments the pistons seem too small and the fact that there are no maker's marks on them suggests they'r not right. Are there any numbers on the insides of the pistons, they're often cast with numbers on the inside - I'd be very interested to know?

Offline Tumbleweed

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Re: pistons and rings
« Reply #10 on: 17.04. 2012 15:00 »
hi beezermacc thanks for your time,  the numbers cast on the inside of the pistons are 11016 , AM2 , B72 , 413.  then there is an AE that seems to be drawn together  . if you can make anything of that beezermacc . its way beyond me, thanks tw 
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beezermacc

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Re: pistons and rings
« Reply #11 on: 17.04. 2012 15:29 »
11016 are correct for A10 and are usually Hepolite or Heplex, the early, low compression, dished pistons. Hepolite was part of the AE (Associated Engineering) group. The markings on the top are often on the rim near the valve cutouts.

Offline Tumbleweed

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Re: pistons and rings
« Reply #12 on: 17.04. 2012 17:13 »
thanks beezermacc you know your bikes,  i found some marks right on the edge of the piston it looks like  040 ,i think i can carry on from here, its rings or rebore ,  thanks again tw *smiley4*   p/s i will have to get a better measuring stick sorry folks.
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Offline ian davies

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Re: pistons and rings
« Reply #13 on: 17.04. 2012 22:08 »
This is a  wonderful forum anything and everything anyone wishes to know can be found here if you own an A10 or A7 some of the guys on here obviously have been dealing with BSAs for many years, and are very good engineers in their  own right. What i like is the way the info can be given out, you can get it as technical as you like or in  plain english, as Muskrat says, this piston would be like a c-ck in a sock, brilliant. Good for a laugh now and then too. *smile*
ian davies

Offline Tumbleweed

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Re: pistons and rings
« Reply #14 on: 18.04. 2012 08:39 »
i agree. but the socks i buy nowdays are very tight round the ankles has any one else noticed  *smile*
Semper in excretia sumus solum profundum veriat.