Author Topic: does my cylinder need a rebore  (Read 3202 times)

Offline bigmike76

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does my cylinder need a rebore
« on: 09.10. 2012 15:36 »
Hi

I have stripped the engine to rebuild and just wondered about the bores, I don't want to spend a lot of money on the engine yet just want to get it running and ridable

the pistons or on +60 anf the bore measurment is 71.5 mm

is that correct for the +60 and will I get away with just piston ring replacement

cheers

Offline Triton Thrasher

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Re: does my cylinder need a rebore
« Reply #1 on: 09.10. 2012 19:10 »
Has it worn a ridge that you can feel, near the top of the bore?

Online Billybream

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Re: does my cylinder need a rebore
« Reply #2 on: 09.10. 2012 19:34 »
Hi Mike.
Std A10 bore = 70mm, so +0.060" should be 71.524mm.
As Triton Thrasher suggests check for a ridge and also look for bore damage.
I find best check is to compare the bottom unworn area with the working zone area.
1960 Super Rocket, owned since 1966, back on the road 2012 after being laid up for 29yrs.

Offline bigmike76

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Re: does my cylinder need a rebore
« Reply #3 on: 09.10. 2012 21:01 »
yes it feels like it has a slight ridge at the top, also the look of the bores is like a polished mirror finish

I pressume if it needs work then it will have to be re sleeved, anyone got any ideas what this might cost roughly?

Online bsa-bill

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Re: does my cylinder need a rebore
« Reply #4 on: 09.10. 2012 21:39 »
My Flash barrels were re sleeved more than ten years ago, then liners were not that expensive IIRC about the same as one piston, the cost of having them put in was roughly twice that of a rebore which is fair enough as they have to bore the barrels to take the liners then bore the liners.
 If your bores are that shiny perhaps you could get away with a hone and new a set of rings
All the best - Bill
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1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online trevinoz

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Re: does my cylinder need a rebore
« Reply #5 on: 09.10. 2012 22:02 »
The first thing to do is get them properly measured for clearance.
If within specification get the bores honed and fit a new set of rings.

Trev.

Offline a10gf

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Re: does my cylinder need a rebore
« Reply #6 on: 10.10. 2012 11:35 »
What's the best procedure\tips for measuring barrels\pistons\clearance?

I am using the tools in the pictures and believe I get quite correct results. I do measurement at the top (under the carbon ridge), at the bottom, and do some checking for ovality using the telescopic tool. And measure the pistons and calculate clearance.


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Online KiwiGF

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Re: does my cylinder need a rebore
« Reply #7 on: 10.10. 2012 11:59 »
The vernier is not really accurate enough ideally you would use a micrometer.

That's just my opinion, verniers can measure to a thou ( inches) or maybe even better, which is good enough but you need skill and a good quality vernier to achieve that level of accuracy.

As per prior posts wear in the bore usually shows as ovality as the bore sides do not wear as much as the front and rear. A few thou wear should be ok and mean you can hone and fit new rings.

Most important is that there is no ridge that might break new rings, honing will not remove significant ridges.

Feeler gauges are a good option for measuring clearance, remembering pistons are not generally made round but bores are! Also pistons are not necessarily all made the same diameter, new bores are usually made to fit a particular piston.

The clearance at front/back in the region below the rings should be about 004 for new bores and I guess (others may disagree) 010 would usually indicate it's time for a rebore or sleeve and new pistons. But if it was running ok you could just it put it back like it was!

What clearance have you measured?
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Offline MG

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Re: does my cylinder need a rebore
« Reply #8 on: 10.10. 2012 19:08 »
Hi Mike!
If you have to rebuild your engine on a budget, and wear in the cylinders isn't excessive, you might get away with new rings. But in any case re-hone the cylinder to allow the new rings to bed in properly, as Trev said!
Damage to the new rings by a (not too bad!) ridge can be prevented by fitting a thicker (or two standard) cylinder base gasket(s).
Beside checking piston to bore clearance (10 thou is absolutely rebore-time I'd say), it is also worth checking the piston ring end gap in the larger bores. Rings of the next oversize can be modified (shortened) to give proper end gaps (and thus sealing) despite the larger piston clearance.
But don't expect top notch performance, you'll rather encounter some piston slap when cold and increased blow-by and oil consumption probably, but you should get a few more miles out of the engine that way.
Cheers, Markus
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Online chaterlea25

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Re: does my cylinder need a rebore
« Reply #9 on: 10.10. 2012 21:58 »
Hi All,
There are various ways mentioned to determine bore diamater and clearance,
To check for wear /ovality I bought a similar item to this,
http://www.ebay.co.uk/itm/2-to-6-DIAL-BORE-GAUGE-TOOL-caliper-mic-micrometer-/360493311046?pt=LH_DefaultDomain_0&hash=item53ef136446

There are 2 little guide wheels which keep the tool centered in the bore, then rock gently to read the dial at its max, (when its vertical in the bore)
 *smile* Works for me!!!
HTH
John
1961 Super Rocket
1963 RGS (ongoing)

Offline Rocket Racer

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Re: does my cylinder need a rebore
« Reply #10 on: 11.10. 2012 01:36 »
yes it feels like it has a slight ridge at the top, also the look of the bores is like a polished mirror finish

I pressume if it needs work then it will have to be re sleeved, anyone got any ideas what this might cost roughly?

If you come to the conclusion your +60 is too worn, most A10 bores will go out to +100 unless already resleeved previously. Resleeved bores are less robust for overboring.
So if the barrel has not been resleeved you should have 2 more rebores left.

A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Online muskrat

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Re: does my cylinder need a rebore
« Reply #11 on: 11.10. 2012 20:49 »
 That's the best tool for bores John. Most engine re-conditioners use them.
I think the worst thing for new rings in an old bore is tapered or bellied bores. The rings expand and contract which causes flutter and the rings can't seal or at worst break. The ridge must be removed, most shops have a tool for this.
Cheers
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Online chaterlea25

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Re: does my cylinder need a rebore
« Reply #12 on: 11.10. 2012 22:11 »
Hi Musky,
Thats how I found a hollow patch in one of the bores in my RGS project  *sad2*
That was after buying a set of NOS Hepolites for it *sad2*
Then lash out a further £260 for a set of Wiseco's  *eek* + a rebore  *eek*

Regards
John
1961 Super Rocket
1963 RGS (ongoing)

Offline wardleybob

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Re: does my cylinder need a rebore
« Reply #13 on: 28.10. 2012 17:52 »
It costs 60 pound per side up here in tyne wear

Online bsa-bill

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Re: does my cylinder need a rebore
« Reply #14 on: 28.10. 2012 19:27 »
Quote
It costs 60 pound per side up here in tyne wear

Whatcher Bob - yep that sounds about right, so it's about doubled in a decade or so
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco