Author Topic: re-bore  (Read 595 times)

Offline Slippery Sam

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re-bore
« on: 27.07. 2017 19:56 »
Hi All,
I'm looking for a guide to the cost of a re-bore.  I've never had this done before and was going to try my local engine builder rather than the postage back and forth etc to one of the firms we talk about on here.
What sort of cost should I expect - what's reasonable and what's not?  A rough guide will do or a range.
I also have a crank I might get ground - what's the likely cost of just getting the big ends done?
Barrels are A10 thick flange currently a pretty good 70.5 mm - so good in fact I was going to simply pick up a pair of +20 pistons and bust the glaze. I have a pair of cracking +40 (71mm) 9:1 pistons so will consider the difference between a pair of +20s and a re-bore to use my +40s.
Crank is large journal A10 - no idea of sizes yet (will check I have enough meat left first) - it's been lying around for a while so more pitted than scored.
I'm near edinburgh so no real classic bike machinists.  Nearest I've used is Rob Wardle in Gateshead but fuel alone is £60 or £70 before the cost of the job (I'm not actually that tight - just don't want to make a £50 job into a £100 job if you know what I mean?).
Any advice will be handy
Thanks in advance
Raymond.
BSA A10 Cafe Racer project
Scotland

Online chaterlea25

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Re: re-bore
« Reply #1 on: 27.07. 2017 20:56 »
Hi Raymond,
You need to first of all get the cylinder measured properly,
The bores usually wear more towards the middle of the bore, a rough check is to measure the end gap of a ring
fitted at different parts of the cylinder, use a piston to keep the ring square, approx 3thou difference in the end gap equals 1 thou wear and so on

Crank grinders are usually reluctant to modify the grinding stones used on car engines to grind the narrower BSA big ends, It is vital that the grinding leaves the correct radaii at each side of the big end journals

In other words I would think that the fuel costs to get to Rob would be a wise investment

John
1961 Super Rocket
1963 RGS (ongoing)

Offline dave55

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Re: re-bore
« Reply #2 on: 27.07. 2017 23:27 »
https://www.a7a10.net/forum/index.php?topic=11382.0        does this firm have the equipment , remembered seeing this post ?
BSA Bantam D7 175  1961
BSA A10 650 Golden Flash 1955 Plunger
Suzuki GSX1400 2003

Online coater87

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Re: re-bore
« Reply #3 on: 28.07. 2017 00:15 »
 
 First, for the cylinder boring:

 You need to have the pistons you are going to use first, take those along with the cylinders to the machinist. He will bore the cylinders to fit the pistons you have on hand. Also do some investigating, some brands of pistons seem to need a little more room than others, you can clue your machinist in on this because he will have no idea.

 Cost here in the states is about $120.00, and thats a good job with the correct final honing. You can get it done cheaper if you look around.

 Crank regrind:

 As John mentioned, first big thing is a correct measure and a machine shop willing to do it. I find here in the states places that do a lot of work on diesels will have no problem doing your crankshaft. Take a copy of the service page that states the radius required, that way they know exactly what you want. Again, do some investigating on things like the timing side grind- if you have this done have them just grind off enough to round it out. No need to go the full .010.

 Cost can very widely here. Figure between $150 and $275.00 for the grind. It is cheapest if you find a place that will do both the grind and the boring. Figure around $300.00 for the whole thing that way. Or about 240 of those funny pound things. ;)

 Lee
Central Wisconsin in the U.S.

Online Black Sheep

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Re: re-bore
« Reply #4 on: 28.07. 2017 06:19 »
Near Edinburgh? Well how about: Charlie Cope, Goodtrees Cottage, Cockburnhill Road, Balerno EH14 7HY
               0131 449 4277, 07801 644 355, chas.cope@yahoo.co.uk
Or East of Scotland Engineering at Sighthill.
2 twins, 2 singles, lots of sheep

Offline Slippery Sam

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Re: re-bore
« Reply #5 on: 28.07. 2017 09:48 »
Thanks guys
Loads of food for thought.
Will sort out a print of the service sheets
Will try Charlie - wonder if that's the guy I've seen at a couple of autojumbles? Been trying to track him down and may well be the same guy!
Will report back once things become clearer😁
Raymond
BSA A10 Cafe Racer project
Scotland

Online Rex

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Re: re-bore
« Reply #6 on: 28.07. 2017 11:29 »
My local engine reconditioners (who myself and fellow riders have used for years) charges £15 a cylinder for a  rebore but he needs the pistons to be present. No ifs, buts or spec sheets allowed.

Online RoyC

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Re: re-bore
« Reply #7 on: 28.07. 2017 15:53 »
My local engine reconditioners (who myself and fellow riders have used for years) charges £15 a cylinder for a  rebore but he needs the pistons to be present. No ifs, buts or spec sheets allowed.

Local to where & what's his name ?
My bike is a 1958 A7SS
Stafford UK

Offline Sluggo

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Re: re-bore
« Reply #8 on: 28.07. 2017 23:07 »
15 pounds per hole is super cheap.  Before 9/11 a guy I know used to fly into Australia and he had some machinist there who did a super job way cheaper than the US. Jerry was a pilot for a well known airline and flying that route he picked up parts in Asia, stuff in Oz and back to the US.  Until 9/11 screwed things up we had a great import/export racket going.
Locally few places will touch motorcycle stuff.  My local guys tend to charge $70 USD per hole for boring, sleeving is a whole different animal. (Few people get it right, but its not that complicated.)  The Oz connection did the work at a fraction of that price.

I have access to a boring bar, but to do it right requires careful fitting and then hone to size,  Specs vary. The manuals spec measurements we cant run now.  a 3 thou clearance was okay back in the day with good fuel, not so much now.  On a typical Triumph I run 4 thou or 4 & half if the guys gonna run it hard. (Chopper guy or boyracer).   I also add a half though if running the speciality coatings as well.  Racers run loose for a reason.  I have friends who do a quicky break in on the way to the track.

Surface finish MATTERS!  depends on ring choice. Most old stonker Britt bikes run cast pistons and cast iron rings but its best to check. A forged piston is totally different tolerances as is Chrome or Molly rings takes a different surface finish (Crosshatch hone).

Bores a funny thing.  Torque plates is a good thing and best results. When asked many shops tell you yes but dont have them and lie about it.  (Usually a mumbled comment about somebodys reading on the internet again)  But without a long rant about why, trust me, Torque plates are critical if you want it right.
BSA stuff tends to be pretty good metallurgically speaking considering the outdated factories and agricultural tech.  But any overbore is fraught with peril.  Castings can have hidden voids, dirt and casting smegma that is exposed when machining.  Cracks show up (typically near the flange).  I can attest to much disappointment when called by my machinist that the cylinders are junk.

I was looking for and did not see proper measurement tips.  A DIAL BORE gauge is critical for checking.  You can check with a inside Mic and snap gauges with a caliper or a feeler gauge alongside a piston up and down the bores.  (As stated you will tend to see wear spots at different points.  )  SOME Bores are machined as a choke. IE: Different tolerances top vs bottom with the thoughts that at combustion temps the top should run looser.  Others bore straight top to bottom.  Not relevant to BSA but good to know is that some engines run cam ground bores.  These bores are slightly oval shaped but when torqued and up to temp go to true round. (Along with fancy stretch bolts and other whiz-bang techy techy stuff)

Different engines run wear different.  BSA-Triumph tend to run a softer cast iron I think. Typical wear on a used cyl is front and rear along thrust faces of the bore.  A dial bore gauge will show this.  Nortons tend to be very durable and I know several people with mileage on original bores of 100,000 plus miles. They hone and fit new rings and pistons.  (nissan-datsun are this way as well, well cared for bores last forever).  But Nortons are some of the worst cast iron castings so
I am always nervous machining a Norton. (Scrap rate is very high) 

Out of the box pistons is a sticky wicket.  Typical NOS or OEM pistons tend to vary wildly in measurements (Dia) as well as weights.  They are SUPPOSED to be graded (Look for paint dots on the undersides) but many seem to have been done by Blind Willy after a liquid lunch.  I have seen piston weights off by several grams from L-R, as well as dimensions (Dia).  Do a little gentle grinding and get in spec. (Weight) and check ALL tolerances.  I am a big fan of Dynamic balancing and it makes a huge difference so a lot of checking before anything goes to the machine shop.

I have found the Emgo-JCC and cyclecraft pistons are excellent quality. Highly consistent tolerances 95% of the time. ( had some A65 pistons a few years back with wildly differnt weights by 4 grams I recall, I would have to look at build notes for exact spec).  I have found though the pins do differ so check those. (Easy to correct. Hone the ID of the pin to even up the weights).  These pistons are not as readily availible for older engines like a A7-A10 though. 

Very few shops will touch a Motorcycle crank in my experience. My Go-To crank grinder said he also had trouble training employees and had a lot of problems. He would assign tasks in his shops to employees but after many expensive fiascos only he would do the cranks. They got done when they got done.  If he was out of town racing or vacation or sick you waited. Sadly he died a while back.  The idiot who took over that shop is a incompetent buffoon.  So, theres 3 shops locally who will accept your crank but they are all boxing it up and shipping it to a shop about 2 hours away in another town.  Mixed results.   The oem crank specs is an excellent idea to print off and INCLUDE in a plastic page protector along with your crank, but in some cases you WANT to INCREASE the radius-filet somewhat.  Certain cranks are known for cracking and fractures at stress points.  Research this.  Some radius and filets were inadequate stock and in some cases they were changed in post rev changes.  (Val Page spent a lot of time researching early twins crank issues. Read up on this, its a great story of Process engineering, which I used to do as well in a previous career)

Many of these parts were never high end quality. Built to a price and economies of scale but 50-70 years on some are very hard to source. Nickel and diming a project over machine shop expense is poor economy and logic.  Can you afford or able to source a replacement if you cock it up?   I spend a lot of time wondering about people who cut corners, reuse worn out parts, skimp on bearings or bushes or generally dont see the long term costs of not doing things correct.   Engine rebuilds (Trans too) is NOT where you cut corners.

Machinists are a bunch of Prima-donnas.  Big egos, fragile temperaments and general PIA.  But a skilled machinist never has to want for work or the next job.  My wife is a production manager at a machine shop-manufacturer and we have many friends with their own shops or work in the trade.  But a skilled machinist is a very rare commodity and very hard to find. (need a job? My wifes company has multiple openings).  For that YOU WILL PAY,,, foolish if you think otherwise.
One old crusty guy I know frequently tells people "F**K-off, go find somebody else who can do this!"
Remember that any advice received on a free internet forum is generally worth about 1/2 of what you paid for it.
We overcharge every 3rd customer to pass the savings onto you.
You can have High Quality, Low price, and fast turnaround. Pick any 2, Never all 3 at the same time.