Author Topic: A7 1958 crankshaft regrind info needed.  (Read 433 times)

Online Ratchet Richard

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A7 1958 crankshaft regrind info needed.
« on: 14.11. 2020 21:05 »
So sent bottom end of my A7 to local old British bike mechanic to have the end-float and sludge trap sorted.  I don’t have the wherewithal to do these things.
I had stripped the bike down to the cases and taken out of frame to try and keep the cost down. 
Just had a phone call with the mechanic with the following info.
New big end shell had been fitted but the journal’s where badly scored the big end shells are -030.   Looks like I am going to need a crankshaft regrind. 
As you might have guessed I am a bit crest fallen with this news.  I have a few questions if possible.
Will I be able to get the crank reground below -030 or will I need to try and get a secondhand crank from somewhere?
I have had a quick look at Dragonfly to see what size shells they do but am I bit lost regarding the difference between a large journal  and small journal.
Does the sludge trap have a cage in it or is it just empty. 
I am sure I will have loads of other questions but I felt like I need to pose some questions as a sort of way of trying to ease the pain.
Thanks
Richard

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Re: A7 1958 crankshaft regrind info needed.
« Reply #1 on: 14.11. 2020 23:09 »
small journal crank and I know of some that have been ground to -40 and shells were available, sludge trap just a hole

Offline scotty

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Re: A7 1958 crankshaft regrind info needed.
« Reply #2 on: 15.11. 2020 00:51 »
I had my small journal crank ground to -40 and got the shells from Draganfly

Scotty

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Online chaterlea25

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Re: A7 1958 crankshaft regrind info needed.
« Reply #3 on: 15.11. 2020 00:53 »
Hi Richard
It is vitally important that the journals are ground with the correct radaii  at each side
Make sure the crank goes to a business that knows about BSA cranks
The grind details are on SRM's website

John
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Re: A7 1958 crankshaft regrind info needed.
« Reply #4 on: 15.11. 2020 04:56 »
Hi Richard
It is vitally important that the journals are ground with the correct radaii  at each side
Make sure the crank goes to a business that knows about BSA cranks
The grind details are on SRM's website

John

It's impossible to overstate the importance of what John has said in this post.

Ignore his advice and you'll pretty soon be looking for a lot more than a new crank.
England N.W
1960 A10
England

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Re: A7 1958 crankshaft regrind info needed.
« Reply #5 on: 15.11. 2020 08:41 »
 Rich.  The good news is that you caught it in time and it didn't go BANG!!!!!! Are the journals ridged and scored from previous wear and new shells just slapped in or scored by pick up on shells running dry?

  As an aside,  lubrication is the single most important factor to consider. Damaged journals have multiple causes, but by far the most common cause is poor oil supply. Make a critical examination of everything from " the tank filler cap to the big ends." The timing bush acts as an oil distribution hub, any wear here contributes to poor oil supply to the big ends, compounded by an obstructed crank sludge trap. Don't forget the PRV Valve.

  Oil pumps are a weakness and a constant cause of problems, as the original bodies change shape over time and in extreme cases blister and crack. You need to search for the cause of the failure, as without being sorted out another expensive excursion is on the way.

 Swarfy.

Online Ratchet Richard

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Re: A7 1958 crankshaft regrind info needed.
« Reply #6 on: 15.11. 2020 08:54 »
small journal crank and I know of some that have been ground to -40 and shells were available, sludge trap just a hole
Thanks Berger good to know that you can go down to -40.

Online Ratchet Richard

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Re: A7 1958 crankshaft regrind info needed.
« Reply #7 on: 15.11. 2020 08:57 »
Hi Richard
It is vitally important that the journals are ground with the correct radaii  at each side
Make sure the crank goes to a business that knows about BSA cranks
The grind details are on SRM's website

John
thanks John I don’t live far from SRM so might go and have a chat.

Online Ratchet Richard

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Re: A7 1958 crankshaft regrind info needed.
« Reply #8 on: 15.11. 2020 09:12 »
Thanks for replies it so helps to talk to people in the know.   I wish I knew a bit more about the history of the bike as I would have a better idea about which came first regarding oil supply.  I have only done About 50 miles on it and the PO said he had done about 50 since complete rebuild. I don’t trust the PO, and think he may have just but new shells on rough big ends.  I would say that I understand the importance of the radaii but I will have to look up what it is first!
Do regrinds cost a lot in the U.K.?
If I have to change the crank can I put an A10 one in or does it have to be an A7.  Also if changing do I have to stick with a small journal or can I fit a large journal?
I am going to have to be very careful about money on this bike, as my wife has already started to make some cutting comments. 
Thank guys
Richard

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Re: A7 1958 crankshaft regrind info needed.
« Reply #9 on: 15.11. 2020 11:46 »
 Rich.  Time to pause and consider. This is starting to run away big time and tho' today it looks a mountain, its a ripple on the millpond of life compared to what's going on around us. Always a worry when your chief sponsor starts to have doubts...time for a bit of optimism and a halt on the sleepless nights.

 The A7 and A10 share a common crankcase and fittings. Crank, Barrel, Rods, Pistons Pushrods and Cylinder head are different. Rocker box is the same. If you go down this route another complete engine will be cheaper than attempting to source individual parts. An A10 crank can be big or small journal, big journal are more prized and cost more, but may in fact be worse than what you have.

   I'd get your own crank cleaned out and reground, an everyday and straightforward machining operation in the engine reconditioning trade. My guess is the PO just slapped it together and took the money. I think the problems are down to selecting parts (a typical best of the rest build) and poor workshop practice rather than some major mechanical malady.

 Swarfy.

Offline mugwump

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Re: A7 1958 crankshaft regrind info needed.
« Reply #10 on: 15.11. 2020 14:34 »
Maintaining the internal radius should be standard practice on any crank re-grind. I don't know why it is emphasised in my AJS/Matchy manual. Its not as though the average Joe will do this kind of  work at home.

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Re: A7 1958 crankshaft regrind info needed.
« Reply #11 on: 15.11. 2020 15:05 »
... my wife has already started to make some cutting comments.
They all do that sir! You'll just have to live with it I'm afraid.

Online groily

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Re: A7 1958 crankshaft regrind info needed.
« Reply #12 on: 15.11. 2020 16:18 »
Maintaining the internal radius should be standard practice on any crank re-grind. I don't know why it is emphasised in my AJS/Matchy manual. Its not as though the average Joe will do this kind of  work at home.

Ha! If you'd had a crank break on an AMC twin you'd wish the radii data was in BOLD TYPE 12 feet high! Radii matter on everything, dead right, and decent engineering firms handle them correctly. But, and here's the sad bit, quite a few don't, or didn't.
When I broke a crank (on a 500 amc twin, not a roadburning tuned beast) it was a mere 40 miles after a grind and a lot of expense. Classic fracture on one end of a crankpin, causing a fair amount of fresh expense. Now, those three bearing engines are a bit rigid down below, and critical oil passages pass quite close to the surface in the area of the centre main bearing, which maybe explains why the AMC literature is spattered with warnings, but the same principle applies to anything. When Austin introduced the better-supported three bearing crank on the late '7' in the 1930s . . . they broke alarmingly frequently compared to the bit of bent wire that passed for the 2 bearing item! Were they just too rigid, or was there a design flaw - I haven't a clue - but many period engines with twice the power of an Austin 7 ran perfectly happily on single-plane 2 bearing cranks.

Thing with the radii is, if damaged or absent they can't be put back, the structural integrity has gone for ever and all you've got is a doorstop. Good engineering firms will refuse to work on anything with damaged radii, as it's the first thing they'll look at. But there be others, reputable and no doubt good at most of what they do, who don't always appreciate how marginal some of these older designs are, and how susceptible to breakage.

I have been the unproud possesssor of a few doorstops  after buying bits unseen, or assembled and uncheckable on the spot  . . . . . .
Bill

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Re: A7 1958 crankshaft regrind info needed.
« Reply #13 on: 15.11. 2020 17:26 »
When Austin introduced the better-supported three bearing crank on the late '7' in the 1930s . . . they broke alarmingly frequently compared to the bit of bent wire that passed for the 2 bearing item!
My 1929 Austin 7 had the two bearing crank with 1 1/8" big end journals. Oil, (at 2 pounds per square inch when hot) was squirted from a couple of nozzles aimed at cups on the crank webs. When those engines were tuned for racing the cars achieved >100 mph. Apparently the middle two pistons might hit the cylinder head when the crank whipped at high revs.

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Re: A7 1958 crankshaft regrind info needed.
« Reply #14 on: 15.11. 2020 17:42 »
The vibration from those 2 brg cranks was horrendous.
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