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BSA A70 Lightning parts vs A65 #766186 02/23/19 12:36 pm
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Hi,

I'm interested in a BSA A70 750cc

How hard/easy is it to find those special parts that I would need next time the engine will be rebuilt?
Please list who might have parts for the a70.

What is the difference in the sludge trap tube and plug compared to A65?
Also the crankshaft shims are different I wonder how or which one to order?
same with conrods..

Basically I want to learn about all differences and I'm grateful for any help here.

See image
[Linked Image]


A70L specific knowledge so far

Pistons
STD 71-2710 stamped 71/2666 = about 396 gram ea complete
+020 71-2884 stamped 71.2667
+040 71-2885 stamped 71.2668 = about 409 gram ea complete

71-2682 Sludge trap plug = UNF 5 / 8” x 18tpi (A65 has 3/4”)
71-2683 sludge trap = smaller diameter than A65

71-2710 std piston =gudgeon pin 5,5mm higher up vs A65
71-2697 TS bush = shorter than A65

71-2673L, 71-2677R Conrods = same as the late 1972 A65 ?

Last edited by Morgan aka Admin; 03/18/19 10:50 am.

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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766189 02/23/19 1:08 pm
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Somewhere, I have the illustrated parts pages for the A70. Let me look around for them and either post them or send them to you.

The changes are pretty significant. Not sure you could easily modify an A65 bottom end.


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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766190 02/23/19 1:31 pm
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Rich the bike has probably the correct bits inside and is working fine.
However have no clue how to find the correct A70 parts for next restoration. It was 25+ years ago last time it was restored.
Example parts number for A70 Sludge trap tube is 71-2683 but no dealer that I looked at list that part.
They list 68-0185 or 70-3903 which is for A65 so I am interested in the difference if 71-2683 is longer, thicker or whatever would a triumph 750cc tube fit... ?
and who could supply or do I have to re-use the old..
Do I need to make the parts my self questions like that comes to my mind.

Are there other service bulletins for the A70 or other


Last edited by Morgan aka Admin; 02/23/19 1:34 pm.

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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766194 02/23/19 2:00 pm
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Also have question on the frame number size, the one I was looking at is ruffly 5,5mm high
It was stamped on the heads left side and it looked like this A70L XX XXXXX see image

How does your frame number look and where is it stamped on a OIF A65 or A70?

Attached Files a70l.jpg
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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766203 02/23/19 2:44 pm
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The A70L stamp looks legit. It's the same as on mine. It's the same as on the OIF A65 except for the 65 being 70.

The only A70 specific parts I have found are pinion gears (there is an eBay seller with a small quantity, oddly it is not listed in the bulletin) and conrods.

Ed V has pistons.

When I started rebuilding mine (still 'in progress') I only needed a bushing & some shims. I found a NOS +0.010 bush but in the end used a Kibblewhite bronze bush and milled off the appropriate amount of material on the gear side (about 3mm IIRC). Shims were unobtainable but I found some from McMaster that were satisfactory.

I bought Clevite A65 big end shells new manufacture A70 rods. My sludge trap came out easily & I reused it. I didn't compare to an A65 trap.

You will need a pinion gear puller as the pinion is flush against the thrust washer unlike the A65. I machined a small bar of steel to slide over the puller bosses on the pinion then used a jaw puller to extract the gear.

Good luck with this!



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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766224 02/23/19 7:58 pm
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Hi Morgan,

you may already know this but Burton Bike Bits in the UK have an A70 register and are probably a good source of informaton and spares, see This Link


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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766243 02/23/19 10:33 pm
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I do trust you'll be riding that to the BSA International this year smile
You just need to make sure the new grandchild turns up at either the start or end of the month.


NOS pistons turn up from time to time, but usually only in std or maybe +.020". Mike's Classics might still have some. Apparently, T140 pistons can be used for the oversizes, but require some machining of the skirt. If Ed V has replacement, they'll be excellent quality.

The connecting rods were also used on some late A65s, and also turn up from time to time. Space is very limited in the crankcases, so alloy capped rods don't have sufficient clearance. Carrillo, MAP, SRM or Thunder Engineering rods may have sufficient clearance.

As far as I know, A65 timing side main bushes can be shortened to fit, as per Ray's post.

Late A65 crankcases can be machined as per A70, but that's cheating a bit.

Forget about finding a new crankshaft for less than the GNP of a small Pacific Island nation. Somebody had a crankshaft and rods listed on eBay in the UK last year, but that seems to have ended.

I think you'll be left to your own devices for the sludge tube, plugs and flywheel bolts.

Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766254 02/24/19 12:26 am
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Hopefully I’ll know soon enough with the thunder rods, they bolt from the top and thread into the cap so you gain a bit of space that way. If you ever needed another crank, I’d look at using an A10 one until someone starts making new cranks for them, as Shane says I wouldn’t bother trying to find a golden egg


Last edited by Allan Gill; 02/25/19 2:03 pm. Reason: incorrect info given

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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766284 02/24/19 3:07 pm
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See my answers in red

Ray Elliott you wrote:
The A70L stamp looks legit. It's the same as on mine. Good!

The only A70 specific parts I have found are pinion gears Do you have partnumber?!

Ed V has pistons. Good! are they 9.5 comp?

I bought Clevite A65 big end shells new manufacture A70 rods. what is the partno for the late conrods that fit A70! I guess that piston guide pin whole is lifted up towards the top with 5,5mm in order to gain the 11mm longer stroke

My sludge trap came out easily & I reused it. I didn't compare to an A65 trap. has anybody compared the A70 tubes with A65?!
-------------

Gunner wrote:
you may already know this but Burton Bike Bits in the UK have an A70 register and are probably a good source of informaton and spares? Yes I know about the register, BBB don't list any specific A70 spares!
---------------

Shane wrote
I do trust you'll be riding that to the BSA International this year smile We'll see about that going to the UK rally, I want but other forces holds me back!

NOS pistons turn up from time to time, but usually only in std or maybe +.020". Mike's Classics might still have some. Apparently, T140 pistons can be used for the oversizes, but require some machining of the skirt. If Ed V has replacement, they'll be excellent quality. Triumph 8,5 comp pistons are in it now and it seems that it has two oversizes bored about one mm over std. Since it has same cylinder as A65 how easy is it to change liners to go back to STD A70 size

The connecting rods were also used on some late A65s, and also turn up from time to time. Space is very limited in the crankcases, so alloy capped rods don't have sufficient clearance. Carrillo, MAP, SRM or Thunder Engineering rods may have sufficient clearance. I would prefer original rods i needed to change so I need a source!

As far as I know, A65 timing side main bushes can be shortened to fit, as per Ray's post. Good! is it same size otherwise?

Late A65 crankcases can be machined as per A70, but that's cheating a bit.is it same size otherwise? only when disaster happen

Forget about finding a new crankshaft for less than the GNP of a small Pacific Island nation. Somebody had a crankshaft and rods listed on eBay in the UK last year, but that seems to have ended.

I think you'll be left to your own devices for the sludge tube, plugs and flywheel bolts. what is the difference with the sludge tube, plugs and flywheel bolts? anyone who knows?


So here is the $100 question. Is it worth spending double amount of money compared to a similar A65?
And over time get into difficulties restoring the A70 engine because lack of parts. I mean next time I pull it apart to service the sludge and control/restore rest of the engine what will I need to replace??? What parts will I don't find??? that is my concern I am afraid that the restoration might stall or cost a lot more than a A65 to restore.
Don't misunderstand me I am very interested in this bike.



Last edited by Morgan aka Admin; 02/24/19 3:15 pm.

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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766287 02/24/19 3:31 pm
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I have never ridden an A70, i do have one motor A65 with a D A10 crank and T pistons , similar to A70. Displaces 770cc.
My good bike has the stock crank and big bore barrels with B44 pistons for 732cc, I much prefer this motor.
As far as i am concerned the Answer to the 100 $ question is, No, its not worth it. its much easier to get big bore barrels than long stroke cranks, they are a tried and tested recipe. John Hills barrels are well made , run cooler, and have a long service life due to the Nickasil bores. i cant speak for the SRM linered type.
Using T type pistons in the A65 head is a bad compromise, too much piston dome, B44 pistons work a lot better with the A65 combustion chamber.
The stock crank is smoother running than the long stroke, less prone to pinking as well.
i particularly dont like the stock bush TS, over the years it got shorter and shorter, A10s have more TS main bearing area than A65s , which have more bearing area than A70s. I have no idea why BSA persisted with this especially given the stock crude oil straining arrangement, fitting a shorter TS bearing seems like a bad idea to me,
End feed and a decent TS bearing is IMO a far better idea especially for an increased capacity motor. YMMV.


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Re: BSA A70 Lightning parts vs A65 [Re: gavin eisler] #766290 02/24/19 3:52 pm
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Gavin I hear you loud and clear, when it's about 650 vs 750 one can get a better option with John Hils upgrade rather than a double priced A70.
HOWEVER I have one more factor to bring in and that is I have my little museum and the small number produced A70 model fits like a glove in there.
HOWEVER I have a also limited size wallet for these things.. and it stretches it to the limit beyond but.. HOWEVER stretchmarks may go away with time I hear wink
Therefor this thread is about getting the A70 or not. And its consequences.
Its not about getting more cc out of another 650cc. It is interesting reading about John Hills kit though.

So keep the feedback coming..

Last edited by Morgan aka Admin; 02/24/19 3:54 pm.

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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766294 02/24/19 4:16 pm
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About the pistons now inside the A70 do you know which model they are for? comp??? I hear it may me 8.5 comp. see photo attachment
Hepolite 19255 std 75,974mm that sounds like two oversizes for a A70 does it not?

Attached Files hepolite19255std.jpg
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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766302 02/24/19 4:36 pm
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I put T140 pistons in my A65 way back. I do not remember the details but I believe that I had to shorten the cylinder because the T140 pistons are shorter from wrist pin to top. I think the T140 pistons are close to A70.
The frame stamp is on the left side of the headstock with the characters going up. They might be partially obscured by the saddles I welded on for the fairing mount.
For me the other consequences are insignificant. I can make most any parts needed.
Gavin, the A70 was intended as a race motor for flat track. It was going to be rebuilt often so shorter life of the main bearing was insignificant plus they had to keep the changes to a minimum.

Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766319 02/24/19 6:35 pm
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BBB have a pair of steel capped conrods currently on eBay suitable for BSA A50 / A65 / A70 1962-72, BSA Part Number 71-1105 / 71-1106, see This Link


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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766320 02/24/19 6:36 pm
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I think the answer to your question is relative to how you will use the bike?

IF you want an all "as per factory" A70 motor then originality will come at a cost,

IF your intending to ride the bike then you may want to make compromise, like Gavin (and Servodyne on here who posted a lot of images of his A70 with A10 crank See Here) I'm using a DA10 crank in mine. I could have saved quite a bit of money and fitted ED's A70 pistons See Here but are 10.5:1. The dome is probably the same as the A65 version but the stroke will alter compression. That said an A10 crank being 84mm not 85mm will lower compression some, but for me I wanted to go as big as I could before having a norton crank fitted, the CC of that motor with B44 pistons will be around 823 (50 Cubic Inches), I want a lot of torque but not bothered about speed or having anything faster than a stock A65 (ideal touring bike)

You could get the rolling chassis sorted, drop an A65 motor in there and then you have a ridable bike until you slowly and surely get an A70 built (By then there might be some custom cranks made which will suit) Or drop in an A65 motor with the A10 crank conversion.

I know one person who has A65's and an A70, he says the A70 is totally different in character to the A65 and really likes the bike.


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Re: BSA A70 Lightning parts vs A65 [Re: gunner] #766321 02/24/19 6:38 pm
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Originally Posted by gunner
BBB have a pair of steel capped conrods currently on eBay suitable for BSA A50 / A65 / A70 1962-72, BSA Part Number 71-1105 / 71-1106, see This Link


Thanks for posting, I was certain I had seen some but couldn't find them again just now.


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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766327 02/24/19 8:17 pm
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Originally Posted by Morgan aka Admin
About the pistons now inside the A70 do you know which model they are for? comp??? I hear it may me 8.5 comp. see photo attachment
Hepolite 19255 std 75,974mm that sounds like two oversizes for a A70 does it not?


If standard T140 pistons have been fitted, the A65/A70 barrel will be on + 40 thou OS. The distance from the gudgeon pin to the crown is around 2mm shorter on a T140 piston to the A70, so unless the effective barrel height has been shortened I can't see the compression ratio being as high as 8.5:1. Also the valve pockets in the T140 pistons are cut at a steeper angle than on the A70, so if the barrel height had been shortened, this could create issues with valve to piston clearance unless the pistons had been machined accordingly.
I bought some genuine +40 pistons for my A70 from Bantam John in the UK last year but be prepared for a good spanking with the price.


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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766328 02/24/19 8:21 pm
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Originally Posted by Morgan aka Admin
NOS pistons turn up from time to time, but usually only in std or maybe +.020". Mike's Classics might still have some. Apparently, T140 pistons can be used for the oversizes, but require some machining of the skirt. If Ed V has replacement, they'll be excellent quality. Triumph 8,5 comp pistons are in it now and it seems that it has two oversizes bored about one mm over std. Since it has same cylinder as A65 how easy is it to change liners to go back to STD A70 size
It costs about twice as much here to install liners as it does to rebore. If it was me, I'd rather look for a good set of late cylinders with an in-spec standard bore.
Originally Posted by Morgan aka Admin
As far as I know, A65 timing side main bushes can be shortened to fit, as per Ray's post. Good! is it same size otherwise?
Yep, the journal diameter is the same.
Originally Posted by Morgan aka Admin
So here is the $100 question. Is it worth spending double amount of money compared to a similar A65?
As a daily rider, probably not. As a rare part of BSA history, definitely. That assumes matching engine and frame numbers, though mismatched A10 engine and frame numbers may not make all that much difference to the price.

Originally Posted by Morgan aka Admin
And over time get into difficulties restoring the A70 engine because lack of parts. I mean next time I pull it apart to service the sludge and control/restore rest of the engine what will I need to replace??? What parts will I don't find??? that is my concern I am afraid that the restoration might stall or cost a lot more than a A65 to restore.
Only the crankshaft is truly unobtainable. Grab a pair of connecting rods from Burton Bike Bits, and a pair of pistons from Ed V while keeping an eye out for NOS pistons. As David said, he can make most of the parts. Engine work is almost certain to be more expensive than an A65, but everything else is identical to the 1971 Lightning.

Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766379 02/25/19 10:41 am
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Thanks for your answers.
Before I go further I need to say I have deleted a couple posts that were a bit off topic. With this thread I only want information about
Original A70 vs A65 and A70 in particular. it is so easy to be distracted and lose focus.
If you also wish to discuss other crank options etc then we can start another technical thread about that.
OK no hard feelings intended.


Last edited by Morgan aka Admin; 02/25/19 10:42 am.

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Re: BSA A70 Lightning parts vs A65 [Re: Ray Elliott] #766398 02/25/19 2:12 pm
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Originally Posted by Ray Elliott
The A70L stamp looks legit. It's the same as on mine. It's the same as on the OIF A65 except for the 65 being 70.


Ray and others The frame numbers above starts from bottom and goes up.

but this frame number on BBB register site goes the opposite down see
[Linked Image]

Are both right or is there a fishy number..? on one


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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766404 02/25/19 4:02 pm
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Morgan,

You are absolutely right. The #s should be top down. This leads me to think it's not legit.

The circle cast into the cases (where a dipstick was years past) should have a 7 in the middle. And this 7 is the same form as on serial numbers. It has a distinct shape.

If you can pull off the timing side inner cover you should immediately see the thrust washer behind the pinion.

After I bought mine & it arrived I immediately removed the head to check the stroke. It has so much carbon that was not certain of the stroke.

I removed the cylinder & it had A70 rods. I was less panicky at that point. Then I removed the timing cover & saw the thrust washer.

But had I known then what I know now I could have identified the crank in other ways. The flywheel is different. The big end journals are (obviously) closer to the end of the journals. An A10 crank most likely would have the alternator rotor attached in a manner not used on A65. Mine was affixed like an A65: on to the crankshaft with a nut.

I can post crankshaft & timing side pictures if you want.


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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766407 02/25/19 4:20 pm
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I doubt who ever did the stamping was job concious enough to ensure that each one was the same way up. or if different people did the stamping.

As there wasn't supposed to be any grey framed A70's the only real way would be to get the paint off and check again.

As a side note my 71 A65 frame is stamped in the same direction as Morgans

Last edited by Allan Gill; 02/25/19 4:22 pm.

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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766410 02/25/19 4:46 pm
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Ray I sure would love to see any photo of specific A70 parts you can publish here.


Allan, on your '71 frame is the is is stamped like this A65X ,,, ,,,XE ,,, ,,, 00101 ? the commas just explain that there is a empty space in between next letters/digits I noticed it was about 2cm empty space in between. Don't think I have seen that before and there is no forward slash as on the photo above. The stamping was not that goog punched either i think cause the E looked almost like an F which BSA don't used.

Its questions like this and the motor questions that makes me hesitate a bit..

I spoke with SRM and they seem to be able to take the engine and restore/upgrade it they have done the bearing conversions on A70's too they said. guess it brings quite a bigger whole in the pocket.


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Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766416 02/25/19 5:17 pm
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My numbers are bottom up on the left side, about 0.215" high.
[Linked Image]
The cobby welding was from stick welding the headstock sheet metal brace years ago.

Re: BSA A70 Lightning parts vs A65 [Re: Morgan aka Admin] #766419 02/25/19 5:35 pm
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Hope this helps Morgan,

I've not added all the numbers on purpose but should give an insight to what you require.

There is a space between the model designation, the month year and the serial number itself.

I suspect that your frame has been powder coated or some thick paint used at some point, mine was originally dove grey (still shows signs of dove grey in places) then painted black at some point.

Attached Files Partial A65T frame number.JPG

beerchug
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