Author Topic: Cylinder angle of turn  (Read 1002 times)

Offline ppanichelli

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Cylinder angle of turn
« on: 08.06. 2015 15:13 »
Hi all!

I start talking about the bike of my avatar, a BSA A7 1949 I started to restore.

I don't know if it's all same around the world, but here in Argentina, ALL the BSA cylinders are cracked and patched up. My bike was not the exception (of course!).

After verifying it, the mechanic adviced me to get another cylinder...(you know it's not just going to the supermarket)...anyway, after a hard research I found a guy who was selling a god blessed BSA cylinder. It was cracked and fixed, but usable.

This guy was an old school mechanic, who once upon a time talked with an engineer that used to be the BSA Technical Country Manager about this issue.
The engineer told this guy that the problem (in Argentina) with the cylinders was that everybody used to rebore them at 90°, ignoring that the angle of turn of the cylinders was not 90°!!! This error generated an extremely thin cylinder wall, which eventually would break.

However, if it's not 90° the question is: which is the right degree of the cylinders?? Anybody has this information? If not, it's still a nice data to bear in mind!!

regards




Online bsa-bill

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Re: Cylinder angle of turn
« Reply #1 on: 08.06. 2015 18:11 »
Hi ppanichelli

congratulations on your excellent English and hope your restoration goes well for you, the issue of the 90° thing, I think you mean +90 which is the measurement of piston size ( = 90 thou over standard), yes it is too much +80 is done but even then some people think that is also getting near to the limit.

When I restored my Flash it was on +60 and needed a rebore, I used liners to bring it back to standard then put in standard pistons.

so to answer your question +80 can be done but +90 a bit much
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

Offline ppanichelli

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Re: Cylinder angle of turn
« Reply #2 on: 08.06. 2015 20:36 »
Hi, thanks for your reply Bill! I'm glad that somebody understood what I wrote!! :D

Regarding your comment, I was not referring to the piston diameter, which is 62 milimeters indeed. I referred the angle of "inclination" of the cylinder:

If you put the cylinder on a table, you would think that the piston would enter through the tubes in a perpendicular way (90°)

What I've been told is that the inclination of the tubes (where the pistons works) are not 90° degrees, but a little bit less: there's certain inclination at both tubes to the front. What I'd like to know it's the right angle of the tubes.

If this tale it's true, then we'd have the reason of why everybody cracks their cylinders and also the knowledge not to do it anymore.

Thanks in advance!

Online bsa-bill

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Re: Cylinder angle of turn
« Reply #3 on: 08.06. 2015 20:56 »
Oh right - well that's a new one to me, never heard of it before.
I would assume 90 degrees to the base of the barrel otherwise how would shops know how to set up their boring machinery, also how would thery machine heads to match barrels.
However would be interesting to hear other views on this (as I'm sure there will be)
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

Online RichardL

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Re: Cylinder angle of turn
« Reply #4 on: 08.06. 2015 22:35 »
OK, let's dispell this, it's 90 degrees. Perhaps the reason the cylinders are cracking around where you are in Argentina is because someone started a rumor that it was something else and local practice was to go in off of perpendicular to the base.

Richard L.
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Offline duTch

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Re: Cylinder angle of turn
« Reply #5 on: 08.06. 2015 22:42 »

 *dunno*...no offense p-panno, but I guess we won't be buying too many spares from Argentina then....? *whistle*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online chaterlea25

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Re: Cylinder angle of turn
« Reply #6 on: 09.06. 2015 13:53 »
Hi All,
Yes, 90 degrees to the base of the cylinder, NOT the head surface !!

Maybe BSA sent all the "reject" cylinders to Argentina  *eek* *eek* *eek* *eek*

John
1961 Super Rocket
1963 RGS (ongoing)

Offline duTch

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Re: Cylinder angle of turn
« Reply #7 on: 09.06. 2015 14:55 »

  Geez- one'd think head and base would be parallel... That could make some people nervous. . *eek*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline cyclobutch

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Re: Cylinder angle of turn
« Reply #8 on: 09.06. 2015 18:45 »
This thread is raising a whole lot more questions than answers right now. Keep going ...
Various, including ...
'58 Iron Head Flash Bitza


Online chaterlea25

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Re: Cylinder angle of turn
« Reply #9 on: 09.06. 2015 19:28 »
Hi All
Quote
Geez- one'd think head and base would be parallel..

They should be parallel,
but if you think about it, it doesnt matter if the head/cylinder joint is a little "off"

The cylinder base must be parallel to the crank and at 90 deg to the bores

The cylinder base must be used as the reference face when reboring the cylinder

HTH
John
1961 Super Rocket
1963 RGS (ongoing)

Offline duTch

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Re: Cylinder angle of turn
« Reply #10 on: 10.06. 2015 01:39 »

 Fairly sure there was some discussion about this in a thread a couple of years or so ago....?
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline East_Coast_BSA

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Re: Cylinder angle of turn
« Reply #11 on: 10.06. 2015 06:22 »
Hi All
Quote
Geez- one'd think head and base would be parallel..

They should be parallel,
but if you think about it, it doesnt matter if the head/cylinder joint is a little "off"

The cylinder base must be parallel to the crank and at 90 deg to the bores

The cylinder base must be used as the reference face when reboring the cylinder


I don't think Parallelism is the best way to tolerance this cylinder business.  When I took my A10 cylinders off, the rings had worn a large "step on the outside of each bore and the inside (where the cylinders were closest together) had no "step" at all.  Clearly these bores were canted toward the center of the motor.  Parallelism would simply have both cylinders wear the same, although both cylinders would be incorrect.  I would say that "True Position" of the bore centerline in reference to the crank center and "Perpendicularity" in the X & Y position.  When you assume that the bottom of the cylinder is a good reference point for boring, also be certain that the mating surface on the block is qualified correctly with the crankshaft.  It may be in some instances that the cylinders were made correctly and the blocks surfaces were the problem.  From what I've seen, nothing is outside the realm of possibilities.

Online bsa-bill

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Re: Cylinder angle of turn
« Reply #12 on: 10.06. 2015 08:24 »
Quote
This thread is raising a whole lot more questions than answers right now. Keep going ...

sure is, including from my point of view(see what I did there) not assuming the writer means something he/she did not state   *red*

Thinking further - the only thing I took to my machine shop was a piston and the Barrels, so the reference point they use has to be the base of the barrels so the onus then has to be with BSA that they got that and the crankcase top face machined at 90 deg (no degree sign on this keyboard) to the centre line
Quote
The cylinder base must be parallel to the crank and at 90 deg to the bores
as John has said
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

Offline cyclobutch

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Re: Cylinder angle of turn
« Reply #13 on: 10.06. 2015 10:34 »
I always tend to presume with this older technology that a whole lot of things really aren’t that important. Metallurgy was nowhere near as precise, tooling wasn’t that much better – even when it was new. Given those factors, I get kind of surprised when we worry about a few degrees difference in ign. advance between cylinders, or when we discuss the need for an intake bias gasket etc. My presumption now, is that excepting the odd low mileage barn find we are now running these bikes waaaaaay beyond their design life, and some of us also somewhat beyond what might in the day have been considered a sensible state of tune. 

However, we are still running them. And hence this kind of dialogue is almost infinitely fascinating (no irony intended).
Various, including ...
'58 Iron Head Flash Bitza


Offline duTch

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Re: Cylinder angle of turn
« Reply #14 on: 10.06. 2015 12:06 »

 Don't want to get too involved but. ...
 
Quote
 (no degree sign on this keyboard) 

  On my Macbook it's not 'on the keyboard', as such- I found it by pressing many combos of buttons until I found it: 'option + K '... depends on the 'puter..
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia