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Modified BSA A65

Modified BSA A65

Postby mark parker » Sat Aug 22, 2015 5:16 am

This is my old long suffering A65. The rolling chassis is RGV 250. The BSA motor is a neat fit and is rubber mounted. It has had daily use in this chassis since 1992. The tank and seat and fairing I made, as with the exhaust. So far it's the best exhaust, though I wish I'd made it all in stainless.

The motor has twin 38mm TM flatslides. It's 883cc with an alloy cylinder with Nicasil bores and JE B44 pistons. Norton 89mm crank offset at 90degrees.

I've had A65s since 1972 when people bagged them out a fair bit.

I put a data logger on it in about 2005 when it was 818cc. It had 48HP on the dyno function and with a lot of runs and messing with stuff I got it to 57HP. I couldn't afford a big bore kit so made some patterns off an old thickened cylinder and had a set cast in alloy. The bigger bore made a heap of difference, and I soon had 72HP. It now has 80HP with an excellent power spread.

Image

Image

It has C/ratio 1st and 2nd gears and is tall geared 3.43-1.

https://www.youtube.com/watch?v=1Bb4XfUkyVU

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Re: Modified BSA A65

Postby worntorn » Sat Aug 22, 2015 6:31 am

Very inventive Mark!
What is the weight of the bike?

Glen

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Re: Modified BSA A65

Postby grandpaul » Sat Aug 22, 2015 7:37 am

Mark has AMAZING build history on this bike on www.BritBike.Com

If you have any interest in this bike just from this photo, you need to check it out.

In my opinion, my use of the word "amazing" is not hyperbole.

Nice bike.
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Re: Modified BSA A65

Postby Fast Eddie » Sat Aug 22, 2015 9:00 am

Very cool Mark, nice one.

I came close to having a go at building a T140 based RGV chassis special, but I chickened out thinking the alloy frame wouldn't handle the weight and vibes of the engine. Looks like I got that wrong!
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Re: Modified BSA A65

Postby 84ok » Sat Aug 29, 2015 4:16 pm

mark parker wrote:an alloy cylinder with Nicasil bores

8) :?:
x74 the torque be with you

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Re: Modified BSA A65

Postby mark parker » Sat Aug 29, 2015 11:03 pm

Another video, shows how it sounds.
https://www.youtube.com/watch?v=RmKv_bNA03k

Not sure of the exact weight, but it's fairly light. The alloy cyl is half the weight of an iron cyl. It's going to be interesting when I get the new head on it. Flow figures are looking very promising.

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Re: Modified BSA A65

Postby Mark F » Sun Aug 30, 2015 3:32 am

Sounds good Mark.
I still think this clip sounds great although I think it may be your brothers bike.
https://www.youtube.com/watch?v=oBD2g_bBog4
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Re: Modified BSA A65

Postby swooshdave » Sun Aug 30, 2015 5:22 am

And what did you do to the timing side of the crank?
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Re: Modified BSA A65

Postby mark parker » Sun Aug 30, 2015 7:56 am

End feed and heavy series needle roller, end float is controlled by a ballrace in a plate outboard of the alternator. The drive side main is Norton. It also has a support bearing behind the clutch. These bearings help resist the primary chain pulling out of line. The BSA box is fairly short between the bearings and is quite strong. It has C/R 1st and 2nd gears which make the BSA 4 speed much nicer.

Image

I also use a 520Xring chain. I'd really like to fit a 5.5" wheel and 180 tyre in place of the 160 but am yet to work out how.

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Re: Modified BSA A65

Postby grandpaul » Sun Aug 30, 2015 8:18 am

mark parker wrote: I'd really like to fit a 5.5" wheel and 180 tyre in place of the 160 but am yet to work out how.


Wouldn't that just be more rubber (and associated unsprung weight) with perhaps a negligible improvement of the rear contact patch?
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Re: Modified BSA A65

Postby swooshdave » Sun Aug 30, 2015 9:45 am

grandpaul wrote:
mark parker wrote: I'd really like to fit a 5.5" wheel and 180 tyre in place of the 160 but am yet to work out how.


Wouldn't that just be more rubber (and associated unsprung weight) with perhaps a negligible improvement of the rear contact patch?


You're questioning his choice of excess? :shock:
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Re: Modified BSA A65

Postby grandpaul » Sun Aug 30, 2015 12:55 pm

swooshdave wrote:You're questioning his choice of excess?


Yes, but politely!
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Re: Modified BSA A65

Postby mark parker » Mon Aug 31, 2015 4:09 am

I put a 5.5" Honda wheel on my SV650 with a 180 tyre and it feels better than the 160. It would be nice to do the same with the BSA, but I'm probably stuck at 160 without making serious mods to the swing arm and spinning two sprockets on it to get the chain past the tyre. It would be a neat way to get constant chain tension but may not be worth the effort.

I don't know if you saw the other thread, but I had a head flow tested like I'm running now. It flowed 158CFM @ 28". I did some research and landed on this Norton site with some great articles on porting and ports. Jim Schmidt had a post with pictures of an XR750 port, so I've copied it into a BSA head fairly closely and built my own flow bench.

The bench is working pretty good and from testing the known head and working out a formula to convert the numbers I get into that 158CFM I can get an idea of how the new port is working. I lifted the guide 4mm tonight and tied a 38mm Lectron carb to the oval port, no manifold made yet, it sits at the wrong angle and the top and bottom of the oval port kind of blocks it, but at .470" lift it seems to be flowing 197CFM without the carb it's around 189CFM. I'll make a manifold and try refining it a bit, it's the same volume as the previous port so it's the shape making it work better, the valve is the same 44.5mm. I can imagine the bigger tyre might be useful when I get this type of head on the bike.

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Re: Modified BSA A65

Postby 84ok » Mon Aug 31, 2015 7:02 am

what do stock and modified snorton heads flow?
x74 the torque be with you

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Re: Modified BSA A65

Postby mark parker » Fri Sep 11, 2015 11:42 pm

84ok I borrowed this screen shot from an excellent thread on here on porting Norton heads. If my equipment is correct my new head flows similar to the green line, which is a head for a big over 1000cc Commando engine. The red and the blue look really good having small ports.

I'll have to wait and see how the power characteristics are when I finish my new head. The port volume is no greater than the ports I'm using, so I'm hoping the BSA will still pull as well in the midrange. The reason those red and blue traces are so good is, with their smaller ports, you would expect them to keep a very health midrange.

Image

Heading for the shed to finish the second port and see how close it is in flow to the completed port :)

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