Modified BSA A65

mark parker

Joined
Aug 5, 2015
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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.

Modified BSA A65


Modified BSA A65


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

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

Modified BSA A65


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.
 
mark parker said:
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.
Click to expand...

Wouldn't that just be more rubber (and associated unsprung weight) with perhaps a negligible improvement of the rear contact patch?
 
grandpaul said:
mark parker said:
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.
Click to expand...

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

You're questioning his choice of excess? :shock:
 
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.
 
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.

Modified BSA A65


Heading for the shed to finish the second port and see how close it is in flow to the completed port :)
 
Hmm, didn't go too well. Cut and filled the port and it looked pretty good, tested it, reads low, so start reshaping a bit, reads lower. Do what I should have done before starting and test the right hand port minus carb and manifold, also reads low. Put calibration head on and check flow at .438" which I know is 158CFM, it also reads low! Work out new calibration, left port before modifying was 183.3CFM with no manifold or carb, R/H port is 184.7CFM, both at .410" lift. R/H port with manifold and carb is 194.5CFM . Trouble is the left port is now at 176.6 and I need that 5-6CFM back. I guess tomorrow is another day.
 
swooshdave said:
And what did you do to the timing side of the crank?
Click to expand...
Thats what I want to do like SRM bushing to bearing conversion..Need an expierienced machinist that can do this conversion like SRM need proper roller bearings and machine shop that do all this for me key word is expierienced with provable track record...need oil holes done in case halves and srm oil pump ...please post info and contact numbers east coast prefered...usa 1969 bsa
 
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