The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: mark on 03.06. 2010 07:10
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I have a choice of using a 356 or a 357 cam in my '55 rocket. It has the correct heavy big journal crank and I've just taken delivery of a set of Lightning billet conrods from Thunder engineering, the pistons are 9 to 1 Hepolites and until I can source the correct head I am using one from a super rocket. What thoughts are there on the pros and cons of the different cams.
Regards
Mark
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It depends what you want from the engine, the 356 is perfectly good for an all round tractable engine, while the 357 is more sporty but gives a slightly less flexible engine.
Are you sure you have the right con rods, A65's are different to A10's?
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Andy,
"Lighning" is the trade name of the rods sold by Thunder Engineering for various bikes.
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G'day Mark,
I agree with Andy. I use 357's in both the A7 and A10 but I'm a rev head. The power comes in at about 4500rpm which means at 60 mph in top I have to go back to 3rd to get motivated.. The 356 will give better mid range.
I'd stick with the SR head.
Cheers
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I have a 357 in my project but reduced the gearing a very little bit to compensate for reduced torque and not really interested in top speed these days but would like a bit of umph at the lights ( just to surprise the boy racers)
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Thanks for the thoughts guys. Since I plan to use a 22tooth engine sprocket it looks like the 356 will be better in regards to flexibility.
regards
Mark
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Hi Mark,
Flexibility of the engine (in riding terms!!) has a lot of of factors influencing it!!
Carburation and ignition settings have a huge influence, even the exhaust makes a difference.
My SR has a 357 cam, manual mag (BTH) and a Mikuni carb,
It will pull easily from low revs and will trickle along in high gear without complaint!!
Whack the throttle open and it leaps into life and scorches off into the distance *smile* *smile*
I'm rebuilding another SR for an older owner and have fitted flat top pistons and a 356 cam as it will be more suitable to his needs, he also has a plunger A10 and a Harley and only recently sold his Gold wing!!! so I hope I'm correct with the spec I'm using ????
Cheers
John O R
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Yes, an old owner will love it, i do......... ;)
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I was wondering, what sort of price are those Lightning con rods from thunder engineering? do they compare with SRMs?
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The Lightning Conrods cost me 250 pound the pair. I'm not sure how they compare with SRM. I am impressed with the quality however but the real test is still to come when the motor is completed and running. I was speaking to a chap in New Zealand recently who told me that he used them in a motor that set some race record over there so I guess that is a positive reccomendation.
Mark
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Thanks
SRM do BSA forged equivalents @ £189 a pair or high strength forged @£150 each.
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For those of you down under (from me at any rate!) theres These guys (http://ridgecrest.com.au/3201.html)
I bought my A65 billet rods from TMS at £280 a pair.
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Yes Ridgcrest even make them for Matchy twins.
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Excerpt from one of BSA's adverts for accessories...
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I thought I'd upgrade my '55 road rocket motor from its stock 356 to a 357. In practice this required machining as there was insufficient space in the cam trough for the additional lift to let the cam rotate! I wasnt expecting it not to fit.
Likewise I replaced my small journal crank with an early LJ and found the big end lock nuts fouled the cases and wouldnt let the crack rotate fully. I had to fit the castled type nuts which were smaller to have a crank that spun. Presumably the super rocket motors have a bit more clearance for cams and big ends...
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Hi Rocket Racer - 357 fitted into my 59 A10 all right, looked close but had room enough.
Have read this before about cam through, could be a batch were cast just within tolerance, fair old difference between 356 and 367 though I've gone back to 356 for now at least until the rebuilt engine frees up.
Good luck with it
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I'm hoping it'll work nicely with alcohol fuel, some light genuine bsa pistons in the 8.x:1 (comp yet to be measured) big valves, a pair of 10TT9 carbs (a '55 type twin port head) and on castor oil... Cant wait to have it going! -but not a road bike...
Another set of '55 A10 cases I have that also had a 357 fitted had evidence of rough dremelling to get the cam to fit by a previous owner
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G'day RR,
it seems strange about the cams. A 357 fitted in my "51 plunger and the A7SS cases with clearance.
I did have the same prob with the LJ crank going into '57 cases.
8 : 1 comp wont be enough to get the full benefit of methanol. It doesn't start really working below 10 : 1, 12 is better. At your comp you would be better off going 100 - 115 oct avgas.
Running my '57 A7SS at over 12 : 1 with 2 X 32 concentrics I would get 12 MPG !!! That's when I could keep the barrels on and SJ crank in one piece.
Cheers
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has anyonr tried the megacycle one ?
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G'day Muskrat - reckon your A7SS might run on diesel at over 12:1 *smile*
Must go like s*** off a shiny shovel and well worth the expense of 12 MPG and the risk of a broken ankle when kicking her into life.
Jim
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Hi All,
I finish the SR with the flat topped pistond and 356 cam and it now has 4-500 miles on it
It is a really sweet motor very quiet mechanically and just what I hoped it would work out like *smile*
BUT compared to my own SR it is a pussycat *ex* *ex* Very much the opposite of mine
The exhaust notes are very different, mine has a much sharper growl and the goldie "silencer" twitters lovely *smile* *smile*
There is a fair difference in performance etween the 2 bikes
I wont be detuning mine anytime soon *ex* *ex*
"Now wheres that shorrocks blower I had" ???? ???? ???? ????
Cheers
John O R
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As a guide to useability, compare the performance graphs on my thread of today (dyno testing SR engine).
You will see that when compared to the 356 cam, the 357 has less bottom end, and a top end that gets going, when the 356 has signed off!.
Bear in mind that the Sr has slightly higher compression, and a bigger carb; however, the characteristics of the different cams is evident.
Dio you need more acelleration, or low down rideability?
Richard
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Those dyno charts were very interesting, thanks for posting them! I'd love to see a dyno of Muskrats A7 *respect*
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Well done Richard. That's real horses at the back wheel.
Might have to do that. A bike shop up in Nowra just installed a dyno. The old A7SS racer is now the A10 Cafe so not running methanol and high comp. Just a few more little things to sort out, like keeping the oil inside the rocker box.. Will post when done.
What about yours RR ?
Cheers
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Still running in the RR; can't see it being ready until October (I have so many bloody bikes to choose from it takes a while to get the miles up!).
For example, two weeks ago I finally got up 1,000 km on this "rocket", and it also had it's turn on Ray's dyno.
At the risk of being branded a heretic, but in the interests of all things mechanical, check out the results: almost the same power as the iron head GF's, similar torque, and 2/3 the weight: Yippee its party time - turn the throttle and hold on!
However, I only get 70 km to a tank!
Any decent run out of town, and i strap extra fuel on the rack at the back.
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi302.photobucket.com%2Falbums%2Fnn82%2Forabanda%2FP1030443.jpg&hash=1b9428f2bb8d65bd915e14e4e58e9fd31621b875)
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi302.photobucket.com%2Falbums%2Fnn82%2Forabanda%2FRichardArgusDT400B1975DYNOGRAPH.jpg&hash=76a1f55f96659a4fa0924de132a320bcad1d9016)
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi302.photobucket.com%2Falbums%2Fnn82%2Forabanda%2FP1030431.jpg&hash=e78b883f30361c6bd72962f762634bd247f53b6f)
I am also ckocking up the km's on this bike below: 400 km to go, and then it gets the tune-up on the rolling road!
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi302.photobucket.com%2Falbums%2Fnn82%2Forabanda%2FP1010202_resize.jpg&hash=761b250e71279c8fa8efb0a5219e5d8d31a7c258)
Richard
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great bikes the xt's love em ,i got a 78 tt500,the only japanese bike i like,and i got enough to build a xt flat tracker in the future.
had an xt when i was travelling in OZ,
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Sorry Richard, I meant Rocket racers chair.Yes those 400's go, I had a 360 years ago. My XT is awaiting time and money. I threw points & condenser in a while back. 1st kick it backfired and I had 3 days off work !
Cheers
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Muskrat,
I got a 360 too.......
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi302.photobucket.com%2Falbums%2Fnn82%2Forabanda%2FIMG_4089.jpg&hash=c953d9eb3952d6d6dc50f16212c4939874c41283)
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi302.photobucket.com%2Falbums%2Fnn82%2Forabanda%2FP1010008.jpg&hash=cd3d7617daf5fd2bd48197a5c02af92cce1bc9fe)
This was my first 360, from a looong time ago....
(https://www.a7a10.net/forum/proxy.php?request=http%3A%2F%2Fi302.photobucket.com%2Falbums%2Fnn82%2Forabanda%2FDT360A19792.jpg&hash=3caf519c57611c4fde9543ee19a282d9eb0a6efd)
Richard
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The intention is to dyno the chair asap...I've got the bottom end assembled, still have to check valves have clearances, paint barrels, have ordered fresh wire circlips as the several new sets I had were only loose fits!! a number of other loose ends too, so wont be this month sadly.
The motor has the "heavy" early type lj crank, a 357 cam, big valves and med comp light BSA pistons. The inlet ports on the head are asymetric, so my engineers making manifolds as the top studs are mighty close to the ports. I'm hoping we'll have a pair of 10TT9 carbs and on alcohol although purely to keep the running temperatures down as chairs work fairly hard. Don't know how well it'll run but its going to look fabulous wink2
I'd been working in Oz but am now back home so its progressing again...
I'm always intrigued by dyno numbers as they appear to be mainly useful to see how the motor creates power rather than the numbers themselves which seem to vary dramatically from dyno to dyno. My old Norton atlas race bike which was claimed to put out 49 hp stock in road trim, in full race trim on race gas put out 49hp on a dyno after fettling... yet we keep seeing A10;s that are claimed to put out 33 -45 hp based on trim, putting out 22 to 28 hp. I appreciate the rear wheel vs crank argument, but I know my atlas wasnt twice as powerful as an A10...
I'll see if I can find a copy of the atlas dyno...
Sorry Richard, I meant Rocket racers chair.Yes those 400's go, I had a 360 years ago. My XT is awaiting time and money. I threw points & condenser in a while back. 1st kick it backfired and I had 3 days off work !
Cheers