Severe Knocking - A10 Road Rocket

[RichardL]

I feel very certain in saying that BSA balanced their prototype crankshafts (at least static, if not dynamic) and applied that balance to all production-run units. I would not say with such certainty, but I like to believe, that each crank after grinding was checked to assure it fell within the balance tolerance that was established. This was not new technology at the time A7s and A10s were made. I have $10 for the first forum member who can prove to me that the great British aircraft manufacturers in WWII (Hawker, Vickers, etc.) did NOT balance their crankshafts. I am also rather certain that almost every combination of crank, rod, rod-bolts and sludge-trap parts is now different than what came from the factory. I believe some sort of balancing, static or dynamic, is worthwhile. Certainly won't hurt and is inexpensive by comparison with the overall cost of rebuild.

Richard L.

[groily]

I don't know if they did or not Richard, but I bet you are correct. As I understand it, the majority of A10s are running a balance factor of about 55% of reciprocating mass. Don't ask me for the maths that go into that.  Way beyond me. But they must have had some sort of static figure in their heads at least, surely? Otherwise, what do you do with the blanks? How much do you zap off when finish-machining the things? And what are those radial drillings to be seen in some crankshaft webs?

That said, when fitting a prototype brand-new crank to another bike, I did splash out for a dynamic balance, and I think it was worth it although i never ran it 'unbalanced' so dunno for sure. The difference between left and right hand sides, dynamically, on initial test was significant apparently (nearly an 'ounce-inch'), but was reduced to 0.11 'ounce-inch' (way below the T&L yardstick 0.5 oz-in). Now, I don't know what that really means - but having asked for a balance factor of around 60 - 63% for that particular engine (using expensive modern rods etc I should add), I got 61% and she is smoother than my A at cruising rpm. Which, given my A is a standard iron Flash setup with 7.25:1 pistons etc and is inherently quite smooth anyway, and the other motor is a CSR-spec 650 AJS (not known for 'smooth' always), is pleasing. Differences in gearing and absence of tachometers make any further comparison odious, but I got what I wanted with the balanced crank - smooth as you like at the road speeds I want to run it at. (About £145 iirc for the balancing job.)

The % factor applied - as I understand it - really only determines at what rpm you get the inevitable vibes that go with 360° parallel twins. For pootling about, it makes no odds at all. For pushing on, a higher factor - eg 70% at the high end - is supposed to make things go tingle-free at Muskrat speeds - but I don't know how true that is because for those speeds I ride something else! (I didn't have the crank on the A dynamically balanced when it had attention a couple of years ago - didn't seem worth it to me either as it was quite a smooth engine before and I wasn't changing any key components.)

I would post the data sheets for the balanced crank here - but I can't because the scanned files are too large and I don't know how to shrink them. If anyone wants the spec sheets just as an example, happy to send them attached to an e-mail.

Cheers, Bill

[Brucie64]

I suppose if the engine doctors of choice offer the ability to balance AND my wife isn't there at the time then I may splash out and have it done however it will be a spur of the moment decision I fear.

[metalflake11]

Sorry Brucie, but some things can't be done on the cheap in my opinion. Some people ride British bikes for years on end with with hardly any problems, others have endless niggles and eventually a major engine failure.
 The right job, by the right people, using the right parts is the only answer. An un-balanced engine for example, will never be happy or pleasant to ride, and will fail long before a well balanced one. Cheap parts are cheap for a reason, and whilst a good mechanic will be able to build the motor, a B.S.A. specialist will do it a whole lot better.
I've yet to meet a fellow Beezer rider who scrimped on an engine build, without living to regret it either financially, or in the enjoyment of riding it in the long run. Relatively simple they may be, but they do not respond well when saving money is the main objective when being re-built. Also bear in mind, some of the practices in a good re-build of a 50 year old engine went out years ago, and these more modern firms may be unaware of them.
Decide in haste, repent at leisure..................Good luck with your final decision!
 

[trevinoz]

I always have mine balanced. Makes a much nicer engine.

[RichardL]

I have $10 for the first forum member who can prove to me that the great British aircraft manufacturers in WWII (Hawker, Vickers, etc.) did NOT balance their crankshafts.

I didn't mean for it to be a trick question, but I think it may have been one, and I am going to pay myself the $10 for the best answer: The great aircraft manufacturers of WWII used engines made by others. For example, Hawker Sea Fury used 18 cylinder radial made by Bristol Centaurus.

Richard L

[KiwiGF]

http://www.a7a10.net/forum/index.php/topic,6086.0.html

Shameless plug of my own post...but that post shows you can do some checks on crank balance yourself....using a kitchen scale to check rod and piston weights etc. but your engine builder should do that anyway.

If you are happy to keep the standard balance factor and are not using heavier Pistons or rods obviously I'm on the side of not doing it, but it is a cost/benefit decision and you might want to spend the cash saved on something else like new rods.

I'm happy with my A10 vibes and it is no worse vibe wise than another I've ridden that was dynamically balanced to a higher balance factor, albeit I've no desire to push beyond 5000rpm especially on someone else's bike!

[Topdad]

I agree with Metalflake and Richard re crank balance, when mine was being refurbed I reckoned that I'd only afford to do it once and so got everything done at the same time including getting the crank balanced .I have never regretted it and without checking receipts I'm sure the cost was very low .The engineers in question SRM ,ihad no hesitation in going with them despite other more local and cheaper offers .Touching wood I've enjoyed 9yrs ,so far of enjoyable riding and not much (if anything ) as fallen off  or needed much tightening !! Richard ,I think yours was a pretty safe bet ,most aero engines of that date coming from Rolls Royce , merlin, griffin etc and I'm sure they would have balanced the cranks however one of our clients dad worked at avros plant near Manchester on merlins as an engineer for RR and I'll ask our client to find out from him. Last time I spoke to him he told me of his time working on prototype jet engines in Barnoldswick despite getting on he was as sharp as a bell even told me that the reason RR jet engines are numbered RB etc followed by a river name    ..Avon Tay etc stands for Rolls barnoldswick .Cheers Bob

[Brucie64]

Finally managed to get the crankcases apart this week and found the root of my problems. Looks like the L/H big end bearings are obliterated, I am amazed it hasn't caused more damage than it has. Crankcases look fine so I am probably looking like a crank regrind, new big ends and con rods I suppose.

https://youtu.be/XrS_Kvfe5Fw

Question for you all, would you strive to find a steel set of replacement con rods or alloy good enough ( I noticed the SRM ones are alloy so they can't be all that bad right?)

[duTch]

 Bruce, (that always immediately reminds me of Monty Python, solly.. )

 I doubt you'll find steel rods for an A10/7, and if you need new rods, you'll have to consider their weight and distribution thereof....I used Thunder rods I think as did KiwiGF, and they're much heavier than stock.. and I have a feeling that SRM use similar to ?MAPP rods..??... also heavier, so you'd need to balance them....but I think that's secretly what you'd ike to hear.. I think the stock rods are ok if up to spec..??

[KiwiGF]

Thunder Engineering do, or used to, make billet con rods for srm, but will sell them directly to one and all, steel rods are theoretically available from the likes of carillo I've been told by someone who fitted them, but only if a wholesaler orders a batch and on sells them.....and they are significantly heavier.

The billet rods as Dutch says are heavier but not at the end that counts .....so in my opinion do not affect balance significantly.

Billet rods are things of beauty!

[chaterlea25]

HI ALl,
Bruce,
Steel rods from MAP,
http://www.mapcycle.com/categories/engine/connecting-rods/bsa-rods.html

I have a set of alloy MAP rods bought some time ago for my RGS, and have had the crank balanced to suit

HTH
John

[Greybeard]

Steel rods from MAP,
http://www.mapcycle.com/categories/engine/connecting-rods/bsa-rods.html

They really are too pretty to hide away. What about putting a glass window in the crankcases?

[KiwiGF]

I certainly would have considered the steel rods at that price....albeit I cannot see me breaking my small journal billet ones!......but do MAP only large journal rods?

[Brucie64]

These steel rods look nice.
http://www.ebay.com/itm/BSA-A10-Late-Model-Connecting-Rods-Conrods-Steel-4340-Forged-H-Beam-/251495166069

I think Carillo also do steels but I have no idea of the price.

Certainly a big debate over what's best long term....steel or billet alloy. I think SRM advise alloy rods should be changed every 30 years, not sure if its the same recommendations for steel or not (either way these would certainly see my riding days out)