Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board A65 that actually 'blew up'

over the past 3 1/2 years i have been partaking of the knowledge and revelry on this forum many is the time dire warnings of A65s 'blowing up' and 'throwing a rod' because of the 'weak bottom end' have come up.....ok..who has ACTUALLY seen such a catastrophic failure??? just curious

I spun the left side bearing when it starved for oil. Rod stayed intact and was re-used once I had it reconditioned (Carillo rods with ARP bolts). Damage to the crank, however, was terminal.

Thankfully, never actually had anything come loose and exit out the case.

RAF,...Although I have not personally experienced this event, I have an A50-RA engine that has experienced it. It has a hole repair on the timing side front about 3" x 2", definitely a rod, apparently repaired with the original piece of shrapnel. So, it does happen but perhaps the frequency has been overstated. Cheers

Do racing engines count? I saw an A65 in the pits at my local dirt track with a big hole in the front of the case. If I had arrived a couple of hours earlier, I would have witnessed the destruction. They said they had to gather some bits from the track after the failure.

I came very close to disaster with my '67 Lightning when it had a cracked crankshaft. It took about three weeks to hog out the main bush and start to lose oil pressure. I was 1/2 mile from home when it started to knock, and I was able to limp it home without seizing. When I tore it down, it was evident that the big end bearings had started to melt.

I recall seeing a picture on this forum a couple of years ago of someones engine that had "let go". The front of the case had a hole similar to what Pokie described on his A50-RA. Don't remember who, what, when.

The origins of the "fragile bottom end story".
One of the US magazines ( think it was Cycle Sport ) ran an A65 ( think it was a MkIV Spit) against whatever was the "sports" HD at the time.
Ran it too hard for too long at too high revs, blew the contents of the oil tank out the exhaust pipes and threw a rod.
Some thing that will still happen with almost any modern engine now days which is one of the reasons why they fit rev limiters to just about every modern road burner.

Similar thing happened with some of the racers.( hence the origins of the end fed crank)
So naturally all BSA's will self destruct and you better go out and buy a HD instead.

These failures were picked up ,and blown out of all proportions by several of the journos at the time and in particular by one R Bacon who seems to despise Unit BSA's and British bikes in general other than his beloved Notruns.

I have been a member of the NSW BSA club for over 25 years and been a BSA rider for 40 years and have never had first hand experience of an A65 throwing a rod, not mine nor any other member ( and we did have some who punished their bikes and in out early years rode with the Notrun club regularly and naturally that meant not allowing those 860's to get ahead).
OTOH I have seen a quite a few US import A65's with the tell tale weld on the left case so it must be possible to do it if you try hard enough.
Then again there are 4 ride on mowers for sale locally because the dim wits ran them without any oil too.

My best freind siezed a rod on his A65 and shut the whole thing down before anything else could happen. I was there when it happened on my trusty Bonneville.

This was before we knew anything about a sludge trap; which was full o' sludge - so it didn't have anything to do with some weakness inherent to BSA's...

What was the expression on your face when you wrote this, Geoff?

My engine (previous owner) snapped it's crank on the LH big end journal due to stress metal fatigue. There is also a welled LH crankcase patch to match, along with a large notch on the barrel skirts.

You haven't read his book on Norton twins, have you? His opinion on the Combat motor makes A65s seem to be paragons of reliability
It was E.T who could do no wrong, but anything Bert Hopwood touched was automatically suspect.

I have a few sets of A65 cases I picked up many years ago which have had the left rod let go. The only set I know any of the history of (Mk 4 Spitfire, coincidentally) came from the original owner. He had rebuilt the motor without cleaning the sludge trap. After it blew up, he stripped it and found the sludge trap completely blocked.

When I was young and silly ( I am no longer young) I enjoyed "vigourous" motorcycling on my A65. I also enjoyed doing oil changes.

I turned off the motor (now there's a novel idea) when it developed a hell death rattle in the bottom end.

The LHS rod shells had lost all the white metal and the steel backings were all that was left, it had "machined" a Std crank down to just over -0.030"...so still one grind left. The rod bolt had streached on the leading side and I recon another few miles even nursing it it would DEFINATLEY have gone bang. The RHS journal rod and shells were perfect. When it happened I wasnt particularly ringing it, it just got louder and louder.

Still have the crank as a souvenir.

so I vote yes ....they do let go on the LHS...at least when you ring them.

I also recon that when a motor is obviuosly in distress step 1 is turn the $%%^&ing thing off before it disintergrates!...a concept that seems to elude some.

Well, then there's very non standard cracking A65 Mark Parker's :
http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=212693&gonew=1#UNREAD

stupid pun intentional

This is the one thing that made me nervous about my first BSA . I heard over and again about the bottom end failures . I have done a lot of reading about this and have participated on this forum in threads on this topic for years . The way I understand it , there was a very real problem with the early A-65 and I have seen a good many junk cases with the left cheed blown out at swapmeets over the years .It was thought to be an oiling issue or a heat issue . The company went so far as to add fins to cool the rocker cover before they discovered the problem . It seems the ignition was the culprit and they use the term "rogue spark" . This was eventually tracked down to the advance unit having a bad cam profile allowing the points to bounce at an inopportune time , thus causing excess heat leading to seizure and catastrophic failure . This was corrected with the 6CA ignition and all was well with the greatest motorcycle on earth.Triumph , luckily, used a different advance unit since they spin in the opposite direction , and was spared this bad reputation . I believe this was a conspiracy by Lucas and Triumph to discredit BSA .... makes me wonder ????

FWIW-BONZO

Looks like we haven't yet come up with any testimonials to A65s blowing up due to inherent lower end design problems, with the possible exception of the ealier AAU design.

With the 4CA AAU, with which you could not time each set of points individually, more often than not the two sets of points were not exactly 180 degrees out of phase, which meant that you either had to let one cylinder run retarded, or vary the point gaps to get both cylinders timed the same, which changes the dwell, and can cause the points with the wider gap to close on the back side of the dwell cam, causing a rogue spark, which reduces the dwell time for, and thus weakens the "real" spark.

I don't know about the difference in cam profile except for what I've heard on the board from Bonzo and others. And I don't know why Triumph was not beset by this problem, but my theory is that there was greater precision in the centering of the breaker plate over the AAU, and possibly that the Triumph points are mounted fore and aft rather than up and down.

HOWEVER, timing problems are just as likely to cause upper engine problems before damaging the lower end, so I'm still not sure we have a correlation.

In regard to racing engines, both Triumph and BSA have the inherent "weakness" of not having a center bearing on the crank. Stock cranks cannot sustain the degree of increased HP and RPMs achieved by racing engines, and no serious racer "in the day" would think of building a really hot British twin without employing a hardened or aftermarket crank.

I do not know if this counts. When I was a lot younger and thought all you had to do was just keep adding oil instead of changing it, I had a lightning seize up coming down a twisty mountain road at about 50 MPH, which was too fast for the road conditions. This was after I had pushed it hard coming up the other side. At that point I personally came close to having a bottom end failure myself until the chain let go. However, the engine did not come apart.

Try about 2/3 down page 12 of post a pic of your BSA. Is this the typical damage?

My tbolt had a large hole welded up under the crank on the drive side.Were every one said thay come apart .I Was not the owner at the time though.


Aka Homer

I had a bush motor do a rod bearing and start making a lot of noise with the piston hitting the head, plus the one in which I found the split rod (through the little oil hole up to the G/pin)which fortunately didn't let go. Plus had an old Commando rod punch holes through the R/H case on my roller converted motor when it let go in about 1999. Motor now is very reliable but has started splitting the r/h crank case, so will have to strengthen a good set of cases in that area some time soon and build the engine into them, be nice to fit a 5 speed into it at the same time.

Brizzo,

There are only 11 pages to that thread on my PC. Can you be more specific on what bike it is?

There is a guy who gets down the Ace Cafe in London known as BSA George, we were chatting about A65's a while back when I was over and he told me he had broken a crank in the sixties thrashing it down the A27 to Southend one saturday whilst out with his mates. In the late seventies I knew more than a few people with A65's one called Lightning Dave who mercilessly caned his BSA, it was often in bits and as we were generally skint in those days things like end feed conversions were the stuff of dreams, I had an XS2 at the time and I remember that in a drag race of the line the BSA was always quicker, and went round corners better, however the Yam braked better ; of all the A65's only one had bottom end trouble and it let another pal know long before it broke. My L/R seems fine, the bottom end has'nt been apart for many years despite being owned by people of very dubious mechanical ability and I'll continue to ride it, as often as possible until I've got the Triple back on the road and then I'll treat it to a rebuild. Johnny.

bsa a65 69 lightning that went bang




saw this at the local bike shop apparently he was trying to pass a semi no other details
except i was a bit worried about the new young mechanic who said it was from lack of oil in the sump ??

Photos make the thread more interesting. This is probably a good illistration of why it may be worth putting in a set of new aftermarket rods at a rebuild rather than save money and use the old rods, or s/hand ones off ebay. I'm not being critical of this owner, but there are guys that go 'I've already spent a heap on my motor, I don't want to spend the extra $400 or so on new rods, I'm not going to run it hard, (you don't have to)then buy old s/h ones and have em resized and new L/ends put in. This motor looks like it was in good nick, its very clean inside, with low comp pistons.

Mark,

From what I have seen over too many years playing with these motors, the rods, especially on early notors are the weak link. Anything goes wrong, and the rod either breaks, or goes out of round. Once out of round, the material has yielded and there is no recovery.

The later rods seem to have improved material/forging. The absolute best stock rods are the late shot peened rods. Since there are some good aftermarket rods, they are worth the money.

owner decided to replace to completely replace the motor !

Here you go: We were returning from a long ride, bombing along on the freeway at about 70mph, my buddy (an ace mechanic) on his A65 just in front of me on mine. Poof! Suddenly a cloud of oil smoke and various unrecognizable bits of aluminum flying through the air. Left rod snapped, sawed through the case and put a dent in the left front downtube.

Passed a few semis today, glad mine didnt do that.

Gary, The picture I alluded is now sitting (on my computer) at 12 out of 32 pages so a bit less than halfway through. Posted by Petersen and about 20 or so posts before your Hornet. BTW thats for the info on the cut-out switch.

Cheers
Ray

Looking at the picture of the blown engine it kind of makes me wonder how the coils are wired. It could be that there is a center wire that I cannot see for the hot lead. If not it looks like it may be wired with two 6 volt coils in series using one set of points with a waste spark like Honda twins.

I seem to recall a certain moderator setting his pants on fire when his lightning motor blew.

now if I could remember his name..........

Craig, it has the telltale red terminal insulators of a Boyer kit.

Ray, I think this it.

'69 Lightning engine on the "Show BSA" thread about page 4.

when i bought my A65T it had a "rod knock." upon teardown, the primary side piston had marks up and down the skirt where it had been grabbing the wall, and the rebuild required .060" oversize, replacing third over pistons. the wear was progressivly worse in the lubrication path away from the timing side bush, indicating poor oil pressure. i thought the bush itself was the culprit, but i've had pressure problems since the rebuild, as some of you know from my thread about it. someone had obviously been in there before with the .030 pistons, so it could have been some mistake post-factory. dunno. didn't "blow up," but it did seem to have the infamous timing bush problem...

Q: Why do Brit bikes always blow up on the left side?

A: Because that's where the serial numbers are stamped.

This engine was just idling, when the right(!) hand side rod broke. No seizure.
http://home.online.no/~oseinbu/bsa2004/veivhusventilasjon.jpg

This 1971 crank just broke, and the bike was still running. It even started after the disaster, but made funny noises...
No damage to the cases or cylinder, but rh rod got some beating.








Best regards

Is it the Lightning/Spitfire motors that blowup the LH rod? Or do the T-bolt motors do it as well. (I have a theory...)

Ola - That crack through the RH Main bearing on that crank looks like metal fatigue/manfacturers defect? The journal on the RH side looks OK?

Don't know about that. I always thought it was all Tri/BSA twins and triples. The LH rod is last in line for oil.
I know every blown triple I've ever seen has a big hole in the left case.

From what I can see in the photos you had a beautiful example of a classic brittle fatigue failure.
Best seen in the 3rd photo.
From nearest to the crank case mouth you can clearly see the step marks.
I can count about 10 of them. This was the crack propogating with each stress cycle.
Then the lower section which looks really clean is the final fracture which happens really quickly as there was now insufficient material thickness to take the load.

There is no obvious distorted ( stretched or twisted ) material so I will hazard a guess that the crank has ended up being through hardened.

It looks like the crack originated in the cheek area so it could have been some bad machining and I would look really close at the alignment of the crank case which would have made things worse.

Being that it is a bike that is 40+ years old most likely to be problem attributed to previous owners .
Well done to catch it before it disintegrated the entire motor and a bit of good luck that you were not in high speed traffic when it happened.

Old cranks should always be treated as suspect until proved to be in good condition. It is worth wile to send them to professionals to be tested and heat treated before being put into service.

Interesting Trevor. Alignment is important. The journals were fine, so most likely factory defect. The present owner bought the bike this summer with "possible engine failure", so what actually happened is hard to say. Here are some better pictures of the breakage.








Best regards

Sure hard to tell from these pictures, but it looks like a regrind without leaving the proper fillet radius. If this is so it is not a factory defect.
HTH

I concur with Trev here. And yes, for possible causes I would look at the radius (since that's where it looks like the failure originated), surface finish of the radius and hardness. It's entirely possible that coolant loss or too high of a feed in the grinding process caused the steel to go brittle in the radius.

BTW, this is my fave:

Note the oil pressure gauge right next to the rod poking through the case (on the RHS, incidentally)

John sez:

"Sure hard to tell from these pictures, but it looks like a regrind without leaving the proper fillet radius. If this is so it is not a factory defect."

What are we going to do with you John. Don't you know that it may not be BSA's fault, but they are going to get the blame for it....

Manufacturing defects are usually (but not always) relatively low time failures. After 40 years....it was something that happened AFTER BSA made the crank.... There is even that pesky thing called fatigue failure.....

I can stare at photos of catastrophic failures for HOURS.

Am I wierd?

Sound like two completely separate topics! The answer to the second is an unconditional Yes ...

Lannis

That is almost funny Alex. As if the oil pressure gage would asuage the gods of bottom end failures! What I want to know was were these twin carb or single carb bikes? (I have a theory forming in my head...) Is one more prone to bottomend failure than the other?

If it is a failure due to the removal of the proper fillet by the crank grinder, which is an important engineering detail if one wishes to be successful at this hobby, it is certainly not fatigue, but the lack of information or in most cases laziness or economic considerations on the part of the operator.

Most American crankshafts have little, if any radius ground into the bearing surface. American engineers just used mass to gain strength. Nearly all British crankshafts, because weight was a big consideration when these motors were designed, use this strength increasing feature. Without the large fillet the cranks are very prone to breaking.

Because the crank grinder has to remove a lot of material to put the wheel back in the original condition after putting the radius on the grinding wheel to grind a British crankshaft they often cut corners. That is they fail to radius the grinding wheel enough to produce a proper filet. Shops that do a lot of British work often have a dedicated machine to do the work so they don't have to constantly redress the wheel.

For the lack of a better technical term for not following the manufacturers specification for regrinds we often call it stupidity, not manufacturing defect.

The only reason I can see for the single carb bikes being less likely to blow up is that, since they do not rev as freely under load, they are less likely to spend as much time at high RPM. Some failures don't show up until you've got her pegged at 7500 rpm for a while. Also, wild-eyed boy racers would have been more attracted to the sportier twin-carb models and, hence, I would guess they are more subject to abuse.

...of course that's all just conjecture. As they like to say on that hard-hitting news show on the Simpsons: "May not have actually happened".

I have to say that over the years, on many forums, I've heard of more catastrophic BSA failures than Nortons, and more Norton failures (90% Combat related) than Triumph.

Considering the fact that I've been far more involved in Triumph forums than Norton forums, and more Norton forums than BSA forums, that only adds to the disparity in catastrophic failure frequency between these three particular "popular" British marques.

What do ya'll think? Is this observation valid?

No.

In other words which engine has the highest percentage rate???? I've seen more Triumphs seize pistons and more BSAs throw rods, Triumphs suffer more often from ameteur mechanicing, and Triumph and Bsa suffer from oil pump problems more than Nortons.
Single carb BSAs are the most reliable of the twins, the a50s lower gearing and not having enough power to hurt themselves, should make them the most reliable. Rick

Are you sure about that Alex?

Ha! Of course I'm not sure, John, but neither is GP. Spouting conventional wisdom, attaching it to what you heard some people say and thus drawing broad sweeping conclusions doesn't qualify as a valid observation to me. Not that I really care about people bagging on BSA's since that reputation as grenades is one of the things that, I think, keeps them as great bang for the buck (I think I made a pun). I mean maybe it's true...I've certainly blown up more BSA's than Trumpets or Notruns. Then again, I haven't TRIED to blow up any Trumpets or Notruns...

Just for the record. The broken crank were never regrind, and it is a Lightning.

Best regards

AH ha a Lightning you say....(two carbs -- theory get a positive stroke).

So highway, you are telling use that the fillet is radius is .120" radius (.304cm) and the journal is 1.685" (42.387mm)?

Looking at the reliefs around the oil feed holes on the journal which look like the crank has been ground and what appears to be less than the needed radius you could have fooled me. Ah, pictures can be deceiving!
HTH

The journal was ground by bits and debris after the breakage I suppose. Remember, the engine was still running, and the owner drove it home...
I measured the LH journal, and it has original diameter.

Well considering BSA's out number Notruns by something like 20 :1 one would expect to hear of more BSA/Triumph failures than Notruns.

And yes John definately looks like it started at the journal radius but not having seen as many as you could not comment about the size without measuring it.

But I can identify a brittle fracture from 100 meters.
A stress fatigue fracture can be initated by bad machining along with 100 other different causes.

To qualify for a fatigue it just has to happen over repeated stress cycles

Is there a calculation formula with shaft diametre and maximum transmitted torque (or hp per rev) to determine the correct radius?
Or do machine builders use the rule of thumb, passed on to them from father to son?

I think this was one of those moments I did not pay attention at marine engineers school.

I know this is an old thread, but I had one disintegrate, took out the cases,lifted the barrel studs clean out of the crankcase, smashed up all of the left hand side of the barrels, a short section of rod found it's way out the back of the cases through the gap and into the gearbox. Witness marks on the inside of the piston skirt and the fact that there was just a naked gudgeon pin indicated that the top came off left hand little end. This happened while touring at about 60mph, I owned the bike from new, it had about 9,000 mile on it and had always looked after the oil changes and other maintenance, never rode it particularly hard. So yep they do let go.

**ck me Lemans never seen one go bang to the point it bent the frame . how many revs were you pulling when it let go?

leemans that's pretty much exactly what my engine looked like, but I've only got a small ding in the frame tube.

Put me down as another that's had the l/h rod give out.
It was on my A65LC which I had no idea what I had back in the day.
Looking at some of the other pictures in this thread I was (if you can be in this situation) reasonably lucky.
No massive holes, but cracked through the engine serial number and around the front and on to the timing side stopping somewhere between the main bearing and engine mount.
Broke the rear base flange of the barrel.
I was only 19 at the time. Pushed it some 6 or 7 miles home!

gladly it is not my bike, but the bike from a belgian bloke.
I was searching the internet for a drawing of an A65 engine, a so called "exploded view" when google presented me that site.
but it is an impressive malfunction

I once had a conrod in a 6 cyl-diesel-engine go in a spectacular way, ended up with a 3 and 2 cyl section.
reg A

With seven more years of significant forum participation and observation, I'm revising my PERSONAL OBSERVATION results to:

Approximate percentage of blown engines between top 3 BritBike brands

Norton - 50%

BSA - 35%

Triumph - 15%

Maybe it's because Norton owners are proud of their accomplishments, Triumph owners are ashamed, and BSA owners don't care one way or the other?

Without a doubt, BSAs seem to blow in spectacular fashion, including entire sections of cases AND cylinders flopping about, bending frames, etc. Nortons tend to blow large pieces of cranks out, sometimes bending frames at the lower crossover tube. Triumphs just blow neatly, and leave it at that!

Grandpaul, would the large amount of Nortons blowing up be down to the cast iron flywheel on the commandos ?

All of them have cast iron flywheels, Nortons just seem more susceptible.

Of course my personal experience is anecdotal, as noted...

Are you sure of that ? I have never heard of triumph or bsa flywheels going, and always thought they were steel.

Okay, I was wrong (as to all being cast iron), but the argument remains the same, relatively speaking...

From the factory workshop manuals:

Crankshaft-

Norton - EN16 (high tensile steel)
Triumph - Forged Steel
BSA - Forged

As a good friend of mine pointed out, the most common Notrun with a blown crank is the rubber mounted Commando.
With the rubber mounting set up properly the rider is isolated from an engine leaping up & down screaming for mercy just before it grenades.
OTOH on our BSA your eye balls have already been shaken to the back of your head, you nuckles are white and your fillings have fallen out of your teeth well before the crank goes bang.

Makes sense...

Uhm, Bon?
I have a long time friend in SoCal, He was riding an A-10, and the flywheel broke into three pieces.

I will have all 6 cranks I'm building engines for magnafluxed.

And get them nitrided as well.
Strait nitriding will not make them harder or stronger but will increase the fracture toughness by many orders of magnitude.
So you will hear them going bang bang bang for a long time before they go boom.
It should be something like $ 10 a hit.
Note CARBO-Nitriding is a case hardening process and that will increase the hardness as well as the toughness but in that case, the one tends to cancel out the other so the net effect is a harder journal but the crank only gets a marginal increase in fracture toughness.
FWIW, fracture toughness is the resistance of the crank to propagation , not a measure of the resistance of the crank to crack in the first place.