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#293718 01/13/10 12:42 am
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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


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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.

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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

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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.


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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.


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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.


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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...


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Quote
on my trusty Bonneville

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


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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.


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Quote
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.


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 smile
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.

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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.


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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

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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


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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.


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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.

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


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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.


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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.


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Brizzo,

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


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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.


What d'ya mean it won't rev to 10?
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bsa a65 69 lightning that went bang

[Linked Image]
[Linked Image]

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 ??

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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.


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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.


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owner decided to replace to completely replace the motor !

Last edited by Jamie; 01/17/10 4:32 am.
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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.


When people who should have known better cautioned me about the dangers of motorcycle racing, I always told them that a fear of death is nothing more than a fear of life in disguise.
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