BSA A65 post blow up repairs 5 Digging deeper into the blown up engine's bottom end.

[@56Spookdog]

Blown up is an understatement.

[@p--n]

I'm looking forward to the story unfolding of how Humpty the BSA power egg gets put back together again.

[@highdownmartin]

Scrambled egg

[@56Model30]

I’ve never been a fan of BSA twins, particularly the unit construction motors which seem to be fragile and lack the rugged good looks of the pre-unit motors. That said, I am looking forward to the investigation and rebuild.

[@p--n]

@@highdownmartin if not totally scrambled, it certainly well on its way to making an omelette...

[@keith-wg2de]

I had a 3000 mile old Commando conrod bolt let go at 4000rpm steady state. It was a 'Better than anyone elses' part from a specialist Norton supplier . While it took out the drive side rod, Maney alloy barrels, cam and the front of the cases I did save the crank which is still running after another 45k miles +. Not as much damage as yours, it does look like a serious overrev at some time.

[@alleyoop1234]

15 or so years ago, I rebuilt the engine in my 67 Lightning. Back then all I could find for HD rods besides Carillo was the HD Triumph rod with a steel cap. So that is what i used. Aluminum conrods have a finite life, unlike steel which is infinite.

[@georgemoskal2098]

Takes me back, would bring tears to a glass eye, oohya, seen the movie. Love your videos Paul.

[@dufus7396]

Here in Brisbane Australia I saw an A65 crank case ..for sale on FB Market place...3 week Jan 2024..will look again

[@hermangibbs8163]

Thanks Paul.

[@conradstone6719]

I agree with your diagnosis certainly the conrod breaking caused all of the damage. regards con.

[@norsehall309]

G'day Paul, thanks for your earlier reply, l have only seen so much damage too a twin motor on a bike that was hit by a car, l have had a conrode let go and pulled away from the piston did some damage to the bore made a hell of a noise but didn't go through the cases, l know not all engine failures are the same but this engine and the bike must have been doing some speed, hope you get to the bottom of this and you get paid for your efforts, cheers mate, Neil 🤠.

[@progvinyl9021]

I am sure you will find the cause of this.Good job.👍

[@martyncozens5654]

Wow, never seen anything like that before, looks like the centre bridge brace ( the bit you had to have welded up on a recent A65 crankcase) on the lefthand crank case has gone maybe the broken conrod hit that as well, I assume it was being ridden when it happened poor guy must have had to change his trousers afterward, I assume he's okay.

[@matthewharmer1656]

That's why I mirror polish conrods and fit new bolts.....

[@alleyoop1234]

That's why I bought brand new, and HD...

[@a65builder67]

hi Paul that is one hell of a mess i would say that the engine has been over revved with that amount carnage, i have seen a65s with a rod let go mostly on the left hand side but no were near that kind of mess, the only thing i can think of is that it as locked up at speed plus those con rods look to be the early type possibly 65/55 and those don't have the small holes drilled in them to squirt oil up the left hand barrel if they are the early type rod that could be a major factor as well with nigh mileage on them but just a thought. anyway Paul take care and time will tell kind regards Adrian. ps the only time i've seen that kind of damage is on the race track.

[@750triton]

A modern bike rider hit the brake which turned out to be the gear lever perhaps. Although I'd expect the primary chain to let go first.

[@alleyoop1234]

Makes me wonder how much stronger a triple row(BSA) chain is over a double row(Triumph) is, if at all..

[@guitarzanbikes1862]

I'm with you on this Paul, a down shift at high revs will do it!

[@williamnethercott4364]

Fascinating to watch the process of working out how it happened. I hadn't realised that the bottom of the drive side barrel had also been impacted. Maybe it is just a trick of the light but there seems to be a lot of carbon on the pistons for a relatively short period in service, not that it is relevant to the devastation, it just looks that way. Do the pistons move freely in the bores? No doubt you'll end up with one really good engine and a pile of scrap metal from the one that blew up.

[@shug831]

What a mess, that must have been one helluva Bang! Maybe trying the 1/4 mile on Salt Lake Flats.

[@trevortrevortsr2]

Gosh it looks like a grenades gone off - The Fatigue life of Aluminium alloy is about 25% that of steel and depending on the alloy will age harden - maybe like an aircraft the con rods just reached the end of their service life?

[@Kevin-cy9cv]

Nasty, but fascinating detective work, makes me wonder whether I should have replaced the con rods on my Triumph when I rebuilt it...

[@frankmarkovcijr5459]

Many people including me have reused conrods with no worries. I reused the conrods in my 1965 Triumph Tr-6. Rods are good forever ♾️. I wouldn't worry about it.

[@obi1kahnobee549]

That has overrevved written all over it a friend of mine who raced sidecars had a collection of similar blown engines one was caused by a missed gearchange.

[@rickconstant6106]

That's certainly done a comprehensive job on the casings. Would you trust the crankshaft after an impact like that, even if it measures up ok?

[@paulhenshaw4514]

That is the million dollar question!

[@vulgivagu]

It was a bit difficult making it out but the end of the small piece of conrod had the granulated appearance of a crystalline fracture. May have been a failure of the heat treatment when it was manufactured. This would explain such a short working life. Was it from a reliable supplier or original part?

[@neilmcintosh1200]

I'm impressed with the overall cleanliness of the unit. I'm not accustomed to 3-piece con rods. No doubt further close inspection may show which of the 2 breaks occurred first. Grim, but fascinating trying to make sense of such disaster scenes.

[@erik_dk842]

Dis-connecting rods, as I Do Cars call them.

[@alexanderpotts7308]

That's worse than when I blew my A65T way back in the 1970's

[@philmuskett265]

It looks like it's been hit with an anti-tank shell!!!!

[@simonrdew]

Whirrr BANG!

[@mickgerard6696]

There is zero chance that this occurred while someone was puttering around on a Sunday afternoon with one’s Mum riding pillion. The truth lies on the owner coming clean on what occurred moments before the mechanical maham.

[@andysmith2013]

When P&M rebuild a Trident motor, they always fit new Carillo rods.

[@dufus7396]

My take is when an engine suddenly revs without load against it this can happen..it this instance likely went into a false neutral when changing up from first to second gear...us oldies were always wary of that..newbies to these vintages not so much

[@paulhenshaw4514]

My favourite theory is a mechanical over rev, from someone changing down by mistake, when they went for the brake.

[@martinfarley2026]

looks like a stress fracture on the rod

[@grateberk6435]

Crikey! Big hole!

[@davefrench3608]

That's a bit catastrophic! Gives an idea of the forces involved when things break. It must have failed at TDC as the head is unmarked.

[@johngriffith5231]

Hi Paul could this have happened if something had jammed up or wrapped around the engine sprocket ?

[@paulhenshaw4514]

That could jam the engine suddenly, but I doubt it would harm a conrod.

[@a65builder67]

HI Paul just thought dose the main shaft turn? Adrian.

[@paulhenshaw4514]

Hi Adrian, yes it does.

[@a65builder67]

ok thanks for your quick reply Paul take care.@@paulhenshaw4514

[@basilwatson1]

nothing a bit of autosol wont fix ( any signs of fatigue cracking on rod? )

[@dog8nut]

Boy that engine went BANG big time. I've seen a fair number of blowed up British twins with holes but never like that. That engine had to be truning at fairly high revs for that much damage.

[@GTMarmot]

Wow

[@geoffreybennett2457]

I am sticking to my old 350 bullet....I did some oil in frame A65s years ago that came back from north Africa....Libya... I mentioned this in the past...they were all single carb jobs but I was never happy with them.

[@carolynmarshall3598]

Drive side piston must be seized surely?

[@paulhenshaw4514]

No, it is damaged but free.

[@carolynmarshall3598]

Any sign of contact with the valves?@@paulhenshaw4514

[@paulhenshaw4514]

None at all, thankfully!

[@MegaTubescreamer]

good heavens! certainly seems to be a failed con rod paul, no use speculating this soon til all the bits are examined, ? but it shows how much force has been generated to force that amountof casing damage ,..its just ripped it apart🤔

[@kevinphipps3644]

Best buy some JB weld

[@PatrickWhitaker-ls2cs]

Jeepers, worst I've ever seen

[@stewartellinson8846]

surely a downshift in a down for up box would actually be an upshift? If the owner stamped down on the gear lever, wouldn't the just go up a gear? Being honest, these are 55 -ish year old alloy rods. OK, they're something like hiduminium (?) but they're old, they're in a long (ish; it's relative) stroke engine with high piston speeds and lots of stress on the rods. After that long, even a microscopic imprefection could magnify and lead to failure. Short of X-raying the rods, I doubt you, or anyone, would ever have seen the flaw that lurked inside that rod for decades.

[@rickconstant6106]

A65 is 1 down, 3 up.

[@stewartellinson8846]

That stymies that theory then!! Still think age is more likely.