BritBike Forum logo
BritBike Sponsor BritBike Sponsor BritBike Sponsor
BritBike Sponsor

BritBike Sponsor

BritBike Sponsor
BritBike Sponsor BritBike Sponsor BritBike Sponsor
Jwood & co JRC Engineering dealers Jwood & co
Home | Sponsors, Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons, "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Member Spotlight
Spitfirebird
Spitfirebird
W MA, USA
Posts: 21
Joined: June 2006
Show All Member Profiles 
Shout Box
Search eBay for motorcycle parts in following countries
Australia, Canada, France, Holland, Italy, United Kingdom, USA
Random Gallery photo
Who's Online Now
17 registered members (Bluehighways), 199 guests, and 440 spiders.
Key: Admin, Global Mod, Mod
Newest Members
hondapete1950, Gaspare, eberhard, Norman Woollons, LandoLando
10257 Registered Users
Top Posters(30 Days)
Stuart 79
Lannis 56
Popular Topics(Views)
610,216 mail-order LSR
Forum Statistics
Forums34
Topics67,138
Posts651,510
Members10,257
Most Online3,995
Feb 13th, 2017
Like BritBike.com on Facebook

Previous Thread
Next Thread
Print Thread
Rate Thread
What breaks on a Triumph 650 twin ? #726334
02/21/18 4:00 pm
02/21/18 4:00 pm
Joined: Dec 2017
Posts: 161
England
F
ferretjuggler Offline OP
BritBike Forum member
ferretjuggler  Offline OP
BritBike Forum member
F
Joined: Dec 2017
Posts: 161
England
I've got quite a good collection of unit 650 and 750 crankcases.
There seems to be two common areas of damage.
One is around the final drive sprocket and I can only blame this on poor maintenance, owners running chains that are worn out or of an inferior quality.
You can't really blame it on poor design.
The second common area of damage is in the crankcase mouth where the cylinder barrel fits.
I always thought that the most common cause of blow ups on old Brits was a broken rod.
Close examination of the cases I've got looks more like tappet failure - the damage seems to be on the centre line where the crankcase halves join, not in line with the bore centres.
Am I barking up the wrong tree here ?

Support Your #1 BritBike Forum!

Check out British motorcycles for sale:
British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Check out British motorcycles for sale:
British Motorcycles on e-Bay UK, British motorcycles on e-Bay North America
Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726336
02/21/18 4:37 pm
02/21/18 4:37 pm
Joined: Aug 2001
Posts: 7,424
scotland
triton thrasher Offline
BritBike Forum member
triton thrasher  Offline
BritBike Forum member
Joined: Aug 2001
Posts: 7,424
scotland
We can't see what you're looking at.

Rods breaking for no reason isn't very common in road use.

Rods breaking because a bearing is seizing, maybe.


Amateur Loctite enthusiast.
Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726339
02/21/18 5:12 pm
02/21/18 5:12 pm
Joined: Oct 2003
Posts: 3,600
Emsworth, sunny south of Engla...
D
dave jones Offline
BritBike Forum member
dave jones  Offline
BritBike Forum member
D
Joined: Oct 2003
Posts: 3,600
Emsworth, sunny south of Engla...
I agree with Triton. The rods are ok if the bearings have oil. The big ends last forever, normally. I would say the weak point on a unit is the drive side main bearing. If the engine is put together carefully then this will last well. The guides and bores have to be really terrible to even make any smoke. It is a good engine.

Dave

Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726340
02/21/18 5:29 pm
02/21/18 5:29 pm
Joined: Oct 2012
Posts: 3,642
Running from demons in WNY
Hillbilly bike Offline
BritBike Forum member
Hillbilly bike  Offline
BritBike Forum member
Joined: Oct 2012
Posts: 3,642
Running from demons in WNY
Piston seizures ...almost always from poor tuning or lack of piston to cylinder clearance...Detonation caused cracked rings or pre ignition punching a hole in the piston...Again, poor tuning and or lugging the engine and or poor quality fuel are the causes..


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
Re: What breaks on a Triumph 650 twin ? [Re: Hillbilly bike] #726343
02/21/18 6:08 pm
02/21/18 6:08 pm
Joined: Aug 2001
Posts: 7,424
scotland
triton thrasher Offline
BritBike Forum member
triton thrasher  Offline
BritBike Forum member
Joined: Aug 2001
Posts: 7,424
scotland
Originally Posted by Hillbilly bike
Piston seizures ...almost always from poor tuning or lack of piston to cylinder clearance...Detonation caused cracked rings or pre ignition punching a hole in the piston...Again, poor tuning and or lugging the engine and or poor quality fuel are the causes..


That lot is so common I'm not sure if it's classed as a blow-up!


Amateur Loctite enthusiast.
Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726349
02/21/18 7:13 pm
02/21/18 7:13 pm
Joined: Jun 2007
Posts: 5,848
Maui Hawaii
HawaiianTiger Offline

BritBike Forum member
HawaiianTiger  Offline

BritBike Forum member
Joined: Jun 2007
Posts: 5,848
Maui Hawaii
I think you may be seeing evidence of ham fisted mechanics. The tappet holes in the case are sometimes broken out when people who don't know what they're doing try to separate the cases without removing the two special screws in the crankcase mouth.

It is an antique motor with antique design. It has high dome pistons and hemispherical combustion chambers when everyone else was going to flat top pistons, squish bands, narrow included valve angles, you know, modern engine designs.

Consequently, it suffers from incompatibility with modern fuels, more so that other designs. These things can be mitigated by applying some techniques during a rebuild.

All in all, I think it's the power characteristics and sound that people find pleasant and even fun. So, the bikes continue to be popular to a number of folks like us.Reliability is a factor, but no more or less than other bikes of the period.

Cheers,
Bill


Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: What breaks on a Triumph 650 twin ? [Re: HawaiianTiger] #726351
02/21/18 8:10 pm
02/21/18 8:10 pm
Joined: Aug 2001
Posts: 7,424
scotland
triton thrasher Offline
BritBike Forum member
triton thrasher  Offline
BritBike Forum member
Joined: Aug 2001
Posts: 7,424
scotland
Originally Posted by HawaiianTiger
I think you may be seeing evidence of ham fisted mechanics. The tappet holes in the case are sometimes broken out when people who don't know what they're doing try to separate the cases without removing the two special screws in the crankcase mouth.


Those thin bits can break and it doesn't matter.


Amateur Loctite enthusiast.
Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726352
02/21/18 8:10 pm
02/21/18 8:10 pm
Joined: Sep 2014
Posts: 617
Naarfuk, UK
T
Tigernuts Offline
BritBike Forum member
Tigernuts  Offline
BritBike Forum member
T
Joined: Sep 2014
Posts: 617
Naarfuk, UK
I reckon Bill's right, those two screws are easily overlooked by the ham-fisted fraternity. I have seen cases which have had these parts of the cadting busted off. I've never heard of a cam follower breaking, as in snapping. I have only come across the Stellite feet falling off, which is pretty inconvenient but doesn't tend to cause much damage in the bottom half.


If anything other than a blank space is visible here, something's wrong.
Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726353
02/21/18 8:23 pm
02/21/18 8:23 pm
Joined: Aug 2001
Posts: 7,424
scotland
triton thrasher Offline
BritBike Forum member
triton thrasher  Offline
BritBike Forum member
Joined: Aug 2001
Posts: 7,424
scotland
People break the tappet blocks trying to remove them from the barrel.


Amateur Loctite enthusiast.
Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726354
02/21/18 8:46 pm
02/21/18 8:46 pm
Joined: Nov 2012
Posts: 606
Isle of Wight, UK
K
koan58 Offline
BritBike Forum member
koan58  Offline
BritBike Forum member
K
Joined: Nov 2012
Posts: 606
Isle of Wight, UK
I’ve not had a chain (rear or primary) break or derail on any bike (other than a pushbike) and in my early years I took chains and sprockets to Armageddon.
Worst example was a rear sprocket so rounded off that to get up the incline to Aust services, had to severely tighten the chain such that as it went round I could feel the tightspot bending the swingarm/frame.
It got me a coffee, and to Newport in Wales, where I got a new chain. This got me to and fro, back home (~200 miles) and the new chain was dead. Quite a few of the roller shells had cracked off.

So, apart from in racing, there is no excuse for chain breakage.
I suspect most instances derive from rear wheel alignment issues and/or putting the “U” clip either the wrong way or not securely in place.

I had 2 blowups in my juvenile years with p/u Triumphs, 1st at 18 when I employed meccano skills to a top end job, naively pressed small end bushes into the rods, and made them fit the pins using wet and dry.
That ended with a small end opening on the M4, but knocked along until I was down the A34, when it stopped abruptly. Hid it behind a bridge, hitched home, came back with a van a week later. Luckily, only damage to rods, barrels and pistons.

The next was with an alloy 500 p/u engine I bought as seen, newly rebuilt, and it did run beautifully while I was running it in for about a month in 1979. On the way to the pub with a few others, to discuss our biking holiday to celebrate finishing uni, it locked up, doing say 30 mph. After pushing it home and opening it up, can you imagine the gloom on finding that one of the cylinder sleeves had cracked near the top, and then pulled down into the crank area? What a mess. It didn’t damage the cases though.

Ended up exchanging those bits, plus an entire road legal but shoddy Norbsa, for the engine I have used ever since. A 6T case with T120 bits in and on.
Never needed to tear it down because of bottom end issues, the 3-piece crank is still standard grind.
Still using the same cams, tappets, rockers that came with it.

I’m not clear how tappet failure would damage the cases?

Bill’s clumsiness explanation may be the answer, in which case, if it hasn’t warped the case over a wider area, they should be ok.
I believe it was only the 650’s that still had the mouth screws?

Re: What breaks on a Triumph 650 twin ? [Re: triton thrasher] #726355
02/21/18 8:53 pm
02/21/18 8:53 pm
Joined: Oct 2012
Posts: 3,642
Running from demons in WNY
Hillbilly bike Offline
BritBike Forum member
Hillbilly bike  Offline
BritBike Forum member
Joined: Oct 2012
Posts: 3,642
Running from demons in WNY
Originally Posted by triton thrasher
Originally Posted by Hillbilly bike
Piston seizures ...almost always from poor tuning or lack of piston to cylinder clearance...Detonation caused cracked rings or pre ignition punching a hole in the piston...Again, poor tuning and or lugging the engine and or poor quality fuel are the causes..


That lot is so common I'm not sure if it's classed as a blow-up!

Yeah, just wait for it to cool a bit and it's good to go again....more ring leakage but it still goes..


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726365
02/21/18 11:22 pm
02/21/18 11:22 pm
Joined: Nov 2012
Posts: 606
Isle of Wight, UK
K
koan58 Offline
BritBike Forum member
koan58  Offline
BritBike Forum member
K
Joined: Nov 2012
Posts: 606
Isle of Wight, UK
The 650's do break crankshafts, it was never uncommon at race tracks both unit and pre-unit types.
3 piece and 1 piece. Many were badly re-ground i suppose but it was a triumph weakness.

I'd imagine that happens in racing conditions with any crankshaft. Why do you say it was a triumph weakness? In comparison with what?

If they were reground improperly, is that a triumph weakness?

What they do is go onwards.

Re: What breaks on a Triumph 650 twin ? [Re: NickL] #726369
02/22/18 12:05 am
02/22/18 12:05 am
Joined: Oct 2012
Posts: 3,642
Running from demons in WNY
Hillbilly bike Offline
BritBike Forum member
Hillbilly bike  Offline
BritBike Forum member
Joined: Oct 2012
Posts: 3,642
Running from demons in WNY
Originally Posted by NickL
They broke with alarming regularity at race tracks, i had 3 go over 2 years. (i do admit one was badly ground and had a 'shoulder' on the journal)
The big end Journal is small on a triumph and allows much flexing. That was the weakness.
.


Nick, is the BSA drive side main is about .060 bigger than Triumph? It makes that much of a difference?


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726370
02/22/18 12:08 am
02/22/18 12:08 am
Joined: Nov 2012
Posts: 606
Isle of Wight, UK
K
koan58 Offline
BritBike Forum member
koan58  Offline
BritBike Forum member
K
Joined: Nov 2012
Posts: 606
Isle of Wight, UK
Fair dinkum Nick, but who was talking about racing, except when I allowed for the possibility by saying:

"I'd imagine that happens in racing conditions with any crankshaft."

Apart from boy racer times 40 years ago, I have no racing experience. What relevance does that have to the original subject?

The topic is a few crankcases, unless I'm much mistaken.

Re: What breaks on a Triumph 650 twin ? [Re: HawaiianTiger] #726376
02/22/18 12:47 am
02/22/18 12:47 am
Joined: Dec 2017
Posts: 161
England
F
ferretjuggler Offline OP
BritBike Forum member
ferretjuggler  Offline OP
BritBike Forum member
F
Joined: Dec 2017
Posts: 161
England
Originally Posted by HawaiianTiger
I think you may be seeing evidence of ham fisted mechanics. The tappet holes in the case are sometimes broken out when people who don't know what they're doing try to separate the cases without removing the two special screws in the crankcase mouth.

Cheers,
Bill



Funny but I didn't think of that even though it's the most obvious explanation.
Looking at my "collection" none of the 750 cases have damage there.
I really can't believe that people would be so stupid but not everyone is as fussy as me.
And you can't see the damage with the engine assembled.

Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726393
02/22/18 7:39 am
02/22/18 7:39 am
Joined: Aug 2001
Posts: 7,424
scotland
triton thrasher Offline
BritBike Forum member
triton thrasher  Offline
BritBike Forum member
Joined: Aug 2001
Posts: 7,424
scotland
Originally Posted by ferretjuggler

Funny but I didn't think of that even though it's the most obvious explanation.
Looking at my "collection" none of the 750 cases have damage there.


750s don't have the screws there, so far as I know.


Amateur Loctite enthusiast.
Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726431
02/22/18 5:25 pm
02/22/18 5:25 pm
Joined: Apr 2015
Posts: 454
UK
D
Dibnah Online content
BritBike Forum member
Dibnah  Online Content
BritBike Forum member
D
Joined: Apr 2015
Posts: 454
UK
With some care and modern oil these dinosaurs have a few decades in them yet.

Re: What breaks on a Triumph 650 twin ? [Re: triton thrasher] #726434
02/22/18 5:57 pm
02/22/18 5:57 pm
Joined: Dec 2017
Posts: 161
England
F
ferretjuggler Offline OP
BritBike Forum member
ferretjuggler  Offline OP
BritBike Forum member
F
Joined: Dec 2017
Posts: 161
England
Originally Posted by triton thrasher
Originally Posted by ferretjuggler

Funny but I didn't think of that even though it's the most obvious explanation.
Looking at my "collection" none of the 750 cases have damage there.


750s don't have the screws there, so far as I know.


That's exactly what I was implying.
IIRC when I assembled my '71 TR6C engine I deliberately left out those two screws.
The 750 twins dont have them, so I reasoned that they can't be critically important.
I won't have to struggle with them the next time the engine is stripped.

Re: What breaks on a Triumph 650 twin ? [Re: ferretjuggler] #726471
02/22/18 9:59 pm
02/22/18 9:59 pm
Joined: Sep 2014
Posts: 617
Naarfuk, UK
T
Tigernuts Offline
BritBike Forum member
Tigernuts  Offline
BritBike Forum member
T
Joined: Sep 2014
Posts: 617
Naarfuk, UK
Originally Posted by ferretjuggler
I really can't believe that people would be so stupid...


Sadly, judging by the horrors I've encountered when dismantling old British bikes, they are!


If anything other than a blank space is visible here, something's wrong.

Moderated by  John Healy 


Home | Sponsors | Newsletter | Regalia | Calendar | Bike Project | BritBike Museum | Spiders Cartoons | "OLD" BritBike Forum | DVD- Manuals & Parts books | BritBike Stickers & Decals
Upgrade to: Premium Membership | Premium Life Membership | Vendor Membership | Site Sponsor Membership
Powered by UBB.threads™ PHP Forum Software 7.6.1.1