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#864343 11/27/21 1:16 pm
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A year or so ago, my 71 650 started making a bad noise while I was riding. It was trucked home. It was disassembled yesterday to find a trashed big end on the timing side. Bearing and crank. The drive side looks new, no damage at all. All 4 rod bolts came off with similar resistance so nothing loosened there. Barely anything in the sludge tube.
Another racer who grew up with Triumphs has said that he has seen rod big ends let go on multiple occasions and they almost all are timing side failures. Can anyone shed light on this? Seems odd that the feed side of the crank would be more likely to fail than the away side.
Thanks

Triumphs on eBay
Mike Baker #864355 11/27/21 2:21 pm
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My experience has always been drive side failures. Probably the reason that there are many more timing side crankcase halves for sale! As you have had a timing side fail, it's much more likely that a bit of cr*p got in there.

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Mike Baker #864361 11/27/21 3:04 pm
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Mike, you have photos?


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
Mike Baker #864362 11/27/21 3:09 pm
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The full volume of oil entering the crank is decreased by the oil coming out the first big end on the timing side, leaving less oil going to the driveside big end, so same pressure but less volume makes for a less happy shell bearing with the likelyhood of maintaining oil film thickness dropping.

Mike Baker #864376 11/27/21 5:49 pm
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Oil starvation of the left con rod is the curse of the BSA A65. Bushing-feed oil system is the main culprit.

It appears it's less of a problem in the TRIUMPH family die to the quill-feed system.

Mike Baker #864388 11/27/21 8:20 pm
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Triumphs have feathers?


1968 T120R
1972 T120RV
Any advice given is without a warranty expressed or implied.
desco #864390 11/27/21 8:33 pm
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Originally Posted by desco
Triumphs have feathers?


Nope and no quill feed either.


Amateur Loctite enthusiast.
Mike Baker #864415 11/27/21 11:40 pm
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Worn out oil pump ?

Mike Baker #864421 11/28/21 12:25 am
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It would certainly make more sense if the drive side failed. It's pretty apparent that it got starved of oil while the other rod was fine.

I had a motor long ago that wouldn't make over 20 lbs pressure. I rode it for 2 years before figuring out that someone had cut the feed end of the crank off enough that it didn't engage the seal but enough that it could pick up oil. 2 years at 20 lbs and no measurable wear on the big ends.

I sent Tony a photo, maybe he can post it

At this point, it'll get fixed and we'll try again

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Mike Baker #864438 11/28/21 4:56 am
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this

8061CE61-1D81-49C3-9343-6BD31B3103B8.jpeg

79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
Mike Baker #864506 11/28/21 6:17 pm
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Classic fatigued bearings (page 5) on the 2 inner edges with the mottled effect and oil starvation where the oil film has disappeared everywhere else (page 8).

https://www.speedperf6rmanc3.com/content/Engine%20Bearings.pdf

Mike Baker #864521 11/28/21 8:01 pm
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Thanks K. Good reference.
This motor was a fairly high mileage engine that has also seen track duty.
Thanks for posting the pic, Tony

Mike Baker #864526 11/28/21 8:20 pm
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Hi Mike, Thinking of your old crank with short snout, what rpm was your 20#?

After installing rods I always fill crank with oil using pumper oil can. This time specifically watched rods for oil coming out. Pretty much came out exact same time & volume. I played around with this spinning rods etc. Visually both sides seemed same from pumper can. 900-4000 rpm who knows?

The sludge trap is huge. The space around sludge trap is huge.

Generally fluids want to fill the space. However particulates in a fluid will mostly flow past openings to the farthest one. I’ve seen this many times in sprinkler systems. Fluid dynamics do odd things.

Keeping this in mind if cap didn’t come loose then both feed holes in journal were blocked. Or low oil volume into crank?? Could that do it? I don’t know.

The feed hole to crank is 3/16”. Plenty large ent for 2 rods.
But if the sludge trap plug is too deep it will partly block oil feed. Pressure test & warning light show perfect. But volume to rods is low. But why to just one rod?

On my crank after cleaning up threads the plug went too deep. I chamfered a flat in bottom of plug.


Thing is these problems have a cause. If cause is not found & corrected it will reoccur. I’ve seen this many times at work. The root problem must be corrected. No problem “just happens”.
Don


1973 Tiger 750
Mike Baker #864534 11/28/21 8:48 pm
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Kommando knows his bearing stuff.
However, even assuming this engine was used VERY hard, that this failure occurred on the timing side (or at all) still requires some explanation.

When I look at the shell pic I see what appears to be a central groove worn through the softer metal.

The oil hole in the journal appears to have material within it (doesn’t look circular).
Also, that hole doesn’t seem to have the relief fore and aft which is usual on a Triumph crank (perhaps lost through regrinds?).

I just wonder if some gritty material may have got into the oil tank/supply.
Such will very readily exit into the timing side bigend, but very little will reach the drive side bigend (because the sludge trap will have done its job by then).
Only the drive side bigend is protected by the sludge trap from abrasive material entering the crank.

Kommando said:
“The full volume of oil entering the crank is decreased by the oil coming out the first big end on the timing side, leaving less oil going to the driveside big end, so same pressure but less volume makes for a less happy shell bearing with the likelyhood of maintaining oil film thickness dropping.”

I’m not so sure about that. Assuming the crank oil cavity is kept full, as indicated by at least some oil pressure, there will be an equal availability of oil to both bigends, and both will take what they allow to pass through their clearances at the enormous centrifugal pressures.

40, 50 or 60 psi is probably unnecessary in a Triumph twin, but rather a consequence of ensuring a minimum of say 10 psi at idling. Hence the relief valve at~60 and the later warning light at~7-10 psi.

Pre-unit Triumphs survived very well with their leaky bush for more than 20 years (prior to the unit seal) and didn’t have a reputation for bigend failure, even when the bigends were smaller.

Over the decades Triumph have introduced the feed oil seal and increased the pump capacity.
The former saved time and money on accurate machining, the latter I suspect may have been connected with diverting oil to the exhaust tappet.

Just thoughts…

Mike Baker #864537 11/28/21 8:56 pm
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Hi Koan; what is exactly the relief fore and aft that you mention? I have 2 crankshafts to inspection.

Thanks

Mike Baker #864549 11/28/21 10:28 pm
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Hi Reverb,

It may not apply to newer Triumphs, I've had a quick look at can only find it on pics of P/U cranks, like this one:

[Linked Image from i.postimg.cc]

Mine is just like that, I just assumed the same with later cranks (I've never seen one).

I imagine there was a good reason for going to that trouble (perhaps a more gradual introduction of particles to the shell).

Of course it would have saved a few pennies to miss that machining out.

The best.

koan58 #864556 11/28/21 10:59 pm
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The later cranks also had the relieved area around the oil outlet holes, but it was machined with a circular cutter rather than passing a flat-ended cutter across the oil hole. As you suggest, the depth of these depressions can indicate whether a crank has been reground. I guess some engineers will go to the trouble of refreshing these as part of the regrinding job but I suspect many don't.


If anything other than a blank space is visible here, something's wrong.
Mike Baker #864589 11/29/21 6:56 am
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Hi All, Thinking out loud… Oil enters end of sludge trap. Oil exit holes are not far apart on sludge trap. Oil exits sludge trap towards inside of crank. Meaning center line of main bearings.

Then oil makes u-turn fills area around outside of sludge tube. Finally oil enters the actual bearing feed bores 90 degrees to sludge tube tube exit bores.
How does this oil path cause different volume? How different is the volume? I don’t know.

Regarding the chamfer of journal bore I don’t know how much difference it truly makes. Many years ago I worked in automotive speed shop. Many older v-8 crank shafts had no chamfering stop all. Bore was drilled crank ground, bore left with sharp edge. Bearings lasted easily 100000 miles. At the speed shop we ground round chamfer. It was thought it promote more even spread of oil on insert improving hydraulic wedge of oil. Pretty much every higher performance motor has chamfered oil holes. Most round or oval, some rectangular. All seem to work well. How do they determine best size of chamfer? I don’t know.

For the higher rpm builds we’d run about 1/2-3/4 though more clearance. At same time used larger capacity oil pump. Depending on hydraulic lifters/type we’d raise pressure. Hydraulic wedge generates heat. The thought was extra clearance with increased volume kept crank & inserts cooler. On solid lifter builds we’d run 70+# pressure. Again most high performance motors run high oil pressure. Mercedes cranks run very high pressure. 300-500k miles almost zero wear. A handful of diesels had over million miles. Head & crank never off. All Mercedes cranks are chamfered like Triumphs.

Actually Triumphs were a pretty high performance motors & well engineered. Machining & assembly at factory maybe wasn’t the best. No center main bearing is huge weakness at higher rpm. I know Turner had to put twin in frame made for single. Too bad they stuck with it. Keep the oil changed & pump & rod insert problems are pretty rare.

I’ve observed running a 650 or 750 twin up near red line invites disaster & shortened motor life.
Don


1973 Tiger 750
Mike Baker #864596 11/29/21 8:57 am
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I'm wondering if the bearing failure was caused by Detonation, it is given as a possible cause of failure on page 5 of the Clevite pdf form Kommando's link and is as follows " If the entire bearing surface shows this condition, it’s an indication of overloading, possibly due to detonation"

I've seen many a Triumph cylinder head with detonation issue on one cylinder only and it is every bit as common for the timing side to be badly effected as it is for the drive side cylinder.


1971 BSA B25T (built as replica of proposed 1972 B25T)
1971 BSA B50 Project
1972 BSA A65L
1974 Triumph T120V
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Mike Baker #864641 11/29/21 6:20 pm
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Hi John Harvey; here is what I found the other day when I dismantled the engine due to the crankshaft broke.
TS shell bearings.
Were perfect lubricated when I disengaged from the connecting rods. The DS ones only have an slight line in the middle. Both journals good. 0.010 under.
I noticed an ugly odor with these ones and not with the DS bearings.

--if you click and maximize you will see the carnage

DSCF7775.JPG DSCF7780.JPG DSCF7781.JPG
Mike Baker #864643 11/29/21 6:49 pm
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Hello Fernando,
I'd expect that, it was the timing side crank that broke, so it was moving around all over the place!
Cheers,
Mick.

TinkererToo #864650 11/29/21 7:16 pm
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Originally Posted by TinkererToo
Hello Fernando,
I'd expect that, it was the timing side crank that broke, so it was moving around all over the place!
Cheers,
Mick.
+1
if your crank has broken... pretty much anything else would secondary to that failure


1971 BSA B25T (built as replica of proposed 1972 B25T)
1971 BSA B50 Project
1972 BSA A65L
1974 Triumph T120V
Mike Baker #864651 11/29/21 7:28 pm
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...yes; of course. I never saw shell bearings like these but I posted due to what you guys mentioned about the TS possible problems with detonation etc. PO had problems with detonation and transformed the head to try to fight it.
Anyway; very little possibility that was the other way around; I mean; failure of the TS bearings etc then failure of the crank...but I decided to upload to have more food for thought.

Mike Baker #864657 11/29/21 8:18 pm
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Reverb, food for thought for me would be knowing where the crack propagated from on your crank breakage?

Rather than hijack this thread I will start a new thread on this and would be interested to know more about what caused your crank to break.


1971 BSA B25T (built as replica of proposed 1972 B25T)
1971 BSA B50 Project
1972 BSA A65L
1974 Triumph T120V
Mike Baker #864716 11/30/21 2:19 am
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I can only speculate about what happened to mine. As stated, this was a standard grind crank, high mileage motor that served backup race duty. It was used hard but not abused. The pistons showed zero sign of detonation. It ran for a short period without a filter not long before it made noise. So, quite possibly, some trash wound up getting blown into the crank causing the initial damage and got worse from there. In any case, it will be rebuilt.
My takeaway, Don't skimp on good oil and filter.

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