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1953 5t crank call
#808819 05/13/20 5:59 pm
Joined: May 2020
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Bjorn Offline OP
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Hi
35 years ago I investigated a scraping noise coming from my engine having just cruised at 85mph on the motorway.
I guessed it was a sleeve bush on the rotor I had added as it was a poor fit, however it turned out to be a split crankshaft. I have no idea how the engine didn't fly apart as the shear was almost straight through on the inside of one of the big ends. Would have been a shame as the engine and frame numbers actually matched!
Anyway, the spare bottom end I bought at the time is in a poor state of repair, and so on a chance I bought some bits which I hoped would sort things out...however measurements show my gorgeous (new) crankshaft is out of a 650. Numbers seem to have been polished off.

Ok, so shim the barrels up a mill and bombs away! Trawling through this forum has also told me I can get a bearing for the timing side that accepts the larger diamater of the new crank... happy days. Now all that I need to figure out is how to get the alternator rotor on. My other cranks had stubby ends, whereas the new one is longer, which I assume was for the sprung loaded cush drive I've seen on mag/dyno machines.
So, questions:
Where do I find this elusive bearing?

[img]https://www.facebook.com/photo/?fbid=10158070772587295&set=a.10158070772837295[/img]

Do I need to shorten the d/s shaft? looks to me like tha rotor will go over it just fine, perhaps with a sleeve bush and a simple nut rather than part#41.

[img]https://www.facebook.com/photo/?fbid=10158070807697295&set=a.10158070772837295[/img]

Are there any dimensions anywhere on #42 & #45?

[img]https://www.facebook.com/photo/?fbid=10158070807712295&set=a.10158070772837295[/img]

I'll leave the conversation about chipshields till later...
Also, my rotor is in a pretty poor state, worsened by attempting to drift out the sleeve I added years ago so it has pushed the whole center out :-/ Maybe repairable, but do any of you heroes know if there's an equivalent to a Lucas 465674?

[img] https://www.facebook.com/photo/?fbid=10158070772482295&set=a.10158070772837295[/img]

Right, thanks for getting this far! I am so looking forward to getting this back on the road. I had a gorgeous T140v as well back in the day, sadly that got lost along my many moves, so this is extra special to me.

oh how do I make the image links work??http://www.britbike.com/forums/images/icons/default/mad.gif

Last edited by Bjorn; 05/14/20 7:59 am. Reason: wth with photobucket???

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Re: 1953 5t crank call
Bjorn #808850 05/13/20 10:32 pm
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Its a bit vague.

Is it the timing side bearing you're looking for?
With a large bearing crank into early small bearing cases?

If your crank is 1 1/8" timing side journal into originally 1" cases, then you're gonna have to track down that elusive, inadequate bearing available at one time from Buffalo Bearings.

Unless you don't intend to use the machine, it is a waste of time. The adaptor bearing is even more feeble than the original 1" bearing. Better to reduce the journal to accept the original 1" bearing. IMHO.

Re: 1953 5t crank call
koan58 #808894 05/14/20 7:49 am
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Bjorn Offline OP
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Sorry Koan.. another hour to try and get the pics working... at least they are clickable now.. what a pita!
So the adapter bearings are rare and rubbish?
I suspected turning the crank down a touch would be the way forward. I'm not planning on thrashing the old girl, just a lovely plodder :-)


In theory there is no difference between theory and practice.
In practice there is.
Re: 1953 5t crank call
Bjorn #808994 05/15/20 8:01 am
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Bjørn, I see the oil feed snout on your 650 crank is shorter than normal, you may want to do something about that? Shouldn't be difficult for a competent machinist.
But you may want to consider the crank balance factor. A 650 crank with pear shaped bob weights will be balanced to 84%. You'll need to use 650 rods, but the 500 pistons are much lighter so you may end up with a BF of over 90%. For all I know it may work well enough, but it will likely tend to move the vibrations to the lower rpm's, which isn't what you want.
To be honest, I'd look to swap the 650 crank with a pre-unit one, they were balanced to 50% most years, and from what I hear they work well in 500 engines. Or try to get hold of an original 5T crank, they aren't all that rare and saves you from all the adaption work.
Rods may be an issue though, but the original rods can be bored out to take C-series shells, which can be shaped with a round file to clear the rod bolts.
Your alternator rotor is toast btw. I've actually repaired a couple with Loctite 638, but get a new one.

SR

Re: 1953 5t crank call
Bjorn #809005 05/15/20 10:27 am
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Bjorn Offline OP
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Thanks Stein... not thought too much on balance factors yet. Another rabbit hole to explore. She used to run very smoothly as I remember

There was a guy inthe UK who used to machine out the timing cover and put a rubber oil seal in there in place of the original (metal to metal) ANyway, I'll need to do this as I put a sleeve in years ago as the original crank end had been hammered. Any idea what sort of component would do this? I can't find him any more.

I'll think build this up in my spare crankcase, if I find a nice 5t crank I'll put that in the original.
Good tip on fitting shells to the rods though, I'll certainly look into that.

ANy idea where to find a new rotor? I've spent a few hours looking. Perhaps a LU466230 / LU465969 will fit, right diamater, just 1/4" thinner...


In theory there is no difference between theory and practice.
In practice there is.
Re: 1953 5t crank call
Bjorn #809180 05/17/20 12:47 pm
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Bjørn I think you have a better plan there. Far less variables to contend with, using original bits.
However, I don’t particularly like the popular oil seal conversion and have actually converted a few back to a bronze bushing. To convert back requires stepped outer diameters but isn’t very hard to do. I just feel there’s little that can go wrong with a bush, whereas a seal can burst or flip. Remember Triumph used bushings from 1937 to 1962 without it ever being highlighted as a possible weak point.

No components would hammer the snout, that would have been done by a “mechanic” some time... Easy to fix between centers in a lathe, and then a bronze bushing made to fit. I believe a thou clearance is good, it’s what I use anyway.
If the crank end our snout is badly damaged you may want to turn it down and shrink on a steel sleeve.

SR

Re: 1953 5t crank call
Bjorn #809211 05/17/20 5:06 pm
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I agree with you SR that conversion to garter seal crank feed is not strictly necessary.
We know the crank feed (assuming adequate pump performance) provides sufficient pressure to the big ends by the centrifugal action of the crankshaft.
Before I learnt this in later years, I used to worry when I saw the indicator button close at lower rpm with hot oil.

I suspect Triumph changed to the garter seal on the units for at least 2 reasons.
The bush required accurate line reaming, the seal is much more forgiving. If the timing side main bearing fails, the bush will need renewing, much more trouble than replacing the seal
The seal does provide higher pressure to the crank (less leakage)

If a pre-unit crank is used, it has a long nose for the bush. Even if you convert to garter seal, there is still enough length to keep about a half-length of bush beyond it, as a safety.
If a unit crank is used, that is not an option.

I've not bothered with the safety bush since the first few years of conversion. In its slim loneliness I found it starting to spin, so dropped it. Subsequently I've experienced one failure of the seal (and I'd not been aware of the importance of Pioneer Weston seals so just whatever seals were supplied) and that seal developed a split, ie it didn't invert.

Since the early 80's I've run an OPG, old Mini type Smiths. With the seal the pressure never goes to zero (~15psi min at hot idle), 50-60psi hot running.
When first started from cold, the gauge shoots to the peg at 100 psi then back to around 75, then with warming settles down.
I think the inversion scenario is overstated. IMHO.

Of course crank noses can wear, as can oil seals. If such a combination can be subject to high cold starting pressure, that could allow enough leeway of the lip of the oil seal to invert.
That is not a fault of the design.

Re: 1953 5t crank call
koan58 #809212 05/17/20 5:45 pm
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Originally Posted by koan58
I agree with you SR that conversion to garter seal crank feed is not strictly necessary.
We know the crank feed (assuming adequate pump performance) provides sufficient pressure to the big ends by the centrifugal action of the crankshaft.
Before I learnt this in later years, I used to worry when I saw the indicator button close at lower rpm with hot oil.

I suspect Triumph changed to the garter seal on the units for at least 2 reasons.
The bush required accurate line reaming, the seal is much more forgiving. If the timing side main bearing fails, the bush will need renewing, much more trouble than replacing the seal
The seal does provide higher pressure to the crank (less leakage)
I don't buy into the centrifugal action of oil fed to the big ends in a Triumph is different than most others engines. On a plain bearing engine, oil is fed into the main bearings and then through drillways to the rod bearings. The oil is still acted on by centrifugal forces...


79 T140D, 96 900M Ducati 81 Ducati Pantah 500 ..On a bike you can out run the demons..
Re: 1953 5t crank call
Bjorn #809225 05/17/20 8:23 pm
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HB, the centrifugal bit is the same in all Brit twins, the supply to the centrifugal bit isn't.
The centre feed of Triumph & Norton is a free-flowing design, the BSA flowing through the timing side main bearing is less free flowing.
The centrifugal action only works if there is adequate supply to keep the crankshaft full. Otherwise the centrifugal action is acting on air.

Re: 1953 5t crank call
Bjorn #809363 05/18/20 8:55 pm
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I think it was Kevin Cameron who said that you can run a Triumph engine with only the head of oil from the reservoir fed straight to the end feed.
Cameron wrote this in a piece on end feed to cranks as opposed to oil fed through the mains. If it was in his CW column or in Vintage Bike I can't recall.
As you say Dave, far less restriction with end feed.

I'm looking to end feed a C series engine, but keep the main bush, shouldn't be too difficult to do. Not because I'm going to ride it a million miles, only because I want to, and to bore everyone with how clever it is.

SR

Re: 1953 5t crank call
Bjorn #809367 05/18/20 9:49 pm
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1971 T120RV (R.I.P.)
1973 T140V/TR7
1993 Ducati 900 SS
Re: 1953 5t crank call
Bjorn #809375 05/18/20 10:31 pm
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SR “I'm looking to end feed a C series engine, but keep the main bush, shouldn't be too difficult to do.”

Will be an interesting exercise! I hope you document and photo it well for our amusement.

I haven’t had much deep involvement with the C-range. Would you be able to bore the crank and extend the nose for a later timing cover?
The original oilways in the crankcase will have to be re-worked and blocked to re-route the feed to the timing cover.
The main bush oil will then be feeding in the opposite direction (in to out).

I think the reason that a plain main bearing on a crank is generally fed first is because it is the most vulnerable to oil supply. Think of the obvious ones like this one, BSA twins and the triples. The centre mains of the triples are especially vulnerable, hence the hugely more powerful pump.
Plain mains have to rely entirely on oil pressure/flow, they don’t get the centrifugal effect.

For most of the C-range life, late 50’s to about 1970, they were all the plain main design. This didn’t reveal any glaring weakness in the design for most of those years.
Some of the earlier T100’s were sh1t hot screaming machines, I’m not sure the 70’s Daytonas have anything on them performance-wise, and no reason to think that performance had outrun the plain main.
As far as I know, plain main C-range had no susceptibility to big-end wear problems either.

I suspect the change to rolling bearing timing side main (and end feed of course) was largely driven by other considerations.
A bush that should be very accurately line reamed is a pain in the bottom end, as well as the concurrent possibility of needing the journal to be reground.
Having a simple ball/roller bearing obviates all this fuss.
It also avoided much of this at the manufacturing stage.
I can also imagine T100 fans saying “why not have the same basic design as the bigger brother?”

To summarise my thoughts, your proposed change to end feed, keeping the bush, I think will benefit the big-ends (which probably didn’t need any more benefit) but the plain main has less guarantee of adequate oil flow. I’d certainly want the maximum possible pressure exerted on the system at all times, as what the bush supply will be getting is just what the big-ends leave available after they’ve taken their share.

Please don’t take this as too negative, I just wanted to give “Devil’s advocate” food for thought. I’d like to see how it works!

Best of. Dave

Re: 1953 5t crank call
Bjorn #809666 05/20/20 7:56 pm
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Hi Dave , and forgive me for the delayed response, I’m at the cabin for a week. It’s a Norwegian thing, most of us have one, or a day cruiser, caravan or an RV. Hate to be home I guess... 😅
Anyway, I take your comments in the best possible way. To be perfectly honest I’m setting out to solve a problem that isn’t really there anymore. Once upon a time it was, all my 3 engines cases have spun their timing side main bearing. However I believe it must have been due to negligence more than any design shortcomings. Racing is different, with the loads imposed overcoming the properties of the oils available at the time. I’m doing it because I want to, not because I think I need to. Or at least I plan to, I’m no Allen Millyard...

SR

Last edited by Stein Roger; 05/23/20 10:14 pm.

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