Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Crankshaft Decisions (now with pics)

Build goals:

-Dead reliable

-Limit vibration

-A pip more power

What I got:

-1973 T140V cases

What I want to do:

-Nikasil Triples Rule T120 Big Bore Kit

-Long Rods

-10 Stud T140 Bonneville Head

Question:

I have two current choices for a crank. Choice 1 is an NOS TSS crank sans flywheel. Choice 2 is an NOS T140 crank

I can get the long rods to fit the TSS crank from Thunder Engineering, so that's no issue.

Given that, which would you choose?

you can also buy a dead reliable billet crank from rody crankshafts.

good to high rpm, light, and you can install higher lift cams without machining

tough units. i threw a rod on one and it went back in after a 10 under regrind.

What are we talking pricewise? Do you have contact info? I've searched, but so far, no joy.

Well a TSS or any other crank isn’t of any use without a flywheel.

Will a T140 flywheel come off that crank and go on the TSS crank? I’ve no idea, and even if it could, I can’t imagine it to be an easy operation.

What engineering facilities/support/abilities do you have? You will need a fair amount minimum if using the TSS crank.
I’d suggest talking with Tigernuts who I believe has or is doing a similar thing.

Are you into racing? Or ordinary road use?
I only ask, because I wouldn’t see the point of going to all the TSS trouble for road use.
But that’s only my take on it.

Best of.

https://www.yellowpages.com/plymouth-mi/mip/rody-machining-6041454

greg blagus. he makes flat track cranks for BSAs and triumphs. he starts wiyh a blank T140 crank and then cuts it to fit whatever bearimgs youre using. i had to have him narrow mine to fit into T120 cases. its been inside two engines now


theyre expensive. $1600 plus custom balancing. but like i said, its a forevrr crankshaft that will last the life of the machine without any diffivulty at all.

even if this isnt what yoore looking for, you have a price now for a top of the line crank to bargain with when somepne tells you his unit is the best there is

Is there anything wrong with your NOS T140 crank? If its good, why not go with that?

I don't have an NOS crank. I have two, very rusty T140 cranks. Believe me, if I had an NOS crank on hand, that's exactly what I'd go with.

How much power and rpm do you expect?

Reading what Tigernuts has been up to is what gave me the TSS idea. It appears it's a direct fit except for the rods, and those can be had from Thunder Engineering (where Tigernuts got his).

As for the bike, it's for road use. But you have to remember, I'm in the US, where highways are long and speed limits on said highways are 70 and 75 mph. Also, reading what John Healy has written about the T12/T140 cranks cracking (and thus, every used crank being somewhat of an expensive crapshoot), and given I'm already without any sort of crank, I figure I should go as best as I can afford.

Frankly, given what Kevin posted, I'm very tempted to go with the Ro-Dy Machining crank.

T140V cases
Ro-Dy Crank
Nikasil Barrel
Nice Cams (have to look into these)
I've thought of contacting Robert Oswald at QPD about an E-Start conversion
1969 TR6R frame
XS650 Front End w/dual discs (ran this before the bike came off the road)
As "stock" or "second day" looking as I can make it

Sorry, I must have misunderstood this from your original post:

"Question:

I have two current choices for a crank. Choice 1 is an NOS TSS crank sans flywheel. Choice 2 is an NOS T140 crank"

Even so, my concerns in post #824896 still apply.

If you have the skills and facilities, you can do anything, if not then don't stray too far from standard.

That's all.

The choices were cranks I have found but not yet purchased. The confusion is on my part, I think.

Power? Like I said, a pip over stock. I don't want to go race-bike crazy, but a couple extra ponies wouldn't hurt.

RPM... and that's the kicker, ain't it? As I indicated to others, I'd like to be able to chase it up the highway at 75mph for an hour without worry.

My bone stock 72 T120RV has done many, many miles at 75/85. Once in Nevada I covered 90 miles in less than an hour. These old turds are way tougher than most people think.

I just figure, since I need a crank, and God knows what I'm going to find used...

That Ro-Dy crank is looking better and better.

A stock crank will do in my opinion...Have it magnified and then ntrided....

I think there may be a touch of crank paranoia here.
Of course JohnH’s racing machines have broken cranks, that is the nature of racing.

How many road-going Triumphs have broken their cranks? Other than a couple of reports on the net, I’ve not known one example amongst my few dozen associates in 40+ years.

I don’t think it is a real concern for road bikes doing 70mph.
If you’re often doing 6000-7000rpm then it’s a different matter, and magnaflux or an expensive crank may be best.

Thousands of us still use old cranks (mine must be at least ~65 years old as its 3-piece) and maybe it will blow apart tomorrow, but I’ve expected that to happen for the 40 years I’ve owned it. Triumph cranks are not that fragile, certainly not the 650/750 variety.

I’m sure Tigernuts has his reasons for using the TSS crank, I haven’t followed the story, but I can’t imagine it as a reason for T140 owners to be replacing their cranks with TSS cranks surely?

If there’s a strength in B range Triumph engines, it’s the crank, they last for such a long time. The valve gear, bores and pistons, that’s another matter.

If all you want is a road bike, don’t waste thousands on a crank, spend half the dosh all over the engine.

Only my view.

You're probably quite right about the paranoia...

And when the bike was together 25 years ago, I thrashed it and didn't worry so much. After all, the crank was only 25, back then.

They're 50, now.

Then again, having the crank magnafluxed, polishing the whole crank, and then having it nitrided should create a pretty durable crank as well, and for a lot less.

I can guess what dosh is but where does it come from? It's roots.

No amount of logic can counter paranoia!

And its all a probability judgement of your crank anyway.

Have you owned this from new?

You know how the crank has been used in the last 25 years (it hasn’t been used?) so it was used for the previous 20 years? I can’t remember the story of your bike, any idea of how many miles on the engine?
What are the bores like? That may give some indication.

Is the original crank one of the rusty ones? Is it so bad so as to be irrecoverable?

You can see where I’m going, your best bet is your original crank.

I've owned the bike since the late 80s--bought it as a box of bit, only some of which seemed to be related.

About 15 years ago, it was disassembled for a rebuild (mild rod knock), and... well... life happened.

It's now been through 3 moves, and was stored, all apart, in a storage unit. I hosed most everything metal down with WD40, and most everything is in perfect shape. Except the cranks (I actually have 2). I guess I forgot to give them their bath, because they rusted up something fierce.

The rod journals, of course, can be cut undersized. But the main journals and the snout are quite pitted.

Thanks.
Rust often looks worse than it is. I think you need to wire wool it off to see where you are.
Any serious pits, grooving, wear on the big end journals will likely need grinding.
Such stuff on the main journals may be survivable, as may be the nose (depending whether it is where the seal contacts).

I’d be surprised if the crank is lost, but we’ll only know after you’ve cleaned the main bearing journals and measured them (show us pics if you can).

I'd agree with everyone who's saying that standard T140 cranks are fine, as long as they're crack tested (Magnaflux or similar), and haven't been abused. There are quite a few ways of abusing them, from punching the sludge trap plug area to death, to mushrooming the oil feed nose with hammers (depressingly common, judging by the number I've seen for sale of Ebay that have suffered this), to running with a loose rotor nut, which hammers the rotor keyway and can even hammer the sprocket splines. I wouldn't buy a crank that had been reground, only one on std and without measurable wear. But if all these potential flaws are absent, and the crack test is passed, I wouldn't hesitate to use such a crank for a normal road bike expected to cruise at a gentle 75mph. I tend to sit at between 80 and 85 on my TR7 when on the autoroutes in France, briefly over 90 for overtaking.

The only reason for my TSS crank is that I stumbled across it incredibly cheap (£125) on Ebay, being sold by someone who didn't know what it was. I paid the 'Buy It Now' asking price and took a gamble - it looked really good in the photos, though without measurements, there was a chance it was a Harris T140 crank (which are essentially TSS cranks but with the big end journals ground to standard T140 big end diameters). I was lucky, it was a TSS. Steve Campbell told me it was the best he'd seen that wasn't brand new - hardly used, in his opinion.

I needed a set of new rods in any case so, for the £40 extra for the pair (£320 as opposed to £280 for T140 Thunder rods), it made perfect sense. I had wanted to build a really fast engine anyway, so that's where the TSS crank is going. An additional advantage of the TSS cranks is supposedly a smoother engine, due to reduced crank flexure.

One of the cranks on my double 650 Triumph land speed race bike had slightly undersized main bearing journals. I decided the fit was too loose...The shop doing the machine work suggested having the mains spray welded. This involves grinding about .010 off the shaft, welding in a controlled process and then grinding to size. I had my doubts but the shop with considerable auto racing engine experience thought if would be fine in this situation.Both cranks were sent out for Tufftriding.
After I completed the bike it went on the chassis dyno for tuning and reliability testing consisting up running the engines at full power near 7500 rpm for 15 seconds , 6 consecutive runs....I felt for sure the dyno room would be littered with pre unit Triumph parts...Nothing broke...
In hind sight the crank welding and machine work cost $200....a replacement may have cost less.

Here are the two cranks I currently have.

As you can see, I think they're pretty much shot.

Crank 1 (this one also has a mushroomed end)



Crank 2

i am personally a believer in paying more so i can worry less. my crank has seen 9000 rpm through the mile lights one time, and 8000 pretty often. i have zero worries about it cracking, bending, or breaking something else.









certainly it might be overkill for a street bike, but the day you spin the crank past the last hour of its fatigue life and it blows up, you lose the motor.

actually, with this crank, you lose the cases. this crank was blown up once already and was tough enough to come right back: