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Ash make sure you check the main caps out too - if it was a violent break, or very rough running then it may have ovalled the forward one. Worth getting checked properly prior to wasting a set of bearings and a lot of time assembling.

 

Tony

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Very sad really, Protek had done a lovely job of the engine and it's still as good as new, but for the crankshaft. Maybe the harmonic damper and thin fan belt conversion is a must.

 

Here's a proper crank

 

7637718602_0002d66237_b.jpg

 

And the poor old TR

 

7637721376_e5be44f654_b.jpg

 

 

 

7637726106_f9d827acd8_b.jpg

Edited by Ashley James
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Ouch!

 

I agree with Brian C about the SDF looking into the supply of 4 cylinder cranks. I had to replace my crank in the 4 recently, and it wasn't easy getting a decent one at a reasonable price. A few years ago (2004) we had the oil pump go on our 3, and a good friend got hold of one for £15 at Malvern!!

 

Many cranks must be coming to the end of their "regrindable" lives now, so it will only get worse, or can they be saved?

 

Mike

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Hi Ash,

could you take a photo of the crack face on the small section - as square on as possible.

It looks as thouigh it has started on the corner/radius of the big-end journal to web interface.

The damaged area is where it clattered in the engine.

 

I am suprised it has gone here as it is usually #4 big-end that dies.

What fan, damper etc arrangements did you have.

 

Roger

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It's nowhere near the big end Roger but there is an oil hole through where it started.

 

The engine was built and balanced by Protek 57,000 miles ago and it's still as new, so they did a good job. It has a wide belt pully and no fan.

 

I'll fit a narrow belt conversion in case that's the reason.

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Have another look - grab hold of #1 big-end. You will notice the front web is missing.

It looks as thought the crack has started in the relief radius at the edges of the BE journal.

 

The big-end journals are much smaller and take the brunt of any flexing.

Usually the front end is quite flexible and and doesn't cause a mess.

The #4 BE journal has to re-act against the flywheel - the flywheel always wins.

 

Roger

Edited by RogerH
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Ash,

 

All you need for the liners is a big thick washer an old socket and the headbolt. Each washer will hold down two liners using the appropriate head stud, although you might need to enlarge the hole to fit.

 

Simples!

 

Willie

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I think Neil is correct. The front end is very forgiving in that it has some flex and this reduces the stresses of bending on the BE/Web radius.

The mechanical fan would stiffen it up very slightly but shouldn't do anything serious.

A particularly high stress raiser in these areas are machine marks when the undercut radius is put in.

 

It would be nice to see it in the raw.

 

Roger

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Jobbies to hold the liners down..... I seem to recall I slid old gudgeon pins over the head studs and bolted them down - similar bits of tube should do.

Rod

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I had an expert look at for me and I'm told there is a fatigue crack starting at the edge of the big end and then a break. Problem probably initiated by crank grinder who did not leave a reasonable radius at the sides of the big end journals.

 

I'm just waiting for the new crank now!

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This raises an interesting issue for me.

I have a 4A crank that has a 'small' crack at the #4 BE position (where they normally go).

I have a cunning plan to have the crack machined off. This would require crack testing at machining intervals - 0.010" or so - followed by a safety cut - 0.005".

 

So my question would be 'how much could you take off with some assurance that it will not snap'.

 

Is there a minimum dimension for the BE undercut and what would be the best radius for the undercut.

 

Taking the absurd one step further could the crack be welded and then machined!!!! :blink::wacko:

 

Roger

Edited by RogerH
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With the chronic shortage of usable cranks and no plan to re-manufacture them, I don't think we can afford to not investigate any glimmer of hope in resurrecting what is left.

 

When the stock of unbroken cranks got down to primarily those with greater than 30 thou under-size journals, there were discussions about metal spraying as a last resort. This was probably 10 years or so ago. I believe methods of dealing with cracks were also discussed.

 

This is not a new problem - just one that has been ignored for far too long). I wonder if anyone reading this Forum has either tried it or has any constructive comments or alternative suggestions.

 

[i know the ultimate solution is to have a solid steel crank but I doubt that many would be able to justify the cost of going down that route except for competition or very serious fast road use].

Edited by BrianC
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Hi Roger,

 

it's been done before, machining off the beginnings of a crack, and it can work - I've never seen any permissible dimensions for the exercise though, probably a suck it and see technique and leave it to the engine builder's discretion. If you're opening up an excessively tight radius that initiated the problem, that has to help. But I wouldn't try it on a competition engine !! Considering just how much extra power and torque over standard spec a TR crank will take if it's balanced carefully, there surely has to be a reasonable machining margin ?

 

Given your professional background, you ought to be able to assess the possibilities a damn sight better than most of us !!

 

Cheers,

 

Alec

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Hi Brian,

the problem with under size journals could be resolved using some form of sleeving - similar to a speedi-sleeve for worn seal surfaces.

Bond the sleeve on, then grind down to a certain size/finish for bearing caps - not imposible.

 

Recovering a cracked crank is a bigger engineering task.

As you remove metal you make it weaker. But if you do it to improve stress tolerance then perhaps there is a gain.

Welding is always problematic. These cranks are not cast iron so should be able to handle the temperture variations of welding. But what heat treatment afterwards.

These are all expensive operations and the idea of new 'standard' cranks may be a better idea.

But this also brings a problem; the market at any one time isn;t big, who will stump up the bucks to produce a loss maker, and who will buy a crank if they don't need it at that moment.

 

Roger

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I don't see much difference between the potential markets for crankshafts and cylinder heads. That's why I think some sort of similar deal could be done involving the SDF and Moss, perhaps with advance pre-paid orders.

 

I was fortunate when my SAH head was wrecked (by the crank breakage!) that I had had the foresight to buy a StanPart head from Pete Buckles many years ago. I also had a couple of spare engines, one with a very good head and crank in and the other crank unknown. Even more fortunate that TRGB were able to source a recoverable crank for me so I didn't have to break either engine (both now sold). I would certainly buy at least one re-manufactured crankshaft as insurance (to sell with the car when the fateful time comes) and maybe I should consider doing the same with a cylinder head.

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Guest Mick RichardsChange...

Roger,

 

"So my question would be 'how much could you take off with some assurance that it will not snap"

 

Given that the relieving of the journal radius is undertaken by various machine shops, and having probably having undertaken at least several of them before for competition use even, I'm sure they have this dimension in mind before they start !

 

Perhaps an enquiry to some of the competition based specialists could give you an answer, TR Enterprises/Racestorations et al.

 

Mick Richards

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