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GEARBOX REBUILD


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Hi Bruce,

I wrote this earlier but didn't press the 'go' button - silly me!!.

For many years the layshaft worked well (or certainly there were very few issues and none that I heard of)

A few years ago in the mid 2010's there was a serious issue as you know,  The failure was sorted and all affected stock removed from sale.                                                      Sadly the sold items are/maybe still out there.

Just to clarify - the shaft is machined to apprx 0.010 oversize. It is then case hardened to a depth of >0.030". The heating will cause distortion.

It is then ground to size and should leave apprx >0.020" hardened surface.   How did TRiumph do it in there hay day.???  See above

Fully hardening the shaft may cause other issues

Just a technicality but the hardness testing has problems.

The Rockwell 'C' testing is for thick fully hardened samples (6mm +)

 It applies a 150Kg load and if this was applied to a case hardened sample you would get an incorrect Reading because the indenting diamond tip would be sensing the softer material underneath the case.  One of the superficial Rockwell testing gauges with a  load of 2 or 5Kg would fair better and then use a comparitor table.

Also testing round bar of small diameter has issues for the correct value you will get a lower gauge reading.

Roger

 

Roger

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1 hour ago, RogerH said:

Hi Bruce,

I wrote this earlier but didn't press the 'go' button - silly me!!.

For many years the layshaft worked well (or certainly there were very few issues and none that I heard of)

A few years ago in the mid 2010's there was a serious issue as you know,  The failure was sorted and all affected stock removed from sale.                                                      Sadly the sold items are/maybe still out there.

Just to clarify - the shaft is machined to apprx 0.010 oversize. It is then case hardened to a depth of >0.030". The heating will cause distortion.

It is then ground to size and should leave apprx >0.020" hardened surface.   How did TRiumph do it in there hay day.???  See above

Fully hardening the shaft may cause other issues

Just a technicality but the hardness testing has problems.

The Rockwell 'C' testing is for thick fully hardened samples (6mm +)

 It applies a 150Kg load and if this was applied to a case hardened sample you would get an incorrect Reading because the indenting diamond tip would be sensing the softer material underneath the case.  One of the superficial Rockwell testing gauges with a  load of 2 or 5Kg would fair better and then use a comparitor table.

Also testing round bar of small diameter has issues for the correct value you will get a lower gauge reading.

Roger

 

Roger

Roger,

The indication one is getting distortion, with that size of bar, shows to me that the soak time is not correct. As I have now found out that EN36 was the original spec for the steel and has the property of deep case hardening as well as high strength as nickel and chrome are added to EN36. There has always been a problem with the thickness of hardness because in many cases it was ground off.

Bruce.

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I would think it unusual to have a component like this subject to through hardening, as you need some capacity to accept bending and torsional loads in operation. Case hardening of a high strength steel like EN36 followed by grinding to final size and to achieve the necessary surface finish is the way to go, as you describe and as per the original design.

 

Andrew

 

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I've watched Pete Cox put the mainshaft into the centre bearing on his video and applied the Buckeye and other guides recommendations. I am having no success getting my mainshaft into the bearing. I can get it started but no amount of gentle persuasion will get it all the way home. Pete just holds the shaft while he taps the bearing home and it all fits together easily.

I'm obviously doing something wrong.

Has anybody any further techniques?

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It can be a tight fit but can be tapped on using a “soft” pipe (I used black abs plumbing pipe as o had some around.

On the other hand, you could freeze your main shaft overnight, warm up the bearing in an oven set at 120 and both the shrinkage of the shaft and expansion of the bearing should make it just slide on

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On 10/13/2021 at 12:55 PM, dblenk said:

John

apologies to sneak in on your thread but also interested in the gbox

i have been reading this as i will be reviewing my box as part of the rebuild nothing wrong with it when it went off the road 28 yrs ago but will need stripping checking etc etc

lay shaft was one to sort however cna anyone advise if just normal use (ie shows occasional meetings and the IWE) is the original way just as good

i find a lot of extra add on's these days which like the rocker feed kit not required if the cyl head rocker shaft is sorted

i ran my 5 when in my early twenties therefore red line nearly everytime and never had any issues (probably fall to bits now i jinxed it)

just looking for thoughts

david

The weak point in the TR gearbox has always been the layshaft. This in my view has been compounded by the years of poor quality replacements supplied by the usual suspects. I had a big ruck with Moss 3 years ago over the heat treatment of these shafts. Then they did something about it. But I still think that there are still plenty of soft ones in the spares system. Personally I would only buy from ORS as there's are made to the BL spec and use EN36 steel. This is what I have in my gear box as ORS rebuilt the whole unit including the O/D. My original BL one lasted 44 years @96k before I got the whine in 1st, second and third. If you buy from Moss do the file test?

Bruce

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Hi there,
I would like to remind you again there is also the problem with the diameter !! And that was partly wrong with new originals.
That's why I only use the part from the Roadster factory USA.
And please always check the cleanliness of the inside of all new parts, including piston pins! How often have I found machining residues there!

Best regards
Ralf

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1 hour ago, astontr6 said:

The weak point in the TR gearbox has always been the layshaft. This in my view has been compounded by the years of poor quality replacements supplied by the usual suspects. I had a big ruck with Moss 3 years ago over the heat treatment of these shafts. Then they did something about it. But I still think that there are still plenty of soft ones in the spares system. Personally I would only buy from ORS as there's are made to the BL spec and use EN36 steel. This is what I have in my gear box as ORS rebuilt the whole unit including the O/D. My original BL one lasted 44 years @96k before I got the whine in 1st, second and third. If you buy from Moss do the file test?

Bruce

cheers Bruce

i did replace my layshaft back in the eighties and then only did about 20K before taking off the road for 28 years so i gues i got good quality back then as original kit was still around

will check it when i strip the box and use ORS shaft if necessary

thanks

david

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  • 2 weeks later...

I posted a question on the TR5 section for help with the bearings, lots of looks but no replies.  May get more response here hopefully?

The parts I have to rebuild the box are now about 10 years old, but just not sure they are correct, one other question the open needle roller bearing for the layshaft I have has a cage locking springs on the inside of the bearing so the cage is then very had to turn, the roller will turn,  is this actually the right bearing, or should I order new ones?

And the sizes of the 2 main bearing, not sure I should fit the ones with the small balls....

John

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1 hour ago, John L said:

I posted a question on the TR5 section for help with the bearings, lots of looks but no replies.  May get more response here hopefully?

The parts I have to rebuild the box are now about 10 years old, but just not sure they are correct, one other question the open needle roller bearing for the layshaft I have has a cage locking springs on the inside of the bearing so the cage is then very had to turn, the roller will turn,  is this actually the right bearing, or should I order new ones?

And the sizes of the 2 main bearing, not sure I should fit the ones with the small balls....

John

Speak to ORS directly as they are probably the largest gearbox restorer for all makes here in the UK and they do not install sub standard parts.

Bruce.

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  • 1 year later...

To continue this older thread, I needed to replace the ring gear and clutch in the TR6 so while it was apart I fitted the gearbox I rebuilt with your assistance. The car has now done about 500kms with no obvious problems and the gearbox is far better than the one I took out. Fingers crossed.

I am now doing my TR3 gearbox. My wife and I took the car to the TR Register Concours in Stanthorpe, about 600kms from home and a round trip of about 2200kms, without any significant problems.

On its first run after we got back reverse gear was very noisy, it lost a reverse gear tooth off the layshaft piece. The gearbox was worked on not many miles ago by one of our club experts (it was a few years ago but the car wasn't used for many decades) and everything apart from the lost tooth are good. A new reverse gear, rear bearing and seals and gaskets will do it. 

Having done the TR6 box in this thread I have not had too much problem dismantling this one and am about to start reassembly. Just awaiting a centre bearing, a bit hard to come by here.

 

 

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