S1 4.2 Gearbox Advice

[alid]

Hi, newcomer to the forum here. I am part way through the restoration of a US sourced 1965 S1 4.2 FHC. The car is believed to have covered 38,000 miles, but has not been particularly well looked after, with the usual bodges and bits missing which often seems to afflict US vehicles. I currently have the gearbox on the bench with the top cover removed and all looks good with no signs of wear or damage. However, there is noticeable radial play in the constant pinion shaft and I wonder if anyone can advise if this is normal. Also, is it possible to remove the shaft without disturbing the other gearbox components? Any information or advice would be much appreciated.

[abowie]

Yes there is usually some play there in the bearing.
I've not ever stripped an all synchro box as we get it done professionally on our rebuilds but if you look in the manual it shows how to do it. It looks fiddly..

[Nickleback]

Did you drive the car before removing the gearbox, how was it ?
If you didn't, then I would suggest getting it overhauled before re-installing as to find you have a problem later means the engine etc would have to be removed again.

[alid]

Many thanks for the responses. I was not able to properly assess the gearbox before I purchased the car, only enough to confirm all gears could be selected. I will get a specialist to check it over. Thanks again.

[phil.dobson@mac.com]

I can recommend Klassic transmissions. They have rebuilt a number of gearboxes for me and the trade use them. IKs a father & Son operation. Old school, great quality, very fair price, only uses proven parts.
I have no association with the company.
best regards
Phil Dobson

[alid]

Thanks Phil, beat me to it! I was about to ask for a recommendation.

[Mich7920]

Hi Alid

As Mike said, it's important to fit the gearbox one time !
I had a really good experience with Angus moss for my 4.2l gearbox.
As I'm far from him, it was important for me to have good relation and of course good work.
In England there's a lot of people who work on these gearbox. It's a privilege.
The choice is made of details.

Mich

[alid]

Hi Mich
Many thanks for the recommendation. I am not far from Angus so will make contact with him.

[Nickleback]

My gearbox had poor difficult selection in 2nd & 3rd gear both up & down the box after 99,000 original miles, Angus's contacts rebuilt it for me and it is now "as sweet as a nut" & I 'm very pleased with it

[angelw]

Hello Alid,
There should not be radial play in the front bearing. Sometimes this bearing is not a great fit in the gearbox housing and wobble of the whole assembly can be confused with radial play in this bearing. There is a caged, needle roller bearing fitted at the bottom of a blind bore in the end of the Constant Pinion Shaft (First Motion Shaft) and its more likely to be excessive clearance between this bearing and the end of the Main Shaft, the end of which locates therein. Clearance in this bearing and the Main shaft allows this slight wobble to occur when examining the gearbox on the bench and confusing it with radial play of the front bearing.

Both theses bearings can be replaced without dismantling the entire gearbox, but for the price of the bearing and the amount of work involved in getting the gearbox out of the car, we replace all the bearings if we have to work on the gearbox.

The rear most bearing in the gearbox that supports the Main Shaft is a rather special bearing that most repairers and suppliers of parts get wrong. The original bearing was made by Hoffmann and has practically no radius between the face and the bore of the inner race of the bearing at the Cir clip end of the bearing. This very small radius is important, because the Gearbox Oil Pump drives from the face of the inner race via friction. If a bearing is used that has the normal 3 to 4mm radius between the face and the bore of the inner race, then the engagement between the Oil Pump drive and the face of the inner race will only be a ring of approximately 0.5mm wide.

I've not encountered any of the many suppliers of Jaguar Parts, such as SNG Barratt, XK Unlimited, DMG, SC Parts, supplying the correct bearing.

The following pictures show the two sides of an original Hoffmann Bearing. Side One shows the face of the inner race that the Oil Pump drives from and you will note that there is a degree of scuffing of this correct width surface due to the bearing race spinning relative to the Oil Pump Drive. A large radius, such as shown in the picture of the other side of the bearing, cuts the bearing surface between the Oil Pump Drive and the face of the bearing's inner race to a minuscule amount and has little chance of successfully driving the Oil Pump much past the short term.

Cheers,

Brent for Bill

Side One.JPG (59.48 KiB) Viewed 9238 times

Side Two.JPG (56.8 KiB) Viewed 9238 times

[christopher storey]

Alidw : here in UK, we are usually able to obtain generic bearings from the major bearing manufacturers rather than pattern parts. Please can you tell us the number of the Hoffman bearing ?

[angelw]

Hello Christopher,
The Hoffmann bearing has the following markings:
M12 1/2K V3 (outer race marking)
N8668 V3 (inner race marking)

Hoffmann bearing company still exists in the UK and I recently sent a request for this bearing to them. They replied that they are able to supply, but to confirm the bearing they supply would have no radius at one end I sent the pictures that were attached to my previous Post; to that I've received no reply.

Over a few year period, we have been in contact with just about every major and minor bearing company in the world chasing the correct bearing. In all cases, the generic replacement for the correct Hoffmann bearing has a 3-4mm radius both ends of the inner race. The following pictures of the bearings supplied by Barratts and XK Unlimited respectively, show the incorrect, relatively large radius at the Cir-clip end of the bearings inner race.

If you find a supply from any of the major manufacturers, I would be please to be informed, but rather gob smacked if you do. A satisfactory work around that we employ is to:
1. Machine a recess to the extent of the radius in the end of the inner race of the bearing
2. Expansion fit ( freeze with liquid nitrogen and allow to expand to be an interference fit in the bore of the recess) a hardened ring to replace the metal removed to eradicate the radius at the end of the inner race.
3. Surface grind face of insert to ensure its flat and parallel to other end of the bearing race.

Both of the following bearings are incorrect.

Regards,

Brent for Bill

Picture of Bearing from SNG Barratt

Barratt1.JPG (11.61 KiB) Viewed 9345 times

Picture of Bearing from XK Unlimited

XK Unlimited1.JPG (91.66 KiB) Viewed 9345 times

[alid]

Brent, thank you very much for your detailed analysis. I think you are correct that I have mistaken radial play for wear in the roller bearing at the end of the constant pinion shaft.

I am now entirely convinced that this is a task which is best left to a specialist!

[Hugo]

Well, that's an interesting little puzzle about the radius (or lack thereof) on the rear bearing. I take it the oil pump drive is just pushed up against the inner face of the bearing? In which case, surely the laws of physics dictate that the area of the surfaces that are pressed together will have no bearing (haha!) on the friction generated between the two? The reduced area (with a radiused bearing) will obviously wear more quickly if there is slippage in the drive, but I presume there is not meant to be any slippage?

[gts2]

Hi,

are there any news regarding the correct rear bearing without a radius?

I'm about to rebuild a 4.2 gearbox and would need one urgently.

@ Brent
would you be willing to supply me with a modified bearing as you described in your post #12?

Raf

[angelw]

Hello Raf,
No joy with the Hoffmann company. It took 6 emails to get to the point of Hoffmann offering me the same bearing I can currently purchase here in Australia on a one off basis, but at a price of more 8 times what I pay here and only if I purchase a minimum number of 40.

Yes, we can supply you the modified bearing.

To Hugo
As can be seen in the attached picture, the oil pump drive has been skidding on the drive surface of the correct bearing. Decrease that bearing surface to around a 0.5mm margin on the commonly supplied incorrect bearing and there is Buckley's chance of the oil pump being driven for more than the short term.



Regards,

Bill

[Hugo]

Yes, it doesnt look like a very clever design. But as I said earlier, the degree of friction, or 'grip' is not dependent on the surface area. If it slips with the correct bearing, you've got nothing to lose really, by fitting a common or garden bearing with a radiused edge.

[gts2]

Yes, we can supply you the modified bearing.

pm sent

[angelw]

Hugo Wrote: Yes, it doesnt look like a very clever design. But as I said earlier, the degree of friction, or 'grip' is not dependent on the surface area. If it slips with the correct bearing, you've got nothing to lose really, by fitting a common or garden bearing with a radiused edge.

So you think a 0.5mm margin, at best, will wear as well as the around 4mm margin? Good luck with that thought. I get to see these gearboxes with both configuration of bearings and I know that it doesn't.

[Hugo]

Yes indeed the narrower contact area will wear faster. But in order to wear, it first has to slip, and in order to slip, it has to overcome the friction between the two parts, and the friction will be the same, regardless of the contact area. That's just physics. By the sound of it, these things are prone to slipping either way. I think if it were mine I would put a bead of mastic (the strong polyuretahne stuff) or Loctite in between the faces. And a bit of the correct spec Loctite on the shaft where the gear lives.
I take it there's a nut that clamps the bearing tight against the gear?
Is there a pressure relief system in there anywhere? Could it be that excess pressure is making the oil pump gear slip?
And to go right back to the beginning of this thread, the answer to the question is yes, it is normal to have a bit of play in the input shaft. The input shaft is supported in three places; the nose lives in the spigot bearing in the back of the crankshaft; the centre (main) bearing lives in the front of the gearbox casing, and there is another support bearing at the back where the nose of the mainshaft sits inside the tail of the input shaft. That is pretty much a universal set-up, although I am not familiar with these particular gearboxes. Once you remove the gearbox from the car, you have lost the front support bearing. All that holds it is the big centre bearing and the little bearing inside the mainshaft, which in turn is now only supported by the rear mainshaft bearing. So the input shaft is free to wiggle about quite a bit when it is off the car - this is quite normal.