Can anyone help with Kelvin J gearbox dimensions?

[agg221]

Hi,

 

Is there anyone with access to a J gearbox who could take some quick internal measurements? I need to know the diameter of the lower shaft. I also need to know the internal width of the gearbox case at this point, together with the centreline depth to the bottom of the case. Basically, I am trying to work out what the biggest diameter thing that will fit within the case on the output shaft is.

 

In the long-term I am looking out for the bits to reinstate the gearbox internals (currently just a straight through shaft as it's hydraulic drive), but for now I may have found a reasonably priced way to reinstate the hand start if the dimensions can accept it.

 

Thanks

Alec

[BEngo]

As it 'appens mine is in bits.  I will poke it wiv a tape tomorrow.

 

What do you mean by lower shaft diameter?  The clutch outside diameter,  the output shaft size (which was different for J2/3/4), or the size of the shaft in the back bearing which was the same for all cylinder numbers.

 

N

[agg221]

22 minutes ago, BEngo said:

As it 'appens mine is in bits.  I will poke it wiv a tape tomorrow.

 

What do you mean by lower shaft diameter?  The clutch outside diameter,  the output shaft size (which was different for J2/3/4), or the size of the shaft in the back bearing which was the same for all cylinder numbers.

 

N

Thanks for that - would be most kind of you. Bear in mind I don't actually have these bits in my gearbox (various missing bits due to the previous conversion) so I am working from a K spares list for part names. If I'm reading it correctly, ahead is engaged by an inner cone fixed to the end of the crankshaft being engaged with an outer cone attached to the clutch shaft which passes through the box front to back, on the axis of the crankshaft (not worried about what happens further astern than that at this point). It's this clutch shaft I am interested in the diameter of, as opposed to the shaft which comes into play for reverse positioned vertically above it, referred to in the spares list as 'upper spindle'. The drawing of the K box parts suggests that the clutch shaft has a major diameter with a couple of features and then steps down at the stern end (for the back bearing?). It's the major diameter I am interested in.

 

Cheers

 

Alec

 

 

Edited September 7, 2021 by agg221

[BEngo]

Your understanding of how the Kelvin box works is spot on.   I will get to the measuring later.

  Edit to add:  The double cone clutch shaft sits in the back bearing on what you describe as the major diameter.  There is then a reduced portion, on which sits a thrust ring, followed by a screw thread for the retaining nut.

Edit ends.

However, my astern clutch, double cone clutch and output shaft are all assembled in the lower half casing so I can't  measure  the clutch  shaft through the back bearing.

 

That said, if you go to Mike Skyners website there are (or were) some of my redrawn Kelvin drawings on there, including the clutch thrust box, the back bearing housing and the whitemetal bearing.  These should give you the size of the shaft.  If the drawings are no longer available post here and  I will dig them out once I am home again at the weekend.

 

N

 

 

Edited September 8, 2021 by BEngo
Add bit on shaft diameter.

[BEngo]

The hole at the front of the gearbox lower casing is 8 3/4 diameter

The ahead clutch is 8 in OD

The hole at the top of the gearbox lower casing is 8 in x 8 in.

 

There is about 1/8 clearance   between the outside of the astern clutch gear and the casing. The astern clutch gear just fits through the hole at the front of the box.

The engine ahead  thrust bearing and  housing occupies the small reduced diameter space at the front of the gearbox casing.

I would say that the largest item you could fit in the gearbox casing has to fit inside a cylinder 8 3/4 in  OD and not more than 8 in long.

 

N

[agg221]

1 minute ago, BEngo said:

The hole at the front of the gearbox lower casing is 8 3/4 diameter

The ahead clutch is 8 in OD

The hole at the top of the gearbox lower casing is 8 in x 8 in.

 

There is about 1/8 clearance   between the outside of the astern clutch gear and the casing. The astern clutch gear just fits through the hole at the front of the box.

The engine ahead  thrust bearing and  housing occupies the small reduced diameter space at the front of the gearbox casing.

I would say that the largest item you could fit in the gearbox casing has to fit inside a cylinder 8 3/4 in  OD and not more than 8 in long.

 

N

Thanks, that's perfect. If I'm reading you correctly, I can work comfortably within an envelope of 8" diameter x 8" long within the box along the axis of the shaft? That should give me plenty of room to do what I am trying to achieve.

 

I have found your drawings on Mike Skyner's site and they download fine. The shaft diameter through the gearcase bush is 2-1/8". Is that going to be the largest diameter on the shaft or is it stepped down where it goes through this (drawing in the K parts list suggested it might be)? I wondered whether the whitemetal bearing diameter may be larger, but that is not on Mike Skyner's site.

 

It all looks very promising at the moment.

Alec

[BEngo]

I think 8 dia x 8 long will leave plenty of room, (provided your crankshaft has not been modified to be longer as part of the hydraulic drive fit.)

I am fairly sure the shaft through the bush is the largest part of the shaft apart from the flange at the clutch end.    I will look at the bush drawing and my spare whitemetal bush this weekend to double check.

 

N

[agg221]

Just now, BEngo said:

I think 8 dia x 8 long will leave plenty of room, (provided your crankshaft has not been modified to be longer as part of the hydraulic drive fit.)

I am fairly sure the shaft through the bush is the largest part of the shaft apart from the flange at the clutch end.    I will look at the bush drawing and my spare whitemetal bush this weekend to double check.

 

N

Thanks, that gives me everything I need I think. The crankshaft itself was not modified, although there will be some form of coupling on there to rigidly connect to the driveshaft for the pump, but that is an extension shaft anyway so can be changed if necessary.

 

In case you (or anyone else) is interested in what I am actually trying to do here - the position is that the removal of the gearbox internals means I do not have a hand start. The electric start works fine, but on a boat which is not used continuously it is very annoying to turn up to flat batteries and have to lug them a mile up a towpath to get them charged. It also has an elderly starter-motor, so again, although in good condition and recently overhauled, if it fails at some point it will not be a quick fix. Additionally, I find it very useful to be able to slowly turn an engine over by hand to listen for the creak of the injectors if there is a fuelling issue, adjust valves etc.

 

In the longer term, I will try to find/make all the bits to put the gearbox back together (have now downloaded the relevant drawings), even if they are not immediately fitted, as that gives me more options. In the meantime, I need a long-term interim solution. Looking at the ratchet and pawl hand start on engines such as a Lister JP2, they are a very simple configuration which would fit on the output shaft. They would require some parts made as they fit to the flywheel so a boss locked to the shaft is needed to replace this. However, it turns out that the Gardner L series hand start ratchet and chainwheel works on the same principle and is an independent unit that locks to the crankshaft, so the dimension questions were to establish whether it would fit. Handedness is not an issue, as there is enough length to allow it to be fitted to the shaft either way around, so long as I can slide it to the right position that the upper chainwheel (which is still in place) aligns vertically above it. I am not likely to be lucky enough that the Gardner chainwheel is a perfect fit (and it looks the wrong type anyway) but this is not a fast running item as it only turns when hand cranking. That gives me options of modifying the chainwheel on a mill (may be possible) or skimming it off completely and bolting the right pitch chainwheel on. Once done, all I need is a collar the other side to stop the ratchet from sliding down the shaft. There is no lateral force when starting so simple collars with locking bolts will do it. The Gardner L unit has a 2" bore, with an inserted bronze bearing. I will have to look at whether it can stand to lose 1/16 off the face and if not I will need to find some material to turn up to make it, but Bearing Boys have oilite bushes in 2" ID, 2-1/4" OD and 1/16" residual wall thickness would be plenty for this.

 

So that's the plan!

Alec

[BEngo]

Sounds an  interesting project.  Being able to hand-start (on petrol) is always a satisfying confirmation that all is fairly well. It is also more impressive to gongoozlers.

 

The collar that stops my hand start chain wheel from sliding is a Jubilee clip!

 

A side issue, and not going to be a problem in your application, but it is not usually a good idea to re-size the working diameter of oilite bushes.  Machining them tends to close up the pores so they do not lubricate properly.

 

If you need material,  Rapid Metals have served me well in the past and they stock some useful sizes of leaded bronze.  Cheap that stuff ain't !

N

[agg221]

Yes - agree you shouldn't generally re-size oilite bushes. I would prefer not to but 2-1/8" does not seem to be available. I should of course use leaded bronze and cut oilways into it, but oilite is so much nicer to machine! In the end I think it will come down to how much pain I can withstand in the machining process.

 

Alec

[BEngo]

I have now dug out the gearcase bush lining drawings.  The Bush lining is  2.124 +/ - 0.001 in OD , 1.875 +/- 0.002 in ID and 4.375 in long.

 

The clutch shaft major diameter runs in the bush lining, which  in turn is retained in the gearcase bush.  The major diameter is therefore 1.873 in minus some clearance, plus nowt.

 

Referring to the picture  in the parts list (which is the same for a model J or Model K though the sizes differ).  The large diameter adjacent to the flange is the feature that runs in the gearcase bush. The next smaller diameter  is to suit the (clutch) thrust bearing and the collar.   The threaded portion matches the nut! The final portion is different sizes depending on whether it  is a 2 or a 3/4 cylinder engine and this is the bit that goes into the split sleeve type coupling to the prop shaft.

 

The astern thrust bearing fits on the outside of the gearcase bush and is retained by the 2 1/4 BSP gearcase bush nut.  The astern clutch and gear then fits on the OD of the astern thrust bearing.

 

Hope this helps.

 

N

 

[agg221]

25 minutes ago, BEngo said:

I have now dug out the gearcase bush lining drawings.  The Bush lining is  2.124 +/ - 0.001 in OD , 1.875 +/- 0.002 in ID and 4.375 in long.

 

The clutch shaft major diameter runs in the bush lining, which  in turn is retained in the gearcase bush.  The major diameter is therefore 1.873 in minus some clearance, plus nowt.

 

Referring to the picture  in the parts list (which is the same for a model J or Model K though the sizes differ).  The large diameter adjacent to the flange is the feature that runs in the gearcase bush. The next smaller diameter  is to suit the (clutch) thrust bearing and the collar.   The threaded portion matches the nut! The final portion is different sizes depending on whether it  is a 2 or a 3/4 cylinder engine and this is the bit that goes into the split sleeve type coupling to the prop shaft.

 

The astern thrust bearing fits on the outside of the gearcase bush and is retained by the 2 1/4 BSP gearcase bush nut.  The astern clutch and gear then fits on the OD of the astern thrust bearing.

 

Hope this helps.

 

N

 

Thanks for that - it's beginning to feel like you are dimensioning up most of the gearbox for me! The clutch shaft is slightly smaller than I had originally thought, but that doesn't matter as I will need to machine the parts a bit anyway.

 

In the meantime, the Gardner L starter parts have arrived in the post today and have a starting bore of 2". The chainwheel part has a bronze bush so it will be easy to turn this away and insert a new one to size. The ratchet part which clamps to the shaft is plain bored so a bush will be needed to take it down to size. Since it is not rotating it probably doesn't matter what I make that out of - a piece of steel tube is most likely to come to hand. The chainwheel is definitely wrong, and I think it would be better to get it as close as possible to the top wheel in size to achieve a 1:1 ratio on the starting handle to crankshaft, so I will probably end up turning it down and re-cutting the teeth when I know what the pitch needs to be. I suspect I will need a chain tensioner - I will probably use a flat spring like the Lister JP as it also provides a bit of friction to stop the chain inching round.

 

I am sort of planning for three phases/scenarios. The first phase is to fit this to whatever fixed shaft is currently in place; the second is to fit it to a proper clutch shaft, reinstating the bottom shaft of the box, which may or may not ever be necessary and the third phase is full reinstatement of the original box, which is not likely but would become necessary if there was an issue which prevented ongoing retention of the hydraulic box at some point, such as unavailability of parts (strangely, this is more likely to happen than the inability to keep the engine going!) It's the same line of thinking which leads to thoughts of installing a thermostart - I will generally start on petrol but the ability to get it going in the absence of a magneto and starter motor is appealing.

Alec

Edited September 10, 2021 by agg221

[BEngo]

There is no need to aim for the ability to wind the engine over by hand, at speed, if you are starting on petrol.  Unlike a diesel, where speed means better compression and higher temps in the cylinder, a petrol engine will start easily just by being pushed over compression provided there is a good  spark and a rich mixture.  Hence the impulse drive to the magneto and the priming routine.

 

Tbe original arrangement has neither chain tensioners nor adjustment, except by adding thicker gaskets.  The chain lengths and the casing dimensions are matched so that it all fits together as it needs to. 

Disengagement of the starting chain is handled by centrifugal loading on the pawls on the upper spindle gear wheel and the starting handle also has a dog clutch to the upper starting chain wheel.

 

I  could measure the pitch of the originalstarting chain, if that is helpful?

 

I would like to see some pictures as you progress, if you could please.

 

N

. 

[agg221]

2 hours ago, BEngo said:

There is no need to aim for the ability to wind the engine over by hand, at speed, if you are starting on petrol.  Unlike a diesel, where speed means better compression and higher temps in the cylinder, a petrol engine will start easily just by being pushed over compression provided there is a good  spark and a rich mixture.  Hence the impulse drive to the magneto and the priming routine.

 

Tbe original arrangement has neither chain tensioners nor adjustment, except by adding thicker gaskets.  The chain lengths and the casing dimensions are matched so that it all fits together as it needs to. 

Disengagement of the starting chain is handled by centrifugal loading on the pawls on the upper spindle gear wheel and the starting handle also has a dog clutch to the upper starting chain wheel.

 

I  could measure the pitch of the originalstarting chain, if that is helpful?

 

I would like to see some pictures as you progress, if you could please.

 

N

. 

Good point on not needing a high rotation speed - if I can avoid modifying the chain wheel it will definitely make life easier - if you are able to measure the chain pitch that would save waiting until I go back to the boat and poke around in the gearbox to see what I need to do. My thoughts over the chain tensioner are mainly because, unlike the original which was presumably designed around a particular measurement for chain length, I am somewhat stuck with how mine comes out which could be up to just under a link out and hence rather slack.

 

The Gardner unit works on the same principle with centripetal acceleration disengaging the pawl, and of course the upper spindle is still the same so still has the dog clutch intact.

 

Very happy to take pictures as this goes along. It might take a while as the boat and the lathe/mill will never be within 100 miles of one another, but I am determined to get this done!

Alec

[BEngo]

My starting chain is 1/2 in pitch.

 

N

[agg221]

2 hours ago, BEngo said:

My starting chain is 1/2 in pitch.

 

N

Cheers - the Gardner ratchet chainwheel has a 1-1/4" pitch so will definitely need the teeth re-cutting. A finer pitch is useful as even at a whole link out the chain may not be slack enough to need tensioning, which would save some work.

 

Alec

[BEngo]

Inch and a quarter seems like a huge chain  pitch and well overkill for a hand start.  It is  more like the size you would use for an excavator track final drive!.  Is the Gardner part you are using really roller chain?

 

The standard Kelvin  reverse chain (duplex, I  know) is only 3/4 in pitch. That handles 22 Horsepower for longer than the starting arrangements.

Provided the chain arrangement will hold in the chain wheels and push the engine over compression, it can be otherwise  as slack as a yak, if it has to.  I reckon you should be able to get an adequate tension by selecting the chain wheel sizes carefully.  You know that half inch steps fit the original spacing  down to upper spindle level, and can use whatever you like below that, provided it is a multiple or  sub factor of 3/4, to get an adequate tension for a daily cold start, which will experience old car style starting handle loads.

N

[agg221]

Yes, inch and a quarter is complete overkill, particularly when you consider that it only has a single pawl on the ratchet which I reckon would be the weak link in the system, I suspect it is simply a case of relatively early designs having not really sorted out the details at the time when they were made. Either that or the part I have got hold of comes off some giant ship's engine but the 2" bore suggests not.

 

While I have the current drive arrangement in place, I am planning to run the chain right down to the driveshaft where it passes through the box as I don't currently have the upper drive spindle. If the bits for the upper spindle turn up rapidly then I may change that plan. That does mean that I am not working to an as-designed distance, and my lower chainwheel will be the modified Gardner part so that won't have the original diameter either. As such, I could be the best part of a link out, but on half inch pitch that won't be much and the chain should stay engaged - as you say, it isn't going to be stressed very highly.

 

Alec