A10 STD Gearbox

[RESTORER]

Hi, please see grub screw item 2 in this sketch from the Haynes book. Does the grub screw lock on to the casing or the selector rod? My grub screw has rusted so badly that the screwdriver slot is broken off and the screw may well be seized so it looks like I will have to drill it out or find some way of extracting it carefully (all the components are still inside the casing).  I have a new grub screw waiting but need to know more about the hole to assess how to do the job.  Can anybody supply me with a section through the hole, screw and selector rod to show the assembly, or describe what happens?  Fag packet sketches are fine.  I have looked through the forum history but not found this problem reported.  Has anyone overcome this problem in the past?  Thanks for reading.

[MJM_58SR]

Hi
I'm by no means an expert but I have taken my box apart and that grub screw doesn't have any locking nut etc on mine, it screws into the casing and into a recess on the selector shaft to hold it in place. I found it needs to come out to take the gearbox apart
I can post a couple of pics if you need as it's still in bits.
Julian sent me a very good article on gearbox rebuild
Martyn

[JulianS]

Photo inside the box shows the drilling for the selector shaft you can just about see the grub screw drilling.

[RESTORER]

Thanks lads, the photo from Julian tells me I should have asked more explicit questions. I have never seen inside an empty casing or a selector rod. I misled you MJM_58SR, I should have said tighten down instead of lock down (no nut involved) and any info at all would be great. I was trying to find out if the threaded portion of the screw protrudes into the shaft hole. I have two ideas, dependent on the screw final position when fitted: 1 If I use a small drill to take out the pip, would the rod then slide out leaving me with just the grub screw body to remove and more room to work with without causing damage? 2 If the grub screw protrudes into the shaft hole it becomes a riskier job to try to extract it (after a long soak in PlusGas) if as you say this must be done before any components come out of the box. Thanks again.

[JulianS]

The threaded section does not enter the selector shaft drilling.

The photo may assist.

[RESTORER]

Thanks Julian, that is what I was after. The screw I bought from Draganfly is very short, with only three threads of 1/4 BSW, see pic, but has a socket head so if it is made out of grade 12.9 material it will be fine. I guess the u/cut in the rod will be about 5/32 (0.156) wide and the pip will tighten on to the selector rod, so it does not revolve but components can slide along it. Now all I have to do is remove the old grub screw. If there is room, maybe a longer Cap Head screw could be used and then a lock nut could also be included.

[RESTORER]

And just to close, the bits of grub screw (3) came out but unfortunately parts of the boss (2) broke away with it and looking at the different coloured metal in the breaks, the boss may possibly have been weakened already, so be wary if ever tackling this area.  Anybody selling a good 42-3005 (or 3006) casing as auction site pics don't always capture the full picture?  Incidentally, as an aside, the selector rod passes right through the casing, so when the box is in use why is that area not prone to oil leakage or have I always been lucky? Thanks.

[RESTORER]

Sorry, just one more thing: there seems to be a difference in the style these casings are numbered (see pics).  Is this because they are cast by different companies but physically should be identical? Thanks.

[JulianS]

All the A and B swinging arm gear cases are basically the same so no worries with the casting number in different positions.

[RESTORER]

Thanks Julian.

[RESTORER]

I bought another case from e-bay, cleaned it up and rebuilt the rest including new bearings.  1. The new main bearing from Draganfly is the -RS type with one seal so I have not fitted an oil seal as it seems unnecessary.  2. I have also added a bit of grease and then a very short 1/4 whit cheese head screw on top of the infamous grub screw, short enough so that when tightened it almost reaches the grub screw, does not tighten on it, but tightens on the box external face.  Any comments on the above things would be welcome. The comments on the Robinson topic (18 June) I am sure will be most helpful in a few days time as I get the box and engine back in.   Thanks.

[Allan G]

If you haven't fitted the oil seal which goes
Most outer, how do you expect to seal any oil which works past the inner race or keep any dirt out? I'm not over familiar with the A10 box but some have a drain outboard side of the bearing to stop the bearing hydraulic locking.

Also if your fitting a new case with a different cover then it wouldn't be a bad thing to change the bushes and line ream them.

Back to the oil seal, I believe they can be a pig to fit but as I found out recently with my A65, if you have the case heat soaked to about 200° or more, the oil seal goes in quite easily
With little to no tapping to get it in place.

[DAVE BRADY]

Morning Restorer,

I would still fit the std. oil seal to protect the bearing seal.  As the inner race of the bearing rotates then so does any dirt that gets in and plenty of it will.  This could abrade the bearing seal rendering it ineffective.
If the old seal looks good and is still quite flexible then use that otherwise fit a new one.  The std. seal will also keep dirt away from the back of the sprocket and protect the splines.  There is also a special sprocket nut from SRM that incorporates a seal to stop seepage through the sleeve gear and again keeping dirt from moving parts.
A bit belt, braces and an elasticated waist but at least your trousers will not fall down.

Dave.

[JulianS]

The large circlip which retains the oil seal also ensures that the bearing remains in position.

I only see unnecessary risk, and no advantage, if you leave them out.

[Bess]

Hi,
   

a drain outboard side of the bearing to stop the bearing hydraulic locking

Interesting, how does a bearing hydraulic lock?

Thanks...