Rebuilding a gearbox

[donsayers]

Ok I have had the top covers off some of the many (broken) marina gearboxes in my collection. (Don't ask OK?)

The best of the bunch seems fine but makes a noise in first gear and reverse. Those who are familiar with the Marina box will know that this is caused by chipped teeth on the reverse idler. And a visual inspection would seem to confirm this.

Has anyone any experience of stripping a marina box. (Also identical to Spitfire single rail and TR7 4 speeder.)

What specialist tools are needed, and how difficult is it.I can run to a puller and possibly a slide hammer, but don't have access to presses.

[b_caswell]

Re: Rebuilding a gearbox

Hi Don it is pos to strip the box without any special tools.
The thing I learnt was to keep all the bits laid out in the order they come off.
Remove bellhousing (note the bottom bolt has a oil proof washer) catch the three srings that sit in the face of the box around the lay shaft. Remove the seedo drive disconnest the remote and remove the tail cover.
Drive the lay shaft out backwards and allow the lay gear to drop into the bottom.
Then using a long drift or big screw driver drive the front bearing forwards out of the casing. Protect the nose of the main shaft and drive the whole assembly backwards out of the casing. Then retrieve the lay gear AND ITS NEEDLE ROLLERS from the bottom of the box.
If you want to strip further, the shafts can be driven out of the bearings. If you want to strip the gears from the main shaft there is a tricky little circlip that sits behind the splines that you have to dig out with a couple of little screw drivers. YOU MUST USE A NEW REPLACEMENT
Check nose of main shaft and inside of input where bearing runs also the lay gear and its shaft where the needles run.... I would suggest stipping the most knackered box first as an exercise!!

[donsayers]

Re: Rebuilding a gearbox

Thanks Ben I have two knackered ones to practice on.

[donsayers]

Re: Rebuilding a gearbox

Ok well I had a go but its not as simple as described. I think that to be honest it's beyond my skill. I will simply stick the best of the ones I have in the car and maybe rebuild one of the others at leisure.

[dave]

Re: Rebuilding a gearbox

Don
i have two spitfire/herald boxes lying in my shed. Not sure of the condition of them, but were apparently ok when i got them. If they are of any use, you are welcome to them.
Dave

[jimbounden]

Re: Rebuilding a gearbox

Don
I have a 1800 marina box in bits should you subsequently find you need the odd part. Not that far away either!

[b_caswell]

Re: Rebuilding a gearbox

Hi Don Just realised that you need to drive the main shaft forward out of the bearing before then drive the rear bearing out of the casing. But I would recomend a copy of the workshop manual for reference point at least. Are you going to the shin dig ? I will bring a photo copy of a magazine article that may help. If not email your address and I will post it.

[donsayers]

Re: Rebuilding a gearbox

Thanks Ben will do. I have got as far removing the rear bearing on the gash box I am practising on, but I am having difficulty removing the speed drive gear, its plastic on a metal inner sleeve and I haven't got a long enough puller.

[b_caswell]

Re: Rebuilding a gearbox

Find an open end spanner that fits snuggly over the mainshaft and mount it in a vice, hold the box with the speedo drive behind the jaws of the spanner and drive the main shaft out from the drive. If you you do damage it and need a replacement make a note of the colour of the plastic bits as they denote the ratios Im told!

[donsayers]

Re: Rebuilding a gearbox

Thanks Ben that was very helpful.