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1500 single rail gearbox rebuild?

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Scott_Hower

Scott_Hower

Luke Skywalker
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So I'm debating what to do with the gearbox in the Spitfire. It's out and sitting on my workbench. I drained the oil and removed the bellhousing. I'm trying to decide what I should do to service it. Front and rear seals are on the list, but what else should I inspect? It has 54k miles on it.

The oil was dirty, but not gritty. Gears all look good, no chips on anything that I can see, including the laygear. Reverse gear has one chipped tooth; maybe a 1/16 of an inch. The magnetic drain plug caught the fragment, plus some fine particles. It shifts fine, the shift forks and shaft are smooth.

Look like the rebuild kits include bearings and synchros and seals and a new layshaft.

I've never rebuilt a gearbox before, but I have rebuilt a few engines (successfully). I spoke to John Espisito at Quantum Mechanics and he suggested that so long as reverse is Ok, it might be best to just replace the bearings and seals and re-assemble it. How hard are bearings to replace? Do the layshaft too? Are the bearings pressed onto the input and output shafts?

Is the whole thing going to explode into a sea of tiny pieces when I remove the giant circlip on the front bearing? I have the Bentley manual and a good selection of tools.

Suggestions?
 
First off, are you experiencing any problems with it? Noisy bearings, grinding gears, ect? If not then it's probably just best to put it back in and refill with the correct oil and keep driving it. If the bearings arn't making noise or feel rough when you spin them then I wouldn't change them. Make sure you measure the endfloat of the gears before you take ANYTHING apart. That said, they are not exceptionally hard to rebuild but you should have a manual handy and be sure to have a big enough bench to lay things out in the order they come apart. Some of the parts look like they can go in either direction but you will find out when you are putting the last part in that something is backwards (ask me how I know). As long as the reverse gear doesn't have a complete tooth missing I wouldn't worry too much about it. Also if you do decide to tackle this project make sure you use a new circlip that holds the gears onto the mainshaft. This clip should not be reused and I have had to redo several boxes that someone else rebuilt and didn't want to pay the dollar for a new clip.
 
Thank you.

I'll probably replace the seals and leave it alone. It shifts fine and doesn't make any strange noises.

The PO seems to have had an affinity for silicone sealant. The top cover and the front gasket were both covered in it. The front of the case has several holes drilled in it; these were all filled with blobs of sealer behind the gasket.

One hole in particular (directly below the selector shaft) isnt covered by the gasket or the bellhousing; is this normal? Seems like gearbox oil can slosh into the bellhousing and onto the clutch? The top cover is vented, so i'm guessing it's not a vent hole.
 
Actually Scott I put random bits of silicone sealer on everything when I test drove it just to drive you crazy...









Ha. I'd just put it back and drive it.
 
tdskip said:
Actually Scott I put random bits of silicone sealer on everything when I test drove it just to drive you crazy...









Ha. I'd just put it back and drive it.
Click to expand...

Ha, I should have known!

You should see the engine. It's a work of art.
 
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