National gearbox

[Jrtm]

Ive tried with a small gas torch still nothing,

 

Dont want to damage the gear as need to use it to make a copy so cant drill it, prob got is to get them out you only have two bolt holes to pull it from and your restricted on size of the bars due to the center shaft. Ill have to give it another shot on wednesday.

[bizzard]

Ive tried with a small gas torch still nothing,

 

Dont want to damage the gear as need to use it to make a copy so cant drill it, prob got is to get them out you only have two bolt holes to pull it from and your restricted on size of the bars due to the center shaft. Ill have to give it another shot on wednesday.

Small gas torch would only slowly heat up the whole thing and not just heat and expand the gear by itself.

[Jrtm]

Was the only thing i had dont have oxy and its not very easy to get to one either, can take it to work but its not like its a light bit of kit either,ill try again Wednesday if not ill have to speak to work. Not exactly a bmw part!

Edited February 5, 2017 by billybobbooth

[Mikexx]

Dont want to damage the gear as need to use it to make a copy so cant drill it, prob got is to get them out you only have two bolt holes to pull it from and your restricted on size of the bars due to the center shaft. Ill have to give it another shot on wednesday.

 

I understand the sentiment, but a gear specialist will want to know the distance between the two shafts, the number of teeth on each gear, the width of the gears and the nominal helical angle.

 

Providing the originals will raise confidence but even if one was seriously damaged, I can't see how a drilling that would be an issue.

 

You may be able to find some off the shelf gears which can be machined to the correct width and fit your shaft diameters.

http://hpcgears.com/n/products/13.helical_gears/helical_gears.php

[Jrtm]

Box is going to steve at brinklow. With boat in dock now i know these guys do good work.

[Jrtm]

Ok gearbox is now fully appart unfortunately they dont have a spare small gear only a spare big gear.

So apart from having the box apart im not back to sqare 1. So unless anyone knows of anyone with a box going for bit im going to have to get new gears made or a replacement box, ill be collecting it all from brinklow soon and taking it to aylesbury for a quote on new gears to be made.

[BEngo]

4 hours ago, billybobbooth said:

Ok gearbox is now fully appart unfortunately they dont have a spare small gear only a spare big gear.

So apart from having the box apart im not back to sqare 1. So unless anyone knows of anyone with a box going for bit im going to have to get new gears made or a replacement box, ill be collecting it all from brinklow soon and taking it to aylesbury for a quote on new gears to be made.

See if you can borrow the spare large gear. Having an example in good order will help the geat cutters quite a bit as they will then be able to know the right tooth form, pressure angle etc. 

It would be best to have a pair of gears cut, although it is more expensive, rather than use one new and an old spare.  That way your gear maker will be responsible for the two gears running properly in both directions and transmitting full power.

N

 

 

 

[Bob Tidy]

Now then.

I have a small gear to copy from which is better than yours, where are you moored?

I  will look for it in the morning and take a picture.

All best

Bob

[Jrtm]

Right i think i have worked out whats happened but not sure how to solve it.

I beleive all the problems have stemmed from my big gear pushing on the small gear at one end upwards. This will explain 5 things ive found.

1. The big gear being worn at one end but near perfect teath at the other

2. The way the gears have chewed themselfs at an uneven angle ive see gears like this do it when a bearing fails and the shaft sits at an uneven angle

3. The fact that drive output flange has rubber at some point on the support block behing the gearbox pushing the shaft up (the main cause of whats happened over the years)

4. No other wear or damage to any other part of the gearbox gears

And 5 the big killer its been the big gear causing the problem the big gear has been rubbing on the back of the housing in an angle.

as the small gear cant move up or down when bolted up the only gear left to move is the big gear. Unfortunately it still puts me in the same position but i now have the clue as to whats caused it and how to fix it.

[Jrtm]

Right im in the prosses of putting parts back on so as soon as the gears arrive i can bolt them in.

My question my rear bearing is already checked and spot on the one thats going to be a pain is getting the shimming right on the reduction big gear anyone know how much play there should be. At the moment its unshimmed.

[Mikexx]

Tapered rollers should be fitted so they have a small perceptible play. They must run with clearance.

[Jrtm]

I didnt know if there was a set amount of play on the bottom big gear bearings.

As my small gear bearings are shimmed

Hence my question

[Monty V]

I, by accident, found this thread regarding what looks like a very tired Brunton gearbox. I also had one in similar condition until I rebuilt it while I was doing the same with my recently completed National engine.

The problems I found were not only wear and tear but poor assembly at some time, probably war time when it was done just to keep it running. For example, Bronze thrust washers with hand cut steel shims behind them, finger tight nuts holding bearings in place, taper roller bearings worn to the point where the rollers dropped out of their cages and so on. As to what I did to rebuild would probably run me beyond my allowed space here but some observations I made might be of help.

• The timing cover on my engine had no location dowels to centralise it round the crankshaft. This is important as the gearbox mounts on it.
• The female forward clutch cone is mounted on a keyed taper with a ball thrust race and necessary shim between it and the timing cover. If the shim is too thick the clutch cone will not tighten on the taper and the crankshaft will be pull hard against the centre main bearing face. Shim too thin will cause the other main bearing face to be used as a thrust bearing went engaging forward. The centre main bearing should only be maintaining the crankshaft alignment to the cylinders. It is important that the key between the crankshaft taper and forward clutch has a small clearance at the top when assembled.
• Oil in the reduction gearbox, according the instruction pages states 'Good quality gear oil'. I've used EP90. I've read about return pipes being fitted between the reduction box oil level plug and engine. This means that the reduction box can only have engine oil it which is probably too light for the job it has to do. The reason this was done was due to engine oil passing through the bearings and felt seals on the forward/reverse selector. I've modified this to lip seals which should reduce the quantity of oil reaching the reduction box, some will pass as there is unsealed clearance between the sliding selector and its bore in the casting.
• I had new reduction gears made by a company near me. Sovereign Gears Ltd. Hill Lane 1, Markfield, Leicestershire. LE67 9PN. To reduce cost (very little) I reduced the width of the gears as I felt that now my engine is in a forty five foot boat and not likely to tow a butty it didn't need such hefty gears. I did look at standard gears from HPC who were very helpful but beware there is only just enough clearance to get the small pinion out of the box and standard HPC gears wouldn't have fitted. Attached is an assembly drawing of a Brunton reduction gearbox which may be of some use. I'm willing to chat further ( bore you to tears) on the subject if you wish.    

 

 

[Jrtm]

Had an intresting day yesterday cleaned out my sump after building engines for years im not 100% but i dont think your ment to have to 2cm of gunk in your sump, on a luck side the gearbox swarf couldn't get into the main engine sump as the pipe conecting the 2 was blocked this was bad in one way but good in another there were no swarf remains in the engine sump only in the gearbox, all gearbox bearings have been replaced and the rest cleaned so no swarf in gearbox or engine.

Jobs done so far.

Gearbox

Gearbox removed and stripped, new seals including felt seal, auto lubrication pit in to replace the manual oiling plugs, put back to independent gearbox oil to run on ep90, re shimmed and adjusted planet gears, gearbox rebuild - reduction gears, gear selectors set in all in at mid points in neutral as before hit selector thread stop before fully in reverse.

Engine.

Heads off cleaned re asembled and new head gaskets fitted, r/n rocker oilers removed and auto self drip feeds added (back to national setup but with drip feeds rather than wicks), fuel tank removed welded and turned around so sight glass on same side as filling handle, fuel taps removed and old style taps fitted, new fuel lines from tank to engine with fuel filter fitted after the tank (old setup had remote fuel filter before injector pump ment any dirt got into the fuel pump and blocked it), fuel pump and main fuel filter resized to take 10mm pipe and modern fittings for ease of replacement and so all pipes are 1 size not 3 like before, new exhaust system, new water pipes, new intake system (r/n system removed put back to national using new parts), new oil lines (going in now)

After gearbox is back together its bolt it all back onto engine beds and do a test start.

[Jrtm]

New gears going in today 

[Jrtm]

Ok major problems, finally got it running to find nearly all the engine oil has gone into the gearbox and the oil pressure is off the gauge.

When i took the box of it looks like all the oil has been forced out the jet in the crank. As behind the forward drive plate is dry and all my plant gears are covered in oil.

The only thing ive done engine wise is remove the standard filter and just run from the remote filter.

Any sugestions or will it be a case or refit the stock filter?

[Jrtm]

Think i found the fault the remote filter dosnt have a way to release or lower the oil pressure so got to reinstall the original one but rather than oil going threw this then the remote im keeping it going threw the remote then original.

Ill know on monday if it works

[X Alan W]

Are you or did you replace the helical cut tooth gears with straight cut ones the only reason I ask if you now have straight cut tooth gears there will be a degree of gear noise/whine more than with helical cut gears,Straight cut gears in race car gearboxes tend to be quite vocal

[Jrtm]

No we replaced with helical gears. We used the company from up north as they had them in stock.

[Jrtm]

3 months later and i finally have drive, not that i can now move as shes sat on the bottom 6 inches out the water as the tring sumit pound is down by nearly a foot, no boating tomorrow for us as really need to test it all for leaks.

Oil pressure now solved by putting stock filter back on i use to get 10- very occasionally 20 psi oil pressure now a constant 25! Guess there was alot of sludge blocking all the lines but 70psi of pressure soon cleared that up!