Laydown Gearbox Shell Width

John Francis previously wrote at Tuesday 26th October 2010. 21:48hrs:

Hi there, I'm currently in the process of building a '48 ES2 engine andlaydown gearboxinto a '59 twin frame. Having great difficulty getting the engine plates to line-up (especially below the gearbox) - bottom plate up to 5mm out at lower gearbox mount! My questions are 1) How does one date a laydown gearbox? 2) Is there something about marrying-up lay down boxes I should know (e.g. weird shell widths etc.) No wonder I can't get my brand new centre-stand to fit! Cheers, John

Hello John,

Would your 1959 Twin frame be a featherbed? If so, I think that some information I have from the late Neville Hinton when I contacted him 5 years ago may interest you.

I asked him what type of gearbox would be correct for my 1954 88. He replied:

"The lay down boxes for featherbed frames was GB8 **** It may be stamped as8.**** but not 102.****. The 102.*** series will not fit."

Although I have never seen one of those 102 series gearboxes, I believe they may have been fitted to the Model 7 (plunger or swinging arm) and maybe the ES2s, but I don't know for sure if that is correct. I think the difference is most likely to be the widths of thetop and bottom mounting lugs; perhaps also the positions of thoselugs. That at least would account for the difficulty you are having.It would help if you give a bit more detail about exactly where and how the 'box does not fit. Also what stampings are on the top of the case in front of the clutch cable entry (not the cast-in letters & numbers elsewhere)

The usual clutch cable entry is more like a 'tower' about 1 1/2" tall, with internal threads for the cable outer location. The GB8 series are different and have this 'tower' machineddown to about 1/8".

The other difficulty you may have will be the various different lengths of mainshaft throughout the model ranges. That is not to say you couldn't fit a GB8 series 'box, then swap the mainshaft for one from an ES2. Mounting a viable box, with the engine installed then taking some accurate measurements to find what mainshaft is actually needed, using the engine, clutch &gearbox sprocketsand plumb lines or straight edges seems like the best approach to me.

Another option may be a Manx 'box, but that could get expensive.You probably already know that the featherbed ES2s (and Mod 50s) all used the AMC 'box. The laydown type having been fazed out in 1956.

Narrowing down when these laydown 'boxes were made is tricky. I knowthat by1954 they were in the region of (GB8) 2500. By the end in 1956 they were in the high 6000s. That's rather academic though. All you need is a gearbox which lines up in all the right places.

By the way, there is a message and picture on one of the Yorkshire Norton forums of some nice work done to someone's laydown 'box by Mick Hemmings. He has welded up a boss to allow a decent oil seal to be fitted, as well as provision for o-ringsto sealthe camplate and quadrant shafts.

Paul

John Francis previously wrote:-  Atlas Box Top lug width 80.5mm Bottom lug width 84mm.

I feel this is wrong as all F/B engine plates are parallel so the lug dimensions would have to be the same. Probably the 3 5/16'' previously mentioned. The AMC box with different lug dimensions may be AJS/Matchless rather than Norton.

The pre-Featherbed Laydowns were prefixed 101 for the singles and 102 for the twins. The only visible difference that I've noted relates to the outer cover and is in the length of the kickstart shaft and spring cover. From memory that from the singles is longer.

Hello Paul and Richard

This does not add up as far as my 1956 ES2 is concerned.The factory records show the gearbox as a 102 but it is now fitted with a GB8.

That's odd Ronald. I've got some extracts from the 1950 factory records and the different boxes are quite clearly allocated according to the number of cylinders, regardless of model type (The '12' code Model 7s are all 102s).

I don't know if the distinction carried on after the introduction of the swing-arm frames. The other possible explanation is that with the laydown being discontinued in 1956, they were using up all the remaining stock and converted a 102 to 101 specification. As I mentioned, the only visible differences are on the outer cover so the code number was probably just for convenience in the factory stores.

Previously wrote:

Hello Paul and Richard

This does not add up as far as my 1956 ES2 is concerned.The factory records show the gearbox as a 102 but it is now fitted with a GB8.

John Francis previously wrote at Thursday 28th October. 21:19hrs:

Thanks ever so much for your very detailed response - extremely helpful. The trail is getting warm now! The engine is the older ('48) type and the gearbox is supposed to be the one which went with it i.e. pre-featherbed. The numbers stamped on the case are G102 A 7354. The approximate dimensions on the fixing lugs are Upper: 83.5mm wide, Lower 89mm wide - I'd already guessed that they should both be the same as the upper dimension for fitting into a featherbed frame.

The information you have supplied also sheds some light as to why none of the available clutch pushrod dimensions work with the "mix" of parts I have. The clutch that came with the bike is the later AMC type - this is trying to work with the earlier quickthread lift mechanism and (potentially) the wrong mainshaft! Oh dear!

If there's anything else you'd like to add please do - all help gratefully received. Thanks again, John

________________________________________

Hello John,

Well, although it was very kind of you to say that, I think detail was conspicuousby its absence in what I posted. With nothing to go on but Factory Records or the (mostly) bitzas people think are original bikes these days, we're forced to make it up as we go.

Something I meant to put in my previous ramble is to suggest that you give Mike Pemberton (Pushrod Performance) a call. You'll find his details in Roadholder. I can't think of anyone who has more experience at fitting various Norton singles into featherbed frames than him. So long as you bear in mind that he needs to make his living doing this, I'm sure a short summary of what you're faced withmight produce some useful information. If you need engineering solutions, he would be the man to sendthem to.

I can confirm that my GB8 'box has both mounting lugs a fraction more than 83mm wide.Therefore, maybe Ronald would tell us whether he can find a 2.25mm washer either side of hiscurrent '56 ES2 gearbox lower lugs?What are the 4 numbers stamped after the 'GB8' on your gearbox, Ronald?

Perhaps another thread here inviting laydown gearbox users (with their 'box stampings verified by Factory Build Sheets for their machines) to send in details, would provide us with a form of database.

Paul

Now for some serious grovelling.........

Iâve been down to the shed and pulled out my gearbox bits. Iâdnever realised there were such variations. This is long and labourious, but mayshed some light on the gearbox question or inspire further debate, maybe evenothers can get out the tape measure....

Four laydown boxes and three AMC type boxes

All four laydown boxes had GT100 VAF cast in raised letters/numbers and three with a similarly cast capital letter âAâ. On three of thecases this casting was down around the cam plate spindle bolt. The other hadonly GT100 and VAF cast up on the rear of the top mounting lug. On this last box the cast 100had been chiselled off the GT100 and the 100 stamped in. Maybe therehad been an issue with adjustment clearance and that couple of mm made thedifference.

Some dimensions to chew on (remember the faces can bebruised and knocked around, measuring to half a mm may not be fair, but shouldbe regarded as a close average):-

G102 2951

Top lug width 83.3mm

Bottom lug width 83.5mm

G101 7545

Top lug width 83.5mm

Bottom lug width 84.5mm

G102 4949

Top lug width 84mm

Bottom lug width 88.3mm

No Stamp, but has the odd GT100 casting number

Top lug width 84mm

Bottom lug width 87.4mm

I looked at the offset of the lugs in relation to the boltup face for the inner cover and the broad flat face on the opposite sideoutboard of the layshaft bearing and the big mainshaft bearing. Looking foralignment secrets.

G102 4949 & the no stamp case were similar. The top lugwas 23.5mm each side to each face, the bottom lug was about 22mm each side

G102 2951 & G101 7545 were similar to each other in thatthe top lug was around 23.5mm â 24mm offset to the same reference faces.However the bottom lug was 23mm â 24mm on the cover side and 25mm â 25.5 on thesprocket side.

Either wide bottom lug, or narrow bottom lug, they also seemsymetrical

A definite difference in gearbox cases.

The width across rear of the crankcase lugs on the singlemotor where the engine plates bolt up is 84mm on each of the three lugs.

On the singles and twins in the single down tube frame thebottom of the motor cases fits between the frame rails and is through boltedthere. The bottom gearbox lug also fits between the frame rails.

The engine plates stretch back from each side of the engine up and past the frame seat post, overthe gearbox to the top gearbox lug. As you can see by the dimensions Iâveprovided the top lug on all four of the laydown boxes is pretty well 84 mm. So,because the top lug is contained between the engine plates in line with theengine, the top lug will be what gives the gear box âlineâ with the motor andwill be a starting point for setting it up in the featherbed frame.

As far as I understand it, basically the rigid full cradleframe, the plunger frame and the single downtube swing arm frames were all verysimilar in the front sections, only having the rear portions chopped off andthe plunger or swing arm adaption grafted on. I know there are a couple ofdifferences in the twin verses single frames because the single motor does notfit the twin frame and visa versa. I had always considered this to bedimensional differences of the motor cases only, resulting in frame engine mountinglugs being put in different places, I have never looked, but assumed thegearboxe lug dimensions would have been the same.

Obviously I have two gearboxes with wider bottom lugs andtwo gearboxes with narrower bottom lugs. I didnât realise this before now.

A quick measurement of the frames between the lower gearboxframe lugs gives:-

Rigid full cradle frame 88mm

Plunger frame, 89mm

Swing arm frame 90mm

I donât have a featherbed frame.

The three other âAMCâ gearboxes.

N21106

Top lug width 83.5mm

Bottom lug width 83mm

Atlas Box

Top lug width 80.5mm

Bottom lug width 84mm

Early Commando

Top lug width 81mm

Bottom lug width 84mm

The width across the rear of the crankcase lugs on my beatup old Commando cases where the engineplates bolt up is 84mm on each of the three lugs.

Having no experience with any of the featherbed twins, itâsobvious to me the heritage of the Commando box in that the bottom gear box lugsare the same dimension to the motor lugs as the gearbox is sandwiched betweenthe same plates, both sides coming back from the motor. The top lug on theCommando box is shorter as there is a spacer for the drive side of the top lugto make it easier to get into the engine plates. The Atlas box seems to besimilar to the Commando, but N21106 has the full 83.5 mm wide top lug as if itgoes right between engine plates.

One of my bikes has a laydown box with the wider bottom lug,the other two have upright boxes, a Dolls Head and the later âTombstoneâ Thebottom lugs on the upright boxes are around 86mm & 88mm wide. Iâve put allmy bikes together from basket cases and have never noticed the difference inthe bottom lug dimension, probably because, as luck would have it, Iâd used âup-rightâboxes with the wider bottom lug and the laydown box I used also had the widerbottom lug. I had never noticed until now, that I had two gearboxes withnarrower bottom lugs.

It would seem to me the laydown gearboxes with wider bottomlugs would suit the single down tube frames and the gearboxes with the narrowlugs, the same width as the rear of the engine cases were for use with largecomplete engine plates as would have been used in the featherbed frames.

My conclusion, my dear Watson...........

Could I presume, that, John, old mate, your gearbox G102 A 7354, with upper lug: 83.5mm wide and lowerlug 89mm wide, is indeed the correct gearbox for your 1948 motor. However, thiscombination should go into a single down tube frame. You need to find a gearboxcase that has the narrower 84mm bottom lug and you should be right. Something Ithink you have already realised.

Iâd hazard a guess to say that if you swapped the internals ofG102 A 7354 into the featherbed type case with the 83 / 84mm wide lower lug, yourmainshaft will still be ok and with any luck your kick start shaft may also beok. I have not seen a difference in kick start shafts, but then Iâd nevernoticed a difference in the cases either.

When I set my gearboxes up in the frame, I still straightedged the primary and secondary drive chain line to ensure all was right inthat department. As you can see with the dimensions I have displayed there is aslight variation even within like groups, especially when it comes to wear & tearon those aluminium lugs.

Over time when these gearboxes came loose and the owner /rider ignored it, they wobbled about and flogged themselves to death.Elongation of the bottom mounting bolt hole is common. On the tombstone box, I bored the bottommount hole out and resleeved it back with a brass bush. I then shimmed eachside in the frame with made to measure washers so all could be tightened upsnugly & securely.

On the laydown box, I bored out each end of the lug and fittedtop hat bushes into the lug ends, making the top hat to the precise width of the space each sideof the lug to the frame. Itâs a lot of fiddling, but makes for reliability anda bit of thrashability in case a Beeza tries to overtake you.

You can still use the later clutch, youâll have to work out apushrod length for youself. Iâve used ?â bright steel rod. Iâve tried hardeningthe ends by heating to cherry red & quenching in oil. Iâve split the rodswith a ?â ball bearing in the middle to help differentiate between the rotating bits & the stationary bits. To help prevent mushrooming of the rodswhere they come up against the ball, you can put a ?â roller each side of theball. An old one from the clutch bearing or a big end bearing will do. Thiswill give a nice flat surface bearing onto the end of your clutch pushrod, withthe nice hardened other side of the roller against the ball. Last forever. Trial& error until you get the right length combinations, but youâll havesomething that will work.

I think youâll be right. You just need to find the right bits. After all the time & effort Iâveput into getting a couple of gearboxes right, especially getting the âup- rightâboxes to change gears nicely my wife has often questioned who I was married to.Sheâs always at me to get out of the shed and get out more!!!! I certainly knowthere is emotion there when your hooting off down the road and your gearboxworks nicely. In no way would I have attempted to belittle you, old mate. Sorryyou took it that way.

All the best, hope you get it together.

Bob

Previously wrote:

John Francis previously wrote at Thursday 28th October. 21:19hrs:

Thanks ever so much for your very detailed response - extremely helpful. The trail is getting warm now! The engine is the older ('48) type and the gearbox is supposed to be the one which went with it i.e. pre-featherbed. The numbers stamped on the case are G102 A 7354. The approximate dimensions on the fixing lugs are Upper: 83.5mm wide, Lower 89mm wide - I'd already guessed that they should both be the same as the upper dimension for fitting into a featherbed frame.

The information you have supplied also sheds some light as to why none of the available clutch pushrod dimensions work with the "mix" of parts I have. The clutch that came with the bike is the later AMC type - this is trying to work with the earlier quickthread lift mechanism and (potentially) the wrong mainshaft! Oh dear!

If there's anything else you'd like to add please do - all help gratefully received. Thanks again, John

________________________________________

Hello John,

Well, although it was very kind of you to say that, I think detail was conspicuousby its absence in what I posted. With nothing to go on but Factory Records or the (mostly) bitzas people think are original bikes these days, we're forced to make it up as we go.

Something I meant to put in my previous ramble is to suggest that you give Mike Pemberton (Pushrod Performance) a call. You'll find his details in Roadholder. I can't think of anyone who has more experience at fitting various Norton singles into featherbed frames than him. So long as you bear in mind that he needs to make his living doing this, I'm sure a short summary of what you're faced withmight produce some useful information. If you need engineering solutions, he would be the man to sendthem to.

I can confirm that my GB8 'box has both mounting lugs a fraction more than 83mm wide.Therefore, maybe Ronald would tell us whether he can find a 2.25mm washer either side of hiscurrent '56 ES2 gearbox lower lugs?What are the 4 numbers stamped after the 'GB8' on your gearbox, Ronald?

Perhaps another thread here inviting laydown gearbox users (with their 'box stampings verified by Factory Build Sheets for their machines) to send in details, would provide us with a form of database.

Paul

Paul

The gearbox I have now is GB8 6830.I am unable to check dimensions at the present time but will let you know later-Ron