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Amateur Manx 40M preparation

25097 Views 130 Replies 9 Participants Last post by  Mike 40M
Starting a thread about my -59 Manx. Should never had bought it 3 years ago, if it had not been raced quite successfully by a friend of mine. We used to ride together on our road Nortons, he on an Atlas and I had a Dommi 99. Learnt a lot from him about race lines and how to stay alive on public roads. For some reasons, I have to get it going asap. Started collecting new bits for it a year ago. In january I started to take it apart. Also got new parts needed. As a motorcycle in pieces takes a lot of space, I started to assemble it yesterday. Frame in good shape, only minor scratches in the paint. Swingarm bushes ok, now greased. Head bearings Ok.
First thing to do was rear mudguard in bad shape., replaced with a new. I think a -59 should have alloy rear mudguard, but as I'll try to set it up as it was when my friend raced it, it got another fibreglass one. Advice and critics welcome.
Bicycle fork Auto part Bicycle frame Chassis Machine
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Alloy rear guard = yes for all years.

The enclosure type guard tuned up as the Manx engine was not factory assembled with sealer (gasket goo) and just two gaskets. The enclosure guard helps deflect oil and keep the rear tyres less oily. BUT as you have what looks like a new engine oil shouldn't be an issue. In fact most oily rear tyres are caused by over filling the gearbox.

Quaife boxes are narrower across the mounts than AMC and need a spacer fitted. Laydown box (Burman) was fitted up to 1956 the AMC box fitted after till 62. Take a measurement on the laydown box from output bearing face to l/h gearbox mounting face. Do the same on the TT industries box and mill off the excess.

What's the small tab for on the frame, front right side top tube? The frame by the way is GP spec as it has fairing mounts on the headstock, these were an extra.

Q. Why not build the original engine?

Modern hard epoxy paints can be as thinly applied as wet paints and show cracks just like ordinary paint. Getting powder type coats off a frame isn't difficult as solvent strippers like Paramose will move it in minutes.

Good luck.
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Thank you, luck needed. Most bikes I have had turn up unsuspected problems.
A. Reason for not rebuilding original engine. Time and a strong desire to race it. A bit worried about strength of magnesium crankcase. Prefer not to kill a matching number engine. If it only should do parade laps, maybe. Don't have enough confidence in my skills. No problem with rebuilding Norton twins or goldies, but a lot of respect for the Manx engine.
Sharp eyes, no idea what the tabs are, one on each side, try to take a photo of them.
Gearbox not sorted out yet, had some other things to do.
By the way, got a stud from Andy Molnar, replacing bottom gearbox bolt. A bit heavier but a lot easier gearbox assembly.
If you are running the bike as a 350 and racing then the 6 speed box is best but a 5 will do fine. Too much of a stretch for a 4 speeder on modern circuits with slow corners and chicanes.

The manx engine really isn't difficult to do, its just a fitting job which only requires 2 special tools, hairpin valve spring pliers and head fitting jig. Assuming the engine is fairly good condition other than bore sizing you can feel your way through a build, loose movement in the big end, mains, bevel backlash etc you can determine by feel once you know what it should be. Everything else is common to building any other motor like squish measurement, valve drops and TDC and valve timing. Many years ago this is what I did - go to an expert and get the motor built, they will provide you with a full build spec sheet. Get the motor home then strip it, measure and rebuild again but feeling and measuring all the clearances. Today even doing valve clearances on brit twins I don't use feeling gauges, I just need to know if the adjuster bolt is UNF, BSF or Cycle then slacken off the adjuster, screw down onto the valve finger tight then back off an hour or 2 or 1 1/2!!

The bottom gearbox bolt is pain but you get used to it. Also putting the engine in or pulling it out and engine plate wiggling.
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Original engine did some parade laps in -95. Not the faintest what oil was used then. "Spare" engine will hopefully commence run in period next month. Old engine looks good on the outside and moves freely. Only rust on bike worth mentioning is front springs and interior of clutch.Some nuts has got a brown patina. Surprisingly good bolts and nuts for a bike which has spent most of its life in a metric country. Most previous owners must have used proper tools.
Spent the afternoon replacing worn parts in front legs. Tomorrow time for finishing front fork.
Thinking of replacing handlebars and levers with modern parts. Original has obviously had some ground contact. Makes it impossible to fix barends yo them.
Seems I soon have enough original parts to build another bike.

Personally I would do exactly that, build a full replica and restore the original to original.

Milling the gearbox is a 20 min job.

Just make sure the oil is fully drained from the old engine or flush it with diesel.

Oil for the new engine, I use Miller CFS 10/60 full ester and it is superb. I use this in all plain shell bearing dry and wet clutch engines.
Fork oil 20 grade. If the damper rods and damper bodies are worn you might end up using 30 grade.

Oil quantity - extend the fork fully then compress without the spring - measure the movement (x) now add 2". Fill the fork till you have an air gap of x+2 make sure the damper tubes are filled but moving the sliders up and down a few times. Don't leave less than 2" Boils law and all that.

Don't use dominator quantity as you don't have an internal spring taking up volume.

So you won't put enough in.
That's me, on a 86 bore forks filled as above and going underneath an ex works Ducati. He had his knee down, hanging off the saddle all very stylish! Me just sitting quiet and letting the bike do it's job. Hated those leathers though they would balloon up - sort of odd looking. Still it looks like he's been blown off by a fat fucker riding a tractor. Managed to wear a nice little flat on the gear change too.


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Just checking if I got it right,.
Using one of those modern tools for setting fork oil level.
Movement =6". Add 2" equals 8".
With fork fully compressed.
Oil level 8 inches below top of stanchion.
With the forks fully extended.

Are your forks manx length Roadholder? Or road? Manx stanchions are shorter.

Manx are 20.375"
Short Roadholder are 21.843"
Or just put 200-210mls in of 20grade and not lighter.

Manx forks (late) are really quite simple but work really well, compression is controlled by the holes drilled around the bottom of the stanchion, rebound by the damper tube. IF compression is too soft you can weld up (or braze) up the holes and re drill smaller. I also find than the original Norton multi rate springs are too soft, even when new in the 60's, and the forks need a little more preload especially as we are all a little bigger, leathers weigh more, heavy boots and space helmet. So don't be surprised if they bottom out, just buy new springs, Molnars are good and maintain original ride height. I have tried adding packing on old springs and it doesn't work, ride height goes up and the spring is still soft.
How is the gearbox fatter, I assumed it was wider across the mounts?

Sometime I have to let the engine plates a little forward of the gearbox to allow the gearbox to pivot on the lower bolt and use all of the adjustment slot. Photo would be good?
When inserting gearbox with righthand engine plate in place, it hits frame about 3/8 before it meets the engine plate.
View attachment 57329
View attachment 57337
OK got it. how much do you need to remove for clearance?

If its not much say an 1/8 maybe 3/16 then option ;-

1 / Heat the frame in the troubled area till red , put a 1 inch bar across the and give it a clout (can't believe I am advising this).


2 / Angle grind and clean off excess from the gearbox.


3 / A little of both (this is most likely what you will need to do.

Same issue on a Petty frame!

Auto part

Mixing new and old often bring problems.
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Hoping that jalsteve will have time to spread his wisdom on rear hub parts, I contnued with gearbox installation. Spent yesterday evening filing LH engine plate to accomodate that fat and heavy TTI-box.
Now the gearbox and LH engine plate is in place. Shortened the bottom gearbox stud 4mm, so now it's possible to take gearbox in and out without raising and/or lowering engine. Norton should have done that mod themselves. As a final touch I drilled a 2mm hole in the gearbox and a washer with a tab also drilled 2 mm. So now I can lockwire engine and gearbox drain plugs.
Only tricky part in gearbox assembly is the top rear engine bolt. To get washer and nut in place below the magneto and behind magneto chain covers is a bit problematic.
Washer was put in place with help of a small magnet. For the nut a thin plastic glove with nut inside (on left hand thumb) worked surpricingly well. Blurry on picture.
View attachment 57705
Springs - There are 3 on the rear brake plate. The shoes have two as normal, one at the cam and one at the pivot. The third is fitted behind the brake operating arm BUT often this one is left off. The brake shoe springs are heavy gauge and not like those you would find on a road bike. Andy Molnar can supply, its probably best to replace anyway.

Have a really close look around all the spoke holes for cracks and ESPECIALLY inside the hub were the large cast spokes meet the outer casting as they are prone to crack. If you find a crack the hub is scrap, don't be tempted to weld, and don't be temped to use.

Auto part Rim Wheel Automotive wheel system Rotor

The problematic top engine bolt - just get a piece of bar (you can use Dural) say 50mm x 20mm x 12.5 (1/2 thick), drill a hole at one end and tap 3/8" 26tpi replace the nut with this. the length allows you to easily fit and its hidden so doesn't affect the way the bike looks. This was a period mod.
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Some photos of a a Manx rear brake plate. Replica but exactly as original.

Looking at the out side of the brake plate you will note a small peg on the plate near the brake arm this is the anchor for an external brake arm spring. And on the photo of the inside note the heavy brake shoe springs.

Auto part Disc brake Vehicle brake Brake Automotive wheel system
Auto part Audio equipment Clutch Automotive tire Automotive lighting

The clutch roller bearings are a point of weakness. There are 15 1/4x1/4 rollers held in a pressed steel cage, a period mod was to replace with 50 1/4x1/4 rollers which gives better support to the chain wheel (basket) and helps it run more true with less movement. Lubricate with a HM lithium non fluid grease, you don't need lots as you will be removing the plates and giving them a clean after every race and can add a little grease at that time?

Which clutch are you using? The Burman type with inserts in the chain wheel or AMC with a friction back plate? They are both good clutches if its original Manx clutch (centre with have 6 bolts) please don't use for racing they are rare today and you will destroy it. Buy and modified a road AMC clutch just narrow it down for 4 plates. Or you can be similar from Andover Norton. Run the primary with about 25mm of up and down movement (that's an easy inch!!!). As the engine warn up it heats the gearbox and engine plates so centre of clutch to crank centre increases. I always run the bike around at low rpm and get all nice an hot then stop and check the tension of the primary chain, when hot there must be a little play. I have seen gearbox main shafts snap in race conditions and drive side main bearing wrecked through over tight chains. Belts are more forgiving.

Ref bearing seals - Correct there are no seals as the wheel spacers or brake plates collars act as deflectors. Just pack with a good quality LM grease.
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Sad to say, have been busy with other things. Not much done to the Manx. My neighbour calls it the mailorder bike. Just because all delivery vans and lorries that come with small and big parcels.
Next week nothing will be done to it. Then I'll do the rear wheel, get primary drive in line and try to fix a leak in left fork leg.
The original (?) clutch is a mysterious thing to me.
View attachment 59961
Notice the spring screws with 1/4" square holes. Basket and pressure plate lightened. No steel cage but filled with a lot of rollers. 6 Allen screws. Friction plates and centre different size of "splines" than other Nortons. Steel plates probably usual size. Sadly it had a hard life, centre much worn. Will use an Andover clutch.
Some small things done. Replaced rubber mount for float bowl and made a gear lever.
Yep that's an original clutch with a modified centre. Usually the extra slots in the hub were done as the old slots get badly notched. The 1/4 x 1/4 50 roller conversion is a common mod. The chain wheel is standard Manx, the copper plate was applied to protect the basket during the hardening process, road clutches don't get this treatment. All Manx clutches have square key bolts and the springs should be square section wire.

Just go through it and rebuild so its serviceable and put it in the bikes heritage box.
its a stud with 5/16 BSCY thread at one end and a 1/4 bscy (same tpi as 1/4 BSF). There is a grommet that fits into the chainguard and top hat washer / sleeve arrangement - the top hat is drilled out 1/4" and fits into the grommet. To get the chain guard alignment correct fit a nut on the 1/4" section of the stud this is used as a backing nut and locates the chain guard. the final bit is a large washers and another nut which fits on the out side to hold the guard in place - will take a photo tomorrow.
What to do if the thread is knackered, new 3/8 thread cut into the old hole (was 5/16). Narrow a bolt head with the correct thread and drill centre to 1/4bsf stud needs to be long enough to be able to move the position of the guard to be centre over the chain.


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As original with stepped stud 5/16 and 1/4 threads. Belt drive primary but it's the same mounting type.


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The rear mount is simple. There should be a flat bracket on the rear curve of the chain guard, it will have a largish hole in it which takes a grommet. With the chain mounted up front this bracket should positioned behind the frame gusset plate and there should be a hole in the frame 1/4. Make a dowel to fit in the grommet with1/4 bore and bolt the frame via the hole in the gusset plate. Note you must fit grommets or the chain guard with be in tension and will crack.
Rear mount.


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Oil tanks in fairings, not sure why this would have been done. There's no shortage of space in its original position and the big foot tank holds 6 pints (specials can hold a gallon!). I guess "if" the bike had a lozenge tank, the type fitted 61/62, which is smaller then a header tank could be made and fitted into the fairing for longer races. Got to remember with open valves and just 2 gaskets in the manx engine was an oily affair. I have seen small side oil tanks in the fairing for primary and rear chain lube?! Early bikes would used engine oil taken off via a boss on the lower front of the oil tank. However Norton abandoned this for 1956 and put the oil in the left hand frame loop.


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Correct colour is silver base or you can use Silver Fox. The lozenge oil tanks were never painted just linished but many do paint them. The original big foot tanks were painted and lined.
That'll be silver base, it's more grey than silver. Early polychromatic colours were pretty poor really base being the starting point for all metallic colours back in the 50's. Silver fox 2 pack is about as close as you can get today, the flake is very small as it was originally.
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