Hayward Belt Drive Hints and Tips
T140 and A65 Fitting Instructions
Always get front pulleys to fit as far inwards as possible. Guide plate
face outwards. Do not bend or damage the guide plate or damage the teeth on the
T140 kit in general - Not usually any modifications to fit the kit, but you may need a shim to add to the rotor spacer.
A65 kit - Early A65: not usually any modifications to fit front pulley. But do change all the early A65 clutch bits to the later three spring T140 type clutch internals. Late A65: clutch is the three spring, but you must remove metal from around alternator stud area. (Sharp chisel and small hammer is much quicker then rotary tool.) Gearing is about 10% taller.
Both Kits: Note the white spot on the alloy drum. Do line up all the white spots on the friction plates to the white spot on the alloy drum. Please note: the first plate to drop into the alloy drum is the half (semi) bonded plate with the big hole. Then the big hole double bonded plates go in and the outermost friction plate is the small hole wide friction plate. Try the plain steel plates in various positions to the cush drive center for the best slide fit.
Cold engine belt tension for T120/40 needs to be 7 to 10 mm total up and down "free play" slack, and 9 to 14 total slack with cold engine on A65. At hot running temperature, due to heat expansion, the belt will tighten up. (After 20 miles of running) Especially on the A65 cold engine slack belt it would be best to use the slipper blade. But do remove the rubber from it with heat or a flame. Then polish the slipper and adjust the belt tension to 5mm (3/16") total up and down hot engine slack.
On A50/A65 twins and pre 70 triumph twins run the kit in 10 grade mono oil (moped fork oil or ATF, etc.) The belt won’t wear on the slipper and the belt doesn’t stretch, hardly at all. (Later Triumph twins share 20/50 motor oil as engine unless breather has been modified to pre 70 style.)
Belt Drive Instructions (General)
Recommended belt tension 3 to 6 mm total up and down slack with a hot engine.
(maybe 6 to 8 mm slack cold.) A primary chain is 10 mm (3/8") total slack. These
belts need to be 5 mm (3/16"). Adjust belts cold.
Belt can be run in oil. (for four years before contamination) To run dry you need air-cooling (ventilation). If run dry with chaincase fitted, the clutch will overheat and expand too, and belt will run too tight. Also max temperature for belt is 80 degrees Centigrade. Alternator could burn out too.
1952 long crankcase pre-unit kit is similar to T120 iron and
alloy kits using T120 front pulley and belt, 30mm wide. T140 front pulley and
belt are 32mm wide. Both are 80 tooth belt (AT10800). Short crankcase kit front
pulley and belt are 25mm wide in order to retain alternator and outer chaincase.
Same kit but with 30mm wide belt and front pulley costs extra. Iron version of
these kits has two cast pulleys and one belt. Alloy version has alloy drum with
the fourteen pins and twelve of modified clutch plates, but still uses cast
1952 Thunderbird long crankcase kit is more expensive than the short crankcase kit due to much longer belt; long crankcase iron kit is 25 mm wide. Alloy kit is 25mm wide to retain outer crankcase (cost is extra for 30 mm wide) Pre-unit short crankcase belts are 89 teeth (AT10890). Pre-unit long crankcase belt are 101 teeth (AT101010). You must use the T120/T140 clutch hub and thrust washer on all unit and pre-unit kits!
It is recommended that belt be run in oil, with an expected life of four years, after which time oil contamination could be a problem. If belt is run dry you must provide air-cooling (ventilation). The belt has an upper critical temperature of 80 degrees Centigrade, above which the belt can melt. If the belt is run dry in a sealed primary the clutch and alternator could fail due to lack of lubrication and/or overheating.
Do not damage (bash or mark) the teeth on the pulleys! Belt should not rub on case or guards, as this will cause premature failure. If belt tension is not correct on a unit construction engine or a MKIII Norton, contact supplier immediately!
Regarding the Commando Belt Drive Kit:
The six screws for the wear plate have not been tightened and Locktited
because the heat needed to expand the drum to fit the bearing would destroy the
Locktite. (120 to 130 degrees C.)
To fit sealed bearing, heat drum to maximum 180 degrees C. Freeze bearing; it should just drop in. Quickly quench with a cup of cold water, else the grease will boil out of the bearing.
Then tighten and Locktite in the six screws. Note: the steel wear plate has a ground outer clutch plate bearing face – the face is turned.
Don’t mix the screws in their holes, as each one is ground to suit each hole. If you mix them they could protrude. If they protrude they must be ground.
Belt tension 8 – 10 mm with a cold engine.
Alloy Belt Drive Instructions
To fit the 350/500cc unit kit - Front pulley must fit as far inwards as
possible. You may be able to remove engine sprocket shim to get the front pulley
as far inwards as possible. Only one outer guide plate is needed. The belt run
needs to be at the back edge of the clutch drum. Or, if possible, overhanging
the back face of the clutch drum, to save clutch twist, belt twist and stress on
bearings and shafts. On gear changing the belt moves outward two to three
millimeters, so get belt to run as far inwards as possible.
Do not bash or damage the teeth on the pulleys .
Do use the big Daytona clutch hub and thrust washer. Use three spring cush drive center if possible. If you use the four spring cush drive unit, then machine off the back face lip, so to use all twelve plates supplied.
The clutch drum has a white Tippex spot. The six friction plates have a white Tippex spot. Line up all seven white spots for the best slide fit. Try the six special plain plates in various positions to the cush drive center and try again for a good slide fit. ( Note: These steel plates are on a reduced diameter and have undercuts in comers of the tabs to assist slide fit.)
Belt tension with a cold engine for unit 350/500 (and BSA A65’s) needs to be on the slack side. Eight mm total free play slack or more. At hot running temperature the belt will tighten due to hot expansion. At hot running temperature (twenty or more miles), the belt tension should be minimum three mm to maximum six rnm total up and down "free play" slack.
You can use the slipper blade to take out the cold engine slack. If you do, adjust the belt tension to five mm total up and down free play, but you must remove the rubber from the slipper blade, by heat or a flame, and polish it.
Gearing is minus five %, so use one tooth bigger gearbox sprocket, or a smaller rear sprocket where available.
Oil for chaincase: Use ATF or mono thin grade oil like moped fork ten grade oil.
The six friction plates: Three types in the "sandwich" - the first plate to drop into the base of alloy drum is a 1/2 bonded big hole plate - then the four off double bonded big hole go in. The sixth outer friction plate is the wide friction small hole plate.
T150/T160 Fitting Modification
The guide plate on the front pulley must face outward. Do not bend or damage
the guide plate and do not damage or bash the teeth on the two pulleys. The
guide plate will foul on three high spots on the outer chaincase. A small hammer
and small sharp chisel is quickest and not messy or dusty as with a rotary tool.
Get front pulley to fit as far inwards as possible. The back edge of the belt
will be close to the protruding threads of the oil pump spindle - best to grind
off the surplus threads. The chainwheel spider must face the normal direction,
but you can face the chainwheel to face either way around. One way will be best.
Try facing the alloy chainwheel both ways - less rubbers for first assembly and
trial. (Obviously eventually fit the rubbers!)
You can only test the belt tension after the modifications are done and the outer chaincase is fitted. A cold engine belt tension of 7 - 11 mm total up and down "free play" slack is OK. After 20 miles at hot running temperature the belt will tighten. Minimum hot engine slack is 3mm; max is 7mm.
If there are any problems please contact us. If the belt is too tight a smaller chainwheel can be supplied. If the belt is too slack, 12mm or more, you can use the slipper, but the rubber must be burnt off and the slipper polished.
Do not bash/damage the teeth on the pulleys as any damage will mark and weaken the teeeth on the belt. Get front pulley to fit as far inwards as possible. The front pulley outer guide plate will foul on the outer chaincase in three high spot areas. So rotary grind some metal from the ourter chaincase where the guide plates will touch. A hammer and small chisle is faster than a rotary tool. Chaincases vary, some need a little metal removed from the top area of the chaincase, in case the belt could rub. Basically, regarding the front pulley guide plate and the belt, there is not a lot of metal to remove but it needs careful looking at.
Back edge of the belt needs to clear the oil pump nut by 2 -3mm. The belt may overhang the front or back face of the chainwheel, this is not a problem. To reduce belt overhang try facing the chainwheel to face both ways. The spider must face the normal way but you can reverse the chainwheel. Try this test with no rubbers fitted for fast assembly and probably one way round will give less belt overhang. (Of course the T160 has the chainwheel end plate and screws facing inwards and the T150 and Rocket 3 has the screws and end plate facing outwards.)
You cannot test belt tension until you have actually fitted the kit and fitted the outer chaincase. Belt tension can be tested through the filler cap hole. The cold engine belt tension should be 7 to 11mm total up and down "free play" slack. At hot running temperature, after 25 miles, the belt tension will tighten due to heat expansion and at hot running temperature the belt tension should be minimum 3mm to maximum 6mm total up and down "free play" slack. If the belt is too slack you can use the slipper tensioner blade, but you must remove the rubber from the blade with heat or flame and the slipper must be polished. If the belt tension is too tight the chainwheel can be swapped for a smaller one, so please do not mark or damage the chainwheel in case it needs to be swapped.
Try the fit of the front pulley in various positions (six positions, six splines) to get optimum fit.
T140 Fitting Instructions:
Not usually any mods or fuss to fit the T140 kit. (or the T120 kit at 25 mm
wide) Just get front pulley to fit well inwards. At most you may need to add a
shim to the existing rotor spacer to bring the rotor a thou or two away from the
front face of the front pulley. Belt tension is critical! A primary chain needs
10mm (3/8" total free play (slack). Hayward belt needs 3 to 6 total slack at hot
running temperature after 18 miles. You may need 5 to 8 mm slack with a cold
engine to get 3 to 6 mm slack with a hot engine. 5mm – 3/16" total slack hot is
ideal. Do not run the kit if belt tension is wrong. If belt tension is too tight
the clutch drum can be swapped for a smaller one. (This is rare though) If belt
is too slack you will need to use the slipper blade, but do burn/bake off the
rubber and polish the part which would rub on the belt. It is a good idea, if
you want to, to slightly introduce the slipper for your cold slack for short
runs so that you maintain a constant 4 to 5 mm total slack. Do not damage or
bash the teeth on the pulleys. On the alloy kit clutch drum (on 1975 onwards)
left hand gear change make sure that the front face is well clear of the left
hand gear change spindle. Also you may need to file the heads on the three
square head spring bolts to clear the thick bearing housing. (Only on the Alloy
Fitting instructions for the Hayward belt drives which use the 14 pin alloy drum and 14 of ½ hole friction plates – and the iron clutch drum with the ten standard type slots to use standard clutch plates. Engines which use belt drives using either the alloy 14 pin drum or the Bonnie type iron drum are:
T140 using 32 mm wide belt and 32 mm front pulley.
T120 choice of 29 mm wide belt and front pulley or 25 mm wide.
Preunit long and short crankcase choice of 30 or 25 mm wide.
(Front pulleys 31 tooth or 32 are available for engines with Weslake big splined cranks)
A65 BSA 32 mm wide front pulley and belt.
A10 BSA 30 mm wide front pulley and belt.
BSA B31, 32, 33, Goldie, M20 and M21 use 25 mm wide belt.
Main shaft converter hubs available to use Hayward iron or alloy Bonnie type clutch drums on Dommies and Commandos so as to have a light clutch and to use the three or four spring rubber clutch cush drive unit.
Fitting the T140 Belt Drive:
Not usually any problems or mods or fuss to fit. Choice of standard gearing or taller racing gearing (+ 8% taller) Front pulley – guide plate must face outwards. Remove any engine sprocket shims so that front pulley fits as far inwards as possible. Very rarely the back face of the front pulley can foul on the crankcase. Rather than shimming out the front pulley it is usually best to file the high spot on the crankcase. You’ll note in this instance that the crankcase will be extra thick or bulged out on a local area. You must use the rotor spacer. The rotor must be clear of the front face of the front pulley by anything, say 1 to 5 thou, 1 to 14 thou. You may (only may) need to add a shim/washer to the rotor spacer. Clutch Drum – make sure that the heads on the three square headed spring bolts do not foul the center of the alloy drum. If the heads foul you need to file or grind one flat only on each bolt (five minute job) The T140 alloy clutch drum is 2 mm wider than the cast iron drum. The front face of the alloy drum must be well clear of the left hand gear change spindle/rod. You may have to do an easy mod. You could file/grind 2mm off the thick part of the spindle, at the welded area, or shim out the spindle from the back. Belt tension at hot running temperature after 20 to 25 miles must be 3 to 6 mm total "free play" slack and not 10 mm as per primary chain. Due to heat expansions you are likely to need 5 to 8 mm cold "free play" slack of belt. If belt tension is not correct contact us for oversize or undersize new clutch drum.
T120 Fitting Instructions:
Using 25 mm belt and 25 mm wide front pulley. Same things to watch out for as
with T140 fitting. But no left hand spindle/rod to be concerned about. You’ll
need to add some shimming to the rotor spacer and you may have to slightly pack
out the stator with equivalent thick washers.
T120 using 29 mm belt and front pulley also 29mm wide. Obviously you need to well pack out the rotor and stator. If you run out of threads on the alternator studs you can buy three long T140 studs or chisel or mill off 2 or3 of the stator sandwich of plates so as to gain some threads for the stator nuts. With the 29 mm wide front pulley you may feel that the rotor looses too much contact on the crank. You could machine the dishing diameter on the front pulley a little wider and machine step the back face of rotor so that it sits into the front pulley a little. You will loose some wattage with this rotor offset but not a problem if you have the 3 phase high output stator.
Preunit belt drive at 30 mm wide, OK if you don’t wish to use outer chaincase and alternator. Preunit kit with front pulley and belt at 25 mm wide, you can use outer chaincase but you will need to use the later slimmer two wire stator and modern slim rotor – late 60’s onward rotor. Rotor and stator will need to be packed out a little. Clutch drum – make sure the heads on square headed spring bolts don’t foul on center of alloy drum. Belt tension at hot running temperature 5 mm total up and down free play. You’ll need 6 to 8 cold slack. Use three spring cush drive or machine the back face lip off the preunit four spring cush drive, so as to use all 12 clutch plates supplied; and do use the T120/T140 big (better) diameter clutch hub and bi-metal thrust washer. Preferably use the late preunit left hand adjuster so that the gearbox can be made parallel to crank.
Goldie, M20/21, B31/33 – belt and front pulley 25 mm wide. You can use 30 mm wide belt and front pulley at 30 mm if you don’t use outer chaincase. A10 kit OK to use standard outer chaincase with belt and pulley at 30 mm. The same rules apply as per preunit Triumph, except you’ll need a spacer on front face of front pulley and a special non standard big diameter mainshaft converter hub and thrust washer is needed. The special big hub and thrust washer are available. You need to use all T140 clutch internals.
Norton Dommie Kit using alloy Bonnie type clutch drum is an easy kit to fit. Similar rules to preunit Triumph belt drive fitting. The only mods are you may need to space out rotor and stator. The normal belt tension is needed. You need all the T140 clutch internals. Clutch plates are supplied with the kit. A special push on/tap on mainshaft big diameter converter hub is supplied. Front pulley and belt 25 mm wide. Front pulley usual taper and woodruff key fit.
3TA to Daytona Belt Drive – Front pulley and belt for racing 30 mm wide. You can’t use alternator. The road kit is 25 mm wide. The T120 etc. 25 mm rules apply here. However, these kits need to run slack when cold. Best to use the standard slipper blade, but with the rubber removed by burning or baking, then the steel now exposed highly polished. You should run in oil if a slipper is used. Gearing is –5%.
A65 kit – Early A65 not usually any mods to fit front pulley but do change all the early A65 clutch bits to the later 3 spring T140 type clutch internals. Later A65 clutch is OK, it is 3 spring, but metal will have to be removed from around the alternator stud area. This engine needs a slack belt when cold and due to expansion the belt will tighten up at running temperature. Best to use the slipper. Remove rubber and polish. Adjust belt tension cold to 4 to 5 mm total up and down "free play" and run in oil. Gearing is about 10% taller.
Commando Belt Drive – no mods or fuss to fit. Adjust belt tension cold to 6 to 8 mm free play then test belt tension at hot temp. (20 to 25 miles) and if necessary readjust the tension. to get 5 mm free play at running temp.
C15 to B50 belt drives – Not usually much fuss to fit. One may need to slightly space out rotor and stator.
General advice for all kits – At hot running temperature belt tension needs to be 3 to 6 mm total free play. If belt tension is not correct on "fixed center" engines – unit Bonnies, A65, Daytona, and unit singles – contact us for replacement pulleys.
Belts go brittle after four years in oil.
Front pulley single guide plate (keeper plate) must face outwards – to outer chaincase.
Do not use a slipper tensioner if system is run dry. And if you run dry you need air ducting.
When you have a choice of chaincase oil do not use multigrade – use thin 10 or 20 grade – maybe fork oil – or auto gearbox transmission fluid.
Do not mark, bash or scratch the teeth on the pulleys.
Note the white spot on the alloy drum, keep all 6 white spots on the friction plates in line to the white spot on the alloy drum.
Please study the T140 fitting instructions.
Fitting T140 & T120 - 29mm Wide
T120 - 25mm Wide Fitting Alloy Kit Belt Drive
T140 kit usually does not require any modifications to fit front fully. It could help to use a shim with the rotor spacer to gap the rotor from the front pulley to assist future removal.
T120 - 25mm wide belt and front pulley - again a good idea to use additional shims or spacer to go with standard rotor spacer for future removal. You may (only may) need to slightly space out the stator with 5/16" washers.
T120 - 29mm wide front pulley and belt: Rotor and stator both need to be packed out and little chance of a rotor to front pulley gap for easy future rotor removal. The guide plate must face outwards.
With all kits fit the front pulley minus the guide plate. Assemble the
clutch, then slide wiggle the belt on and last of all fit the front pulley guide
plate. Once you fully tighten the four guide plate screws it is doubtful you
will ever get them unscrewed unless you use a center punch. Do not bend or
damage the front pulley guide plate. Do not bash/damage the teeth on the two
Watch out for the square heads on the three spring bolts fouling the bearing housing on/at center of the alloy drum. You only may have to file and chamfer on each of the three heads (five minute job if you have to do it) Belt tension with a cold engine is 7 to 10mm total up and down "free play" slack. At hot running temperatures after 20 or so miles the belt will tighten due to heat expansion and at hot running temperatures belt tension should be 3mm to max 7mm total up and down slack.
Try fitting the front pulley in all six positions to find best fit. (This is only sometimes necessary.)