Timing Belt Information
by Tim Engel

Esprit S1/S2 Workshop Manual (1978,  re-issued 1982).

Technical Data Section,  Belt Tensions,  Page 3

Toothed timing belt (133 teeth)

With both types of belt tensioners,  set the belt tension to an average reading of 90 – 95 units cold  (120 – 125 units hot).  Check toothed belt tension between auxiliary and inlet camshaft pulley,  with Burroughs Gauge Type  BT-33-86A  5-20.  Important:  Check the belt tension with number  1 or 4 cylinder at TDC after rotating engine at least one full turn clockwise (normal running direction).  Repeat this operation twice to obtain specified average reading.

Section E.9 - Camshaft Driving Belt (Toothed Belt),  Page 16

To Adjust: 

Do NOT attempt to tension a hot engine.  Only carry out this adjustment at an engine (ambient) temperature of between 15° - 25° C (59° - 77° F).

Use a Burroughs Gauge T000T0290A between the auxiliary shaft sprocket and the inlet camshaft sprocket in the following manner:

Fully  extend the hook by pushing the handle completely down before inserting the belt between the nose piece and hook, ensuring that the hook is between the belt teeth.  Release the handle with a rapid action.  A slow release will result in a  HIGH  reading owing to the small amount of internal friction present stopping the hook from fully returning.  Note the indicator reading.  Repeat action several times to "get the feel".

Take a further two readings at intervals of 120 crankshaft degrees,  turning only in the normal operation direction.  (No crankshaft timing starting point is specifically called out,  however,  the previous assembly section called for the crank to be set to TDC before installing the timing belt. --- tse)

The correct belt tension setting for all engines where  NO  air pump is driven off the back of the belt is:  90 – 95 units,  cold.  (120-125 units hot).  If the reading falls outside this range,  adjust the tension as follows with  No. 1 piston at TDC after rotating the crankshaft a minimum of one turn clockwise.  (clockwise as viewed from the front of the engine – tse)

Manual Tensioners:  Slacken the nut securing the pulley,  and by means of the hexagon on the front of the pulley,  adjust the tension of the belt.  After adjustment,  re-check t he tension with the Burroughs Gauge.

Semi-automatic Tensioners:  Where no air pump is driven off the back of the toothed belt,  slacken the locknut,  and screw the spring seat (adjusting screw) in or out to obtain the correct Burroughs Gauge reading.  Tighten the locknut.

On Federal engines where an air pump is driven off the back of the toothed belt,  first slacken of the air pump fixings.  Screw the spring seat (adjusting screw) clockwise until only one or two threads are showing above the locknut,  and tighten the locknut.  Tension the air pump to 5.5 kg-m  (40 lbs-ft)  using special tool part number  T000T0320A  and a dial torque wrench.  Entirely release load on air pum and then re-torque to a final tension of  2.8 kg-m  (20 lbs-ft)  and tighten all air pump mountings in that position.

Misc. Notes:

4b)  Slacken off locknut and release adjusting screw (spring seat) by turning anti-clockwise until the adjusting screw is protruding a  MAXIMUM  of 12mm (1/2 inch)  from the tensioner housing.  (12mm = .472"  /  0 .5" = 12.7mm…  choose your poison – tse)

 4d)  Force idler towards tensioner body (merely tension timing belt by hand) until groove on piston aligns with locking pin hole in housing,  insert a 4mm diameter pin.  This locking pin hole may be located on the lower side of the piston bore,  or on the upper side,  obscured by the upper fixing bolt/ nut washer,  which must therefore be removed.

 Adjust the inlet pulley snubber  (where fitted)  for a clearance of 0.50 – 0.75mm  (0.020 – 0.030 in)  between the back of the toothed belt and the snubber bracket.  Tighten the securing nuts via the pulley holes to 2.2 – 2.5 kg-m  (15 – 18 lbs-ft) using Loctite.  Service Bulletin 1976/03,  24 Mar 76,  added the inlet pulley snubber to 907 engines  WITHOUT air injection to prevent the belt from jumping teeth on sub-zero temperature cold starts  (sub zero C = sub-32 degrees F)  due to reduced belt tension owing to thermal contraction of the engine.

 Adjust the auxiliary pulley snubber for a clearance or 0.4mm  +/- 0.1mm  (0.16"  +/- 0.004 in) between the pad and the toothed belt.  (0.3 – 0.5mm  or  0.012 – 0.020 inch).

Esprit S3 / Turbo Esprit Service Notes (1985,  re-issued 1986).

Same as the Esprit S1/S2  and  Elite-Eclat with the following minor exceptions (noted in red above as well):

Technical Data Section  TD-A,  Ignition System,  Page 4

Engine belt tensions – Toothed timing belt,  using Burroughs gauge part number T000T0025J,  90 – 95 units cold (60° F, 20° C)  See Section EA.8.

Technical Data Section  TD-B,  Ignition System,  Page 3

Engine belt tensions – Toothed timing belt,  using Burroughs gauge part number T000T0025J,  90 – 95 units cold (60° F, 20° C)  See Section EA.9.

Section EA.8. - Camshaft Driving Belt (Toothed Belt),  Page 17

Prior to '86 M.Y.  all engines use a trapezoidal  (nearly square)  tooth profile belt with originally,  a manually adjusted eccentric belt tensioner,  and later a semi-automatic spring loaded tensioner.  1986 M.Y. Excel and U.S.A.  Turbo H.C.I. models and other engines at a later date use an H.T.D.  (High Torque Drive)  cam belt and pulley set,  having arounded tooth profile.  A manually adjusted eccentric belt tensioner is generally used with the H.T.D.  belt,  and no snubbers are required.

Use Cantilevered Burroughs Gauge  T000G0025J  between the auxiliary and inlet camshaft pulleys in the following manner,  removing the belt guard upper section and such ancillary equipment as may be necessary to gain access.

The correct belt tension for all engines where  NO  air pump is driven off the back of the belt is:  90 – 95 units,  cold.  (120-125 units hot).  If the reading falls outside this range,  adjust the tension as follows with  No. 1 piston at TDC  after rotating the crankshaft a minimum of one turn clockwise.

SYNOPSIS  of Lotus timing belt tension specs through the years:

Jensen-Healey Workshop Manual  (No Date Found,  P/N 8739).

 907,  with trapezoid belt tooth shape.

Elite – Eclat Workshop Manual  (1974,  re-issued '76 & '79 with Service Bulletins)

Lotus Service Bulletin 1977/1,  (15 Jan 77)

Lotus Service Bulletin 1978/19,  (24 July 78),  and…
Esprit S1/S2 Workshop Manual (1978,  re-issued 1982).

Esprit S3 / Turbo Esprit Service Notes (1985,  re-issued 1986).

910  & 912,  with HTD belt tooth shape.

Esprit S3 / Turbo Esprit Service Notes (1985,  re-issued 1986).

Lotus specified tension gauges:

Non-cantilevered Burroughs Gauge BT-33-86A 5-20
   Lotus Part Number T000T0290A.

Cantilevered Burroughs Gauge
   Lotus Part Number T000G0025J.

Burroughs sold the gauge line to SPX Kent-Moore.
   US$250 -- Out of series production, special order only.

Aftermarket Belt Tension Gauge:

HMC International Division, Inc.
Krikit KR1
Belt Tension Gauge,  Model Number 91107).
US $17.00 suggested retail  /  US $14.00 at

Tensioning Procedures:

From Lotus Workshop Manuals & Service Notes"

  1. Midway between auxiliary and inlet camshaft pulley
  2. Cold engine, before it's been started for the first time that day.
  3. Do NOT attempt to tension
  4. 15° - 25° C  (59° - 77° F) ambient temperature.
  5. Rotate the crankshaft a minimum of one turn clockwise.
  6. Crankshaft at TDC.

Take three readings at 120 crankshaft degrees and average (0 °,  120 °  &  240 °)

Tension Spec's  --  Lotus 9XX 4-Cyl Timing Belt:
FROM Lotus Workshop Manuals and Service Notes
(Krikit values are mine, YMMV, yada, yada, yada...)

HOT values given for reference only.
Always check timing belt tension COLD

1974  Burroughs  90 COLD,              120 hot
  thru  Krikit  KR1  50 lbs COLD           60 lbs hot.

1976  Trapezoidal Toothed Belt

 1977  Burroughs  95-105 COLD,  120-125 hot.
         Krikit  KR1  52-58  COLD,     66-69 lbs hot
         Trapezoidal Toothed Belt

 1978  Burroughs  90-95 COLD,   120-125 hot.
  thru  Krikit  KR1  50-52 COLD,       66-69 lbs hot

1987  Trapezoidal Toothed  and  HTD Toothed Belts

 1988  Burroughs  95 COLD,                125 hot.
  thru  Krikit  KR1  52 COLD,            66-69 lbs hot

1995    HTD Toothed Belts 

Tim Engel's Guidelines  --  all caveats apply,  YMMV,  yada, yada, yada.

Burroughs  =  Krikit ranges (my judgement, not Lotus – tim engel).

           <82 = 45  Park it... proceed at your own risk.
             90 = 50 
Normal minimum.
             95 = 52  My routine target tension.
           100 = 55  New belts, to allow for initial stretch (just me, YMMV).
         >105 = 58  Too tight, IMHO.

CROSS-REFERENCE -- Lotus 9XX Timing Belts:


Prior to 1986:     907,   910,   911,   912  Standard engines  (ie,  NOT  HC  or  HCI)

A907E0191Z,    trapezoidal tooth,  133 teeth,  912,  910  -  pre 1986

A907E0191ZE,  trapezoidal tooth,  133 teeth,  907
.......................... Z and ZE suffixes are interchangeable in terms of fit and function.

B907E1050FL,  trapezoidal tooth,  137 teeth,  907
.......................... Elite/Eclat  with Federal air injection pump

I have a new Lotus OEM belt on hand that measures  1.032" wide
Gates  5146  is  1.0" wide,  133  trapezoidal teeth.

Message from Gates Rubber UK

In response to your inquiry I can confirm that the 5146 timing belt does fit your car.   You can double check against the old belt, but belts should have 133 teeth and be 1" wide.   However,  I would be careful fitting it if it has been lying loose in the trunk with the possibility of it being "crimped" or folded by having heavy objects placed on top of it!   If it has been protected in say a box which saved it from being crushed it should be OK but if you have any doubt about how well the belt was protected don't fit it.!

If you contact any motor factor who stocks Gates belts they would be able to get you a new 5146 belt from their supplier.   Also,  look to fitting a new belt tensioner at the same time to avoid problems with belt tensioning.

Best regards,

Iain Mitchell
Sales and Technical Coordinator
Automotive Aftermarket
Tel No   01387 242075
E-mail   iainm@gates.com

HTD,  ROUND  tooth timing belt

1986 Onward:    NOT 907,  912HC,  910 HC,  910 HCI,  912 HC  (high compression)

A912E6697F,    HTD round tooth,  133 teeth,  912,  910  - 1986 onward

B912E6697F,    HTD round tooth,  133 teeth,  912,  910  -  1995 on,  Calif

.......................... HSN, California requirement for a 100k mile timing belt.

Written on the side of a new  B-prefix  Lotus OEM  HTD timing belt is:

"Gates PowerGrip HTD  Made in UK  B912E6697F  (464DS)"

DS on end of part number indicates Made in Scotland

The B-prefix  version of the HTD belt is made with HSN rubber  (Highly Saturated Nitrile rubber).  That's a very tough,  wear resistant rubber,  and Lotus gave the longest service interval to that belt.  It was introduced in response to California's requirement for timing belts to last 100k miles,  but I believe it became the default service replacement timing belt.  If you want the best belt for your 1986 or later HC engine,  then that's the one you want.  You can get an B-prefix,  HSN,  HTD  timing belt from Lotus  or from most independent Lotus parts suppliers...  ask if they sell the HSN version.  I know Jeff at JAE  in the US only sells the HSN version of the HTD timing belt.  To the best of my knowledge,  the trapezoidal belt is not available in HSN rubber.

A Gates Rubber Co.  T-188  is a 133 tooth HTD timing belt that will work on 9XX engines 1986 onward.  I'm not sure if the Gates T-188  is the same as the Gates PowerGrip HTD  belt that is the Lotus B-prefix  HSN belt.  Or what the appropriate change interval would be for the T-188.  The safe interval would be to treat it like an early,  pre-California belt until you can confirm otherwise.

Gates T188  Cross-Reference  applications:

In the US/ Canada,  just order a Gates T-188.

UK-owners have reported getting no where when asking for a Gates T-188,  but advise that asking for a 5168NS works (NS  =  Non Standard).  The belt that's delivered often shows up with the following long part number: 5168-58133-1-209DS. "5168" is the main identifier portion of the number.DS on end of part number indicates Made in Scotland. It's a T-188.

The Nissan Maxima belt reference is for the  VG30E  SOHC  engine as used in Nissan Maxima, Pathfinder, some? Pickup Truck,  1987-88 200SX and 1984-94 300ZX non-turbo.  It uses a 133 tooth timing belt that will also fit on Lotus 9XX engines. However,  like the Lotus engines,  the Nissan went through an evolution of timing belts.  So not all years of Nissan VG30E timing belts will fit your Lotus. More importantly,  not all Nissan VG30E  round-tooth timing belts will fit a Lotus.

(Ford used a variation on the same Nissan engine in the joint-developed Villager/Quest mini-van. However Ford insisted the engine be re-designed for a clearance valve train.  The result was the  V40 engine  =  Villager/Quest mini-van.  But I'm not certain the Ford-spec version used the same  T-188 timing belt ??  Something else to check out.)

The earliest versions of the Nissan VG30E engine used a trapezoidal toothed belt that will also fit on early Lotus 9XX engines.

Later versions went through a series of round-toothed timing belts.  Don't make the mistake of assuming all round tooth Nissan VG30E timing belts are created equal and install just any round tooth Nissan belt on your 9XX. Only the last iteration  (the HTD tooth belt)  will fit Lotus engines with HTD belts…  see below.

Nissan round tooth belts:

Lotus owners want to use the last version of the Nissan belt (Aux 1994 onward – Gates T-188  HTD timing belt.