Service Bulletin - Compressor "Clatter"

Date: Updated 08 March 2021

Subject: TS3 Rear Mounted Compressor "Clatter" (NZ and Australian 3DB and 3DD-215 models).

Author: Mark A Erskine.

Reviewed by:

  • Mr Don Kitchen, former Rootes Diesel Engineering Division Design Manager, Chief Engineer and Technical Administration Manager, UK.

  • Mr Wayne Fisk, Mechanical Engineer, Lower Hutt, NZ.



In New Zealand and Australia, the last series of export model Rootes TS3 powered Commers (3DB & 3DD model engines) were fitted with the Clayton-Dewandre SC-9, rear mounted compressors.

Rootes new owners, Chrysler had terminated Rootes TS3 production in 1967 to protect their investment with Cummins and Perkins and the decision to fit the last of the export model TS3 powered Commers for New Zealand and Australia with the larger SC-9 compressor was a Chrysler decision.

This arrangement became renowned for the metallic "clattering" from compressor drive components while charging of the air tanks.

I have discovered there are critical differences between the same model TS3 Commers supplied to the UK market with rear mounted compressors and the export models sent to NZ and Australia. These differences result in the UK models having little or no timing gear "clatter" at all.

The differences are:

  • UK models use a smaller SC-6 rear mounted compressor (same as used on Perkins 6.354 and some Bedford models).

  • The SC-6 compressor crankshaft pulley is fitted with a balanced harmonic damper to maintain compressor momentum and absorb most of the "back and forth" loading to timing gears from compressor induction and compression strokes.

Cause of Clatter:

Without a harmonic damper fitted to the larger SC-9 compressor, the fierce back and forth motion created by the compressor induction and compression strokes causes the helical cut TS3 engine timing gears to thrust backwards and forwards against their thrust washers and as these thrust faces wear, this is what causes the "clattering" sound.

The greater the thrust washer and housing register wear , the greater the amount of end float on the gears and this causes the volume of the "clattering" to increase.

The louder the "clatter", the more likelihood there is of timing gear damage or failure.

As the non-dampened SC-9 compressor runs at crankshaft speed, the frequency and force of the point loading to components becomes progressively more severe as wear and damage to components increase and it is likely the compressor drive and timing gears have only survived this long because they were originally over-engineered by Rootes Diesel Engineering Division Designers and Development Engineers.

It's reasonable to assume after Rootes were taken over by Chrysler in 1967, that their termination of the TS3 and TS4 production to favor their new joint venture Cummins V6 and V8 4-strokes and Perkins inline 6-cylinder engines, influenced their decision to not bother to install dampers on the larger SC-9 compressor.

Chrysler management of the day would therefore be amazed to discover that these same Commer TS3's with the non-dampened SC-9 compressor are being preserved, restored and used in increasing numbers in NZ and Australia – 50 years later.

By 2021 - being decades past their projected "use-by" date - all TS3 model engines in NZ & Australian Commers with the non-dampened SC-9 compressors will now have varying degrees of wear to:

  • The timing gear thrust washers and registers either side of the timing gears.

  • Pitting and other damage / wear to timing gears.

  • Wear and other damage to the compressor drive components.

  • Worn compressor drive pulleys

  • Worn / stretched compressor drive belt

This Service Bulletin seeks to correct these issues.

Drive Belt Wear & Stretch:

Normal wear and tear over many years, plus the considerable and ongoing back and forth loading from the non-dampened SC-9 compressor, will have contributed to the compressor drive belt stretching slightly and the internal "teeth" and internal surfaces of the belt to wear.

The resulting "slack" in the drive belt will be adding to the overall force on impact caused to the thrust faces, timing gear teeth and compressor drive connection, therefore the belt needs to be replaced with a new belt (from Saeco-Wilson Ltd in NZ).

Compressor Pulley Wear:

After decades of use, the “teeth” on the top and bottom compressor drive pulleys are now worn and the pulleys slightly reduced in diameter from wear.

New pulleys or used pulleys in much better condition must be installed to increase the pulley diameter and to better fit the new drive belt.

Repair Procedure:

The rear mounted SC-9 compressor can be retained providing a series of modifications and repairs are undertaken to eliminate the "clatter" as follows:

  • Remove the compressor drive belt and SC-9 compressor.

  • Remover gearbox, flywheel and timing gear housing to inspect all timing gears and compressor drive components for damage / wear.

  • Replace any gears with pitting or other damage / wear to the teeth as per engine workshop manual instructions.

  • Check all timing gears have correct factory backlash clearance.

  • Re-shim all timing gear thrust clearances to .004" to .008" in total.

  • Replace worn compressor drive components including bearings with new or good used parts that comply with workshop manual clearances.

  • Install new compressor drive pulleys (or good used pulleys).

  • Reassemble and trial mount compressor to engine mount flange to check belt tension complies with workshop manual instructions.

  • If new belt remains “loose”, remove gasket between compressor and engine mount and re-check belt tension.

  • Where drive belt is still not tensioned correctly, install a sprung loaded belt tensioner (also available from Seaco-Wilson Ltd in NZ) to the "unloaded" side of the drive belt, OR have a competent engineering company machine the compressor “sump” flange to tighten the belt.

  • Check compressor crankshaft end float and shim to .006" to .008" clearance as required.

  • Refit compressor to engine mount using Loctite 518 flange sealant.

Harmonic Damper:

  • Once all repairs to compressor drive components including bearings, timing gears, timing gear thrust clearances, compressor drive pulleys and drive belt are completed, the supply and installation of a new harmonic damper to the compressor pulley may be considered.

  • The truck can be used without a harmonic damper fitted to the SC-9 compressor if required.

  • Where no previous harmonic damper was designed or developed by Chrysler engineers for the SC-9 compressor, companies who specialize in the design and manufacture of harmonic dampers should be approached to design and manufacture this item.

  • The mass and dimensions of the inner hub and the outer ring and the elasticity between the two need to be calculated and designed by specialist engineers.

  • Spigot the damper to the pulley as shown in the drawing and photos attached that depict the UK SC-6 layout..

  • Use high tensile 5/16" diameter UNC thread studs (not bolts or socket head cap screws) to secure the damper to the crank pulley.

  • Due to the thin surrounding metal on the compressor pulley, secure the studs at least 1" / 25mm down into the compressor crank pulley and Loctite the studs in place with Loctite 243 Threadlocker.

  • The exposed thread on the studs should be 5/16" UNF thread with a 1/4" / 6mm blank section on each stud protruding above the face of the compressor pulley.

  • Use 5/16" UNF nylock nuts and lock washers to secure the harmonic damper to the compressor pulley.

  • Dynamically balance the pulley / damper assembly before mounting to the compressor.


  1. For all trucks with noisy timing gear "clatter" during charging, DO NOT continue using the truck until the faults are remedied as per this bulletin.

  2. It is very important that ALL of the repair items listed above are carefully undertaken by qualified, experienced engineer.

  3. A partial repair or a repair done to a poor standard will (not might) result in accelerated damage / mechanical failure to timing gears and / or compressor drive components.

  4. The SC-9 pulley is not designed to carry a harmonic damper, therefore owners and their engineers should consider the additional cost of machining a new, more robust design pulley for use with the new harmonic damper.

  5. Where the original pulley is used, high standards of machining tolerance, alignment and dynamic balancing are very important.

  6. The new harmonic damper should then be inspected every 5,000 miles with all retaining nuts being checked for tightness and condition.

  7. Please DO NOT take short cuts or deviate from the sequence of repair procedures set out in this Bulletin.

  8. Once the timing gears, timing gear clearances, compressor drive components, belt and pulleys have all been repaired or replaced, the “Compressor Clatter” will be significantly reduced.

  9. Please DO NOT experiment with your own version of a harmonic damper or solid flywheel for the SC-9 compressor.

  10. It is better to run an SC-9 compressor without a harmonic damper than to fit an incorrect home made or after market damper of incorrect mass and / or dimensions.


This Service Bulletin is provided to all NZ and Australian Commer TS3 owners so that repairs can be undertaken by local, experienced diesel mechanics and local engineers / toolmakers.

To assist qualified local diesel mechanics and engineers:

  • A drawing is provided showing the exploded view of the smaller SC-6 damper and pulley arrangement as a guide only.

  • Photos are provided of the UK option smaller SC-6 damper and pulley as a guide only.

An update on this 08 March Service Bulletin will be issued once a harmonic damper manufacturer has calculated / designed a harmonic damper specification for the larger SC-9 compressor.

Dayco Australia have recently manufactured a damper for a customer, who has bolted this damper to his SC-9 compressor without undertaking all of the initial repairs listed in this website.

Dayco advise no calculations were undertaken by the customer or the supplier to determine the correct mass of the outer ring, inner hub or elasticity between the two.

Instead, this damper is based on estimated dimensions and estimated total weight, which this Service Bulletin warns against and this damper has been incorrectly attached to the SC-9 compressor pulley