Service Bulletin

Date: December 2015

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.

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Introduction:

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 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 timing gears while charging of the air tanks and this is now known to be causing damage to timing gears and or compressor drive components. 

Previously, it was thought the "clattering" was coming from the compressor drive connection to the timing gears and / or backlash in the timing gears, however this is not the case unless significant wear or damage has taken place in these components.  

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 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 remove the fierce "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-dampered SC-9 compressor runs at twice engine crankshaft speed, the frequency and force of the point loading to components becomes progressively more severe and it is likely 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 Chrysler (not Rootes) engineers did not envisage the last of the export model TS3 powered Commer trucks (to NZ and Australia) with the SC-9 modification would last more than 10 years or so in "the colonies", so the harmonic damper may have been deleted for that reason.

They would no doubt be amazed to discover that these same Commer TS3's are being preserved, restored and used in increasing numbers in NZ and Australia - 45 or so years on.

 So by 
2015 - being decades past their projected "use-by" date -  all 3DB & 3DD-215 engines in NZ & Australian Commers with the non-dampered 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.
This Service Bulletin seeks to correct these issues.

Drive Belt Stretch:

Normal wear and tear over many years, plus the considerable and ongoing back and forth loading from the non-dampered SC-9 compressor, will have contributed  to the compressor drive belt stretching slightly and the internal "teeth" on 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 and possibly a sprung loaded belt tensioner fitted.

 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:
  •  Engineer and fit a 6" / 150mm diameter, 5lb / 2.3kg  harmonic damper for the compressor crankshaft pulley as per attached Rootes drawings. 
  • Your engineer will need to machine an existing automotive harmonic damper to match this size and weight. DO NOT exceed the specified weight and diameter.
  • Choose a damper that is as close as possible to 6" / 150mm diameter.
  • DO NOT use a larger diameter damper and machine the outer ring down to 6" / 150mm diameter.
  • The SC-9 compressor crank is counter weighted, so DO NOT use a counter weighted harmonic damper from a V8, V6 or rotary engine. 
  • Spigot the damper to the pulley as shown in the drawing and photos attached.
  • Use machined, 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 1.1/2" / 38mm 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. 
  • Remove the flywheel and timing gear housing to inspect all timing gears for damage / wear. 
  • Replace any gears with pitting or other damage / wear to the teeth as per engine workshop manual procedures. 
  • Re-shim all timing gear thrust clearances to .003" to .006" in total.
  • Replace the compressor drive belt with a new belt (from Seaco Wilson Ltd).
  • Where the new belt remains "slack", install a sprung loaded belt tensioner (also available from Seaco Wilson) to the "unloaded" side of the drive belt .
  • Check compressor crankshaft end float and shim to .006" to .010" clearance as required.
  • Inspect and replace or repair any compressor drive components including bearings if wear / damage is found. 
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CAUTION:

  •  All trucks with noisy timing gear "clatter" during charging,  DO NOT continue using the truck until the faults are remedied as per this bulletin.
  • It is very important that ALL of the repair items listed above are carefully undertaken by qualified, experienced engineers, because 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. 
  • 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 6" / 150mm harmonic damper.  We can supply if required.
  • Where the original pulley is used, high standards of machining tolerance, alignment and dynamic balancing are very important.
  • The new damper should then be removed every 5,000 miles so the condition of the original pulley can inspected and the center nut retaining the pulley to the compressor crank checked to tightness. 
  • Please DO NOT take short cuts or deviate from the procedures set down in this Bulletin. 
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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 local engineers:
  • A drawing is provided showing the exploded view of the  SC-9 damper arrangement.
  • Photos are provided of the UK option SC-6 damper and pulley, 
  • A photo is provided of the UK option SC6 assembly on a 3DB-215 engine
An update on this Service Bulletin will be issued once harmonic damper suppliers have responded and a standard harmonic damper has been chosen for these mods. 

Pre-modified dampers and compressor pullies can then be supplied at that stage, however providing engineers adhere to the Repair Proceedure (above),  a suitable new or used 6" / 150mm  harmonic damper can be locally sourced and modified 
(to 5lb / 2.3kg) as per the attached photos by experienced local engineers. 

Where technical assistance or repair work is required:

Contact: Mark Erskine.
P: (09) 2706001
M: 021 2541939
E: mark.erskine@actrix.co.nz