| AMS OD WP PULLEY and Parrallel-Offset FAQ This articles intended purpose is to shed light on OEM and aftermarket tolerances and/or variances with regards to ‘parallel offsets’ with relation to accessory pulleys, accessories and belts. There have been "unjustified" rumours and "undocumented’ claims that certain offsets will prematurely wear out accessories like the water pump when using aftermarket OD pulleys such as the Pexzed and AMS. What will be demonstrated is that such variances that lead to offsets are present within OEM water pump pulleys, OEM water pumps, OEM brackets and other OEM accessories! These variances contribute to ‘parallel offsets’ with the belts. There were certain pictures showing a deviation or technically speaking a ‘parallel offset’ of a miniscule scale of 2 mm. This measurement was taken with a rudimentary ruler akin to what was termed grade 3 level measurements. It was also taken at only one point across the belt interface (i..e water pump). This malleable rubber accessory belt spans over 15” from the water pump to the alternator. This same accessory belt loops around the crank and back to the WP pulley. For consistency we will use a ruler and also a micrometer to show variances in OEM components and how these variances will contribute to ‘parallel offsets’ and what ‘if’ any consequences are noted and documented! So let’s begin with some test subjects using an OEM New water pump, some used OEM water pump pulleys, a used OEM water pump and the AMS OD pulley. 
What was noted from the beginning was that ‘parallel offsets’ are present for various reasons in this case the water pump. Lets just take the aftermarket pulleys out of the and do some simple tests. We took a brand new OEM Nissan WP and a used unit. So we started measuring to determine if OEM Nissan components have variations themselves? As an ‘accredited’ master technician that has worked and owned Z32’s since 1992 I have seen several factors contributing to this! I alluded to the fact that bearings as they wear out can factor offsets. Same can be said regarding torque specs, gaskets and even rust! Varying production batches from OEM can also have variances in tolerances! An important characterization with the parts that we are analyzing is that we are dealing with ‘non-critical’ assemblies! These are not camshafts, cranks, pistons, rods etc. and as such can have higher tolerances without detrimental results even from the factory! We first measured a brand new OEM pump with a used pump (approx 40k). Pictured below is a brand new pump. We measured the total length with a micrometer to be 99.5mm. 
We then measured a used OEM pump pictured below at 100.52 (variance over 1mm): 
We then decide to measure the mounting flange for the water pump pulleys within the two pumps to show other variations! Pictured below is the new OEM pump flange: 
The noted thickness is 7.74 mm Again we measured the used OEM pump: 
The noted thickness is 8.11 mm Thus far we are showing that even in OEM components there are acceptable and non-detrimental variances in non-critical assembly parts! Now we decided to measure the pumps on a level surface with two OEM water pump pulleys to show how the offset is visible even with the naked eye. 
Once again we are showing variances in OEM parts on non-critical parts which will affect ‘parallel offsets’! We decided to take some measurements towards the first belt rib to show the variance: The new pump measures 68.86 mm: 
The old pump with an OEM pulley is measuring 70.08. Total variance is 1.22 mm 
What we have noted as well is that within OEM WP pulleys themselves there is a variance of .25-.75mm in three samples we measured. Very hard to see with the naked eye or measure with a regular ruler! As noted above when the pump is installed the variances can further change depending on gaskets (whether it is used and thickness), silicon, torque specs, rust/debris on mating surface. So we have dealt with the one interface point of this accessory belt – the water pump/pulley area and demonstrated that tolerance differences exist on these non-critical assemblies straight from the factory! To date there have been no recalls and or documented premature failures of water pumps. We can theorize that it may be accelerated but the facts remain that the Z32 has been out on the market for nearly 20 yrs and no evidence to support this unfounded theory should one argue! When we consider the alternator and crank these variances will further differ within OEM batches. Whether it be within the pulleys themselves or the brackets for the alternator! This variance is further offset when aftermarket alternators and crank pulleys are installed which all have tolerance variances. To demonstrate how much an offset can change just with an accessory mounting bracket we decided to measure the PS bracket due to location and ease of measuring. Anyone that has tore-down and re-assembled a Z32 or any vehicle for that matter will note that there are variances in how brackets mount. Very difficult to see with the nacked eye but present. We measured the PS bracket with it pushed and torqued towards the back of the car: 
We then loosened pushed the bracket forward and torqued and measured again: 
With the simple ruler it is evident that there is a deviation of over 1mm! So when the PS assembly is mounted this will ‘offset’ the pulley about 1 mm one way or the other. What is important to note is that we haven’t even factored in rebuilt pumps, deviations within OEM pumps, or pulley deviations (OEM, aftermarket). I can assure you they are there in varying degrees! The same scenario can be applied to the AC compressor brackets and pullies (OEM and rebuilt aftermarket), crankshafts and alternators. When one starts measuring all the variables you will quickly note that the assembly of accessory parts and their respective belts are non-critical parts with loose tolerances from the factory much less the aftermarket! If such variances or technically speaking ‘parallel offsets’ are extreme then the first indications are noisy belts and or prematurely worn belts. Once again these are in extreme offset circumstances which have yet to be noted and often time related to other factors (install error, debris, worn components). Lastly, we decided to show a couple pictures with the AMS OD WP pulley affixed to a used pump which arguably has more offset that a new one. We then installed a belt and took some straight on pictures to look for any extreme or visible ‘parallel offsets’ on the belt. Photo below depicts the AMS OD pulley looking down towards the 15.5” belt span towards the alternator pulley: 
Another photo showing the AMS WP OD pulley looking straight down towards the OEM crank pulley! 
There is not even a slight indication of any belt ‘parallel offset’ . We could take all the variables and combinations above and measure endlessly only to come up with difference offsets for seemingly every combination possible. Trying to get a 100% parallel alignment with the accessory belts even with OEM components and belts is not possible due to variance differences and tolerance allowances within non-critical assemblies straight from the factory much less the aftermarket! This FAQ was written to highlight the term ‘parallel offset’ with relation to tolerances and variances not only to the water pump pulleys (OEM and aftermarket) but other accessories assemblies on vehicles in general. To date there have been no documented failures or any adverse effects with OEM or aftermarket OD Pulleys due to OEM tolerance variations causing miniscule 'parallel offsets'. The importance of installing accessories and aftermarket assemblies properly is much more important! Improper belt ‘deflection’ (tension) can lead to premature belt/accessory wear. Consequently worn fans and clutch assemblies can lead to premature water pump wear. I hope the FAQ will bring some perspective in parallel-offsets and the variances in tolerances on non-critical engine assemblies! Regards, Vuk@AMS
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