The cost of a cheap tool kit

This brief casefile is about the use of a cheap timing kit used to replace the timing belt on a 2015 Volkswagen Polo 1.2L TSI

I was asked to take a look at the car, whilst I was onsite for another job. The car was not running very well, apparently since it had a service and cambelt replacement.

The mechanic told me he road tested the car after the service and hadn’t noticed any problems. There were no DTC’s recorded when I looked at the car. It had only been a week or so, since the work was done.

I noticed that when I brought the revs up to around 1500 rpm, there was a slight misfire condition. I was surprised at the lack of DTC’s. I looked at the misfire counter in serial data, and noticed random misfires across all cylinders.

I also looked at the manifold pressure, which appeared reasonable at just over 320 millibar at idle, but it was a concern when coupled with the misfiring across all cylinders and the service carried out.

I didn’t have time to setup a cam and crank synchronisation check and I didn’t have a known good sample to hand. So that lead me to carry out a quick ‘in-cylinder’ pressure analysis.

Once I saw the results, I was convinced the timing was not quite right, even although I had no comparison for this engine. Take a look.

Polo ‘In-cylinder’ pressure, after cambelt replacement

Now take a look with the 4 cycle rulers in place.

Polo ‘in-cylinder’ pressure with detail rulers

Now you can see how the exhaust valve opening appears to be late, in comparison with the more common position’s I have captured. Of course I couldn’t condemn this as such, as it could be a particular characteristic of this engine, but the pattern didn’t look right. The garage went back and re-set the timing and I returned for another capture, as the vehicle was still not running right. The pattern was the same.
I was still convinced the timing was wrong and so I managed to find a known good vehicle to use for comparison. Take a look:

Known good sample taken from a VW Up!, with the same engine.

When I took this capture, I could then say, with confidence, the timing was definitely wrong.

The garage then borrowed a genuine manufacturer’s tool kit and re-set the timing. They also compared the quality of their tool against that of the considerably more expensive tool and noted a discrepancy in the accuracy of their cheaper tool.
After completion of the refitting of the belt, the car ran absolutely fine.

They have now purchased a genuine tool for doing cambelts on that engine.
An expensive tooling choice all together.

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