I hear you knocking
In the August 2021 issue of CM, I’d handed over the Daihatsu Terios to its new owner, Classics Monthly magazine Editor Simon Goldsworthy, after servicing the vehicle and trying to solve a slightly worrying problem. On start-up, a bottom-end knocking noise could be heard if the engine was revved or driven under load, but only within the first couple of minutes. At the time, my investigations had drawn a blank, but Simon was happy to collect the vehicle and look further into it.
Simon and I agreed that the knocking noise couldn’t be caused by worn or dry main and big end bearings because the problem would get worse once the engine oil had warmed up. Several people suggested piston slap, which can happen on older engines due to the materials the pistons are made of. CM’S Technical Editor Steve Rothwell doesn’t think this is the problem on the Terios, but explains, “The expansion of the pistons when warm will ensure that it then becomes a better fit in the bore, and the noise you are hearing which I believe is piston slap will disappear.” However, he also thinks this is unlikely to be the
cause of the Terios’s problem, because the more modern materials that the pistons are made from should not have a different expansion rate from the bores on the 3SV engine in the Daihatsu.
Other thoughts
Simon did wonder whether the problem could be caused by a leaking exhaust manifold gasket or possibly a cracked manifold, as that could allow gas to escape when cold, but be slight enough to close as the metal warmed and expanded. Pinking was another thought, perhaps if one or more sensors were sending duff information to the ECU. Finally, some research online did suggest that the VVT-I system on Toyota engines (yes, this Daihatsu has a Toyota engine) was a potential source of problems, especially if oil changes had been neglected and the valve timing mechanism had gummed-up as a result.
Armed with so many potential causes, Simon opted for changing the combined oil control valve and camshaft timing solenoid, as a new one was less than £30 online. “I thought it would be worth replacing that, if only to help rule one possibility out,” he explains. “The new valve made little difference – the noise did sound slightly quieter afterwards, but that could have been my imagination, or perhaps because the weather had warmed up considerably since the last drive.”
The next idea was to hand the Terios over to Simon’s local workshop, Hall’s Garage, who spend a lot of their time working on classic MGS. “I left it overnight and then tried to show them the noise the next morning,” he says. “Of
course, the noise was no longer there. We did manage to provoke a slight trace of it on a test run, and Michael suggested it might just be a slightly sticky tappet, and that some regular use, plus a hydraulic valve lifter treatment, might be all that was needed to sort it out.”
Simon bought a 325ml tin of Wynn’s Hydraulic Valve Lifter Treatment for £8, extracted some engine oil using a syringe and windscreen washer tubing, and poured the treatment into the engine. Unfortunately, this didn’t cure the noise, so it wasn’t a tappet-related problem.
Returning to Hall’s Garage, Simon left the Terios with them for a few days to use, driving back and forth between home and the workshop. They wondered whether changing the oil inside the automatic gearbox would help. “The gearbox oil was a long shot after Hall’s had had the car for a few days to drive to and from work,” says Simon. “They found that if you knocked it into neutral while driving, the noise went away. I am sure that this was because the engine was no longer under load, but we figured an oil change would be relatively simple and rule that out.”
Sadly, the new oil inside the gearbox didn’t cure the knocking noise. Simon is now understandably metaphorically
running around in circles with his Terios. The leaking exhaust manifold is a vague possibility, but there’s no sound when the engine is revved from cold but not under load, so that pretty much rules out such a problem. He’s even contemplating fitting an oil pressure gauge, having bought a deep 24mm socket to undo the oil sender gauge, but everyone agrees that low oil pressure would have resulted in more clonks from the engine when it’s warm.
For those of us who have experienced a similar niggling problem, we can all sympathise with Simon’s dilemma, especially considering he bought the Terios for his wife to use over winter, so
The plastic syringe had only cost a few pounds online.
he doesn’t want to find the engine fails due to a problem he could have fixed.
Toyo tyres
On a more positive note, at least the Terios’s tyres are ready for winter use, having been changed for a set of 215/65 R16 98H Toyo Open Country Urban Terrains (U/T) – the tyres that were fitted when we acquired the vehicle were worn and the sidewalls had started to perish in places.
Just like me, Simon likes the way the Terios drives, explaining, “It is a surprisingly decent car to drive. For a robotised manual, the gearbox is pretty smooth and not too lethargic. The ride is very smooth, soaking up bumps well. Visibility is generally good. It is not a sports car as there is some bodyroll, but it was not bought for chucking around. It is a spacious and fairly versatile car on a compact footprint that really doesn’t feel to me like a 15+ year old car. The only niggles are a speedo that is calibrated in even numbers (20mph, 40mph, etc) instead of odd numbers including 30mph, and having a rather pointless rev-counter instead of a temperature and/or oil pressure gauge.”