The C word

November 9, 2016 - 12:04 pm

The main vulnerability to be aware of with the XU10J4RS engine is it’s appetite for Cambelts. Because the engine is whats known as an interference engine, if the timing belt snaps and the crankshaft turns independently of the camshafts there will almost certainly be internal engine damage. There have been countless occurences of cambelts snapping over the years, and despite Peugeot initially rebutting any problems they lowered the service interval from 72000 miles to 36000 miles. Yet even this interval has proven too long for a few individuals who ended up nursing a damaged engine. The main theory for the cause of the snaps is due to the RS’ heavy valvetrain with double valve springs and a relatively high rev limit putting added strain on the belt. There have been occurences of belt snaps as low as 10,000 miles after being changed, but these tend to be from incorrect fitting or a failure to replace the belt tensioners and/or water pump as the same time as the belt. If a tensioner is excessively worn it can disintegrate, seize and throw the belt. Similarly a worn water pump can also cause the belt to jump, hence why for the relatively low cost it is recommended to replace both when doing a timing belt change. An interval of 30,000 miles or 3 years seems to be a figure that most people feel confident a properly tensioned belt should last.

Tapping engines

October 28, 2014 - 10:10 am

With even the latest GTi-6s now reaching 15 years old, many cars are now exhibiting a tapping noise from the engine. This noise rises as the revs rise and can often sound like a sticky tappet. However more often than not the cause is more sinister;

1. Bent Valves following a Cambelt snap
Because of the GTi-6’s XU10J4RS appetite for snapped timing belts, a common cause of the tapping is in fact down to bent inlet or exhaust valves in the cylinder head. This occurs when the cambelt snaps and the pistons hit the valves as the XU10J4RS is an ‘interference’ engine.
The garage doing the repair may visually inspect the valves and decide they are fine to reuse without checking them in a lathe or similar. They can be very slightly bent, and that is all it takes to make the engine tap. These bent valves won’t show up on a leak
down or compression test as the double valve springs are very strong, the only way to diagnose is by someone with experience with these engines or by removing the cylinder head again and inspecting them.

2. Damaged valve guides following a cambelt snap
Another potential cause of tapping can be the bronze Valve guides that may get slightly damaged when the belt snaps and the valves hit the pistons. These are an interference fit in the head so need need changing by a machine shop.

3. Valve to valve contact
The third cause could be when timing up the cylinder head, the camshafts have been turned independently. When this occurs it is possible for exhaust valves to touch inlets as they overlap slightly. This ‘touch’ is enough to bend them and a few engines have become ‘tappers’ this way.

4. Crankshaft pulley slippage
A common problem that occurs with the crankshaft pulley is that due to its construction, the timing hole used to set the engine timing can slip round from its original position. This occurs through hundreds of heat cycles, torque stress and age as the bonded outer ring of the pulley moves in relation to the inner ring. Since the timing hole is on the outer part of the pulley its position can move. Thus if the pulley has slipped and is used to set the timing on the engine, after a cambelt change for example, the timing can be out and piston/valve contact can occur. It is essential to use a known good pulley to time the engine. A triple check would be to check the pistons are at half height in the cylinders and as a rough guide the woodruff key is pointing to 9pm (if you visualise the engine as upright not leaning back in the engine bay). Many people use a lighter solid crank pulley to eliminate this problem and reduce some of the rotating mass.

There are cases of ‘tappers’ dropping a valve after operating fine for thousand of miles. The valves may be weakened from being bent/impact with pistons and decide to snap, decimating the engine, often requiring a new engine block.

Some people decide to replace the whole engine to save on costs but there is no guarantee, the engine you’re buying is in better condition than the one being replaced. Generally speaking the best way to solve the tapping is to replace all the valves and guides in the cylinder head and have it replaced by a competent mechanic.

5. Loose spark plug

To end on lighter note, not all causes of tapping are expensive to fix – it may be caused by something as innocent as loose spark plugs. Simply removing the coilpacks and re-torquing the plugs can stop the noise.