Check Valve AP8104251 – symptoms

Aprilia Caponord ETV1000 Rally-Raid AP8104251vacuum check-valve exploded viewA couple of folks have asked what the symptoms where that prompted the replacement of the check valves (AP8104251). Well, for a while I’d had an intermittent ‘cough’ or momentary stumble when lifting the throttle off idle …. maybe once every twenty times or so. More than enough to make your heart skip a beat when you think she’s about to stall just as everyone’s powering away from the traffic lights! Other than this annoying habit, everything in the garden was Rosie. Or so it seemed.

I’d cleaned and rebalanced the throttle bodies and all the vacuum hoses and inlet rubbers were perfect as they’d been replaced – but it kept happening. In the end with nothing much else to go on, I’d pulled the check valves and found them both to have failed.

Since replacing them, I realise there were other symptoms – very subtle –  and the sort of thing you adapt to without realising it.

  • Reduced engine braking. This was really noticeable within a couple of miles after the valves were replaced – Engine braking  is certainly  stronger now
  • ‘Burble’ from the exhausts on overrun. This is greatly reduced, especially at low RPM
  • Eratic idle during warm-up. The idle became lumpy at 65°C then smoothed out again by 70°C – now stable throughout.

With a few hundred extra miles under the belt, it’s fair to say that the intermittent off-idle stumble has well and truly gone which is great of course …. but I do miss that bit of ‘Burble’ on the overrun! So if you have idle issues and any of these symptoms ring a bell, then take a moment to check the valves as well as the usual old favourites – IACV, vacuum lines and inlet rubbers. You might be surprised.

Vacuum check-valve …….. part2

Aprilia Caponord ETV1000 Rally-Raid check valve AP8104251The new vacuum check-valve (AP8104251) arrived yesterday and today, while the rain poured endlessly from a depressingly black sky I set about swapping out the bad one on the front cylinder. Just to be Boy-Scout ready, I’d also made sure to have some new hose and stainless steel click-clamps to hand – just in case! Getting the old one Aprilia Caponord ETV1000 Rally-Raid AP8104251 failed check valveout is a real trial of patience and dexterity believe me! Here is a pic of the old valve cut in half and you can see that the valve has broken up completely.

 With the valve cycling anywhere between an estimated 11-73 times a second depending on RPM, it looks like the 0.5mm thick valve flaps suffer from fatigue and  rips develop where the material flexes most. The valve doesn’t completely fail until the flap is ripped away as my other (rear cylinder) valve is testimony too. That valve flows in one direction but also a very small amount in the other and when Aprilia Caponord ETV1000 Rally-Raid AP8104251 valve stress testviewed end on, light can be seen through the valve flaps leading me to think that rips have already begun. So now another new valve is on order and I guess I’ll make a note to check these again in 15K miles or so, it’s easy and quick to do – simply pucker up and suck or blow! 😳

Aprilia Caponord ETV1000 Rally-Raid AP8104251 one way valve sectionOh and I’ve been asked a couple of times …. why not use a cheap Ebay ball-valve replacement? Well it seems to me they’re just not designed to cycle rapidly, a ball/spring valve may well be susceptible to the same phenomena as an engine valve train at high rpm – valve bounce/float. Of course in the real world it may make no damn difference what so ever and I’m just a sucker for buying genuine Aprilia parts! 🙂

UPDATE

Aprilia Caponord ETV1000 Rally-Raid check valve AP8104251Second (rear cylinder) valve replaced and all now in perfect condition. In this case the valve was leaky as it had a tear down one side – so a partial rather than total failure. It also seems that these parts were upgraded some time ago, this looks like it’s a modification to the plastic body …. on the old one the case is simply presses together, on the new one it is welded. Maybe they had instances of the cases coming apart in service, who knows.