check-valve | Moto-Abruzzo

08/10/2015

Check Valve AP8104251 – symptoms

Aprilia Caponord ETV1000 Rally-Raid AP8104251vacuum check-valve exploded view A 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.

25/09/201527/10/2015

Vacuum check-valve …….. part2

The 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 valve out 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 test viewed 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! 😳

Oh 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

Second (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.

04/09/201514/10/2015

Pucker up and suck or blow …. your choice!

Here’s todays little quiz ……

What’s this?
Where does it go?
How many are on YOUR bike?

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Of course the smarty-pants among you will scream out the answers to 1 & 2 in double quick time – it’s a check-valve or none-return valve and it fits between the throttle body and clutch in the vacuum line. Excellent stuff, spot on …… but question 3 …… one valve or more than one? Hmmm.

Here’s what Aprilia show in the parts manual (click for photo of matching engine) …..

The front cylinder throttle body port has nothing but a piece of clear hose and a bung – the manometer/VAC gauge test point. All the slipper-clutch hose/valve assembly is ONLY attached to the rear cylinder throttle body port and TPS port. This may well be fine and dandy for an 01-03 bike.

But if you have a Rally-Raid or an 04-onward bike, next time you’re under the fuel tank/airbox take a good look at the front hose …… my guess is you’ll have a ‘T’-piece and more black hose disappearing downward below the mire of cables and wires running alongside the frame. Now this might be no surprise to you, but it had me scratching my head for a while I can tell you! 😕

And this is what I’ve got on the Rally-Raid (click to enlarge)……

A second complete set of pipes AND a second check valve connecting to another ‘Y’-piece. Why do this? Well this is my hunch, guesstimation, call it what you will ….. the 01-03 Capo has I believe a clutch pack that is 43.6mm thick, the 04-08 is 44.9mm thick. A difference of 1.3mm – in other words the valve springs will be compressed an extra 1.3mm on later bikes and that means a little more spring preload for the vacuum system to overcome when getting the clutch to slip, hence the second set of connections to improve the vacuum – 2 cylinder are better than 1! Also, two sources of vacuum from cylinders running out of phase (60° remember) may well help smooth out the pulses you can sometimes feel through the clutch lever. It simply looks like Aprilia modified our blessed Caponords and just didn’t bother to update the parts manual.

So what’s all the hullabaloo, why rip this poor little thing from the Capo’s delicate innards? Well the long and short of it is that one of them is pooped, shot, completely knackered ….. where air should only flow one way, it flows happily in both. Looking at the defective duckbill valve reminds me of Daffy-Duck cartoons, the ones where Elmer Fudd rearranges his bill with a shotgun! No worries, simply order a replacement …….

……. Aprilia part no AP8104251 Just make sure you’re sitting down when you look at the price! 🙁

I’ll shortly open up a new page with some more 3D images to try to better illustrate how the system is operating at different stages and how to go about testing the valves and what to expect.