Sprag worries and related stuff

[rick]

A few times since I've owned the Falco I've had situations where I press the starter button and the bike sounds as if its going to start and stutters. If I let go and press again its starts fine. This has never bothered me, I've always assumed its bad contacts on the switch but have never inspected it.

Now a couple of weeks ago when riding out in the fine british countryside I pulled over for a comfort break and when I went to ride off my dash reset. I hadn't ridden the bike for maybe a week preceeding this, and although its on a trickle charger at that point it was only on for 6hrs a day. Up to this point I have never had a reset problem in the past - and actually haven't since (although have only ridden it a handful of times since).

All these threads I've been reading about changing batteries, wiring loom mods, soldering caps to back of dash, changing the solenoid to a yammy one all seem sensible... but the one that scares me most is the dreaded sprag clutch!

My usualy startup procedure is generally full choke and press the starter... she instantly fires up and I immeduately reduce the choke so that the revs are typically 2k. I never blip the throttle and intermittently hold the clutch lever in. I figure this is a good way to start the bike, reducing the kick back that may be present by opening the throttle on startup. There is not scary sounding mechanical rattles apart from the normal sounds!

So my question is... what can we do to ensure we seriously reduce the chances of getting a sprag clutch problem? If I perform the wiring loom mod, change battery, change the solenoid and keep her on a trickle permanently (together with good starting procedure) will this considerably improve my chances of not getting a sprag clutch failure?

I have so many other things to do to her when she's in bits over the winter and extra job or two won't hurt!

[mangocrazy]

I was talking to a guy a while back I've known for around 20 years and who has serviced all my bikes pre-Falco. His name is Ron and he works at Wylie & Holland in Wellington. To call him simply a mechanic is demeaning, really. What he doesn't know about motorcycles, keeping them going and fixing them isn't worth knowing, IMHO.

We got to talking about Aprilia V-twins and I raised the topic of the sprag clutch. Ron was adamant that the absolute No. 1 priority for avoiding sprag clutch failure was to never start the bike with anything less than a fully-charged and A1 condition battery. If you get dash resets, then investigate the problem and fix it, before it fixes the sprag clutch. So as long as the battery is kept on an Optimate/Accumate when not in use, that will ensure good battery condition, assuming the battery is not on its way out.

The other mods (new solenoid, new battery, soldering caps to the back of the dash, doing the wiring mod) may or may not be necessary, depending on the overall health of your electrical system. If you have good reason to suspect your battery, it's probably smart to replace it before you next use it. Otherwise, just keep it on a suitable trickle charger expressly designed for bikes.

And your starting procedure is the one I use - hold the clutch in, give the bike full 'choke' and press the starter. It should instantly fire up and then immediately reduce the choke so that the revs are typically 2k or slightly less.

[fastasfcuk]

i had tha same problems a couple yrs back after a run the dash would reset. after talking to saun at corse performance, who races aprillia's,told me to nip my battery terminals up even if they seemed tight.it cured the problem never to return. got to be worth a go.cost nothing.

[rick]

Cheers for the replies guys

I'm going to check the battery health tonight... check voltage at ignition, during startup at idle and 4k revs. The battery was new in March and has been on an optimate ever since but only for 6hrs odd per day on a timer... its now on permanently

When the bike is stripped down in the next few weeks I'll also check all connections make sure good contacts are being made. After this, and depending in the results above, I may invest in a new battery or perform the wiring mod...

Is it a good idea, as preventative maintenance, to upgrade the solenoid?

[rick]

Taken some measurements (old drunk geezer in the close behind my house knocked on my garage door which always makes me laugh). The dash voltmeter appears to be between 0.2-0.6V down on the independent voltmeter applied across the battery terminals.

Readings (voltmeter across battery):
IGN OFF: 12.8V
IGN ON: 12.6V
STARTING: ~10V
IDLE: 13.6V
4K: 13.5V

The bike was *nearly* up to temperature, the choke was fully back in, but I started to feel pretty bad when the bike neared 4k due to neighbours complaining

The voltage at ignition off, ignition on and starting seem fine, as does the idle value, but I'd expect to see the volts climb with an increase in idle speed, which they didn't... thoughts?

I didn't have time to look at the cables under the rear right-hand side fairing but will do at some point.

[anzacinexile]

The voltage at ignition off, ignition on and starting seem fine, as does the idle value, but I'd expect to see the volts climb with an increase in idle speed, which they didn't... thoughts?

Perfectly normal. We have alternators not dynamos which means they produce AC current, not DC. As the revs climb, so does the frequency of the AC current and the rectifier diodes in the voltage regulators get less efficient as the frequency rises.

Your values are within spec according to the manual but voltage readings are no indication on how healthy the battery is unless its completely buggered then the volts will collapse as you pull current

[rick]

ok thanks for that... next time i can brave the weather (and the annoying neighbour!) I'll repeat, put a load on the system and also check the temp of the connectors under the rear fairing.

electrics was never my strong point at uni, but i do understand the basics of what rectifiers do and how the conversion to dc is smoothed with capacitors etc... but why do they get less efficient with higher frequency? is it related to some some of time constant of the system? the diodes can't keep up or something, experiencing some sort of dead time?

[anzacinexile]

Nothing complicated. Diodes have a switching time and during the switch, current is dissipated in the diode (be it very briefly). The switch speed/time is constant so the slower the frequency, the less switching (and hence time and current dissipation) is spent so as frequency increases, so do the losses.

You can mitigate the losses by using higher speed diodes but they are more expensive but what the heck, the regulators work fine and what's a 100mv between friends

[rick]

Did a couple of checks at lunch... although I previously said the voltage on dashboard is within 0.5V this is only true when at idle... when any load is placed on the system it undereads by at least 1V.

I let the bike warm up, main beam on and indicators... dash said 12.3V whereas the independent voltmeter initially decreased by 0.5V or so and then recovered pretty quickly to 13.8V. As the idle speed increases this decreases slighty, consistent with anza's explantion.

I did find that if I put the brake lights on as well the voltage dropped to around 13.1V.

All in all I think its ok... but when I strip her (oo-er) I'll give all contacts a bloody good going over, as well as checking out the connectors near the rectifier.

ta all.