Has my sprag clutch gone? Aprilia RSV

[MarkJ]

Morning all,
The other week the RSV wouldn't start after work. It was the first properly cold day we'd had round here. The starter motor was turning but the engine just wouldn't catch which gave the dreaded banging sound against the RSV's world famous weak sprag clutch. After trying to start the engine for a few minutes the battery died. I left it overnight and fitted another fully charged battery the next morning. It still struggled to start but kicked into life when giving it wide open throttle (at this point I was thinking it was flooded). I turn it off as it's dinner time.

Come home time it's being awkward, it starts after much protesting and idles fine with the fast idle on, but turn the fast idle off once it's up to temp and it dies. I leave it at work again and trailer it home the next day - Saturday.

Fast forward to this weekend, which was the first chance I've had to look at it, and it won't catch at all. The starter just spins without the engine catching at all with no throttle and full fast-idle. Give it WOT and you get a few 'puffs' out of the exhaust every now and again but that's it. It did kick back again when trying to start it which I think might have been the final nail in the coffin for the sprag.

Now, I've never had to replace a sprag on any of my bikes before so I wanted to make sure it was this and not something else before I started taking the left side of the engine apart. Has anyone with a Mille ever had the sprag go? Do these symptoms sound like the sprag? The morning that I rode the bike to work it was running fine, no misfires or anything.

If it is the sprag, does anyone know the tools (with correct sizes of threads/head sizes) that I need to buy to inspect the sprag. Guides online seem to suggest I'd need a flywheel puller and crank holding tool.

It's a 1999 Aprilia RSV if that makes any difference.

TLDR: Starter turns, engine doesn't fire. Sprag broken?

Cheers

[hmmmnz]

it sounds very much like it,
its a weakness with all rotax based engines,
on the plus side its an easy fix

here is my write up on the mzforum
https://www.mzriders.com/viewtopic.php?f=26&t=4014
____________________
the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[stonesie]

What you didnt say is weather the engine is turning over or not, the sprag transmits the torque from the starter to the flywheel to turn the engine, if it fails the starter will spin like hell but the engine will not crank and there may be a rattling from the sprag as it's trying to engage.


Reading what you did say..
The engine is turning over but not fireing unless on full choke.
When it did run it would not idle.
When you knew the battery was dying and the sprag was banging you kept trying to start it anyway.

Sounds like carb problems and you might have knackered the sprag by trying to start it with a goosed battery.

[MarkJ]

I'm not sure if the engine is turning over or not, which is why I'm asking for the symptoms of a busted sprag. I'll try starting it when I get home to see if any gasses are being pushed out the exhaust when the starter button is pressed.

There's no rattling from the sprag/flywheel area when the starter is turning.

It won't fire at all now regardless of fast idle or throttle settings (it's fuel injected and doesn't have a choke as such)

The bike only hit the sprag once on the old battery.

If the sprag is duff does it definitely give a grumbling sound?

[MarkJ]

Ok, I've just checked it, it looks like the engine is turning over after all.

When I thumb the starter button you get air coming out of the exhaust. It actually feels more like a vaccum where it's sucking your hand in but I assume this is back pressure? So looks like I'll have to check for a spark etc.

I'm away from tomorrow morning with work so won't be able to have a proper look at the bike till Saturday now unfortunately. I do have a 2002 Mille R track bike though, so at least I can swap working parts between the two to try them out!

[Pete.]

Is it turning faster than normal? Sounds like a busted cambelt/chain or other top-end issue.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[MarkJ]

I did think it was turning over slightly quicker than normal, yes

Not loads though - I'd put it down to the 14Ah battery I put in instead of the 12Ah.

Do you think the timing has gone off, Pete?

[Pete.]

That or you broke/bent/burnt a valve. I would run a leakdown or at least a compression test.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[MarkJ]

Will do. Shall have a gander Saturday.

[MarkJ]

Finally compression tested it after buying a comperssion tester that actually works.

Did a 'normal' test on both cylinders - one spark plug out of each cylinder so there was no interference from the other (it's two spark plugs per cylinder), no oil down the bore, turned over by shorting the starter solenoid so there was no fuel being pumped in, WOT.

180 psi on both cylinders - Aprilia forums say it needs to be 160-210 psi

So I take it a leakdown and compression test with oil down the bore isn't needed now?

When I bought the bike last year the bloke said he'd changed the spark plugs for me because it had been fitted with the wrong ones. He showed me one of them to prove this and said "oh, getting the front plugs out is a bugger isn't it!", it sort of is as you have to take the airbox out to get at them, the rear plugs are revealed when you tip the tank backwards so are nice and easy. I had no reason to suspect he hadn't done this.

Turns out he just changed the rear plugs
The front had Denso XU27EPR-ZU and rear had NGK DCPR9E. They can both apparently be used on the RSV but the DCPR9E's are the factory recommended ones. The top connector cap was loose on the XU27, the electrode gap was visually larger, and I'm not sure if something funky is happening with the elctrode - it's definitely a smaller diameter and I'm not sure if it's also got a little bit of gap bridging going on.

Time to check the ingnition system to see what spark I'm getting on all four spark plugs?

[MarkJ]

Pics attached, big so you can zoom in on the electrodes. I think the XU27 might be an iridium plug.

[stonesie]

The Denso is an irridium plug and the other is just a normal basic one, stick a complete set of new plugs (Irridium or standard is your choice) in it just so you know they are all as they should be.
A massive plug gap will make it harder to start and could even misfire.

Compressions sound good and even, and that indicates no bent valves or skipped timing

[MarkJ]

It's working I don't know what I did

I've had the starter solenoid off when manually cranking the starter, I've had the LT side off all the coils when compression testing, HT caps off just now as I checked the spark on all of them with a new spark plug (all worked) and I've had the fuel injector connectors off just now when testing the spark.

All I can think of was a poor connection on one or more of those connectors! Oh well, cheap fix! Going to give it a full service now anyway.

Thanks for all your help