Alternator Chain Slack

Coose · Post by **Coose** » Sat Feb 27, 2021 6:57 pm

Evening all,

I'm chasing a strange whine on my 1990 EXUP, which is loud at tickover but gets quieter once you rev the motor. It does also get quieter once the motor warms up, but it's still there.
You can hear it here...

https://youtu.be/5xRCqZvuH8I

I've been scratching my head for a while and have checked the camchain and tensioner but all is fine. So, I bought a cheap endoscope which is actually quite good, where the only issue I think I've found is the amount of slack in the alternator/starter hy-vo chain. There's no mention in the Haynes manual, but does anyone know how much there should be?

Here's a link to a video I took with the endoscope, where you can firstly see the top run with the chain lifting off the guide, and if you bear with it you'll then see the slack in the bottom run (I accessed the chain through the sump, hence it may seem to be the wrong way up).

https://youtu.be/gwS4T_EaBc4

Coose · Post by **Coose** » Sat Feb 27, 2021 8:35 pm

Thanks for your comments, that's reassuring about the chain. The whine you can hear in the video is quite loud, certainly louder than any other EXUP/Thunderace etc. that I can find on YouTube. Strangely, having gone around it with a garage stethoscope (i.e. a screwdriver and an ear) it's loudest at the thermostat housing!

I'm going to whip the clutch out and check the basket, although it doesn't get any louder when you remove the filler plug.
One other question, would you know the primary gear clearance value? In the box of bits I got with the bike was another clutch basket so I'm wondering if the primary gear clearance might be too tight if the baskets were "graded"?

Coose · Post by **Coose** » Sun Feb 28, 2021 12:37 pm

I've just dropped out the clutch basket and there's nothing to report there. There's a sensible amount of primary backlash, and although the three yellow damper springs are loose they would tighten when you pull the clutch in, which doesn't make any difference to the noise.

Now, I can see the hy-vo chain where it runs on to the crank. The guide looks good, but if I pull the chain away from the guide there's at least 8mm of clearance. Does that sound about right for an EXUP as it seems a lot to me?

You can just see it in this photo, where you can also see a nice Carillo rod.

Coose · Post by **Coose** » Sun Feb 28, 2021 1:37 pm

Thanks again for your input, it's greatly appreciated!

I think I may have had a breakthrough. I was just reassembling the clutch and noticed something which sparked off something that the guy who had the bike built had mentioned a while ago: -

"Just a point the clutch basket has cut outs on the outer ring, this was caused by the throw of the crank with the Carillo rods."

Here's a couple of interesting photos: -

Notice the marks towards the end of the fingers on the clutch jacket, and also the hammering on the outer friction plate. I think a little dressing may be in order....

Coose · Post by **Coose** » Mon Mar 01, 2021 7:22 am

The other basket I have is the same, so in that case I'm assuming that they skimmed two baskets at the same time.

I'm not too worried about the basket as it's been in there for nearly 30 years, with the first few as a race bike. (Yep, 30 years!

)

I put it back together yesterday afternoon and it still whines, although I did notice that the starter gears do "jangle" a fair bit so I'm wondering if it's a sum of the whole?

So, I think I'm going to fit a new sump gasket, change the oil again and ride it!

Thanks again to both for your input.