MRC Forum- brought to you by www.morini-riders-club.com

Hi all,

I have a 1980 3 1/2 Strada and changed the timing belt last weekend. It’s a type C belt and everything appeared to go well, with the bike starting and idling well. The issue came yesterday when I took it for it’s first proper ride - after about 20mins the bike began making a secondary low whining noise (tricky to describe) at low revs, but clearing as I accelerated. The noise kept reappearing, albeit intermittently around tickover. I’d ridden it to work, so mindful that something wasn’t quite right, I rode the short route home in the evening, with the bike running perfectly until it came up to operating temp, when the noise reappeared.

I’m assuming this is belt related, as it’s the only change I’ve made to the bike. I’m also assuming that the belt doesn’t require ‘bedding in’, so wondered if anyone has any insights? The bike is safely back in the garage ready for a strip down this weekend…

Thanks in advance guys
Tim

Hi,

If you are going to do a belt check over the weekend and everything has gone back together correctly, it may be worth checking for any play in the camshaft bearing (does the pulley wobble?).

I had a ball race fail on a bike, albeit a main bearing, and it made a discernible “whine” when warm.

Sincerely hope you find the problem and it’s not serious.

I’ve had a few belts recently which have not been a great fit on the pulleys- either too loose or too tight. If too tight they tend to whine and it’s particularly noticeable if you rev in neutral you’ll hear it whine on the overrun.

If you bought a graded C belt from Mdina then of course the fit should be perfect but don’t rule out wear in the pulleys over the last 40-50 years which could change the tolerance so it’s always best to still check the slack in the belt, as described in the blue book.

I find that placing a straight edge between the pulleys along the belt and then pushing an Allen key in between the edge and the belt is a good way to measure slack without any special tools. In my experience a 4mm Allen key is about right, a 3mm will whine and a 5mm will be too loose

Measuring belt slack. Bear in mind that there will be differences in tension depending on where the cam is so always rotate the engine clockwise a couple of times by hand and align the timing marks before measuring for mists consistency.

Brilliant - that’s really helpful. The belt did come from Mdina Italia, but I’ll be checking this weekend!

I had a belt that was a struggle to fit. Started the bike and it whined worse than an MP not being able to claim for a paper clip. The belt was tight. I now use Conti belts. At £16 for two delivered I change annually, regardless of mileage and tension

Can I ask where you source them from please? Also, How important is the A, B or C sizing now that we no longer use Pirelli?

I use RS Components. I have a B sprocket. It took a bit of searching. It works for me, but might not for you.

Yep I know the feeling just bought a brand new dunlop belt and it's a slack fit , couldn't get a gates belt as the local bearing supplier has closed down your welcome to it if you want it, have put the old gates back on , I have changed the crank pulley when I did the engine rebuild many years back , it was a b pulley but not sure now, trial and error maybe I will try the conti from rs see how it fits , it's worth getting it right as the engine runs so much better .

Got last Conti belt from RS Component's in January. Only £7.70 and fits a treat. No distinguishing mark on my pulley that I can see.

Rocker62 wrote: ↑31 Jul 2025 17:37 Got last Conti belt from RS Component's in January...

Is that 'your' last belt, or 'their' last belt?

What size would one order... length, width, number of teeth? Is there a product number or code?

The reason I am curious is that I fitted a new belt to my 3½ recently and it seemed to be a really tight fit. I haven't run the bike yet as I want to check the cylinder heads and carbs properly amongst other things. The bike hasn't run in twelve years, so if the belt is way too tight it would be good to have a spare to hand.

Hi Jen, my last belt purchased. See attached photo for details.RS number 4749793 if you find it difficult to see.

Thanks, that's very helpful.

Both bikes had belts changed this year. I usually get RS belts. Both whined. This can stop but in this instance they did not improve. I changed my Sport pulley from a C to a B, so both bikes are now the same. I have fitted a graded belt to one bike and the other has a belt from a local factors. The latter in my view may be a bit slack.
I was told that during belt manufacture the first part of a run is tighter, the end of the run is slacker. Whether this is true or not I cannot say.
I’ll try the allen key trick.

The diferent pulleys A,B,C were made to be able to use the whole "Kalotte" 1 m of belt with the tolerances of production of all the producers Pirelli; Yates, Optibelt, Dunlp or whatever. A measured belt will allways cost more then an unmeasured standard 124 L.
I´ve used normal unmeasured Optibelts for many years and they are not allways the same fit. In theory all should be "B" but they are not.

When we obtained our "Optibelt Special Editions" (better material, better arming much better gasoline-, oil- and heat resistance) they also came with tolerances. Hartmut has made a sofisticated tool to measure them before distribuiting the belts.
I´ve used one of them them for more than 35.000km and almost 6 years Wouldn´t have dared that with a normal industrial belt