Mystery Vibration

Howardr · Post by **Howardr** » Mon Dec 03, 2012 9:33 pm

Okay, i have a 2007 Stella, with 14k miles. I've got a Malossi 166 kit with a stroker crank. The kit has about 2000 miles on it.

The problem - Over this past weekend, it developed a vibration throughout the scooter. It is only detectable between 40 and 45mph (roughly) and is worse when decelerating. It goes away once above 45 or so.

I got up to 50mph or so then pulled the clutch and shifted into neutral and did NOT feel the vibration.

Any ideas? I have not noticed it in any gear other than 4th which would mean it is speed connected, not engine RPM connected.

Howard

BuddyRaton · Post by **BuddyRaton** » Tue Dec 04, 2012 12:44 am

what crank was installed? Were the bearings replaced?

az_slynch · Post by **az_slynch** » Tue Dec 04, 2012 1:00 am

BuddyRaton wrote:what crank was installed? Were the bearings replaced?

Mazzucchelli 60mm stroker crank. New Italian-made bearings; Nadella on the fly side and SKF on the clutch side.

He noticed an air leak in the last few miles of the ride back from the rally. My guess is the fly side seal. The other item of note is that the original clutch is starting to slip a little; cranking up the horsepower on a 12K stock clutch guaranteed that this would happen.

My plan at this time is to check and possibly replace the fly side seal, give the flywheel a wiggle to check for bearing play and to build up a new clutch with a 22T drive gear, new stock springs and Malossi plates.

fisher1 · Post by **fisher1** » Tue Dec 04, 2012 3:17 am

It is only detectable between 40 and 45mph (roughly) and is worse when decelerating. It goes away once above 45 or so.

I have not noticed it in any gear other than 4th which would mean it is speed connected, not engine RPM connected.

Which means something like wheel balance, wheel bearings, brakes or transmission 4th gear right?

Howardr · Post by **Howardr** » Wed Dec 05, 2012 9:38 pm

I'll be checking the tires, too.

Howard

BuddyRaton · Post by **BuddyRaton** » Fri Dec 07, 2012 2:01 pm

az_slynch wrote:
BuddyRaton wrote:what crank was installed? Were the bearings replaced?
Mazzucchelli 60mm stroker crank. New Italian-made bearings; Nadella on the fly side and SKF on the clutch side.

He noticed an air leak in the last few miles of the ride back from the rally. My guess is the fly side seal. The other item of note is that the original clutch is starting to slip a little; cranking up the horsepower on a 12K stock clutch guaranteed that this would happen.

My plan at this time is to check and possibly replace the fly side seal, give the flywheel a wiggle to check for bearing play and to build up a new clutch with a 22T drive gear, new stock springs and Malossi plates.

Don't forget to scuff up the metal clutch plates a little bit for more bite. And I'm sure you know to soak the corks overnight.

If you're going to check the fly seal might as well replace it...it's sitting right there. Yeah...you gotta find the air leak but I don't think it has anything to do with the vibration.

The set up sounds good, you can twist a Mazzy crank but it's realy not that easy to do. I would also re-torque the rear hub nut (use a new cotter pin...I'm sure you know that but others might not.) And then I would start thinking about checking the front bearings and axle. After that I would be checking the fork retaining nut.

az_slynch · Post by **az_slynch** » Fri Dec 07, 2012 6:51 pm

BuddyRaton wrote: Don't forget to scuff up the metal clutch plates a little bit for more bite. And I'm sure you know to soak the corks overnight.

Good points. I also know to not use the Malossi springs; way too much stress on the clutch cable. Rebuilt my 7-spring with their stuff and I could barely get it to disengage. Bet it's a cable-snapper in the long run. I am interested in mixing springs on a six-spring clutch (3 stock, 3 Malossi) to see if that helps longevity. Considering a banded clutch basket, but I'm not quite convinced that this bike needs it. I consider the 22T clutch plate esssential on this build and I almost wish I had a 67T to put on the cush so I could spread the power out a bit more.

BuddyRaton wrote: If you're going to check the fly seal might as well replace it...it's sitting right there. Yeah...you gotta find the air leak but I don't think it has anything to do with the vibration.

Yeah, I agree on the irrelevance to vibration. It was just a thing that manifested at the end of a ~500 mile weekend and according to Howard, the carb hadn't come loose. I was going to pull the flywheel and take it to my machinist; It's a stock weight and the stock late Stella flywheel is about 2.4Kg with a starter ring on it. I wanted to see if we cound check the balance on it and possibly knock it down to 2.1-2.2Kg so it wouldn't stress the crank too much at higher RPMs. Just another item on my recipe list for building up a good-all-round modded Stella. I just need him to get the 200cc oiler gear so we can skip the 1% in the tank nonsense and fine-tune the jetting a bit more.

BuddyRaton wrote: The set up sounds good, you can twist a Mazzy crank but it's realy not that easy to do. I would also re-torque the rear hub nut (use a new cotter pin...I'm sure you know that but others might not.) And then I would start thinking about checking the front bearings and axle. After that I would be checking the fork retaining nut.

The Mazzy's are tough, for sure. When my P's crank is finally tired, I want to put in a Worb5 crank, but that's me being overkill on a gas-flowed and laser welded crank. The Mazzy stroker that I put in another friend's Stella stayed true even after a nearly-catastrophic flyside bearing failure that even twisted the bearing race on the crank and slightly ovalled the hole in the case for the clutch-side bearing (not visible, but discovered with a bore gauge when the replacement bearing was too easy to install). Not sure how it happened, but I had it checked out by a good machinist before I pitched it and was amazed by his findings.

Rear axle is a definite possibility. I just need to make time to go over the bike with a fine-tooth comb, but with the semester ending and Christmas coming, it may not happen before New Year's. I need less responsibility and more time to mess with scooters.