Modern Vespa

Castle nuts are stupid. Can we use this thread to source info to make a NSM WIKI article so I can google this in 2 years after I have forgotten?

I switched the clutch on a P200 motor and went to reinstall and couldn't get the castle nut retainer to line up to the nut to a satisfactory level. Also torquing these buggers with motor in the scoot is a #%£$*. No problem I had the BGM hexagon nut w/ Schnorr washer (BGM 7671201) on hand, why was I bothering with castle nuts anyway? Torque to 45 ft/lbs andddddddddd was stranded 5 miles later. No comms between transmission and crankshaft.

I removed the clutch cover and the clutch nut was backed out but still (barely) on the crankshaft . It obviously smoked the woodruff key but it put up a fight and had to tear its way off. It also took out the clutch back plate. Thankfully crankshaft survived.

After consulting with Birdnest, I most likely had the conical Schnorr washer pointed the wrong way. It should be pointy side to the nut. Slightly annoyed at my stupidity, but it was late and I didn't think through. Sharing my lesson to save you heart ache.

Once I get a new clutch back plate, I'm going to use the DRT SIP 11351940 nut & washer. Mainly bc I have it on hand but also I think it is a better design bc it is 21mm OD vs stock & BGM of 19mm. Also the DRT one uses a flywheel style star washer that I keep on hand vs a very specific conical washer. Note: The DRT comes with 2 washers, the star one for standard and the wavy for Cosa. Don't use both washers at the same time.

Torque: What are you guys torque the BGM style and DRT style to? Stock is 32 ft/lbs. I went to 45 ft/lbs for the BGM, but with incorrect washer install it is a moot point. Any thoughts on torque for the DRT style?

Loctite: Do any of you use loctite on the nut? I would probably go with blue 243 if I did anything, but if you use the correct washer you are probably good.

I like to torque to whatever the factory shop manual calls for. Just replaced the clutch in my Stella and used the castle nut with the tabbed washer. I'd stick with the castle nut, torque to 32 ft lbs and if you can't get it to line up a tighten a bit more to line up.

On my 2005 px150 clutch I did today I just reused the Cosa style nut (no wave washer). Not sure if one time only or not on those but torque to 32 ft lb also. Guess time will tell.

Nobody is recommending castle nuts, except that guy in 1957. And masochists.

No idea what the BGM nut looks like, but have used the flanged type (labelled DRT here) on and off for years. Note that they have a deformed or non-standard thread, and should be used once only.

Have never seen that serrated washer used for a clutch. I have some that came with my aluminium Pinasco split rims, and you can see that they bite in slightly to the rim.

This application is a hardened nut and obviously hardened crank, no biting just slipping. The contact area between the nut and the washer is miniscule.

You know, it would help if I took pictures of the front of the nuts instead of the back. Doh! Attached pic that will actually be more useful 😂

I used an M12 nordlock washer (pair) one time on a PX clutch to solve this problem but the extra height of the washer meant the nut protruded further than the crank and prevented the clutch from fully disengaging. I got it to work but had to take 3mm off the height of the nut in the lathe. So not exactly plug and play

SERIOUSLY.

Use a DRT nut and the appropriate washer for your clutch. Or the Cosa nut and wavy washer if you have a Cosa clutch, This is also sometimes called a "top lock distorted thread flange nut"; and should be easily found with your favorite hardware supplier

+1
And tight, tighter than the spec, 70lbft is not too much.

I dont have a specific torque I use

Whatever my battery impact wrench pushes is what I fasten the flywheel and clutch to. Seems to work fine. Been doing this for about 15 years or so

Edit: just did some quick maths and its in the 70sft/lb +

60-70 ftlb for me. I torque all engine bolts to spec, and most all critical components; cuz im a geek

Nowt wrong being a geek... I do call my workshop Bodgineering HQ

70 ft lb seems massive. I do cosa nuts at 65 Nm (so like 45 ft lb) as per the manual. Also because the oil pump pinion under the clutch is prone to cracking when over-tightened.

New wavy washer, blue loctite on the threads, and most importantly, a cosa clutch. Because there's no point in getting all technical with nuts and washers and torque settings if the crappy 6 or 7 spring clutch behind the hardware us going to explode anyway.

Curious if the BGM nut with Schnorr washer has anything included that points out the dome of the washer should be towards the nut? 50/50 shot for anyone taking it out the pkg and not knowing there was a difference.

After learning the hard way, I have settled on 45 ft/lbs plus red Loctite.

https://modernvespa.com/forum/topic187126.2#2680318

I appreciate the input and back calc'ing the maths to get a torque value. Makes me feel better about torquing my flywheel with battery impact only and going a little over the factory spec.

FYI for others the scooter center site for the BGM nut specifically say don't use an impact bc the material hardness is hella hard and an impact can cause fractures to form.

"The nut must not be fitted with an impact wrench.The nut has enormous toughness and tensile strength. However, due to its special design, which is due to the limited space available, it is not suitable for the extremely high load peaks of modern cordless impact wrenches. These not only easily reach twice the guaranteed tightening torque of the nut, but also generate load peaks that can no longer be absorbed by the elasticity of the nut."

For the DRT/SIP nut I looked on the SIP page and also the DRT website and didn't see any warning about using an impact. Maybe theirs is made of a softer metal.

—— The BGM nut just comes in a small ziplock bag with the part number label and no instructions. The Scooter Center website for this part does not mention anything about washer direction. This is why I made this thread so hopefully someone can learn from my mistake.

——-

Kowalski great thread you posted, it did not come up in my searches. Bummer the BGM nut exploded on you, but thankfully it happened while it was still on the bench. Did you hand torque or use an impact?

Also in your thread a great point was mentioned about not using a flywheel holder to use as backup for when torquing the clutch nut as that put torque across the crank that could twist it. Not sure if I have done this before, but could see myself being mid-job and doing this without thinking.

Great points brought up here about making the oil gear cry if you use the upper end of torque.

Maybe just overtightening, or maybe with the help of an oversized woodruff key x an undersized Pinasco crank key slot, but this is what happened to my T5: