Modern Vespa

the original vespa repair manuals just had you fill with epoxy and machine that, no metal over the top at all.

Correct. But he's essentially building a whole new pad. He's also looking for something that won't melt when he heats the case to install the bearing. I suspect someone makes an extreme heat thick paste epoxy product with metal or ceramic filler that would work. Just need to do some research.

Just catching up here... I am also biased against the SS solution for the thermal expansion differential problem with hundreds of heat cycles considered. It seems the bond would fatigue and weaken over time. But beyond that I can see NO advantage to stainless here, sure it's harder, but that's no benefit if something gets in there. With minimal clearance and lubrication steel on steel is usually avoided because of possible galling risk before it gets up to temp, but steel running on aluminum is common.

My preferences would be

1. Weld up and remachine to spec

2. Machine down, bond new aluminum pad, and machine ala Saint's

3. Hi temp epoxy molded with crank web, then lapped in

You've likely seen this: Welding and remachining rotary pad?

Reeds MRP block and vforce 4 block,

Well - I'm certainly enjoying the ideas and insights flowing in.
Thanks gents.

So-cal. I looked at the TDS on that epoxy. Good temp and hard as hell. Not sure if it's got enough flexibility for the differential elongation.

Voodoo! Thanks for weighing in.
If I were cutting on lathe - there would be no question that your order would be the preferred - or something like it anyway.
Cutting that pad and keeping concentricity is hellaciously challenging with the mill.
It still may be the final solution - but I am first going to revisit a molded no cut solution.
I think the differential elongation is a risk - but it's not by definition outside the envelope of what will hold up. In my view - this one falls into the test and learn - no calc available.

- Noted that metal on metal not often done - does that assume contact of the two surfaces ?(when you have a wear surface that is replaceable?)

OTC - I just don't see the all epoxy solution as durable enough - particularly at the edges of the hole where the edges would likely chip away. Given that I want to be at the minimum - this would concern me for longetivity.

Christopher - that is always in the back pocket...

Edit: was a bit rushed.
Voodoo - I have seen the thread - helpful. If honest - I wonder how precise other repair shops are able to get their clearance to crank web - for the total length of the crank web. FMP says they have to be replaced at over 1.0 - or 1.5, I can't remember - but I'm not sure what science lies behind that.

SoCal - I left off - I will still call Loctite and see what they have to say/ query them on the option. Wasn't writing off outright/ just commenting on one aspect I need to keep an eye on - elongation.

Of course - this could all end spectacularly. Until I get my materials in and have a chance to fit them up, I won't really have a sense of its feasibility.

Back from travel.
Pondered Voodoo's comment on stainless.
Did a bit of research.
Was surprised to find: engine rod to crank bearings clearance is normally... .005mm.
No wonder it's been such a bear to cut a new pad - these are as tight fitting to the crank as a rod end bearing.
But now seeing the rotary pad more as a bearing - I can understand Voodoo's POV better.

While I was traveling - this other idea came to me.
What if you used the side of the crank to seal with?
Now - I know what your thinking, and frankly, that's not very charitable.
Further, some of the language violates the policies of this forum.
So settle down a moment and lemme explain before you start throwing tomatoes.

I've had good success with the retaining compound looking the bearing in place.
I can do the same with the crank - so I can position it axially where I want in the motor.
That's a fancy word for toward the clutch or the flywheel.
And then - I can lock it in place.

So the new plan is: have the pad seal one side with the top of the crank web, and the other with the side of the crank web - giving me a full width opening or very close to 16mm of the 17mm crank web.

Lemme show it with pictures - then you guys can all throw the tomatoes.
Still in the thinking stages with this one.
What I like about it from an execution side is - its precut to exact shape and it is bonded in with concentricity using a .05mm shim.
Back off plan would be to just cut off lip and bond in standard style.
That would take about 1.5mm of width away from this concept tho.


I turned a ring that is .1mm larger ID than the crank (giving .05mm on all sides).

Note - it has a lip at the bottom. This lip will create a side seal with the crank. See next pic with the side of the crank in blue that will seal to this surface.

Hacked out a section of it for the pad

This blued edge will seal with that lip on the side - allowing the inlet opening to go right to the edge of the web with no overlap on the top of it

Here is the pad placed in the case half. Seams like if you are going to bond in the pad - it's better to just pre cut it to size - so that it is getting bonded in with exact position.

Tomatoes at the ready
Might actually not be a terrible idea. If there is a slight overhang remaining on the top it will help with the axial movement as the bearing wears. Your almost full circle crank doesn't go to the edge anyway. Straight cut primary will reduce the lateral (like axial but a different word) load.
The pad doesn't need to seal as well as you think it does. Some of the fastest I have seen have had pads in really poor condition. It does need to shut but won't hold pressure, even if perfect.
Interesting

I think the clearance between the crank cheek and rotary pad is something like .002-.004"...which is as you have said about the oil clearance for rod or main bearings (at least in a VW bus).

I thought about the idea you suggested for using epoxy to skim the surface and install the crank with a piece of tape or wax paper .002" in thickness between the crank cheek and pad until the epoxy sets. I also thought about gluing a piece of wet dry to the crank cheek and laying it inside the case half and turning the crank back a forth to lap it.

I'm surprised that heating the case to install bearings causes the epoxy to fail. The case shouldn't need to be heated very much and epoxy can resist fairly high temps.

What about boring the crank opening larger and making a sleeve with an integrated rotary pad? Sleeve would be a light interference fit with the case....Stake it to lock it in place. Slight lapping of the pad to lock it in place....just thinking out loud.

He's resisting this path out of sheer desire to finish out this path of inquiry at this point. I've tried...

Tomato incoming ...

The pad failed because it was welded, not fully bonded. Just glue it in better. Done.

Play this: While you watch this:

Then have a look below and repeat steps 1 and 2.

Ok - bonded in the new L shaped pad. Used oiled .05 thick paper (oiled so it wouldn't stick) and EA9460.
To speed and improve cure a bit - I put a space heater under it and tented it with some radiant barrier - my new oven.

While it's curing - moved to my gear selector box.
Some discussion going on elsewhere on this.
I had this on my list and had procured a few parts - so might as well get to it while glue cures.

Back when I used to ride these things - I wore out a new selector box in about 3 months.
I admit to a lot of shifting up and down.
Like to keep it in the power band.
what can I say?
¯\_(ツ)_/¯

When I say wore out - I mean - to hit second gear - you had to know its exact location.
There was no feeling of hitting a detent.
Why?

What happens is - the bat wing's tips wear.
Additionally - the swing arm that interfaces with the bat wings is hopelessly flexible.
1 mm of flex and imprecision at the selector box is magnified at your wrist.
So I want to beat out some of the guess work.

I was all prepared to stiffen up the selector swing arm - when I found that SIP sold one for about $10 - so I threw it in the order.
It's nothing fancy. They just welded a tube in to stiffen it.
Oh - and they painted it a shade of close-out green.

Anyway - I heated the crap out of the selector box and took it apart.
I used an old drill bit and welded with it - so that I could have some super hard steel for the bat wing tips.
Job was a bit crude - but suspect it might work.

Oh - and special thanks to CM1 for help making a GIF work
🙂


Paper is providing the .05 clearance. Oiling it made it stick nicely in place.

Oven curing just like they tell you to do

Bat wing ready for weld

Close up of worn tips - using my fave microscope. You can just see how soft the metal is.

I just used the drill bit like it was a welding rod. Would have been better to use a smaller one! but I couldn't bring myself to wasting one of my precision carb drilling ones...

Here is the ugly green reinforced one. Maybe they could have just cleaned it up after adding that piece of tubing between the two arms. you can see the original one next to it

Bat wings re-shaped, now with hardened steel tips

Back together. Certainly feels like it is much more positive between neutral and second where the issue was. tried to make sure the detent low spot is still on center with where it was before. We will see...

okay...that fix for the batwing was effin' brilliant. I'm sure my batwings are all worn to hell, but I hadn't given any thought to 'em as a wear part until now.

Nice!

How does the pin that the detent lever pivots on look?

I've seen the two contact points of that lever wear half way though the pin, then the detent position can move around even when the lever and bat wing are fully seated.

A "heavy duty" lever would be sleeved, maybe with bronze, so it distributes the load across the whole pin.

I'll have a close look at that "pin" that the lever pivots on.

Perhaps that tube they added is actually bar stock bored for the pin.
If not - maybe I will mod my original one.
Fully bushed would make sense - good thought.

Nicely done!





as long as you got it clean and didn't screw up w/ the epoxy, you should be good to .

I saw this and thought of you YD30mm carburetor downdraft.


https://www.sip-scootershop.com/en/product/carburettor-yd-30mm-diagonaldraft_20101800

I'm running the 24mm version of that on my 4T MotoBi. nice carb when it fits, sticks out in all directions.

Ha!
Well - I have to admit - this is the carb that gave me the idea to tilt mine at an angle.
It's a nock off of a super expensive Japanese one - I think.
The Japanese one is kinda like the smart carb.
It has a needle with holes in it - rather than traditional jets.

OTC - looks nice!
Ever considered running on your Vespa?

If you believe the EngMod software - the 28MM should be all I need on a rotary valve.
That said - I am not sure it takes into account the efficiency of the cylinder (as a pump) or the draw that the pipe can put on it - both of which perhaps allows for more carb.

More on that later - assuming I have bonded the new pad in correctly...

Looking forward to the results of your rotary pad repair. I was looking at photos of the pad I bead blasted. I thought it had aluminum debris smeared on it but I think it might have been epoxy.

Good info on gear selection. Poor gear selection scares the hell out of me after a hard seize when the cruciform broke many years ago. I never figured out why as it had low miles. It could be from push starting it for a month after the kick start lever stripped.

Thanks for sharing.

poor gear selection was how I cracked the cases of my LML back when it was in my Sprint. Shifted from 3rd to 4th under hard acceleration, missed the shift just enough that it jumped out and back into gear (after revving up a few thousand RPM's with the load suddenly removed), and it was game over.

the YD is 50° from horizontal IIRC. I've got the real one with the fancy metering tube, I'd not go for that on a 2T but it works great on my MotoBi. The copies should tune just like a PWK. I'm not sure there is room under the cowl for it. Also the bell bolts on making it rather long, but could also replace it and make it very short.

I made an integrated bell/K&N filter mount for the 24. could do the same for the 28 and 30.
https://www.shapeways.com/product/MNV363H6E/yd24-r1260

Well - for a second time - I was within a hair of closing up the cases - but got tangled in my own feet.

L shaped inlet pad came out great.
Clearances are tight and consistent.

Since the depth that I pull the crank in is critical - I have the bearing set a hair low.
This allows me to use a shim between the crank and the main bearing if needed to control the gap between the crank's side web and its new sealing surface on the L shaped inlet pad.
In addition, my plan was (is) to use a retaining compound
(glorified super glue for engines) to lock everything in place.
- The crank in the bearing
- The bearing in the bronze seat
- The bronze seat in the case.

This will give me a zero movement crank axially - which will allow the side of the crank to maintain it's clearance to the bottom of the "L" of my inlet pad.
In theory.

The bronze seat is bonded to the cases, and the main bearing (was) bonded to the bronze seat.
I pulled the crank in to figure out if/how much shim I would need to position the crank perfectly.
Man - it was so sweet!
The clearance is so close - but no scraping or galling.
The hole for the inlet is just plain BIG.

So I disassembled and applied the retaining compound to the crank - but first - cause I read the TDS (tech data sheet) and saw that I could have another 1000LBS of sheer by using a primer - I primed it with the special loctite primer.
The TDS says it fully cures in about an hour with the primer - so great!

However - about 15 seconds after I applied the glue to the primed surface - and about 5 seconds after I started pulling the crank in - the glue snap cured.
I mean - snap.
I couldn't get the crank in.
I couldn't get the crank out.

Knowing the glue would only get stronger for the next hour - I mainicly blow torched the bearing - and managed to press it out.
Well - not exactly.
What I did manage to do, was press the entire bronze seat out - still bonded to the bearing.

For the next 2 hours - I used heat and every trick I had to remove the bearings from the crank - and the bearing from the seat.
Eventually managed - without mangling anything.

Seat is back in the cases - curing.
Will try again tomorrow.


L shaped pad - seals on top of the crank on 3 sides of the hole, and on the side of the crank on one side.

Then some light work on the edge of the crank to help the flow from the wider inlet

It's a big hole. You can see the gap on the side of the crank is just a hair bigger than I wanted - so I took out the shim.

Then disaster struck. To get the crank out - the bronze seat also had to come out.

Managed to get the bearing off the crank - but had to get creative to get the bearing out of the seat... blow torch and parallels were my friend.

cleaned it up - no damage done - good learning on working with the retaining compound. Don't use primer unless you can just drop the two parts together, and when its time to disassemble - just get out the torch.

Back in, bonded in place, even used some primer. Tomorrow is another day.

All's well that ends well!

I know that horrible feeling when things go from "This is awesome!" to "This is terrible!" in a split second all too well.

Glad to see that you were able to save the day.

How wide *is* that opening now?

There was some verbal fireworks in the garage t'day - not gonna lie.
Rare for me - but this tweaked me.
No wrench throwing.
Don't think I've done that since I was a teen.
(but give me time).

Gaping hole:
Hair under 16mm.
Let's call it 16.
~ 185 timing: will double check it when crank is back in and cylinder on.

Should add some power.
We will see...

Good catch. Glue sounds like powerful stuff. Will make you feel better when doing WOT down the freeway.
Inlet looks big. Probably the biggest width anyone had. If it has plenty of torque to pull the rig, next time apart it could go longer.
Getting more interesting by the week. Once the casings are together, you'll probably be riding it the next day.

Good save from one of those "oh shit" moments. And good thing part of your finger didn't somehow get glued in the mix

Gracious - this has been a bear - but it's close.
To what exactly - remains to be seen.
There is a fine balance when trying something experimental.
I would love to have a 10K mile motor - but if I keep taking it apart and perfecting the execution - I'll never find out if some of the experimental stuff actually works!

And - it's a question mark.
The L shaped pad is untested.
I managed to get the crank pulled in - won't bore with the additional tear down and rebuild that occurred...
It's bonded in place - and it's not going to move.

Unfortunately - that place has a .60 gap between the side of the crank and the L shaped pad - where it will seal.
If I were doing it again - I would bond the pad in when I pulled the crank in - but that ship has sailed - and I'm not going to rip this down to the bones again. (again).

So I will put my money where my mouth is on epoxy - and fill that gap.
I'll be able to monitor its condition by pulling the carb - as it is visible from above (see pic below).


Will assemble this weekend - baring any other unforeseen issues popping up/ some O ring I forgot to order/ etc.


Here is the gap - red arrow. I will squeeze some epoxy in there after oiling the crank to close it up. It doesn't really bear any pressure - so perhaps it will work nicely ¯\_(ツ)_/¯

Is it too late to put the crank in the lathe and take 0.5mm from the seal land that touches the bearing? Crank is already highly custom, bit more won't hurt.
And while the crank is out the inlet hole could be squared up tidier. Losing some important area with those inside corners.

Ha! Inside corners image was included just to check that you were watching.
You passed.
Will be a square ~ 15.8mm width before assembled.
No need to remove the crank for the fine work.

Part of this game is bonding everything in with the new fangled retaining compound.
A pressed part - with that stuff on it - is crazy strong.
To disassemble it takes direct heat.

So here's the catch/ learning.
You need to fit everything - then bond it all in one.
Otherwise - if you have to disassemble something - there is no way to just spot heat it.
You generally fail all the bonds = start the whole house (of cards) build from the ground up again.

I did that 4 times.
Time to see if it that honkin' big L shaped opening will even work.

When time comes to re-do this motor (assuming that is not next week) - I will fail all the bonds with heat - so I can tear it down - then assemble in one go with the pad bonded in only when the crank has been pulled into position.

I've done it enough times now that I'm pretty good at it.

Understand all the glue, I do the same, put it on everything. 603 is even pretty good as thread lock. One thing I don't glue in is the crankshaft. Bolted in pre-yield tight, they tend not to move.
Not sure that crankshaft is helping. A regular rotary crank would have more open space. Going to be a strong runner no matter what. Case reed will need more bell shape anyway, if ever that happened.
Might be all jetted in this time next week.

Been a process of discovery.
Agreed - regular rotary crank with cut out might take a bit more advantage of the wider inlet.
That said - one thing I like about this crank is that the side surface of the pad never meets an edge - so there is less opportunity for wear or damage.

I'm using 603 and 620. The 620 is a high heat version. I have to make a call on using any 603 on the rubber seats. I have the DRT kit that allows seals to get replaced from the outside. If I go no 603, it will be far easier to change them - and not delaminate everything else. Think I will start there and leak test. No leaks - no 603.

As for the rotary pad replacement - TBH - I'm not sure why Joe Casola bonds then cuts his pad
The second operation - cutting - adds variance and opportunity for a lesser fit.
Of course - he has a super precise machine made for boring engines that he uses.
But it still relies on centering - and I can pretty well assure, that every set of cases out there has a bit of oblong shape where the main bearing sits - so centering on WHAT becomes the question.

Anyway - if/when I do it again - I would stick with cutting a precision pad outside the motor, on the lathe - and then bonding it in place with the crank to nail my tolerances.

Jetting next week.
Assuming it starts...
🙂

As I type this - there is at least a 50% chance I am epoxying my crankshaft permanently in place in my cases.
This was, as you may have guessed - not exactly my plan.

My PLAN was to use a slip of .05 thick paper to separate my crank from the epoxy - leaving a perfect factory gap and leading to a standing ovation from my entire family and friends network.

In practice, basically, the paper got all gummed up, the epoxy got everywhere (lord it's sticky) and I was lucky the acetone spill didn't just disintegrate it out right.
But before I share those pictures - a few other steps taken/ reminder for me the end solution.

Prepped fly side cases.
Can I just say - I hate pressing bearings in.
Yes - I have a hot plate.
Yes - I froze everything.
But its so damn easy to gall/press in sideways/ generally fubar the parts.
And don't get me started on trashing the brand new seals - with heat - while trying to pull this all off.

No wonder the Piagio engineers reversed the order of the seals and bearings.
Everyone was screaming at them! (in Italian - with a lot of hand gesturing - and that whole flick of the fingers under the chin thing. I don't think its good.)

The "book" says to press the bearing on to the crank - then put the case on.
The advantage is - your bearing and crank act as a big mass - so they stay cool and relatively small when you press the case on.
The downside is - you end up with your bearing only partially seated in the fly side.
I'm not such a fan.
I wanted the bearing fully seated in the cases.
Some pictures below of the activity...


Mangled first attempt lead to me having to push the bearing back out. The bronze seat decided to follow (original - not my creation).

Note that little pin. I saw it in a manual at Bar Italia. I think they drove some kind of brass pin in to hold the seat in place - in 1961... since then - retaining compounds were invented.

Decided to press my bearing in to the bronze ring first. Advantage - mass of bearing helps keep it cold/shrunken. The brass is too light on its own - and will expand on contact with the hot cases otherwise.

Worked. These have retaining compound on both parts. Without direct torch heat - they won't move.

Tis the season. Gave the carb surface a "fresh cut" just like my tree. Someone had dinged it up. Musta been the elves. Its always the elves.

Just before cases closed. This is my proof positive pic that I didn't forget the kick start gear. I think we should all post pics of our kick start gear before closing... Note: trying just grease on my gasket.

Scribed the crank and rotated it to where I could see it (before)

Then rotated it back to the inlet - and used the marks I had made on the crank, to transfer over to cases where I needed to take more material out.

No wizard sleeves here bitch. Can I say that on this forum?

And then this. It may undue me. We shall see. You will note - there is no gap at all between crank and my custom L shape pad. If I managed not to bond it completely in place - open to ideas for lapping it .05mm back... !

We all have our fingers crossed for you!

My vote is that you're going to pull this scheme off and have a First Start Video for us in the immediate future.

All I heard was wizard sleeve. Then I got distracted.

cosign

Thanks gents.
Ok - quick update.
Honey do list is bumping into paying job list - and there isn't much space between.
Here is where things stand for the next few days.

FINAL TIMINGS with torqued down cylinder and cases:
123.1/180.8 according to buzzzwangle.
123.5/180.9 according to lambretta calculator and vernier calipers/feeler gauge.
Pretty close!
So lets call it 123.5/181
Inlet : 117.9/57.3/175.2 = 175
This is a little shorter than I had planned - but I cleaned up the overlap wit the transfers and it shortened it a bit.

Squish .81 on one side, .76 on the other. = ~ .8 Not sure why the variance.

Inlet - there is about a .05 gap at max - and 180° later on the crank as you turn - it has just a hair of interference. I am thinking this will wear itself back naturally as it breaks in - OR - it will act like brake shoes and stop the thing from turning completely.
🙂
Its just a skoash (technical term = .01 > than an RCH) of interference at a small part of the crank. I'm gonna run with it.

Since the cases were machined flat - and I had only dinged them up a little.... - I chose to assemble using the nice SIP gasket, and some grease. No Hondabond.
That was such a please to do vs putting goopy RTV on - that I got carried away and did the same for the base gasket under the cylinder.

Lemme know what you guys think about this.
I will leak test before proceeding...

Edit: Oh wait! what would a post be without a calculation you ask? you don't ask? well - here it is anyway. If I take my transfer total time - 123.5 and subtract it from 360, then divide by 2, I get: 360-123.5/2 = 118.25. That is where my transfers close, and it is basically what I observed when I turned my crank to the point that my inlet opens (117.9). Calling that a win.


Current state of affairs

Zoom in on my little timing indicator

inlet

Zoom in.05mm gap on side of crank where it interfaces with L shaped inlet pad. One interesting thing about this pad design. I can re-fill that gap without splitting the cases (maybe without pulling the motor).

Timing is a bit dull 123.5/181/29 but should go solid. Question will be if its fast enough. Going to be strong for sure but might run out of high rpm power on the straights.
Ignition timing down to 17 degrees by 7000 is a fair starting point.

Can all be changed once the performance is assessed. Port timing is way too low to make the expansion work. Will be good on the box though. Expecting great things.

been my theme for last 4 pages [/quote] Tweaked packers until I got to .8 squish - no head gasket - 62mm crank. Could go lower if head gasket added. Can always go up.

I've heard it said that 180ish is top of what i can get out of a std box - so made sense to put it there.
(Side note That S line pipe design box looks interesting/ and Xmas is soon.)

I figure I could move to expansion and or raise cyl if not enough in it. Guessing it'll be about 1000 RPM short of my riding style - but itl be a good start as noted.

Thanks for timing input/ will use.
Was kinda pleased with my milled timing indicator plate - now welded on case.


Used a hole centering bit and just sorta etched the ribs in place. Should make setting timing less guess work

This is pretty slick.