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A setback?

The thing inside the selector box (operating arm) broke. I guess it is supposed to go inside the selector rod? When I installed it, it was tight and I forced it in, eventually when I turned the drive shaft, I heard snap and that was that. Annoying...
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Forum member supplied image with no explanatory text
⚠️ Last edited by npn on UTC; edited 1 time
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Isn't the "gap" in the selector rod constant? (gap between the red arrows)

Why would the slide box not fit in?
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Evil
Parmakit Primavera -74, Polini Primavera -68, VR-One 228 150 Touring -59, VMC 177 Bajaj Chetak 125 -95
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That should slide right in there. Maybe cleaning the groove with a file will do the trick.

Did you already check around the intake rotary pad for damage? Also I'd call for replacement of the crankshaft while you are inside the engine. My Chetak had a failed crankshaft big end bearing in it's early years and was sitting for +20 years after that with engine disassembled by the previous owner.
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This is mind boggling. It just won't fit! And it's supposed to be a good fit too because the rod rotates.

Anyone else thoughts?

As far as other fixes and replacements - I think everything is fine. This bike had been sitting for some time and all the gaskets were basically dry and cooked. Then the last/2nd owner attempted to just run it and hell broke loose- was sucking oil and/or leaking fuel inside the gearbox (that I was told it could happen if you don't turn the fuel off before storing the bike for years). The carburetor was loose too so fuel was leaking over the engine and not to mention obvious loss of power.

So I bought it for $500 and have about that much in already plus 50+ hours and there's definitely more work. So I'm losing interest TBH.

I mean, this selector mechanism is kind of bad design and why wouldn't the little block fit back in is frustrating!
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Is it an incorrect part that someones put in in error and its never worked? you did get the bike with a few bits that werent fitted so it was obviously a work in progress.

Since its broken, you'll need to replace it so you can see if there is any difference compared to the new part.
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Matchlessman wrote:
Is it an incorrect part that someones put in in error and its never worked? you did get the bike with a few bits that werent fitted so it was obviously a work in progress.

The selector box was intact when I got it and it was shifting... at least from gear to neutral. I've ordered the broken arm but I'm thinking of replacing the selector spindle too. That would mean I have to split the engine again, which means new gasket...
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Not sure if people are reading this thread as it's gotten quite literally long but I found what the problem was: inserting the main drive shaft with the cruciform, I tapped it with a rubber mallet first and then are the end with a regular hammer bending slightly the end of the the selector rod end inwards just enough to trap the little block and break the arm.

Lesson learned!

Most videos and even manuals show that you need to assemble the whole drive shaft with the four gears first and then insert it. I found that to be more difficult. Not only you don't see how far the shaft goes into the bearing but also it's difficult to line up /match the the gears together.

You don't even need to remove the drive shaft if you need to replace the cruciform either. Why does the manual describe that more difficult way is strange to me.

So, with the gears off, I tapped the whole thing into the center of the bearing, made sure visually it was all the way in, then installed the gears one by one making sure they lined up properly.

Replacing the broken arm in the Pic above gave me the opportunity to clean up thoroughly the whole selector box and lubricate it properly.

Another thing - F the main gasket and air leak test. I'll be using Permatex gasket/seal maker. Much easier, cheaper, effective (doesn't matter if the surface is imperfect) and in the long run probably more durable than paper based gaskets. I've done a similar work on my harley and car manufacturers I believe have been using this approach for some time now.
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We're all still reading, rest assured

I'm glad you're making progress and figuring it out. You have a real jewel there (to me anyway) and I'm glad you're posting. And, as always, pictures make it oh so much better Razz emoticon
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I'm still reading along. Lemme know when your thread gets to twenty pages. Razz emoticon

Personally, I assemble the axle, cruciform, and shifter, then pull the axle into the bearing. No need for tapping. I'm glad you figured out what the issue was, though.

As to pressure testing, I think you're making a mistake skipping that step. There are a LOT of experienced builders here and we all pressure test, even though we also all use permatex or some analog. Ignore us at your peril.
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chandlerman wrote:
As to pressure testing, I think you're making a mistake skipping that step. There are a LOT of experienced builders here and we all pressure test, even though we also all use permatex or some analog. Ignore us at your peril.
+1 on this!
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Pressure testing saved me a lot of mystery down the road. Figuring out the bits and bobs I needed to do the pressure test took the most time. Once I had the setup, it takes only a few minutes. The first time I found little leaks at the head and intake that would have bedeviled me until I dropped the engine out and did it over.
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I'll probably end up doing the pressure test. I'm just impatient I suppose.

The easiest test I've seen done is by using a inner tire tube with the valve on. The cut off ends go in the exhaust port and the carb air intake. Then you just pump to about 6psi and watch what happens. I have a high pressure pump with an indicator that I use for the air shocks on my bicycles. I think I'll do at least that much
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Good call

Motors with air leaks run poorly and fail expensively.
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You guys like pictures? Well, here it is, engine sides put together using Permatex Motoseal instead of the main gasket. Now it's drying and tomorrow I'll do the pressure test.
Forum member supplied image with no explanatory text
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It will have all short of leaks with just the sealant. The cases flex cause of the stupid bolt and nut combo. Motoseal and gasket is my way...
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SaFiS wrote:
It will have all short of leaks with just the sealant. The cases flex cause of the stupid bolt and nut combo. Motoseal and gasket is my way...
This is supposed to be a gasket maker, not just a sealant. I admit it's the first time I've used it and it was a bit more liquid than the red Permatex I've used in the past. It was also more sticky.

I guess air pressure test is now a must
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Ok gents, this is discouraging...

So I did the pressure test by sealing the carb inlet and pumping air through the exhaust port. It will not hold air for more than 10 seconds!

The two immediate visible issues are with the head and the main seal. Note, the main seal doesn't leak air where the rubber o-ring meets the axis but from around it where the arrows point in the picture.

I'm kind of stuck - the seal is new, the head - what's there to do? And I certainly don't feel like splitting the engine for a 3rd time.
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I think you should have a copper crush gasket on the head (you can see the outline of an old one in your picture) and I like to use copper spray-seal along with whatever else I do on the head.

For the fly side seal on that case, you're going to be splitting the cases again, I hate to tell you.

I use Loctite 680 on my seals. Some folks here use Loctite 603. Either will work and help ensure no leaks on the outer lip of the seal.
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chandlerman wrote:
I think you should have a copper crush gasket on the head (you can see the outline of an old one in your picture)...
I guess it didn't even occurred to me. When I took the head off, there was no gasket between the head and the cylinder. So this is not the first time someone did this.

I'm taking a pause here to think about what I want to do next. There are a few unknowns - why was the flywheel taken off and put in the glovebox for example. Now this finding too?

Thanks chandlerman, sometimes it takes a second person to see pretty obvious things.
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Glad I could help, even a little!

You might also want to check that the head and cylinder deck are even. Mark the mating surfaces with machinists' blue (or sharpie...whatever's handy) and give them a quick rub on a piece of 600 grit emery paper taped to a piece of thick glass. It should rub off evenly. If it doesn't, lap it 'til it does. The head will be easy since it's aluminum, but the jug will be significantly harder since (I'm assuming) it's cast iron.
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Not sure what I want to do at this point... I mean if someone started messing with the engine and abandoned the project good 10-15 years ago, who knows what else is messed up.

So the head leaks a bit, maybe that's ok... the fly side seal - if it's not leaking where the rubber is, I'd say it's holding pretty well. There's no way oil would pass through where air does and when the engine is running, there will be oil in there to serve as a sealant in a way. Right now the engine is completely dry...
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Bummer, splitting your cases just to deal with a slightly leaking brand new seal. Livid emoticon . After thinking this over, I would be tempted to try this:

External inline image provided by member with no explanatory text

I'd set up the motor so this surface is horizontal, facing up. I'd plumb it like for a pressure test, but hook it up to a vacuum source. Then I'd dribble either Loctite 680 or 603 around the seal perimeter and let the vacuum suck it in - Find out which has the lowest viscosity, or some other suitable sealant.

Who knows, it could work and not much additional trouble at this point. Be sure to pressure test again after plenty of time for sealant to set up. If it works out, be sure to lap your flywheel in to your crankshaft, it looks kinda rough (be sure to keep lapping compound to a minimum and AWAY from the seal!). If you do have to split the cases again, lap it out of the case. Good luck!
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Voodoo's on it. While not technically a factory approved repair, I seem to recall charlieman at one point successfully plugged a leaky flyside seal by gluing a big washer on there with some Hondabond or something similar.

Yoo hoo CM2 … come in
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CM2 wound up installing an inside-to-outside (PX-style) seal converter with some sort of hardcore aviation epoxy. He might have eventually just said "screw it" and welded it in place before all was said and done, too.

Or maybe he tried to weld it, then got tired of chasing pinholes and slathered it with epoxy. I forget which. I'm usually a "try to weld, then slather with epoxy guy" myself. Razz emoticon

I like the "suck Loctite into the seal" approach. I'd definitely try that at this point if I were you.
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Yeah I really don't want to split the case again. There's a limit to how many times you split an engine and refit stuff. Eventually something will fail. One of the biggest things for me is that ballbearing on the fly side that the crankshaft goes into - when I split the engine the first time, it was stuck on the crankshaft (not the case), when I closed it, I put in the case (after freezing it overnight) and when I split it the second time, I found it on the crankshaft again...something just doesn't feel right.

I only replaced the cylinder gasket the first time, I'm sure I can't reuse it more than once, right?

I'll see if I can get the head leak fixed and check for other leaks but if the only thing is the fly side seal, I'll just have live with it. Eventually I can experiment with patching it with Permatex or JB or locktite
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Try adding loctite around the edge of the seal while you can still put the engine on its side, even if you don't have the ability to pull it into the seal. It can't hurt and might even help.

And copper spray seal on the head will make a big difference. That was the only thing I could ever get to seal DR top ends, which are pretty comparable to what you're dealing with.
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Never used copper spray sealant, is this one good? Permatex 80697 Copper Spray-A-Gasket Hi-Temp Adhesive Sealant, 9 oz. net Aerosol Can , Orange https://a.co/d/cLQBwSW

Also any tips for using it?
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Yup. That's the one I use. Mask off the cylinder and inside of the head. You probably have a spray can lid that's about the right size.

Spray a couple of thin coats on each side when you're about ready to assemble, then install and torque to spec. I wear gloves because it's super sticky and really hard to wash off.
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This is the post of legend chandlerman mentioned above:
https://modernvespa.com/forum/post2342984#2342984
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spacecat wrote:
This is the post of legend chandlerman mentioned above:
https://modernvespa.com/forum/post2342984#2342984
Thank you. My leak is relatively small but it's his solution is an option. I really don't want to split the engine again.
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Stick with it! Theres bound to be highs and lows but you have what looks like the makings of a really nice scooter.
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sdjohn wrote:
get that bit out and take it to a locksmith, they will make it work for you
I have a locksmith friend who told me a technique he sometimes uses to remove broken key pieces from locks. He uses WD40 & gently tapping the metal of the lock, in attempt to make the piece bounce out enough to grip with pliers.

I suggest removing the glove box door before trying this.
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In preparation for applying the Copper Spray.
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I use copper spray on the head but hondabond on the base, it seals well
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sdjohn wrote:
I use copper spray on the head but hondabond on the base, it seals well
Hondabond in place of the aluminum base gasket?
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I personally put a thin layer on both sides of the gasket, then install.

And I try not to get it everywhere, like the piston, stud threads, etc. Razz emoticon
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qascooter wrote:
I personally put a thin layer on both sides of the gasket, then install.

And I try not to get it everywhere, like the piston, stud threads, etc. Razz emoticon
Ditto. I use RTV Red--the kind you use on exhaust flanges and the like.
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Hey guys, serious question - these early scooter engines from what I read were bullet proof. Back in the 70s or 60s or earlier, were there such compounds such as Permatex or loctite and if so, were they used in those engines?

You know there's a difference between air and oil, so how necessary is the air leak test? See when the engine is hot, metal expands and things fit together better. When there's oil, oil does go into tight places and serves as seal.

You know like these air tight houses for improved efficiency in the winter and all, they actually cause other problems such as extra work for the AC...

Anyway, I'm re installing the cylinder and head with "improved" gaskets and really hope that's it. I have literally over 100 hours in so far and haven't even touched the electrical part nor bike's front yet.
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npn wrote:
Hey guys, serious question - these early scooter engines from what I read were bullet proof.
Yes, to an extent. Consider that these were designed to run on crap oil and much, much slower speeds.

If you want an engine to run it's best, no leaks, and keep up with modern traffic, there is a learning curve to making this a reality.

The old two stroke engine isn't for the faint of heart and you're doing a great job. You got this.

The folks that have done a couple of engines and have found what "works" are sharing their knowledge here on this forum. It doesn't mean it has to be done that way, or this way. It's what works for them.

Lots of issues can creep in, like a tiny oil leak, or air leak, or it's stalling, or running rough, or stalling, or, or, etc, etc.

This is why we are all rooting for you and putting in our two cents.
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That's a legit question, and as best I can tell, the answer is that they used to rely on a combination of gaskets on all mating faces and low expectations when it came to motors.

Look at how much more power these motors are capable of than what came from the factory. For example, your motor is going to make about 4.9-5.5 HP. By comparison, a bolt-on tuned motor can put out 15+ HP and a highly tuned motor will make 25+. That's a LOT more capability and much of the advice we're giving is arguably aligned to the 15+ category of builds, but that doesn't make it any less relevant.

Also, like QA said, these bikes were really designed for slower speeds and crappy running conditions, not modern traffic. It's totally normal, for example, to pull the head off a stock motor and see a massive head leak, for example.

What I can definitely tell you is that an air tight motor will run better, cooler, longer, and more reliably than one with air leaks.

If you're about ready to pack it in, there's arguably nothing wrong with saying "good enough" and moving on to the next tasks. If you're planning to replacing cables or wiring, dropping the fork, or changing out suspension, do it before you put the motor back in. It'll be infinitely easier since you can shift the bike around to whatever angle is most convenient for the task at hand.

Everyone's first rebuild or two is pretty rough. I was ready to set my VBB motor on fire by the time I finished that first rebuild. My first Stella rebuild was differently hard, but by then I'd started to accumulate the necessary tools and experience. Now, a rebuild is a day's project if I have a block of time to focus on it and knock it out.

You're making good progress, even if it may not feel like it. Given that your frustration level is up, I'd say figure out the minimum task list to get it rideable, enjoy it for the balance of the summer, and once the weather goes to hell in a few months you can worry about the rest.

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