Modern Vespa

Back from the dead

Here comes a writeup on my Bajaj Chetak 125 1995. Bear with me, it's a boatload on this first post.

I bought this Bajaj in 2019 as a mystery project, unseen and with only a blurry picture for info. No paperwork, but the condition is generally quite good. However, the engine came with the scoot as a basket case. In terms of parts the engine was mostly complete, although bit rusty since it had been stored dry for a long time after dismantling. The reason for disassembling the engine was probably the lower end of the rod bearing giving way. In the end, the only missing parts of the engine were the cylinder, piston and rear wheel.





Engine inspection, new cruciform, bearings, o-rings and Clutch plates in. As a crank, BGM's thin coned Sprint crank.


Getting to this point took some swearing. It must have been the eighth or ninth time before the blocks were successfully connected. When was oil seal lip sticking out, when did the bearing not go to the bottom. Then, when the other things fell into place, I noticed that the kickstarter buffers are facing the wrong way and the little wheel was constantly rattling against the teeth of the Christmas tree. Rinse and repeat...


Then it was the cylinder's turn. I bought this VMC 177 SuperG to replace the missing standard cylinder. And again, some more cursing. The sealing surfaces are so skinny that they are not nearly wide enough to cover the bottom sealing surface of the cylinder.


At this point, I thought that the priority was a running engine and after a small break I returned to the motor. Whipped up a adapter piece from the piece of stainless steel I had laying around.


After some shaping, it finally became like this. The solution is far from optimal, so be it.




A couple of millimeters still need to be planed off the cylinder due to the adaptor piece, in order to get the squish clearance to reasonable numbers


Added the ignition and got a spark too.


The crown nut on the clutch side was a new thing to me as I've previously worked only on smallies. Whipped up a makeshift tool from a socket.


Engine buttoned up.


Borrowed rear wheel from my GL and in goes the engine.


A small spray of brake cleaner in the throat of the carburetor, one kick and out came first smokes in probably about 25 years. Excited of the first smokes, I quickly put the oil in with a syringe, cleaned the fuel tap sediment cup and put the tank back in place. The Indian fuel hose has remained elastic surprisingly well and did not need replacing. At this point, I also had to borrow a standard pipe from the GL to suppress the sounds. After a couple of kicks and idling adjustment, the engine was happily idling. Some work with cables, connecting the wiring harness and tidying up. A first ride maybe since 1996?


Cut the rear wheel holder off the rear rack since I had no spare wheel to attach to it. Gave it a wash with motorcycle shampoo, which cleaned up the scoot nicely.


Some paint lifted off the nose since it had been painted on unsanded plastic surface at the factory.


The original spark plug that came with the scoot was a tad short for the VMC head.


Pulled the cylinder and measured the PBT to be 1,87mm with only silicone under the cylinder. Took the cylinder to a local machine shop to have it decked for 1,5mm. By raising the cylinder with adaptor plate exhaust timing goes from 172 -> 177 and transfers 106 -> 114.


Whipped up a suspension-thingy to hold the scoot from the roof.


Cylinder decked


Thin gasket under the cylinder and some tin wire taped on top of the piston.


Looking good


Goods arrived from Germany. Originally this scoot had brake drum with shoulder for 27mm oil seal but since the whole drum was missing I updated it to Lusso hub with 30mm seal. Mated the spare wheel that came with the scooter on the rack with the new hub.

The new hub had some tabs that interfered with the brake backing disc.


Burr em' off


Fits like a glove


Original tires from 1995. Not so far away from plastic.


Took it for a spin.


Then for the epic story of registration. The scooter still had the plate with it and an old tax disc ... from UK. And since I live in Finland, it's kinda far away from here. The story is that the previous owner bought it new in UK and according to tax disc this has only been ridden between 6/1995 to 6/1996. Engine broke down and disassembled. Project got never finished and the previous owner passed away. The disassembled scooter came from UK to Finland with other personal belongings as inheritance to PO's parents. I bought the scooter from his father so it's kinda sad story.


Because of Brexit the local inspection station did not have any means to get the needed registration data from DVLA so I had to get lil bit creative. They needed a official document that shows both the registration ID and VIN. Due to GDPR things there was no way to get this info over internet. DVLA also required a UK address for the registration so I was SOL.

It turned out that a colleague of mine has a relative in UK and he was willing to give me a hand with DVLA. I printed out the V62 form (used to report new owner information to DVLA), filled it up with my information along a UK address. Scanned the paper and sent it to my helper to be printed out and mailed to DVLA with £25 payment. For some reason the first letter got lost in the process and was re-sent after two months of waiting.

The day finally came in February 2022 and I got my hands on the god forsaken document.


Couple days later I was off to the inspection station with the scooter.


After checking the VIN, getting some dimensions it took couple hours of paperwork from the staff to get the information filed in the registry correctly. It appeared that they had to create the manufacturer from scratch, since this is the first Bajaj in Finland that is actually registered as Bajaj. Handful of others have been registered as Vespa in manufacturer name. After having lunch I picked these papers up.


After the inspection it was time to tax the scoot. After getting my tax statement and paying a whopping 16 and something eur of tax I was off to the inspection station again to get a local plate for the scoot.


I recently fitted the scoot with BGM Big Box, since GL needed it's original exhaust back.




Replaced the fugly old PX rear light with a genuine indian rear light.


Then it was time to assess the rip on the seat cover front seam


Some hand sewing later the cover was whole again


Now it's time to ride this thing.

Love your bike, love all the pics and most of all love your tenacity & epic story .

Budget Big-Block Build

Found a Motovespa 200 lump from Spain on eBay. Missing the cylinder but otherwise quite complete. Bought it and couple weeks later I had it on my bench.




The first owie was quite obvious - splines on the shaft were damaged and completely gone on the hub.


Popped the flywheel - all minty here


Split the cases - nothing wrong here either


Found a clutch under all the crud!


Sealing pad is also spotless


Off to the washer with these parts

Out of the washer - much better but still needs more attention to get all the stuck grit out




Threw the cases into bead blasting cabinet and started blasting. Bearings will be replaced so no worries about them.


Looking spotless again

great work on the Bajaj and nice clean lump of a 200 to play with, what are you going to hang it under?

Man, all that crud probably added a couple kilos on shipping cost.

Definitely lost some weight on the cleaning

Going to replace the original Bajaj block with this. Already got a Malossi 210 cylinder for it too.

A Spanish motor in a Bajaj? Never seen that done, but I'm positive you will do it well based on your other posts.

Since it is basically a PX200 engine, to my belief it should drop about right in.

Yesterday I got a Malossi 210 cylinder from a friend and today I did something unholy. A slight fault with the cylinder was a nice lil' hole on top of the piston and a stuck ring. Cylinder also has couple scratches but nothing too bad. Used a dremel sanding wheel to remove the molten and re-solidified aluminum from the top of the piston. Wiggled the ring free after sanding off the lava off around the exhaust port side. Then opened the surface with a rotary burr and hitted it with steel brush.


Gave it some pre-heat with a torch, lit up the thing with TIG and laid down some AlSi12 filler.


We shall see how this works. Feels quite good though. Video:


Reshaping with flappy wheel and quick sanding by hand to finish off. The cylinder came with extra rings and they went to their grooves nicely.

I like it, one question, would you be better off using metal from another piston? Are the two metals going to expand the same or at least close enough?

I'm not such worried about that. To my knowledge pistons are usually some kind of AlSi alloys with some other herbs and spices. This matches the used filler quite well.

Using another piston as a filler might be closer as a material but is also more dirty and porous. This brings more "junk" and inconsistencies in the weld and might not adhere as well as clean filler.

Color me concerned.

It is a particularly violent and vibratey environment in that combustion chamber.

Your scoot, your rules, but I would spring for a good used piston. At least it is soft metal.

This is of course far from an optimal solution. The cylinder kit was toast anyway so it is more of a trial if this kind of dirty fix can get an engine going again. When it fails, it will be interesting to see what gave way and how. This gives me a chance to learn something.

Optimal situation would of course be that it will just wear out and not fail at all. But as a realist I don't give that so much hope

As long as it's not a precious motor... and you do have a hi silicon alloy, this should work if you keep temps down and don't flog it too hard. I'd be into this just to see what happens too!



Did you happen to get a pic from the inside? Would it have been possible to weld from there too for a little extra 'insurance'?

You are right. There is still a hole under there, but has plenty of meat on top of it. I was kind of a wuss on getting too close to the edges of the hole with the arc. Edges on top of nothing are kinda finicky basterds on alu since when you get a molten pool, gravity kicks in and you quickly have even bigger hole. Tought about hitting it from behind too, but my torch and cup were way too big to fit in there let alone see anything.

Don't worry, the lava on the ribs has already been scraped off

Just remembered that FMP had a video on Youtube showing the cutout of an old Asso piston. It too had a crater on the top but still shows there is plenty of material on the top.

Screengrab:

200 lump slowly going together.

Can you spot the not in this picture


Hint: finest indian spare parts

Not sure what the question means…

But, give up… what's the answer? Lol

the spring isn't seated in the quadrant

Left is the new indian spring, on the right is used Piaggio original

Scratched my head for a short moment trying to remember how to wind the spring to the quadrant before I noticed something was off. Confirmed by pulling the original from the bin of parts destined for VR One cases.

Marked up the cases and scribed transfer ports with a pick


Bit of burring and we have transfers for the Malossi. Used a base gasket and scissors to transfer the last port shape on the cases.


Also found an owie from the P200 original piaggio cush drive

so somehow the spring is a mirror image of what it needs to be?

And yes, tearing the cush drive apart can be eye opening, had the same happen to me on my last build

Wonder how many dozen were bent upside down? I bet these springs were wound with straight leads then bent when finished. Some of that great quality control. Doesn't that make you wonder about quality of metal in gears and process used for hardening etc.

Yep. Wound the wrong way

I wonder how failing like this is even possible

The other parts are some no-name ones but the big parts are GR Gears branded. The feel on quality is on another level on the branded parts so I'm not too worried.

Isn't the backward spring for a small frame?

Fill up the dead space on the base ports with JBweld or similar

Good catch! Smallframes do indeed have opposite winded kickstarter and sprocket.

Got the GR gear cogs to fit by sanding their contact surfaces down for a bit. Definitely took a while with a sheet of sandpaper and piece of glass. But now I also have extra shiny shims and lock rings


0.20 clearance - good to go


Remembered to take a picture of the smoothed out intake port too.


Also picked up a pack of Bison Metal Epoxy to fill up the dead space in the transfer ports since there is no JB Weld available here.

good work all around!

I'd like to see the finished product of the epoxy work

Cleaned up the transfers with a wire brush


Added some DAS modeling clay. I'm hoping I can get a accurate enough negative out of the transfer ports. If my plan works out, I will shape them to my liking and use some glue to fix them on the cases. Then just fill up with metal epoxy to get away with hopefully minimal mess and sanding.


Couple uncertainties still on the road that will be answered in couple days as the clay hardens:
1. Air drying clay will shrink a bit as it dries. We will see if this becomes a problem.
2. Shaping the negative, will it be too brittle?

Questions answered:
Shrinkage was no problem, molds came off the block easily and clay was real nice to shape with small rotary burr. Gave them a good looking shape and finished by sanding the surface smooth.


Fit feels good and there is the gap I'm looking to fill


Sanded the cases, wiped clean with acetone and mixed up the epoxy


Decided not to glue the molds in place since the epoxy is rather paste-like and there seemed to be no risk of run-off


Slapped on the negative and wiped off the excess


Rinse and repeat for the other side of the cases


It's now drying and tomorrow is the moment of truth if any of this were at all worth it

Molds came off rather easily by prying them off


Some clay was glued on the epoxy


After giving the cases a quick burr and sand, the transfers are finished.


The burring of the epoxy was very easy because the shape was already there under the clay and needed only blending with the existing shape. Now the ports match up to Malossi quite nicely and there is no big gap at the "ears" of the transfer ports.

Nice job. Came out better than I was expecting. On the main side of the boost port channel, the corner should be shaped. Just a little.

Did you cut the piston to match the transfers? On those old kits they don't quite line up. Especially on one side.

What about the rotary inlet. Looks like stock duration there.

Yep, the corner of the casing will be matched too. I've left it to the last as it's kinda hard place to mark the shape and since it's really a small detail.

Piston is still untouched. Good tip on that since I've just thought it should be ok and not given any thought on that.

On rotary inlet I've just smoothened out the drill-bit shaped hole but left the shape otherwise alone. I've got some studying, measuring and calculating to do with the stock crank before even thinking about touching it. One important thing I already remember is that you should not widen the intake port sideways according to Mr. FMP.

The crank I'm looking to use is either SIP Premium 60/110 with 115°/4° post TDC or Polini with 138°/5° post TDC. Intake timing target should be somewhere around 200?

Save your money and get this crank
https://www.sip-scootershop.com/en/product/long-stroke-crankshaft-mazzucchelli_45020000?q=60%20crank
Will suit the old kit really well.

Modifying the pad is scary business. One slip and it's ruined. Can be fixed but not like original. Width must overlap the crank more than 1mm each side. This isn't 1mm on each side of the pad. It's the overlap to the crank. All cases and cranks vary and a unique situation for each.
Without lengthening the inlet duration, the performance potential is restricted.

Thanks for the tip again!

I'm currently looking at 181° exhaust, 29° blowdown, 124° transfer and 158° intake (107°/51°).

Are these all the timings now, with one of the 60mm cranks? Or what you plan to do?

Those numbers are with the stock crank I have on my hands currently. Baseline for future use.

As it is with stock crank it will go but it will lack bottom end or top end. Mid range will be ok, once it gets there.

Decide on the crank and it can all be adjusted to suit.

If my measurements are somewhat correct, I'd end up with 185° (107º/78º) intake with Mazzu crank and untouched pad. What kinda intake timing should the Malossi like?

Cutting/changing the crank adds to the after TDC timing and opening the pad adds mostly to before TDC timing since there is not much room to go the other way. I'm at loss on what kind of balance these two should have?

When I fitted a Malossi 210 onto my P200 motor, I did the same as you, Yoshi: ported and filled the transfers & boost ports, fixed the shape of the intake, but left it otherwise stock-ish. It has a good torque, but definitely still slower than any of my small block bikes with an SR 3.0 on it.

I need to show it some love and $$$, but it'll have to take its turn behind the smallstate.

I like the idea of using molds to ensure things are finished nicely and match where required.

Ever since rebuilding a motor & having a ring expand and go into exhaust port hole, then stop suddenly, I've been more cautious with the WIDTH of ports, as the wider they are, the easier it is for a ring to try to jump out the port and those look reasonably wide (not that I really know much about 200 motors.

The old malossi is intended for sport use. As you will use a 60mm crank and have a Dremel. It's possible to adjust it to many different outcomes.

It sets up well as fast road but needs exhaust port adjustment. As well as the correct packers and a decent head. Inlet at 205° (120/85) has good success.