Modern Vespa

Finally after how many years there is an option now for GS 150. Bollag Motos in Switzerland has released a batch of aluminum cylinders for the Gran Sport. My GS has been parked waiting for motivation to replace a leaking clutch side main seal which has arrived.

Cylinder seems fairly straight forward with a new inlet manifold and exhaust manifold with a modern slip stub to accommodate modern day PX type exhausts with a swingarm bracket.

The crankshaft is a 60mm DRT with a PX type clutch side axle offering many options there.

Plan is to rebuild engine match case transfers new main bearings and seals. Going to need help setting up cylinder port timing.

That's a great looking scooter. The kit looks very interesting too.

Do they recommend a carb and air filter that will fit under the cowl as well?

Beauty.

Both the kit and the scoot!
Looking forward to your report on the kit.

Thanks, yes Bollag offers a different inlet manifold to convert to the CP21 but I’m inclined to use the original carburetor.

Well done if you have a UB23S3 that doesn't leak

Most of the carb conversion kits for gs150 spec the slightly larger CP23, in case you want to change later on.

I'm looking forward to following this build.

I probably meant CP23. What did you mean about the carb leaking?

Well the original carb is at least 60 years old now. Yours sounds like it's running good, and rebuild kits are available. But along with the original ignition and charging systems, the carb is well known as not the most reliable.

Sure if it's not broken, don't fix it.

OR, hear me out... if it ain't broke, fix it till it is! You've got a beautifu scoot there, and Bollag makes great products. With that crank/cylinder/exhaust/porting/etc, its going to want lots of fuel and air! Let it breath. Pop on a modern big carb and get the most out of your powerplant. Worth the investment, as you're already going this far. Not that I'm trying to spend your money for ya

Love it…..
The intake shroud on the side-cover looks great.
Intrested how it will run after you get the Kit set-up and run-in…should be a great tourer.

Are you in Switzerland? Im living 25 years here but never heard of this supplier. Will check them out…

👍

This is cool. Hard to get in that condition. Will be a much nicer ride with some power. GS150 is always the one people prefer to look at.
Not a fan of the air scoop spoils the lines.
Is there any reed block option? Piston ported non reed inlets are not the best, as opposed to reed piston inlets which are. With reeds a boost port could be cut in.
Going to be an interesting project.

Pinasco has just come out with 4 stud WB cases including reed block. The cases allow you to run any small block cylinder of your choice. Not exactly what you are asking for, but just nice info and some better choices.
The Bollag cylinders will be a great choice for those that want plug & play on their original GS cases.

dellorto ssi can be set up for down draft with a 90° float mounted on the carb, or with a remote SS2 float.

It's what all the factory race bikes ran, would look fantastic with the rest of the setup.

After 2+ years I am getting back to the GS. Today I removed the engine, wasn't bad everything went smooth no broken skin.

Oh this should be a good one. Can't wait to see the end of this project.

Can not wait! I have a 58 GS 150 sitting in my shed in backyard that is in need of some lovin! Definitely watching this one!

Have to admit BajaRob has provided motivation with his GS project to get back into mine. Don't know how many Bollag produced and was getting impatient with rumors of Pinasco releasing one so I went ahead with Bollag. Don't recall where I'd seen something about SIP releasing one maybe Bollag sold his designs to them. At the time I had to place my order before they were actually produced and anxiously wait. It was a relief when it finally arrived.

?si=C3_uVIBD571hJSYp

Going to start breaking the engine down is there any reason to take any measurements on the current piston and port timings?

Plug and play yes? I cant think of any, but interested to see what others say?

Excited to see your progress. woot!

Dismantled the engine and found a problem that is most likely the reason the scooter wouldn't run correctly and had fuel in the gearbox. Everything looked fantastic otherwise piston looked fresh and great cross hatch on cylinder. So good kinda sad it's going to retire for the ultimo.

I found the clutch side seal loose in the aluminum carrier. I could move it in and out below the main bearing.

I made a rookie mistake didn't undo the gear selector before I attempted to split the casings. Once I figured that out my impatience and general lack of knowledge got worse I only removed one of two retaining screws and cracked the selector plate a new one is required. Still pleased with the process.

https://youtube.com/shorts/NGNHYT0GX1g?si=qkqCVd1B6GLziN44

Plug and play after some detailed work. Just the other day I commented on fellow member Norman's thread about his cowl fitting issue with a 110mm connecting rod and that it was new territory for me. Little did I know I was actually on the same Ark because I ordered a 60mm crank with a 110mm connecting rod didn't even realize I was joining the long rod club. Not sure what I'm in store for with this project.

Got some plastic dummy bearings in the casings new crank, piston, 5mm base packer, cylinder and head to check things out. Piston is pushing head up so need to raise cylinder and or head but need to take a step back.

Ballog suggests port timing for the 60/110 to be:

Inlet 154
Transfer 118
Exhaust 165

The following are measurements I got:
Base Packer 4.90
Transfer 49.80
Exhaust 39.80
PBT 1.55 = U
Head collar 3.55 = K

Bollag suggests 1.2 for squish but I'm not sure it's relevant yet. Instructions say subtract PBT from head collar: 3.55-1.55=2. I think by adding 2 gets me to 0 and still need to add to get squish. But I think before that can be calculated I first need to establish the cylinder height to get the suggested 154/118/165.

I'm very confused it's been too long since I've done this and I think this might be more complex and above my knowledge level asking for a life ring.

Bummer on the selector. Mine was worn out, glad new ones are available. Scooter Center has special machined crank bearings and viton seals. Apparently all the new seals are thicker than the originals and will rub on the bearings. If you haven't gotten the new book, it's a gold mine of useful goodies and talks about the selector install too. It's cheaper to get it from SIP. I'll be assembling my engine after my upcoming Baja trip.

Thanks Rob I got the bearings and seals you described but couldn't remember why the bearings were machined exactly. Think I got lucky today but did some damage. Last night I was reading the Bollag instructions and I realized I had the 110 rod I went on SIP frantically to look for the 5mm packer. In the description it says makes a smoother running engine with the longer rod. Then went to look at my parts and found Bollag supplied the 5mm packer. Still couldn't stop thinking about what I'm going to do if the cylinder shroud needs extending…

You might end up being around 15hp with your setup. Don't sweat the shroud. You can buy the after market one for the stroker and I can mod it for you to fit the full length. That way your original can stay intact.

Can you post a picture of the head? Assume is is inset and fits inside the bore. Is that the 3.55mm head collar? First thing to do is what you said; set it up to get their numbers.
On these cylinders the inlet duration is the most critical. Without a reed block, the piston port can easily get spluttery and flood easy. If there was a reed manifold option, it's worth getting.

Thanks Jack yes I'm using bollag's nomenclature the head collar is the inset that fits into the bore which is 3.55mm.

I'm not aware of a reed option but I'd really like to maintain the original carb for originality even if I need to de-tune other things. I got a Polini box to go with this but I could easily go with a standard stock P exhaust if it will make tuning the stock carb easier as there are no larger jets for them. It's weird the transfers almost look smaller than the original.

I have lost my bookmark for the calculator page can you suggest one.

Here is a picture of the head. At first I wasn't sure the collar was the collar but according to Bollag that is the head collar.

When I was looking for a new exhaust I discovered SIP concluded that through their testing the road 3 was the best pipe for your kind of setup. They have a bracket that ties it to the GS cases.

Of course SIP would make that conclusion haha! Curious where you came up with 15hp I'm skeptical but it sounds good. Ideally I want to have this working good with the original carb that was my original goal and having 2nd thoughts now about enlarging the case transfers and if the chosen exhaust is going to call for more than the stock carb can deliver. I'm not aware of larger main jets than the 105. Might need your sheet metal skills glad you offered!

Are you sure about the port measurements? if that head goes 3.55mm into the bore. With a 1.2mm squish, 49.8mm main transfers to top and 39.8mm exhaust, on the 57mm/110 crank, it comes out at 123/169. Which is a lot. On the 60mm/110 crank is 135/177, which is too much for an old scooter. Some thing is no measured correctly.

What is the dimension of the inlet port to the top of the cylinder? If no reed this really matters. if too much it will difficult (pita).

Spent some time on Lambretta-images.com port timing calculator after confirming dimensions again. With the 4.90mm base packer and using 1.0PBT 1.55PBT 1.65PBT and 2.0PBT. Also tried 40.0 and 40.5 for the exhaust dimension. The top of the port is slightly arched.

A slight deviation on the inputs seem to fluctuate the results enough to add much confusion on my end. Not sure where the focus should be hitting the exhaust number or the transfer. Blowdown didn't seem to have such change at 22 and change.

The INLET number came in at 125 and not close to 154? Also that didn't change with different PBT inputs in the other fields. Maybe it's a different calculation Bollag is using?

To hit the 165 exhaust spec using 40mm & 2PBT would need to reduce 0.45 from the base packer and end up with 4.45mm. With those specs the transfer is 120 2 more than Bollag spec is that better?

I checked the dimensions again and this is what I measured

INLET 67.5 top 88.5 bottom
TRANSFER 50
EXHAUST 40 maybe 40.5
PBT 1.55
HEAD COLLAR 3.55

Does it use a head gasket? Pbt cannot be 1.55 if the head is inset 3.55. If the squish is 1.2 , pbt is 4.75mm. If it isn't I'm missing something.

Yes it most likely will need a head gasket to adjust the squish but I thought the first step was to set the cylinder height.

Not sure this is useful but I measured the original cylinder:

INLET 70.9-83.25 (12.35) [ultimo 21]
TRANSFER 46.15-63.7 (17.55) [ultimo 11]
EXHAUST 37.65

Noticeably the Ultimo has shorter transfer length and longer inlet length.

Think I misspoke on my post above. If I ADD a 0.5 base to the 4.9 it should give a 2.05PBT. Then I get 120.83 transfer 165.25 exhaust and 22.21 blowdown. How does that look?

You can get up to a 122 main with this kit.

Yeah you would have to match port and get a different carb and the right exhaust, ect.

https://www.sip-scootershop.com/en/product/jetting-kit-dell-orto-100-122-o-5-mm_40100000

I get the same. Its not going to be super fast but it will be strong.

For the inlet, the top and bottom measurements of the piston inlet window to piston crown are needed.

I'll be damned, Rob you made my day had no idea the main was a 5mm like pilots in phbh. Wow this great THANK YOU! I just tried one from my pilot collection and confirmed they fit! Way to go delLorto! On my list now.

https://youtube.com/shorts/i5Iv3oGtdKM?feature=shared

Here's the SIP video. Soon to be released!🤣🤣

Wow I was so wrong about that the SIP looks like it has a much larger exhaust port compared to the Ultimo and general differences. Maybe more performance but I'm still jazzed with how this one is coming together. Still high from learning about the jets best day ever!

Awesome so if the math is correct and PBT is 2.05 - head 3.55 = 2.05 + 1.2 = 3.25 needed for head gasket. Does this look right?

The piston does not have an inlet port but it has a slight cutaway from the bottom. I measured 60.65 from the crown to the cutaway. What should be entered in the empty fields?

I entered 60.65 for piston height and 88.5 for inlet floor = 148.82 less than the 154 spec. The cutaway goes above the inlet port at TDC. Does the cutaway need to be raised to get the 154?