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Ginch wrote:
Not sure. Your xmas tree/input shaft may not match with that clutch, not just because of the teeth. I'm struggling to remember what size the primary gear on the xmas tree is on a VNA, I have a feeling it's a smaller diameter than later ones. Measure the overall diameter and see what it is, and whether you can swap it for a more suitable gear. I don't have one handy to measure right at the moment.

If you are able to swap the 67t for something else, you'll get more choices. If not, maybe you'll have to downgrade your clutch ideas.
Oh... that change everything of course.
Is it really that the diameter of the primary gear size is smaller?
Well, i can buy a another that fits better.
No problem.
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addebaddelej wrote:
Is it really that the diameter of the primary gear size is smaller?
Well, i can buy a another that fits better.
No problem.
I'm not actually 100% sure about that, that's why you should measure the diameter of what you have and we can compare. I can dig out a late primary gear over the weekend.
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So, the engine case is done.
The case is blasted, the top deck is machined, reinforcement are done and the ports, including a third port is cutted and match ported against the cylinder.

I got a small hole in the block when I sanded it. Put some JB-weld on it. Hope it will do fine.
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Looking much better now. Might be a good idea to get some dummy bearings and do a dry build to check the port timings and squish after lowering the deck.
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Ginch wrote:
I'm not actually 100% sure about that, that's why you should measure the diameter of what you have and we can compare. I can dig out a late primary gear over the weekend.
I would be very greatful if you would do that for me 😊.

I need to do some more research about the christmas tree, outgoing axle and gearbox.
If I understand correctly, I dont only need the correct diameter for the primary gear, I also need to check rhw amount of springs as well, right?
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hibbert wrote:
Looking much better now. Might be a good idea to get some dummy bearings and do a dry build to check the port timings and squish after lowering the deck.
Thank you sir! 😊
Yes, I think I will need to buy those dummys and do as you say.

Stupid question, but how do I calculating the port timings if the engine already is put together?

I had never heard anything about squish before I started to renovate this engine, but I have done my research now.
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You might want to do the dry build so you can set up the optimum performance which could also be the most dependability aside from speed. Since you have put some effort into the welding, porting and decking the cylinder setup is easy compared to what you have accomplished. A degree wheel is also instrumental get one and the holder for the wheel that threads onto the crankshaft. You'll need a micrometer to measure the port distance from the cylinder deck. When you have that you can post the exhaust and transfer dimensions here and more knowledgeable folks will help. This will help determine if any cylinder base gaskets will be needed to set the cylinder appropriately. Then you can look at the squish and see what needs to happen there.
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addebaddelej wrote:
I would be very greatful if you would do that for me 😊.

I need to do some more research about the christmas tree, outgoing axle and gearbox.
If I understand correctly, I dont only need the correct diameter for the primary gear, I also need to check rhw amount of springs as well, right?
So my new primary gear for the input shaft has an overall diameter of 115mm. The inner diameter (yours might still be hidden by the pressed metal cover) is 91mm.

The correct springs will come in a repair kit.
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Checked the christmas tree today. Cut the sprints and measured the diameter.
Outer diameter of the primary drive is 116,7mm
Inner diameter of the primary drive is 91mm
67 teeth helical cut.

Looks like its the same as yours Ginch, if I would guess that your is 65 teeth?

See pictures
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I don't have anything as accurate as your to measure, I was using a ruler...

This one I tried to be a little more precise! So yes, yours is the same size.
This all occurred to me because when I was changing my VBC motor to EFL gears I had bought something that didn't fit. I was pretty sure it was the primary gear but could be mistaken. Anyway doesn't hurt to check!

So now you have the opportunity to upgrade the primary ratio, and you can do just about anything you like. I would change it to a straight cut, if you're going to maximum power then that makes sense to me. They say that the helical gear is quieter, but as all the rest of the gears are straight cut I don't know what difference it could make... in reality in my 252 you can't tell.

You'll want a longer primary ratio (smaller number) than you have now to make the most of the power you'll get. Some of the available gears can accommodate more than one ratio - meaning you could buy two clutch gears and swap to a shorter or longer one for a different riding style. Not sure what to recommend there, you might like to lift the front wheel regularly so you go for a shorter (bigger number) ratio, but that would still be longer than your current ratio.

This is a very useful calculator to help visualise your gearing - http://gearingcalc.free.fr/ Maybe start with the Sprint base and adjust to your current gears and go from there.
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External inline image provided by member with no explanatory text

These gear teeth don't look right - the notch at the corner of each tooth looks like the mating gear is only hitting half a tooth and you likely have tons of backlash ( https://fg-machine.com/blog/the-basics-of-gear-backlash-and-techniques-to-reduce-it/)
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Ginch wrote:
I don't have anything as accurate as your to measure, I was using a ruler...

This one I tried to be a little more precise! So yes, yours is the same size.
This all occurred to me because when I was changing my VBC motor to EFL gears I had bought something that didn't fit. I was pretty sure it was the primary gear but could be mistaken. Anyway doesn't hurt to check!

So now you have the opportunity to upgrade the primary ratio, and you can do just about anything you like. I would change it to a straight cut, if you're going to maximum power then that makes sense to me. They say that the helical gear is quieter, but as all the rest of the gears are straight cut I don't know what difference it could make... in reality in my 252 you can't tell.

You'll want a longer primary ratio (smaller number) than you have now to make the most of the power you'll get. Some of the available gears can accommodate more than one ratio - meaning you could buy two clutch gears and swap to a shorter or longer one for a different riding style. Not sure what to recommend there, you might like to lift the front wheel regularly so you go for a shorter (bigger number) ratio, but that would still be longer than your current ratio.

This is a very useful calculator to help visualise your gearing - http://gearingcalc.free.fr/ Maybe start with the Sprint base and adjust to your current gears and go from there.
Finally geting some sorted out now 😅.
Thank you for your help!

I was thinking about this kit maybe instead then:
https://www.10pollici.com/en/homepage/classic-vespa/engine/clutches/largeframe/clutch-bgm-pro-superstrong-2-0-cr80-ultralube-primary-gear-25-62-straight-cogs-set.2.1.35.gp.12846.uw

Straight theet, good for enought power if I go for the xxl-springs, correct ratio if I calculted it correct and it will physically fit and work.

It would be easy to just use kit directly i think.[/url]
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V oodoo wrote:
External inline image provided by member with no explanatory text

These gear teeth don't look right - the notch at the corner of each tooth looks like the mating gear is only hitting half a tooth and you likely have tons of backlash ( https://fg-machine.com/blog/the-basics-of-gear-backlash-and-techniques-to-reduce-it/)
Yes, I saw that too.
Didn't mind about it since I am changing it anyway with a new adjustment with the new setup.
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It's easy enough to put that kit together yourself, you can't go too far wrong. The Superstrong is a good clutch, but you might get better value from the VMC 10 Mille. Getting some good reviews here.

The repair kit for the primary gear (2 pressed metal covers, springs and rivets) you can use just about any one. Though it probably doesn't hurt to get the heavier springs.
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Ginch wrote:
It's easy enough to put that kit together yourself, you can't go too far wrong. The Superstrong is a good clutch, but you might get better value from the VMC 10 Mille. Getting some good reviews here.

The repair kit for the primary gear (2 pressed metal covers, springs and rivets) you can use just about any one. Though it probably doesn't hurt to get the heavier springs.
Ah, nice!

I looked into the VMC mille, looks really good.
Would this work together?
For what I understand, It doesn't matter if the cluch gear cog is for 8 springs, even if the clutch has 10, or am I wrong?

The BGM kit seems to work out well for 115mm clutches overall.
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hibbert wrote:
You might want to do the dry build so you can set up the optimum performance which could also be the most dependability aside from speed. Since you have put some effort into the welding, porting and decking the cylinder setup is easy compared to what you have accomplished. A degree wheel is also instrumental get one and the holder for the wheel that threads onto the crankshaft. You'll need a micrometer to measure the port distance from the cylinder deck. When you have that you can post the exhaust and transfer dimensions here and more knowledgeable folks will help. This will help determine if any cylinder base gaskets will be needed to set the cylinder appropriately. Then you can look at the squish and see what needs to happen there.
I sure will do.
Bought some dummies for rhe bearings.
Not quite sure how to measure the port distance from the cylinder.
Have to google that and read how to do it properly.

This is all new to me.
I have built some car engines before but not these kind of 2-stroke engines where you have to do a lot more calculating.

I try to learn by doing 🙂
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You need to measure accurately the dimension from the top deck sealing surface of cylinder to the top of the exhaust port and transfer port. Also you need to measure the dimension for the piston top when at top dead center. If the piston is coming above the cylinder deck you will enter that dimension as a -x.xx dimension I believe.

From there you can change the PBT (piston barrel top) dimension entry to experiment with different base gasket thickness to see how the port timing will be altered using different size base gaskets.

Once you have some measurements see what you get using the calculator at Lambretta-images.com. You will need to find the link on the home page scrolling down the page. Once you post your dimensions I'm sure others more capable will be able to provide some guidance on what to shoot for setting up the gaskets and optimum port timing.

Once you have the cylinder and timing set you can move to the squish. Mount the head with a piece of solder as close to the edges of the piston and cylinder and squeeze the solder so that can be measured. You may or may not need head gaskets to achieve the optimal squish. Might also need to machine the head just depends on the dimensions you measure and the configuration of your assembly I'm not familiar with your set up to know as of writing this my apologies.
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addebaddelej wrote:
Ah, nice!

I looked into the VMC mille, looks really good.
Would this work together?
For what I understand, It doesn't matter if the cluch gear cog is for 8 springs, even if the clutch has 10, or am I wrong?

The BGM kit seems to work out well for 115mm clutches overall.
To be honest I'm not sure if the BGM clutch primary gear fits the VMC 10 Molle clutch... I've only ever bought a clutch with the primary gear already assembled. The product listings on SIP don't seem to offer any help either. I suggest you contact 10 Pollici. Matteo was very helpful when I bought stuff there some time ago.
hibbert wrote:
From there you can change the PBT (piston barrel top) dimension
Hey Hibbert, what exactly is the "piston barrel top", I've seen "PBT" bandied about here but can't understand what it refers to? Is it the top of the cylinder?
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Ginch wrote:
To be honest I'm not sure if the BGM clutch primary gear fits the VMC 10 Molle clutch... I've only ever bought a clutch with the primary gear already assembled. The product listings on SIP don't seem to offer any help either. I suggest you contact 10 Pollici. Matteo was very helpful when I bought stuff there some time ago.




Hey Hibbert, what exactly is the "piston barrel top", I've seen "PBT" bandied about here but can't understand what it refers to? Is it the top of the cylinder?
Cosa clutch cog gear is a Cosa clutch cog gear; it will fit any type of Cosa clutch.
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GickSpeed wrote:
Cosa clutch cog gear is a Cosa clutch cog gear; it will fit any type of Cosa clutch.
Cheers. They certainly look the same but have never swapped one before.
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Ginch wrote:
Hey Hibbert, what exactly is the "piston barrel top", I've seen "PBT" bandied about here but can't understand what it refers to? Is it the top of the cylinder?
I'm probably not the best to describe this on my limited knowledge but I will try to explain my understanding. The PBT is the position of the piston when at TOP DEAD CENTER. If the PBT is at 0 degrees the calculator will interpret the location of the piston in relation to the opening and closing of the transfer and exhaust ports on the 360 degree rotation of the crankshaft. If the piston is measuring 1.00mm PBT below the cylinder deck you can enter a different number for example 1.50mm to see how the timings would be altered if a 0.50mm base gasket was used.
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hibbert wrote:
I'm probably not the best to describe this on my limited knowledge but I will try to explain my understanding. The PBT is the position of the piston when at TOP DEAD CENTER. If the PBT is at 0 degrees the calculator will interpret the location of the piston in relation to the opening and closing of the transfer and exhaust ports on the 360 degree rotation of the crankshaft. If the piston is measuring 1.00mm PBT below the cylinder deck you can enter a different number for example 1.50mm to see how the timings would be altered if a 0.50mm base gasket was used.
That makes sense. Thanks.
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hibbert wrote:
You need to measure accurately the dimension from the top deck sealing surface of cylinder to the top of the exhaust port and transfer port. Also you need to measure the dimension for the piston top when at top dead center. If the piston is coming above the cylinder deck you will enter that dimension as a -x.xx dimension I believe.

From there you can change the PBT (piston barrel top) dimension entry to experiment with different base gasket thickness to see how the port timing will be altered using different size base gaskets.

Once you have some measurements see what you get using the calculator at Lambretta-images.com. You will need to find the link on the home page scrolling down the page. Once you post your dimensions I'm sure others more capable will be able to provide some guidance on what to shoot for setting up the gaskets and optimum port timing.

Once you have the cylinder and timing set you can move to the squish. Mount the head with a piece of solder as close to the edges of the piston and cylinder and squeeze the solder so that can be measured. You may or may not need head gaskets to achieve the optimal squish. Might also need to machine the head just depends on the dimensions you measure and the configuration of your assembly I'm not familiar with your set up to know as of writing this my apologies.
Aha! Very good information!
Thank you for all that.
I will hopefully testbuild the engine next week.

Build it with dummy brarings and try to measure the gearbox and orher related parts, like gear selector and the input shaft. I think I have all the information i need for that now.
After that I will measure all the dimensions in the transfer ports. Will be interesting to use the calculator you added here.
Will update about that, once I have all the measurements.
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Ginch wrote:
To be honest I'm not sure if the BGM clutch primary gear fits the VMC 10 Molle clutch... I've only ever bought a clutch with the primary gear already assembled. The product listings on SIP don't seem to offer any help either. I suggest you contact 10 Pollici. Matteo was very helpful when I bought stuff there some time ago.

Yeah, I had to check with 10pollici and as another one wrote above, if it's a cosa 2 clutch it will fit with a cosa 2 gear cog.

I have decided to go for BGM gear cog kit, with a including primary drive. I think I go for 23/63 cogs.
I used the calculator and top speed @7500rpm would be around 110km/h. Maybe a little to much, but if it wont work I can buy a 22 teeth gear cog instead.

I also decided to go for the molle clutch, a lot of bang for the bucks, and the information I found about it was rhat many users prefered it instead of SIPS supersport.
Thank you for the tip mate!

I still struggle a bit with using original gear shaft.
But still, many users have built machines with 40hp+ without problem.

I have not decided about gear selector. I found that 10pollici had this one: https://www.10pollici.com/en/homepage/classic-vespa/engine/gear-cogs/largeframe/gear-selector-box-vespa-px-arcobaleno-98-my-t5-cosa-with-idle-speed-indicator.2.1.112.gp.1505.uw

For what I can understand it have a lot of better tolerance, and Is the same as a lusso.
Would you recomend it?
Otherwise SIP had a version called "Selector Box SIP "PX alt"". A lot more expensive though.



Hey Hibbert, what exactly is the "piston barrel top", I've seen "PBT" bandied about here but can't understand what it refers to? Is it the top of the cylinder?
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addebaddelej wrote:
Yeah, I had to check with 10pollici and as another one wrote above, if it's a cosa 2 clutch it will fit with a cosa 2 gear cog.

I have decided to go for BGM gear cog kit, with a including primary drive. I think I go for 23/63 cogs.
I used the calculator and top speed @7500rpm would be around 110km/h. Maybe a little to much, but if it wont work I can buy a 22 teeth gear cog instead.

I also decided to go for the molle clutch, a lot of bang for the bucks, and the information I found about it was rhat many users prefered it instead of SIPS supersport.
Thank you for the tip mate!

I still struggle a bit with using original gear shaft.
But still, many users have built machines with 40hp+ without problem.

I have not decided about gear selector. I found that 10pollici had this one: https://www.10pollici.com/en/homepage/classic-vespa/engine/gear-cogs/largeframe/gear-selector-box-vespa-px-arcobaleno-98-my-t5-cosa-with-idle-speed-indicator.2.1.112.gp.1505.uw

For what I can understand it have a lot of better tolerance, and Is the same as a lusso.
Would you recomend it?
Otherwise SIP had a version called "Selector Box SIP "PX alt"". A lot more expensive though.
The box from 10Pollici is not correct. SIP used to have a diagram showing the position of the lever when in third gear (with the selector box not connected) and it's different between old and PX Lusso/Arcobaleno. There may be differences between old P and pre-P motors, I'm not sure exactly.
SIP does say the "PX Alt" will fit old motors - yours is a VNB right? SIP are not always correct though...

This one appears to be correct - https://www.scooter-center.com/en/gear-selector-box-oem-quality-4-speed-vespa-rally180-vsd1t-rally200-vse1t-sprint150-vlb1t-ts125-vnl3t-gt125-vnl2t-gtr125-vnl2t-gl150-vla1t-super-vnb5t-till-vnb6t-vba-vbb-4350043?number=4350043 Can't say anything for quality however.

The other option is to repair yours. I have a bookmark at home for a repair guide from SLUK, I'll try to remember to find it for you.


Hmmm. Seems like the photos have disappeared... here is the video, it's for a PX box but the principles should be the same.
?si=_7EEJhH5klzytuUm
https://youtu.be/ZavNTSYmcxU?si=_7EEJhH5klzytuUm
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Ginch wrote:
The box from 10Pollici is not correct. SIP used to have a diagram showing the position of the lever when in third gear (with the selector box not connected) and it's different between old and PX Lusso/Arcobaleno. There may be differences between old P and pre-P motors, I'm not sure exactly.
SIP does say the "PX Alt" will fit old motors - yours is a VNB right? SIP are not always correct though...

This one appears to be correct - https://www.scooter-center.com/en/gear-selector-box-oem-quality-4-speed-vespa-rally180-vsd1t-rally200-vse1t-sprint150-vlb1t-ts125-vnl3t-gt125-vnl2t-gtr125-vnl2t-gl150-vla1t-super-vnb5t-till-vnb6t-vba-vbb-4350043?number=4350043 Can't say anything for quality however.

The other option is to repair yours. I have a bookmark at home for a repair guide from SLUK, I'll try to remember to find it for you.


Hmmm. Seems like the photos have disappeared... here is the video, it's for a PX box but the principles should be the same.
?si=_7EEJhH5klzytuUm
https://youtu.be/ZavNTSYmcxU?si=_7EEJhH5klzytuUm
Ah! Very good, thanks once again mate!
I think I am going to try to repair it. It looks good actually.
Will keep you updated!
@ginch avatar
UTC

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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Veni, Vidi, Posti
@ginch avatar
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
Joined: UTC
Posts: 8697
Location: Victoria, Australia
UTC quote
addebaddelej wrote:
Ah! Very good, thanks once again mate!
I think I am going to try to repair it. It looks good actually.
Will keep you updated!
That's great! Perhaps you could do your own tutorial on your experience for the members here?
OP
UTC

Enthusiast
Vespa vnb6t
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Posts: 52
Location: Växjö, sweden
 
Enthusiast
Vespa vnb6t
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Posts: 52
Location: Växjö, sweden
UTC quote
Ginch wrote:
That's great! Perhaps you could do your own tutorial on your experience for the members here?
I will do my best! 😊
OP
UTC

Enthusiast
Vespa vnb6t
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Location: Växjö, sweden
 
Enthusiast
Vespa vnb6t
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Location: Växjö, sweden
UTC quote
What do you guys recomend as sealing for the engine cases?

Gasket only, gasket and sealing compound or only sealing compound?

There is some alternatives. I found a gasket made of steel and silicone. However that might not work to well with sealing compund i guess?

What's your ideas?
@grumpnut avatar
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Hooked
'58 VBA
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Location: Chico CA
 
Hooked
@grumpnut avatar
'58 VBA
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Location: Chico CA
UTC quote
Gasket and sealant. No on the BGM gaskets
@ginch avatar
UTC

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
Joined: UTC
Posts: 8697
Location: Victoria, Australia
 
Veni, Vidi, Posti
@ginch avatar
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
Joined: UTC
Posts: 8697
Location: Victoria, Australia
UTC quote
Definite no for gasket only, I think traditionally a bit of grease on a gasket was thought to be all you need. But 50+ year old cases do need some help.

The BGM gaskets with silicone seem like a good idea, there have been mixed reviews. Also, they are quite thick and can potentially upset spacing - it's definitely an issue with smallframe cases at least.

Sealant only would be the answer on the Malossi cases, they've been designed that way.

My favourite is Threebond 1104 (same as Hondabond/Yamabond) with a normal gasket. It's horrible stuff to work with but as a sealant I don't think you can beat it.



Before you assemble your cases, what have you done about the intake so far?
@geeklion avatar
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The Dude
Too Many piles of Junk that need too much work and too much money
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The Dude
@geeklion avatar
Too Many piles of Junk that need too much work and too much money
Joined: UTC
Posts: 1738
Location: PNW from LBC
UTC quote
Ginch wrote:
Definite no for gasket only, I think traditionally a bit of grease on a gasket was thought to be all you need. But 50+ year old cases do need some help.

The BGM gaskets with silicone seem like a good idea, there have been mixed reviews. Also, they are quite thick and can potentially upset spacing - it's definitely an issue with smallframe cases at least.

Sealant only would be the answer on the Malossi cases, they've been designed that way.

My favourite is Threebond 1104 (same as Hondabond/Yamabond) with a normal gasket. It's horrible stuff to work with but as a sealant I don't think you can beat it.



Before you assemble your cases, what have you done about the intake so far?
+1 on threebond/yamabond/hondabond + gasket. Although I prefer the piaggio or sip premium gaskets, for the Pseries atleast. Grease may have been ok 50 years ago, but we live in the future
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