Polini 177 kit removal?

[doctorbob]

Hello all.

I joined a while back as i have started my first ever vespa project. Its a 1980 p125x. I had a few surprises when i was stripping the body down, but now i had a few more when i start on the engine.

i noticed that the previous mechanic has not been so gentle with the engine and there are a few scratches on the mating surfaces, but that not my main question.

I opened up the engine and it seems that the previous owner has made it into a 177 with a polini cyclinder and piston. That of course means that the engine cases have been modified.

I want to return this motor back to 125 original. Whilst i can get head, cylinder and piston. I am concerned whether the modifications to the ports will affect the engine operation in anyway and whether i have to do something else to get back to 125 status so it functions normally (perfectly)

Thanks so much in advance

Bib

[ironsloth]

Was led to believe that a Polini 177 kit was just a bolt on affair, should get away with replacing the top end. Mind you, a standard 125/150 always seems like a seal dragging its ring piece once you go back to that. I'd consider leaving it on if it's in good order, that or go for the LML 5 port 150 kit if you want standard stuff.

[doctorbob]

Nov 30, 2019 20:17:29 GMT ironsloth said:

Was led to believe that a Polini 177 kit was just a bolt on affair, should get away with replacing the top end. Mind you, a standard 125/150 always seems like a seal dragging its ring piece once you go back to that. I'd consider leaving it on if it's in good order, that or go for the LML 5 port 150 kit if you want standard stuff.

Hey thanks for the reply. Indeed the polini kit is bolt on. But my i was thinking more about the mods done tonthe ports on the engine case. These appear to have been made bigger and i am wondering it that will affect the operation when i go back to original 125.

It may indeed be a bit slow, but i want to get started that way. The scoot needs to be re registered and it will be a pain to get it through with a mod like that where i live.

Thanks

[ianmartin40]

I don`t know anyone who admits to fitting a big bore kit, where do you live? and are they going to check the engine internals? I think it will be ok to fit standard parts to your cases, just make sure the base gasket covers all ports or you may need to use a base gasket for a kitted motor to have a seal, the standard base gasket is smaller than that for a kitted motor, but like Ironsloth says if it seems in good order I would keep the kit on, fairly sure your carb will have been jetted to suit the kit also.

Ian

[mijapxman]

If you are set on taking the 177 kit off, just make sure, whatever base gasket you use, covers what needs covered on the engine case, be it using a standard 125 gasket or a standard Polini 177 gasket. I have opened up the cylinder transfers and case transfers on these and DR kits, so wide, that you need to use a Malossi 166 gasket and enlarge the transfer ports on the gasket, to line everything up.

Hope the above Kind of makes sense?



Mij ☺

[doctorbob]

Hello again and thanks for the responses.

ian. I live in switzerland and they are a bit strict on vehicles and also tough on modifications. Therefore i want to be as by the book as possible.

@mij, thanks and yes it does make sense. I was a bit worried that the modified port on the engine case would cause some problems with the smaller port on the cylinder. I thought maybe it would cause some turbulence for the mixture coming into the cylinder.

Can i ask why you modified both cylinder and case... id it wasnt for a larger piston? Also... anywhere i can read more about what will affect performance and how?

Thanks again and please keep your eye out for more novice questions..

Bob

[ianmartin40]

My cases are ported to match the larger than standard ports on my polini cylinder, if you compare standard and kitted cylinder you will see the difference in openings, also look at standard piston and one from kitted motor and see the difference.
Mij can probably give you a better explanantion, this was a motor I bought like this and it is fairly quick so I like it, I upped the gearing to make it more relaxed at cruising.

Ian

[mijapxman]

doctorbob, I used to do it, as it was mentioned in here...

beedspeed.com/products/manual-tuning-vespas-the-norrie-kerr-way

Tuning has moved on a bit, since I bought a first edition of the above. If you are worried about turbulence you could fill the extra space with JB weld or similar.

This guys YouTube site is well worth looking at, here are a couple of his examples of how to tune a standard 125 or 150, cylinder and piston:




[



The rest of his YouTube channel is highly recommended. 👍 👍 👍


Mij/Jim ☺