Modern Vespa

Trying to figure out how to stop the MMW head from leaking on the Pinasco aluminum cylinder. I've tried permatex copper but it leaks rather quickly once hot. Makes jetting rather challenging.

In the photos you can see the 4 unused bolt holes are just outside the rim edge. The original does have full coverage.

-Check to see if the gaskets surfaces on both cylinder and head are true. address as needed.

-Have the head drilled to allows 8 bolts. may not be a great option here.

-purchase an 8 hole head.

The depths of the steps ?

Check to see if the head is not warped.

MMW head appears level on glass, with a 2mm step. I mounted the original Pinasco head this afternoon for some test runs but rain arrived before I could take it out. I will pull it and the cylinder off tomorrow and check level/step height.

Any thoughts on installing studs in the 4 unused bolt holes and filling the hex hole with permatex copper?

https://www.fastenere.com/m8-125-metric-socket-set-screws-cup-point-din-916-stainless-steel-18-8

I would put grub screws in the holes and see if it stops the blow out.

are you saying you have air coming out through one of the holes? that is a different problem all together.

Those holes shouldn't affect sealing. With the MMW head the combustion chamber is inside the cylinder. Or am I missing something?

my 4th option would be to. .. .

Scrap the Pinasco cylinder and go with BGM 177 cylinder kit, add black rubber sheath to the gear cables, and add gear cable bracket.

No, no air is escaping the holes. I do have burned oil/fuel leaking from the lower portion of the head/cylinder filling the bottom bolt hole. MMW head is flat, but I haven't checked the cylinder yet.

If I entertained the BGM 177, which one? Its a 64 VBB2T engine.

I don't know if this is a good idea or a bad one so please shoot it down quick if it's bad. If you had the cylinder OFF could you lap the head and cylinder together with valve grinding paste?

is this a 2 or 3 port motor?

Which one is the MMW head I see a Malossi and a Pinasco. Why aren't you using the Pinasco isn't that which came with the piston and cylinder?

MMW head is a machined Malossi with a 'step' to fit inside the Pinasco cylinder. Pinasco head tends to ping like crazy that's why most of us bin it from the start. I did a similar thing on a friend's Sprint V.

Cool I see some machining on the Malossi. Guess I'm lucky have 2 Pinasco engines neither ping.

That's a great idea Hibbert!

Might also be worth checking that the step on the head is definitely touching the step down in the cylinder. If it didn't quite touch then that would explain why it keeps blowing the sealer out.

Gick, its a 2 port case.

okay. you are stuck with 2 port cylinder then.

Can I run the 3 port BGM 177ONE cylinder with a 2 port spacer?

https://www.scooter-center.com/en/cylinder-base-spacer-bgm-pro-177-cc-2-transfer-ports-vespa-vnb-vba-vbb-vnc-vbc-gt125-vnl2t-gl150-vla1t-sprint150-vlb1t-0150000-2.0mm-bgm1772bs20?number=BGM1772BS20

https://www.scooter-center.com/en/cylinder-bgm-pro-177/187-cc-also-for-elestart/electric-starter-vespa-px125-px150-cosa125/150-gtr125-ts125-sprint-veloce-vlb1t-0150001-lml-star/stella-125/150-motovespa-px125-iris-99m-px150-iris-75m-125-cl-9cl-150-cl-9nc-bgm1770ne?number=BGM1770NE

you could. you would need to machine the bottom of the cylinder. It would not be plug & play.

What do you mean, Gick. Open ports or something else?


Step depth on the Pinasco cylinder is 1.5mm, and the height on the MMW is 2mm. Also the width of the Pinasco is 73.7mm and the MMW is 73mm. Lots of play.

I've lapped the cylinder and the MMW head on 320 grit wet sand paper and will re-mount with permatex copper. Not holding out hope with so much play in the step.

Clearly the step is not the issue then..

Even with 0.7mm play, the sealing surface still should be wide enough to create a seal easily. Not sure why it doesn't.

Did the lapping show up any high or low spots?

Gick means that if you put in a spacer to cover the third port in the BGM cylinder, you would need to take that thickness off the bottom of the cylinder. Pinasco make a 3-port 177 for 2-port case that comes with a spacer, and already has the cylinder shortened.

Of course if you were to put a 60mm crank in there you'd have room for a 1.5mm (give or take) spacer, then you could fit the BGM if that's what you really wanted. You'd probably need to make that one yourself I think.

Lapping the cylinder the way I understand you did it may not help. The top of the cylinder isn't the sealing surface it's down in the step. That's why I mentioned removing the cylinder and lapping the cylinder and head together. You can rotate the head when studs are out of the way.

I understand what you're saying now. I will give it a try. Not on the head but I haven't checked the cylinder step yet. Top of the cylinder had a slight low spot but as I now understand its not the mating surface.

I was looking on my phone and thought the dark part (the sealing surface) was dark from lapping...

I would just buy a proper Pinasco head. The one with eight holes was (I think) introduced with the 177/187 Magny Cours kit, and can be purchased separately. I think it's marked A3703 or something.

The 8 hole is also a center plug I believe. I haven't had trouble with the A3606 4 hole head but apparently others have.

I lapped the step and will install tonight. Here's hoping for the best now that it should be flat and smooth surfaces.

That looks good from here. I use copper silicone on the step.

Yes it is center plug. I did similar on my 225, swapping out the 4 hole 810 (VRH) for an 8 hole, center plug A3611(10?). Definite improvement, but not sure which characteristic made the most difference.

No leaks after lapping and assembly with copper silicon.

Thanks for everyone's responses

Glad it worked out for you.