125 to 175 conversion

[Adam_Winstone]

Without doubt, my choice would be to use the SpeedClic cutting discs as these allow you to shape the bowl as you go. Other cheap cutting discs are nowhere near as effective and cutters/grinders tend to clog with the alloy.

We need to have a chat about where to remove metal from.

Adam

https://www.google.co.uk/search?q=speed ... 0034740024

[Scooterdude]

IMG_2298.JPG

For anyone who's still interested in this thread, the af 175 head came today the combustion chamber measures the same 20cc as the poorly made one but the squish band has been machined correctly and is quite a bit deeper than the old one.

Put it all together and instead of 150 psi it now makes 120psi and is considerably easier to kick, anyway it all works ok now.

[Adam_Winstone]

Hi Scooterdude,

OK, I'm getting confused now that we have 2 different people posting about 2 different motors, which may or may not have 20mm volume in the combustion chamber and/or in the trapped volume, which would incorporate the squish volume... giving a very different geometric ration depending on who is measuring what and how.

Is this where we need to break into Keith's head/thread and Scooterdude's head/thread?

Adam

[kclewis]

Hi, thanks for posting that scooterdude, certainly looks different. I am glad it has worked out for you.
Adam, sorry if its all getting confusing, it is my first Lambretta build and I had no idea about all of the head variations etc, thanks for your help. I will for now probably go along a similar route and get a new head.
Many thanks Keith.

[Scooterdude]

Adam, guess im guilty here of jumping in with both feet onto Keith's thread....

[Adam_Winstone]

LOL... don't worry the discussion has been good and hopefully provided food for thought for those that might be considering whether their head is suitable for their motor, how to check and what to look for if not.

All the best, I wish you both well with your motors and don't hesitate to come back with comment, updates or to ask opinions.

Adam

[Scooterdude]

Keith. Did you get sorted out with a new head from Rayspeed?

[kclewis]

Yes mate, sorry forgot to post. Ordered and arrived next day, measured the chamber 20 CC (old one was 14CC) refitted it all and got 125psi, kicking it over it seems about the same, so I am wondering if the overall trapped volume is the same? Did not measure that, but the squish was set at around 1.6 so I will use this head. I am still waiting for the registration to come through, had my application rejected on Monday because ( I think) I sent a copy of the dating certificate, they need the original, my mistake.
So as soon as it arrives I can get out and try it.
Thanks for your help and I had really good service from AF.
Cheers Keith.