Blueprinting or sacrilege?

[Knowledge]

I am preserving my TV175. No kits, no tuning, but the squish is 2mm without a head gasket fitted.

Am I allowed to skim the head to get a decent squish, or is that against the rules?

[Fast n Furious]

Personally, doing the job right by blueprinting is hardly sacrilege. On the contrary, it's perfectly good Engineering practice to optimise, even original parts, to improve performance and reliability.

[dickie]

+1

[Storkfoot]

The squish on my standard TV175 is about 3.2mm. I had the same thought process but just left it on the basis that it must have always been like that.

It has run really well although top speed is not what Innocenti claimed I must have done over a thousand miles now. As yet, I have had no reason to take the head off.

[jonw]

Try it with the "original" 2mm squish first, you may be quite happy with its performance.

[Adam_Winstone]

As Storkfoot has said, you regularly find standard motors have 2-3mm squish clearance, yet they run perfectly well. Indeed, I ended up machining a Vespa P2 head for a mate as he was so concerned about the 3mm that his factory assembled bike measured. He'd done thousands of reliable touring miles and performance was 'book' but he figured it could be better.

I machined the head, reprofiling to more accurately match crown profile and result in 1.0-1.5mm squish clearance. As expected, he said that the motor felt good but there was no real performance increase... more a sense of satisfaction that the squish band might now actually function as theory suggests it should.

Reality... not world-changing. It worked before and it still worked afterwards.

[vegansydney]

I'm having the same dilemma with an SS180 (sorry! ) I'm currently building. The squish is a whopping 2.25mm. Recalling the 'Bang for Buck' article in Scootering several years ago on the performance gains to be had (~1HP) just by getting squish right, I'll most likely machine the head.

On another standard 200cc Lambretta I own, it's as per the factory, sans full DC electronic ignition and squish set to 1.2mm. Its my favourite scooter to ride.

[Adam_Winstone]

The thick head gasket version of the SX200 always has a massive squish clearance as the piston crown is always lower than top of barrel to start with! Whilst these can be addressed by gasket reduction or removal, it does illustrate that Innocenti were not quite so anal about squish as we've all become.

Yes, Innocenti may have also used thick gaskets to lower compression ratios but at the cost of resultant squish clearance, to the extent that squish function is compromised. Innocenti didn't appear to be too bothered. As the 2 examples mentioned, Piaggio don't seem too bothered either!

Personally, I'd rather reduce squish so that it falls into recognised values.... as much for world order as function.

[martyn dwane]

i remember Harry Barlow )pro porting ) telling me the squish on his vespa he ran at Nuremberg ring ran with 2mm squish

[hullygully]

were all those 'whopping' head squishes used with the old 4*, with todays fuel I'd still try to bring those clearances down

[Knowledge]

Too late now. The head has been on the lathe and the deed is done.

I will post photos of the mashed piston crown as and when this occurs.

[coaster]

Back in the day there was no mention of squish clearances, just 'side or center squish as wayts of directing the chatge towards the spark plug. The idea of using a tight clearnce squish band came more recently I THINK possible the |Japanese?? I dont think the Lambretta tuning manual mentioned even Maybe leaded 4 star didnt burn as hot as modern fuels?