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I have just taken the head off my 200cc engine for a decoke.
I was astonished to find no head gasket just a residue of a sealant.
I'm old school so I think it should have one. Any other views or is it a more modern way just using a gasket sealant?

No gasket or sealant on my LIS150, and touch wood, no problems. I did 'lap' both top of barrel and head base to get nice smooth surfaces before fitting though!

You must be old school I can't remember the last time I needed to give an engine a de coke!! With modern synthetic oils they seem to be a thing of the past lol the gasket was probably removed to increase compression I would put a thin gasket on as they are designed to use one

Since the 70's, I have never used a gasket on any Lambretta engine that I have built, regardless of the state of tune. I would suspect that many of my contempories with some history in racing (arguably the 'caretakers' of Lambrettas, along with the Northern hard core, during the time when ownership was not so fashionable) would hold the same opinion about head gaskets. That probably qualifies me as "old school" as any, albeit with some attitude.

Whatever squish is required, & I always aim for 1.0 mm, along with a tried & trusted compression ratio, it can be achieved by eliminating the weak link....

Currently, I use the Loctite Golden Silicone, though I haven't known a failure with the common or garden sanitary stuff. Virtually every engine that I have stripped has shown witness of head gasket seepage, so elimination has been the best cure IMHO.

Warkton Tornado No.1 wrote:Since the 70's, I have never used a gasket on any Lambretta engine that I have built, regardless of the state of tune. I would suspect that many of my contempories with some history in racing (arguably the 'caretakers' of Lambrettas, along with the Northern hard core, during the time when ownership was not so fashionable) would hold the same opinion about head gaskets. That probably qualifies me as "old school" as any, albeit with some attitude.

Whatever squish is required, & I always aim for 1.0 mm, along with a tried & trusted compression ratio, it can be achieved by eliminating the weak link....

Currently, I use the Loctite Golden Silicone, though I haven't known a failure with the common or garden sanitary stuff. Virtually every engine that I have stripped has shown witness of head gasket seepage, so elimination has been the best cure IMHO.

+1

Thank you all for the comments.There was evidence of weeping so I will do belt and braces with silicone and gasket. Cheers Pacemaker

I have always made sure the mating surface on the head was 100% true. (Sheet of glass and emery) and used a thin gasket with a thin wipe of a sealant on both sides. I do the same with the base gasket. And I torque to 16 ft/lbs with elongated head nuts.
Cleanliness and sound engineering practices are the key. Gasket for me is my preferred choice.

pacemaker wrote:Thank you all for the comments.There was evidence of weeping so I will do belt and braces with silicone and gasket. Cheers Pacemaker

I would not use silicone sealant and a gasket, it would be better to use a gasket compound such as hylomar.

My belief is that cylinder head gaskets were used by Lambretta as a convenience. Undoubtedly, the main principle in using a soft, crushable alloy, was to allow for machining deficiencies in the surfaces in the sealing faces of the head & cylinder.

However, most of us are aware that really thick gaskets were also used principally to lower the compression in the SX 200 engine. If anybody is naïve enough to continue to use them in an original specification engine & be unaware of the effect upon the squish, then I suggest they research the importance of optimised piston to head clearance with regard to combustion & heat transfer. Isn’t that what we do with regard to ignition timing, fuel tap flow & two stroke oil, rather than use things as originally intended?

I have worked on many engines in my life, & cannot recall ever unveiling a Lambretta cylinder head gasket that did not indicate some level of leakage.

That is the reason that many of us eliminate the weak link, in conjunction with a good sealant that can stand the conditions within the combustion chamber of a two-stroke engine. Sorry to contradict anybody, but Hylomar is the only one I would never use again & many friends liken it to blue snot. The packaging used to name Rolls Royce as some form of recommendation, but as impressive as that may be, a more meaningful name drop would be Wartburg or Trabant in terms of relevance to my mind.

If using a soft alloy gasket is such a good idea, then there must be advocates willing to build a 70 mm bore engine with a compression ratio of 10:1 using a gasket as the only sealant, that is, fitted ‘dry’

I would like to witness the stripdown of such an engine after nominal mileage, as I would be amazed if leakage was not apparent.

A better option would be no gasket @ all, in conjunction with checking the mating surfaces for fit & flatness, with a smear of grease.

But the safest choice is to omit the cylinder head gasket & use a good sealant, whether the engine is built as a racing powerhouse or a long distance tourer

With your preference for a good sealant WT, did you never like me as an enthusiastic teenage DIY engine builder stand on a tube of red hermetite and then walk it through the house into the carpet and then find it all over the door handles. I digress but in my time I have got it everywhere lol.
Interesting debate. Do the Castrol R40 one next ?

There's also the fact that a gasket introduces twice as many potential leaks as no gasket

CHRIS in MARGATE wrote:With your preference for a good sealant WT, did you never like me as an enthusiastic teenage DIY engine builder stand on a tube of red hermetite and then walk it through the house into the carpet and then find it all over the door handles. I digress but in my time I have got it everywhere lol.
Interesting debate. Do the Castrol R40 one next ?

Never did the Red Hermetite through the home, but my Mum used to say: "The Black Hand Gang has been through the house again"

On that theme, when I see people oblivious to their surroundings (such as traffic having to take avoidance because they are texting or "on the phone") I often think to myself, in one way, it is a pity that there's not so much dog sh1t on the paths these days.....

No head gasket ideally, just a thin smear of sealant. Eliminate the weak links.
Best to decide this prior to machining of components thou