Piston Position in Barrel.

[Martin20]

Evening All!
Newbie, novice mechanic here, so please bear with me if any of the following seems blatantly obvious!
A couple of weeks ago, due to a blown exhaust gasket, I dropped my LI 150 S engine, took off cylinder head and barrel. There was no base gasket under the barrel, just the remains of some sealant. When I built it all back up again, I used a base gasket, smeared in silicone (didn't measure thickness, but from memory, I would say with sealant, probably2.5 to 3mm). Lapped head and top of barrel, and added aluminium gasket. Tightened it all up, but as I did not have a suitable torque wrench at the time, didi it by feel! Yeah, I know, stupid! Anyhow, bike started, but within a few days, starting became more and more difficult, and noticing oil seeping between cylinder fins, guessed gasket was blowing. Stripped down again today and sure enough, oil on gasket and head.
I have now bought a suitable torque wrench, and new head gasket but reading loads of different posts on here re: gaskets,versus no gaskets,squish tolerances etc, I am looming for advice on the following:
1. The shoulder of my piston when at TDC is sitting approx 2mm below the top of the barrel. Is this OK, or should it sit flush with the top?
2. If piston needs to be at top, should I remove base gasket and just re fit using sealant?
3. Will not fitting a head gasket maintain the 2mm squish (is 2mm OK, or should it be less?)
4. Will highering/lowering barrel by fitting or not fitting a base gasket affect timing?
Hope above makes sense and sorry for length of post!
Cheers
Martin

[eden]

base gasket or packer? most base gaskets are between 0.4 and 0.5mm

[Martin20]

I ordered just a standard base gasket.Just felt thicker than 0.5mm! Might be wrong though!

[corrado]

General consensus is that squish should be around the 1.2 to 1.5 mm range. Start by putting barrel and head on [torqued up] but without any base or head gaskets and measure the squish. Then depending on squish measurement you can work out whether you need any gaskets. Position of piston at BDC in relation to port heights also comes into play. If I got "dry" squish of 1mm I'd add a base gasket of 0.5mm and do without a head gasket, just use a quality sealant.

[Martin20]

Thanks for reply 'corrado'. Will give that a try. Not 100% confident in measuring 'squish', but have done loads of reading on 'how to, so hopefully will be oil
P.S. Will excess squish cause low compression?

[bristolmod]

whilst I appreciate the thinking behind a correct "squish" measurement- back in the day in the 1960's no one had heard of squish and just bolted up their tops ends and drove their scooters!!

[dennis]

Yep,have to agree with bristolmod about the squish, used to bore them out to 225 and stick the 200 head back on,never shimmed the the gears either,used to to be ridden every day to work all over hertfordshire as plumbers mate.

[bristolmod]

Yep,have to agree with bristolmod about the squish, used to bore them out to 225 and stick the 200 head back on,never shimmed the the gears either,used to to be ridden every day to work all over hertfordshire as plumbers mate.

ah..."old school" tuning!! Love it. Get me a Wal Phillips and I'll be a happy chappy!

Chris

[Martin20]

Cheers for replies guys. Got my first scoot back in 1970, and knew nothing about things like squish. As per 'dennis' , just used to pull it to bits with my Dad, put it back together, (never knew torque wrenches existed back then, so all nuts and bolts tightened until tight!!)and generally off I would go!
Think I am going to leave base gasket as is, as it is looking nice and dry, then trial fit head gasket, with 'v' shaped solder on piston crown as per Sticky's manual, and see if I can get an idea of squish. Will try without head gasket if it looks too big!
Will let you know outcome.