higher compression requires better head sealing

[butre]

On my Suzuki 100 it was getting too hot running 150psi compression so I reduced it to 135 and there was too small a difference in power to have any regrets. So now it runs cooler and it doesn't have the power loss at peak operating temperature like it did before.

Heads-a-mess, how do you get the two ends of the teflon tape to join together?

don't bother joining them together, it'll compress into itself and seal. even if it didn't, you'd just have a spiral leakage path which is slow enough that it doesn't matter for the thousandth of a second that you're operating under pressure

What about brass or bronze gaskets? Or stainless Steel ?

the big thing a gasket needs is compressibility, so you need a soft material that won't melt or rupture. nylon may work until you overheat, but teflon is the best option. ideally you would stamp out a proper gasket from teflon sheet, but that's not always doable, especially since teflon is one of those things you can't really buy in small quantities other than in products. plumbers tape is the most convenient of these products for our purposes.

 

[skyash]

Like oven bake stuff ?

 

[HeadSmess]

plain old teflon tape. plumbers, gas works, whatever. i use white because its all i see the point in buying (aka cheapskate).

you take a length that will make two full turns or so around the cylinder. twist into a string, then simply lay it in a loop around the cylinder, pop the head on... no issues with joining the ends together, the overlap is more than adequate.

it squishes down to less than a thou, whilst filling in the small gaps that will always be present (unless you got a surface plate and can use marking blue and a scraper?) it resists temperatures up to about 350C, which virtually no other "plastic" can do. as it squishes, it also spreads and covers virtually the entire sealing surface (if you remove the head, this will become apparent) almost like a liquid sealant will do.(of which none will take such high temperatures OR pressures other than lead based paints)

it doesnt harden, it doesnt stick, its easily replaced, and did i mention , its CHEAP? there is a special purpose teflon string available, but its expensive, and the string is about 3mm in diameter...way too much.

if any gets in the cylinder itself, it doesnt cause any damage, either.


and yes, i use it on exhaust gaskets too, as long as its not a hassle getting it to stay in place during assembly.

i would not advise using nylon... it melts, sticks to everything, absorbs water, goes hard and brittle when it dries out, and produces highly toxic fumes as it melts. it also has very little compressibility. teflon has the ability to "ooze"...


i only ever experienced one slant fire head, and it warped exactly as mentioned in all these posts. always on the plug side. whereas centre plug heads, always stayed nice and flat.

when you compare the two, side by side, you notice that the fins provide strength in one direction, why they never warp that way, but the slant plug heads have no "beam" to prevent warping on the plug side... whereas the centre plug heads have a nice heavy "beam" of ali between studs at right angles to the fins. on both sides. and it seems that in every thread or post about warped/leaking heads, its always on the edge on the plug side. removing material just makes them even weaker.

peeking at the head on one of those 500watt 2stroke generators... they DO have a "beam" under the plug side of the head. never bothered to check the distance between studs to see if they would fit.

 

[Steve Best]

You cannot improve on Headsmess's plumbers tape. I tried the thicker yellow gas tape, no gain.
He has it pegged. Works wonderfully.

If you really want to make that stock head work for you, cut the squish area to match the piston dome plus a tiny bit of taper and out to the full bore.

Don't shave 0.5mm off the stock head. More prone to warp and as Jag mentioned, little gain.
Sand the head flat, sand the cylinder flat, use the teflon tape gasket, check your squish.
Adjust with base gaskets to get squish within 0.5 to 1.5mm, ideally 0.75mm from my experience.
I really agree with Jag about keeping the compression moderate for chrome and bearing reliability.

There is Creme and several other motorcycle tank sealers at about $30-$50.
Polyester fiberglass resin will eventually break down.
I suggest epoxy fiberglass resin will keep you happier in the long run.

Nice looking bike Street Riderz.

Steve

 

[Street Ryderz]

thanks Steve ! Is Creme or the others a two part epoxy?

 

[Steve Best]

thanks Steve ! Is Creme or the others a two part epoxy?

They are. I've never used them, so I cannot tell you how well they work.

Steve

 

[Street Ryderz]

I used to race sea fleas with a modded 25 merc motor and home built hull that was thin marine ply and glassed. And at the end of each season where my fuel tank sat against the transom the epoxy resin would soften and some times turn milky white due to fuel spills sitting there not even large amounts!So i am curious if that is what will happen in the tank over time?

 

[Steve Best]

I've sealed leaking rusty old car gas tanks with epoxy and polyester fiberglass.
Filled them with water, sandblasted them, patched up the leaking areas with epoxy and then coated the rest of the tank with polyester and cloth for strength. All held up for years. 62 Comet, 67 Mustang, 67 Cougar, 70 Maverick, 78 Fairmount etc.

 

[Street Ryderz]

Ok good to know ty!And as for that head there is no squish band at all its not the best pic but look closely at the last pic!Thats why i was curious about the teflon tape holding up to higher cr.because i assumed that the chamber design was going to spread its pressure across the entire piston top and have more pressure at the seal between head and cylinder.

 

[Steve Best]

Ok good to know ty!And as for that head there is no squish band at all its not the best pic but look closely at the last pic!Thats why i was curious about the teflon tape holding up to higher cr.because i assumed that the chamber design was going to spread its pressure across the entire piston top and have more pressure at the seal between head and cylinder.

The weird looking star like thing on the back of the drill press table is a home-made squish cutter. It is mild steel bars welded to an 8mm bolt and sharpened to cut the same radius as the piston dome into the head chamber. I plunge it in gently to cut the squish surface out to 47mm. Nasty little device, it could take a thumb off so be careful if you make one. Adding any squish at all will speed up the burn (better than advancing timing) and make the engine more like a homogeneous charge compression ignition engine. This is where the charge ignites from the heat of the plug and the compression change and becomes less sensitive to timing changes. Almost like a pre-chamber diesel or a glowplug RC engine.