Lapped my head

Well It's not beneath me to make a double entendre crude joke.

No problem.

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Spark plugs are an easy way make minor changes in the powerband. Some plugs are weak on the bottom end, but have better performance at higher speeds. A hotter plug may give better bottom end torque, but will run hotter and leaner on the top end. It all depends on how you ride, and how you maintain your ride, that determines how far you can push the edge of performance. As far as cutting down the head, it will improve bottom end power and torque, but can lower the motors max rpms slightly, in theory. After seeing the bike compression chamber, compaired to the stuff im used to working on, I think its a drop in the ocean. If any real performance is gained, its probably from the overall better fresh seal your now getting, compaired to before you took it apart.

I respectfully disagree that a spark plug can effect torque or mixture (you said a hotter plug will cause a leaner top end).

The heat range describes the ability of a spark plug to conduct and dissipate heat. Heat supply to the spark plug in the combustion chamber depends on the specific engine type in each case.

The heat range is important because on the one hand, a certain minimum temperature (self-cleaning temperature) must be reached to prevent "sooting" and associated ignition misses, but on the other hand, a certain maximum temperature (auto-ignition range) must not be exceeded if auto-ignitions are to be prevented. For these reasons, the working temperature of the spark plug (operating temperature range) that is set depending on the engine power specified, must be maintained by design within the above set limits.

The heat range of a spark plug is determined by the heat-range code number and must be adjusted to suit the specific engine characteristics. The heat-range code number is a component of the Bosch spark plug type designation.

Low code numbers (e.g. 2 to 4) signify "cold" spark plugs, in other words, low heat conduction in hot engines (e.g. Ferrari).

High code numbers (e.g. 7 to 10) signify "hot" spark plugs, that is, high heat conduction for cold engines (e.g. VW Beetle).

A too hot plug may cause preignition ( not leaner running) on the top end. A too cool plug may foul easily particularly in a 2 stroke setting running these very rich oil mixture settings.

Good post Skyliner - just to clarify - NGK plugs are the inverse. IE, the lower the number, the hotter the plug.

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Thanks for the post skyliner, you said what I was thinking

I did the same thing the other day but I lapped both the head and barrel to a baby smooth and flat finish then did away with the head gasket altogether! Big boost losing the gasket and no leaks because I got the surfaces so flat. My bike now eats hills for breakfast! Seriously a massive improvement to compression.

I just read on another thread that someone removed bothe upper and lower cylinder gaskets to improve compression with success. Did glass and wetsand on head. Said it was huge diff.

I'd be kind of scared to completely eliminate the gaskets.

That was me! Use gasket silicone on the bottom. As for the head gasket if you lap both surface baby smooth and flat then I promise you that you will have no problem. Works for me. My cylinder (replacement) was too tall so I needed to get rid of both but for everyone else I would start by doing away with just the head.

If you want to use a rel gasket eliminator here is the stuff to use
Loctite Gasket eliminator 515 sealant flexes with flanges.
Item number 51531
This stuff looks like grape jelly and its an anaerobic sealant which means it sets with out air so when you bring the parts together that is when the stuff starts to work. It takes only a very thin film to work so no need to slather it on like your buttering toast. It will tolerate flexing and temp range -60 to over 300 F. there is also an activator you can use called clean and prime by permatex sold at the Napa store this stuff is sprayed on one side of the surface that your putting together when both parts come in contact the act. will set off the gasket eliminator and make the stuff set quicker but I only use the clean and prime on vw crankcase halves or on screw compressors when in a hurry to get them back on line. Now the bad news this stuff is pricey but you can get it at auto parts stores once you buy the stuff the part stores will be able to take the rest of the week off.

When going naked on the gaskets check to make sure the piston does not smack the head if its gong to then you will have to make adjustments with gasket either on the cylinder base or head so the piston will clear.
Norman

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