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· Registered
2003 honda trx400ex
2 Posts
Discussion Starter · #1 · (Edited)
Hi all! New to the forum and to the 400ex i recently bought a blown up 2003 Honda 400ex tore it down, split the case and found it needed a new engine.

Found a good/used engine for it. I picked it up and upon pick up the guy said it has a 6 degree crank key.

my question with everything torn down and no flywheel on the used engine starting from scratch, how would you time the crank and cam?

everything that im reading, says to pull off the flywheel put the key in bolt everything up and your done.

In my head if I Were to time the engine off the “new timing mark” everything would be outta time not just the flywheel being 6° advanced.

or am I just over thinking this?

Thanks in advance!!!

· Super Moderator
4,879 Posts
The cam is timed at TDC of the piston - a 6 degree flywheel key just has an offset to it and the flywheel may be installed either 6* advanced or retarded as to the spark timing (thanks to Curtis Sparks Racing). When running higher than 94 octane fuel an advanced spark is desired to get the slow burning fuel a head start before the piston reached TDC to prevent detonation - 6* advance will promote pre-ignition when using 91 and lower octane fuel.

Is this as clear as mud to you or do you grasp the concept?
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