Port heights - does this look ok?

869 Views 5 Replies 4 Participants Last post by jaguar, 6 mo ago

arjay125

Hi there. I've just had my air-cooled KDX200 cylinder re-chromed and I installed a new Wossner piston kit. I've never checked the port heights before, and this is looking odd. At BDC the main exhaust port is 3mm higher than the piston. The bottom of the transfer ports are 2-3mm lower than the piston surface. Are there any problems with the way this would run? Is it normal? The motor has never run to its full potential (it's a custom build with many variables). The deck height also looks a bit high too. I can't find any squish or deck height info for the '87 KDX. Thanks for any thoughts on it.

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pygmy warrior

· #2 · 6 mo ago

Yea, That doesn't look right. Are you sure that is the correct piston for the cylinder? Also, you need the chamfer the port edges before you run it. They look really sharp and can snag a ring.

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jaguar

· #3 · 6 mo ago

The exhaust port being higher than BDC actually benefits low end power which is what the KDX is all about. But you should use JBWeld to make a ramp for the transfer bottoms so that edge won't exist and won't hinder top end power. But there's an art and a science to using JBWeld in the ports so it never falls off. Eric Gorr knows how.

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marsheng

· #4 · 6 mo ago

Most new motors have the exhaust port higher than the piston at BDC. I've seen a few motors where the transfer ports are lower than the piston. Not ideal but works fine.

Squish is normally > than 1% of the stroke length.

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arjay125

Discussion Starter · #5 · 6 mo ago

marsheng said:
Most new motors have the exhaust port higher than the piston at BDC. I've seen a few motors where the transfer ports are lower than the piston. Not ideal but works fine.

Squish is normally > than 1% of the stroke length.

Thanks for the squish guide.