"How to port a scooter cylinder" instructions?

[Black Thunder]

Has anybody followed the "How to port a scooter cylinder" instructions in the advanced documents section?

Link to article

It says to follow the Exprees numbers for the Spree but when I measured .95in down from the top of the cylinder it was right at the top of the exhaust port already.

Just wonder if anyone else has tried this or has a spare cylinder to double check me on.

Also what about his idea to just use RTV instead of a base gasket to increase the compression. Sounds a lot easier then getting the head milled.

[Kenny_McCormic]

I wouldn't do the rtv thing, just have .020 shaved off and use regular gaskets

[stillspeeding]

You can raise the compression all you want but it will not make the engine go faster unless you change the gear ratio

[Dac]

higher compression will give tons more take off. but like StillSpeeding said with out a gear change your top speed is never going to be that good. But thats not what this topic is about.

my answer. no i have not tried it.

[Black Thunder]

"But thats not what this topic is about."

Thanks Dac. I knew I shouldn't have added that RTV question.

Come on guys!! I can't believe that there is this many people working on scooter engines but no one has ported a cylinder??

[Kenny_McCormic]

I have only heard about it, never actually attempted it. When i need new rings maybe i will try it. My dad claims a ring width is perfect.

[noiseguy]

I agree with your dad; a ring's width is about right.

I recall the Spree exhaust port being 9mm tall (and 25mm wide). That means you'd remove 0.17" of material from the top of the exhaust port according to the article.

Maybe it was 11mm tall, that would mean removing 0.09" of material according to the article. I think the 11mm tall was from an Elite model though (and closer to 30mm wide).

I find that the porting is slightly different on everything I measure, including Spree. Maybe it's just manufacturing tolerance, but it would go a long way to explain why some Spree are much faster than others.

9 or 11mm tall port, either way, you're not removing much; this is 2-4mm of material we're talking about. I'm not sure what you'd get out of it in terms of performance.

The one data point I have is some snow-mobile tuners here that said they'd played with porting on the Spree. They found that removing 1-2mm of material from the top helped; anything more than that (or messing with the transfers) was a waste of effort or made things worse.

Have I personally tried it? No, so you've been warned. And I would limit experiments to stock bores; the performance bores have already been optimized, so just clean them up as needed.

Best of luck.

[tru72]

i have ported stock elite bore before with pretty nice results. 51 mph . I was using after market pipe with that set up, stock carb rejetted with air box, 9.1 gears. Porting is a hit or miss thing , especially if you never did it before. I have been porting since the mid 90s and have very specific numbers for diffrent styles of riding. Good Luck if your going to try it..
aloha
p.s. my only tip to you is biggers isnt better

[harley_fixer]

Does anyone know if I can use 86 or 87 crank in a 1985 spree? Key way in original is screwed.

[Kenny_McCormic]

I want to say the 84/85 and 86/87 have different cranks.

[veedubh20]

metal base gasket high compression
paper base " low compression.

why mod stock spree motor

[Kenny_McCormic]

metal base gasket high compression
paper base " low compression.

why mod stock spree motor

Its a challenge, playing with bases messes with the port timing.