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Categories: all aviation bicycle gadgets misc motorcycle theater Wed, 24 Feb 2010So, last fall, I made myself an improved camshaft for the CL175 streetbike. (Seriously, if you're not into engines and tuning, you can completely skip this entry.) Then, life got in the way, and I've only been able to get back to it in the last few weeks. Finally, a couple days ago, I got all the bits and pieces put back together, clean, beautiful, new oil seals, the works. I had stalled enough. Time to degree the cam. Degreeing the cam is not, in concept, hard to understand. The camshaft is locked to the crankshaft with a chain. The tensioner makes sure there's a minimum of slop in the chain. As the crankshaft moves the pistons up and down, the camshaft controls the opening and closing of the valves. Easy enough. If a valve opens too early in, say, the power stroke, then some of the expanding gas gets blown out the open valve instead of powering the crankshaft. If that same valve opens too late, then the exhaust stroke isn't as effective, wasting some power on compressing the exhaust against a closed valve. Likewise a bunch of similar scenarios -- the cam has to open and close the valves at exactly the right time, if you want to make the most power. Degreeing the cam is just the act of making sure the cam is lined up exactly where it should be in relationship to the crankshaft, so that the valves open and close as the manufacturer intended. Honda, at least with the 60s and 70s era 160/175 motor, wasn't always super precise when pressing the cam sprocket onto the camshaft, as far as how everything lined up. It could be off. It could be off by a lot. According to Mr. Bateman's article on cam degreeing, even 1 degree of cam timing is pretty significant. That's what made my degreeing experience so interesting. After first bending a valve and cursing a great deal, and then remembering that I had a couple spare valves from the race engine (note to future cam degreers: no really, don't stick the piston stop pin in the cylinder with the valves adjusted to .002"! Really!), I got my shiny new adjustable cam degreed. What should I find, upon degreeing the cam as I'd pressed it back on (admittedly without any precision at all)? 98°. The 175 is supposed to be at 105°. Yeah, that'll never work. I did the math real quick, and decided I had to move the cam 3.5° thataway (the cam rotates at 1/2 rotation per crankshaft rotation). I did, and was almost blown away by how easy it was. Turn the crank around a couple of times, loosen the three bolts, and give 'em a quick tap with a drift and hammer. Done. Without the adjustable adapter, you have to take the head halfway apart, pull the cam out, press the sprocket off, and press it back on to do the same thing. I'd taken a ~30 minute operation and performed it in about 3 seconds. I had marked 5° increments on my adapter (you can see a few more pictures of this stuff here), and moved the pointer what looked like about 3.5 degrees, more or less. I re-tested, and found I was at 103°, so I'd gone the right direction, and adjusted it just a tiny bit further. The numbers worked out to 105° on the nose. Hot! So now, the engine awaits final assembly, and I can finally put it all back together, and see if it works! I really hope the old cam was actually at 98° (but don't expect it was, I'm not sure it'd run at all in that condition) -- the performance increase from re-setting the cam at 105° would be huge! And the best thing is that the increased performance would come along with improved fuel economy. I've got my fingers crossed. Posted at 11:40 permanent link category: /motorcycle Categories: all aviation gadgets misc motorcycle theater Written by Ian Johnston. Software is Blosxom. Questions? Please mail me at reaper at obairlann dot net. |
