cam/crank timing - cam events question
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Road Warrior
Joined: Jun 2009
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From: Michigan
cam/crank timing - cam events question
i just wanna make sure im doing/understanding this right - ie cam install.
rear cyl TDC - cam and crank sprocket are dot to dot and cams are dot to dot.
and when front cyl is top center the crank dot in same spot but cam dot 180deg from where it was at rear TDC. like 11 clock on both gears.
now, for the front cyl should the exhaust valve be opening already when the rear cyl is at tdc.
rear cyl TDC - cam and crank sprocket are dot to dot and cams are dot to dot.
and when front cyl is top center the crank dot in same spot but cam dot 180deg from where it was at rear TDC. like 11 clock on both gears.
now, for the front cyl should the exhaust valve be opening already when the rear cyl is at tdc.
Road Warrior
Joined: Jun 2007
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From: Here
Since these engines use a single pin crank, the events are not going to be like a car engine or another bike engine. Forget about which cylinder is at TDC. The cam and crank sprockets are keyed so they will only go on one way. As long as the cam dots are lined up when the two sprocket dots are lined up you will have everything timed correctly.
Having said that, if the rear cylinder is on the compression stroke, the front will be on the exhaust stroke so the exhaust valve would be open.
Having said that, if the rear cylinder is on the compression stroke, the front will be on the exhaust stroke so the exhaust valve would be open.
Banned
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If the rear cylinder is at TDC, the front cylinder should be on the last of it's exhaust stroke... I think. The exhaust valve on the front cylinder should be open, but closing as the front piston travels upward to complete the exhaust stroke...
Advanced
Joined: Feb 2007
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From: appleton wi
I just did the cams on my first harley and there is a rule which applies to four stroke engines that has never failed me.
Valve Overlap. If you have valve overlap on the bottom of the exhaust stroke you cant be wrong. What that is is both valves will be open at that point. The exhaust valve will be closing and the intake will open right on the bottom. Someone may chime in on whether or not this holds true for them, maybe some radical cam selection in some motor but it has never failed me on cars, motorcycles, lawn mowers, small engine class in high school is where I learned it, anything four stroke.
Hope that helps.
Valve Overlap. If you have valve overlap on the bottom of the exhaust stroke you cant be wrong. What that is is both valves will be open at that point. The exhaust valve will be closing and the intake will open right on the bottom. Someone may chime in on whether or not this holds true for them, maybe some radical cam selection in some motor but it has never failed me on cars, motorcycles, lawn mowers, small engine class in high school is where I learned it, anything four stroke.
Hope that helps.
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