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Old 02-10-2019, 05:58 PM   #1
Junkie
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Valve checks: do you really need to be at TDC?

This is a general question rather than specific to any given bike.

If I have the cam's lobes nowhere near pushing on the rocker arm or bucket (depending on type), am I going to have any problems from the engine not being at TDC? It's easier to put the cam lobes directly opposite where you measure than it is to see in the little hole where the timing mark is.

I know that for shim under bucket, if you have to pull the cams to adjust you need to get timing perfect, but that's different than checking.
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Old 02-10-2019, 08:04 PM   #2
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You know it's funny, I had an '02 GSXR 600 and it said to check them lobes facing sideways. I've done maybe a dozen valve adjustments on about as many different models and almost all of them say facing up.. so it's probably not absolutely necessary but probably depends on how degree'd the cams are?

Thing is, i think you get a cleaner 'feel' for how much drag there is when the lobe is upright, so I always rotate the wheel/crank for that cylinder and measure it. Never thought about it a whole lot, wonder what the rest of the garage thinks on this.
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Old 02-10-2019, 08:13 PM   #3
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This is the factory service manual for my Tiger 800. Doesn't even mention TDC.
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Old 02-10-2019, 08:49 PM   #4
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No, the base circle goes about halfway around the cam and the clearance is the same the entire way. I check them up to almost 90 degrees.
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Old 02-11-2019, 08:12 AM   #5
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I think I measured a slight difference between lobes pointed away from stem and then at TDC. Maybe it's bike/cam specific?
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Old 02-11-2019, 08:14 AM   #6
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Old 02-11-2019, 08:26 AM   #7
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Originally Posted by ctwo View Post
I think I measured a slight difference between lobes pointed away from stem and then at TDC. Maybe it's bike/cam specific?
The diagram above is a great illustration. The base circle goes way past 180 degrees.
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Old 02-11-2019, 08:33 AM   #8
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that's what I thought, just wanted to make sure.

the diagram above seems a bit off to me as far as the beginning/end of the lobe, but conceptually seems right
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Old 02-11-2019, 08:39 AM   #9
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Originally Posted by thedub View Post
This is the factory service manual for my Tiger 800. Doesn't even mention TDC.
Yep. Although maybe it was just me but that engine won't turn over with the wheel. I always had to pop the cam chain cover and use a wrench.
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Old 02-11-2019, 08:42 AM   #10
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Yep. Although maybe it was just me but that engine won't turn over with the wheel. I always had to pop the cam chain cover and use a wrench.
did you pull the plugs?
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Old 02-11-2019, 08:43 AM   #11
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did you pull the plugs?
Yep. Turns over fine with a wrench though.
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Old 02-11-2019, 08:46 AM   #12
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Most manuals say that the cam lobes should be facing away from each other. Even if the manual doesn't mention it I would stick to TDC. I zip tie the cam chain to the sprockets to be sure.

I never have to pull the plugs but makes sense to release compression.
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Old 02-11-2019, 11:09 AM   #13
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It might turn easier in a higher gear?
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Old 02-11-2019, 11:44 AM   #14
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Maybe if you are turning it with the rear wheel
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Old 02-11-2019, 12:17 PM   #15
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Originally Posted by Junkie View Post
t
the diagram above seems a bit off to me as far as the beginning/end of the lobe, but conceptually seems right
The step isn't there, but the numbers are right. Cam lobes don't go anywhere near the 180 line.
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