Claviger

Aspiring Student
Joined
Jul 25, 2014
Messages
6,934
Location
Olympia Washington
Ride
'21 Z H2, '14 R3R, '02 Daytona 955i
Im going to degree my cams to find their profile info. I have the list of tools. Will be doing this sometime next week.

For those who’ve done this before, is there anything major this video misses out on? Seems all correct to me...

Start at 22 minutes in:
 
Well first off his method of finding piston TDC is BS. Second, he dismisses asymmetric cam profiles as if they don't exist. Maximum lift may not be at the geometric half way point between 1mm open and 1mm from close. So, the profile centerline can be rather arbitrary depending on the lobe profile. No standards followed here by the aftermarket. If you think you have the tools and setup correct and have good numbers, run the test in reverse: rotate the crankshaft the opposite direction. Cam closing position becomes cam opening. Do the numbers match? They should be very close. If not, your measurements are not accurate.

One caveat here, belt or chain driven over head cams with tensioners can have different numbers due to the change in tension on the chain. Weak springs installed on the valves can be used to reduce or negate the effect as was done in the video.

Degreeing the cams is important. All engines are different. But, the data you can garner about the cam profile is about useless other than to confirm the cam matches the claimed lift and gross duration numbers. These numbers on their own don't mean much about how this cam, brand X, will work and compare to brand Y's camshaft.

Even with cam inspection equipment that can take hundreds or thousands of measurements per revolution and generate cam lift/area/degree profiles, without understanding the impact of bore/stroke ratio, rod length to stroke ratio, cylinder displacement to intake runner volumes, wrist pin offsets, and on and on, on the data you won't be able to compare a cam profile used in one engine with how it functions in another with different attributes.

An example: one of my bikes uses the exact same intake lobe profile as used in a Perkins V-8 diesel running 150 PSI boost at 4,800 rpm. Do you think they run the same?
 
Thanks for the intelligent response. In particular, the point about asymmetric profiles, no idea if mine are symmetrical or not, but I’ll find out.

I’m more interested in gaining an installed baseline so I can remove the head and set it back up as it currently sits, as well as simply learning the spec of the cams I have.

Once I understand the cam, do all the chamber measurements, and have the real numbers, as you say, then I can (with some more knowledgeable assistance) determine if the cams are optimal for the chamber or not.

Since I’ve already torn the engine open, I figure I might as well learn a seat much as possible and maximize the value of opening the motor in the first place.

Plus, it gives me something to do while the repairs are being done and I’m waiting on vendors.
 
That is the best way. You can do a rough plot of the cam profiles by finding the degree at multiple lift points on both open and closing. Say at 1mm increments. Any asymmetry will show up doing this. Also do the same on both intake and exhaust cams.

With the Carpenter springs installed and the plugs out you may find the cams want to turn the engine when a lobe is at the point of maximum closing rate. This will make reading the degree wheel difficult as you then need to hold the crankshaft to prevent it from rotating past the lift point you are trying to measure..

With an idea of cam profiles for both cams you can speculate about what and why.
 
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