11 replies to this topic

[Chappb]

I've only ever heard of timing the cam in by using the 'max lift' method but after seeing another topic on here, namely this one:

http://www.theminifo...iming-question/

the original poster talks of using the 'lobe centre' timing method.....what is the difference between these two methods and how do i time the cam in using the 'lobe centre' method.... slightly confused....
cheers Ben.

[KernowCooper]

Timing the Cam by Lobe Centre

Remove all valve lash (clearance). Place your dial indicator on the valve spring retainer, or tappet. If you are degreeing in a pushrod engine place the indicator on the valve retainer. Please be sure the angle of your indicator travels at the same angle that your valve travels. Zero the dial indicator, then turn the engine until you reach full lift and record how far the valve traveled off its fully seated position. This will be the actual valve lift of your desired cam profile. Note: Rocker arm engines can vary. At this point make sure there is additional clearance with your dial indicator to verify plenty of travel for our next step.

Rotate the engine until you are back to Top Dead Center (TDC). Zero your dial indicator. Next you will start turning the engine until you are .050 off the seated position of the valve (It is very important to turn the engine its normal way of rotation). Look at the degree wheel and determine how many degrees the valve opened. If we are working on the intake valve this will normally occur Before Top Dead Center (BTDC). Record that number in degrees. NOTE: Some low overlap engines may open After Top Dead Center (ATDC). Record that number in degrees for further calculations.

Look at your inner dial on the dial indicator and record that number to help achieve our next step, however some dial indicators do not have this feature and is not needed to proceed. Proceed to rotate the engine until your inner dial is back on the number it left from. You will notice your big dial is almost back to .050. Slightly move it until it is exactly reads at .050. If you pass it back way up and come at it again. You are now .050 from closing on the opposite side to achieve your next number on the degree wheel, which is normally After Bottom Dead center (ABDC). Now you will use the following steps to properly calculate what actual lobe centers are on the opening valve timing events.

If the valve opened Before Top Dead Center (BTDC) do the following calculation:

Take the open number plus the closing number plus 180°, which will be the duration at .050. Next divide the duration into 2. Subtract the open from that number, which will equals the centerline of the intake cam.

Example:

+10° Opening Before Top Dead Center (BTDC)

+39° Closing After Bottom Dead Center (ABDC)

+180° Distance from Top Dead Center (TDC) to Bottom Dead Center (BDC)

=229° Total Duration @ .050 inches of lift

229°/2 = 114.5°

114.5° - 10° = 104.5° Lobe Center

Thats how to find the Lobe Centre

Summary

Lobe center is the amount of camshaft degrees between the point of maximum lift on the intake lobe and the point of maximum lift on the exhaust side of a given pair of cam lobes. As an example, lobe center is calculated for cylinder number one only and does not deviate between number one and the other cylinders in the engine. To make a representative sketch of lobe center, draw a line between the very center of a camshaft intake lobe and then draw a similar line through the respective exhaust lobe for the same cylinder. The number of camshaft degrees between these two imaginary lines is the camshaft lobe center.

Cam Lobe Profiles
An asymmetrical camshaft features a lobe shape or profile that is different on the opening side than the closing side of the same lobe. For example, a camshaft could feature a very rapid valve opening profile, but when the valve is closing on the same lobe, the shape could be extremely smooth and gentle.

A symmetrical camshaft makes use of the same profile on the opening and closing side of a specific lobe. In other words, the opening side of an intake lobe features a shape that is exactly the same on the closing side of the lobe.


If that all makes sense ?

Edited by KernowCooper, 18 February 2013 - 10:47 AM.

[Chappb]

I only thought i would be getting a few lines for an answer! Haha, thanks for all that but i'll be honest it did go a bit over my head. So for an asymmetrical cam then it HAS to be timed in this way?

[jaydee]

Another way to dial the cam in is to measure and advance until you get equal lift at overlap, you really cant go wrong with it.

[daenesh]

what about a 1098 cam.. i've heard that it needs to be set as 107 degrees?

[jaydee]

All BMC camshafts are 110° deg iirc, we need to know what camshaft you're going to use to give proper advice

[KernowCooper]

I only thought i would be getting a few lines for an answer! Haha, thanks for all that but i'll be honest it did go a bit over my head. So for an asymmetrical cam then it HAS to be timed in this way?

Thats correct way for a asymmetrical unless instructions from cam grinder says different

[Chappb]

Is that 110 degrees at max lift or 110 degrees at lobe centre?

[daenesh]

how about a 1098 camshaft with 2 rings.. cause ive just fitted that into my 998cc A plus engine and someone on this site told me i have to set it to 107 degrees for the best performance..

[Chappb]

All BMC camshafts are 110° deg iirc, we need to know what camshaft you're going to use to give proper advice

I'll be using an SW10 cam

[jaydee]

All BMC camshafts are 110° deg iirc, we need to know what camshaft you're going to use to give proper advice

I'll be using an SW10 cam

107° LCA iirc

Ask swiftune for further infos, they're really helpfull

[Chappb]

All BMC camshafts are 110° deg iirc, we need to know what camshaft you're going to use to give proper advice

I'll be using an SW10 cam

107° LCA iirc

Ask swiftune for further infos, they're really helpfull

Nice one, thanks again