Engine rebuild question

[Jim D.]

Looking at the receipt for my engine rebuild on one of the lines it says
" Degree Cam " would that mean ?

[John H.]

Re: Engine rebuild question

Jim -

It means that the valve timing (cam card specs vs. actual) was verified with a degree wheel when the engine was assembled.

[Chuck R.]

Re: Engine rebuild question

If you change the geometry of the original cam by adding one with increased lobe separation, this throws the timing aspect of the engine off significantly.

Simply put, your mecanic rotated engine one direction and took a degree reading at the timing marks. He then rotated the engine in the opposite direction and took the degree reading again. He then combined the two readings and devided by two. This tells him just how many degrees your engine is now reading at the timing marks with the new cam.

If it is too far out, he would have drilled out the upper timing gear mounting holes and install inserts that are eliptical which would move the timing gear in a direction to get the cam back into the correct timing window.

Very simply put

Chuck

Chuck

[Jim D.]

Re: Engine rebuild question

If you change the geometry of the original cam by adding one with increased lobe separation, this throws the timing aspect of the engine off significantly.

Simply put, your mecanic rotated engine one direction and took a degree reading at the timing marks. He then rotated the engine in the opposite direction and took the degree reading again. He then combined the two readings and devided by two. This tells him just how many degrees your engine is now reading at the timing marks with the new cam.

If it is too far out, he would have drilled out the upper timing gear mounting holes and install inserts that are eliptical which would move the timing gear in a direction to get the cam back into the correct timing window.

Very simply put

Chuck

Chuck

Sounds way over my head, so my timing mark on the balancer should still be good to time from, correct ? Is the any way to be sure ?

[Jim D.]

Re: Engine rebuild question

This was done prior to my owning the car, I just want to be sure that I can get the correct timing when I tune it.

[Joe C.]

Re: Engine rebuild question

If you change the geometry of the original cam by adding one with increased lobe separation, this throws the timing aspect of the engine off significantly.

Simply put, your mecanic rotated engine one direction and took a degree reading at the timing marks. He then rotated the engine in the opposite direction and took the degree reading again. He then combined the two readings and devided by two. This tells him just how many degrees your engine is now reading at the timing marks with the new cam.

If it is too far out, he would have drilled out the upper timing gear mounting holes and install inserts that are eliptical which would move the timing gear in a direction to get the cam back into the correct timing window.

Very simply put

Chuck

Chuck

Chuck,

You meant to say "Lobe Centerlines", not LSA, right?

Joe

[Joe C.]

Re: Engine rebuild question

This was done prior to my owning the car, I just want to be sure that I can get the correct timing when I tune it.

Jim,

Don't worry about it!

Degreeing a camshaft is a racer's tool, and not necessary for the average engine build. It's a good way for the engine builder to "clip" the customer for a few more "sheckels".

If the camshaft card says that it was ground on the same Lobe Centerlines as the original cam, then there's no real need to verify it.
The reason that an engine builder would "degree" a camshaft, would be to alter its timing (lobe centerlines) from original. Racers will retard cam timing to gain horsepower at the expense of low/midrange torque. THE EXTENT OF THIS IS USUALLY LESS THAN 4-6 DEGREES.

To answer your question. YES. Changing cam timing WILL affect ignition timing in direct proportion to the radian measure that the cam was either advanced or retarded.

My guess is that the engine builder "verified" the accuracy of the cam grind, and left the setting @ "mark-to-mark" on the sprockets. In other words, both cam and ignition timing are probably synchronous with TDC.

Joe