Why is this important to do when putting together a new motor rather than relying on timing marks (valve cover + lower timing belt cover)? My own idea is that using the timing marks is just not that accurate and you could be losing power if you are out even just a couple degrees.

Am I on the right track?

 

Serious engine builders do exactly that, simply because it is not uncommon for a camshaft to be slightly out of spec. On a race car, a couple of degrees off is enough to make the difference between winning and losing.

 

Tolerances on all the parts can be slightly out of spec causing the timing marks to be inaccurate. Especially when you're using aftermarket parts. Degree-ing (is that a real word, lol) eliminates these variables and makes sure all the valve timing events are occurring at precisely the right time. Definitely worth the extra bit of work.

 

An interesting example:

I recall dealing with an engine that had ~0.020" shaved from the cylinder head deck. That small difference created just a slight bit more slack in the timing belt, which when taken up by the engine rotation, caused the camshafts to be retarded by several degrees. We didn't know this until we used a degree wheel and dial indicator to figure out what was happening.

One wouldn't expect such small changes in geometry to make such big differences elsewhere, but they often do.

 

I have a puzzling case that after reading this I may need to investigate. My cam gears are getting worn down. They, somehow are getting eaten up by the belt. By visual looks, I would say at least .040" per side is gone. Do you think this would also cause a funky timing issue. My car seems to work intermitently well (by a small margin of course, mostly response and lag are a bit different from time to time). Could this be the cause?
Did not mean to highjack the thread.

On to the thread: Why would it matter to degree it perfectly with adjustable gears? Getting on the dyno and moving them around until the car behaves as needed would be as effective, no?

Sigfrid

 

so if the cam gears are keyed onto the cam, and the crankshaft gear is also keyed, and sense the belt is toothed, how does one get to the <1deg precision? for example, if on one tooth you are 2 degrees off, so you move the cam gear over a tooth, and now you are 4 degrees off...


i'm guessing that there are around 54 teeth on the cam gears. thus there should be half that on the crank pulley, or about 27 teeth. because 360 degrees on the cam has 54 teeth, that means each tooth is about 6.6 degrees of cam adjustment, or 13 degrees of crank adjustment. likewise for the crank pulley... 27 teeth in 360 degrees gives you +- 13 degrees of adjustment with one tooth.

so my question is, just by observation, if you are one tooth off with the timing belt, you are way off on crank timing so small adjustments cannot be made by the belt alone. where and how would one go about "dialing in" the timing? am i incorrect in assuming the crank pulley is keyed? sense i've only taken the accessory belt off and never the crank timing belt pulley i'm just guessing.

the only other way to make the adjustments would be to have an adjustable cam gear...

 

I'm right there with you Kevin....I know you can get it dialed in exactly using adjustable cam gears, a degree wheel and dial gauge...

 

the factory timing marks "get you into the ballpark"

while dialing in your cams with a degree wheel & properly finding tdc allows you to know exactly where your at = like having a assigned seat within the ball park!

all gears & cranks are mass produced & drilled / broached with some type of tolerance that is acceptable by the manufacurers. all these tolerances can stack up for you or against you.

that is why some people have different cam gear settings while expecting similar engine traits.

 

good thread thus far...might help explain why piston met valve in my car

 

My friend and I, with our mechanic, are gonna be putting together his Buschur short block and head. I have a degree wheel and dial guage. I have a pretty good idea of the process, but could someone explain in detail what steps to take to help us out?

 

Basically, so long as you have the degree wheel positioned accurately with respect to TDC, and set the dial indicator on the valve such that it is at "0" while the follower rides on the cam's base circle, you are set. You will do this for both intake and exhaust cams.

Record the initial crank position where the valve reaches maximum lift, then record the last crank position where the valve is at maximum lift. The point which falls exactly in between these two positions should be the published lobe centerline for the cam tested. If the recorded LC does not correspond to the published LC, make the correction with the adjustable cam gear to achieve the desired setting.

 

Ted, can you review these steps? I've never done this before but have done a good amount of reading on engine building. My goal is to simply help my friend get his Buschur head and shortblock put together properly.

1. Before you bolt the head on, use the dial guage to find TDC
2. Bolt the head on lining up the cams with the factory timing marks
3. Install the timing belt.
4. Attach the degree wheel to the crank pulley
5. Create a reference point for the degree wheel. Take note of what TDC is.
6. Put follower of dial guage on intake came lobe for cyl1
7. Find lobe centerline (center of dwell at peak lift)
8. Take note of degrees ATDC
9. Compensate for deviation from cam manufacturer spec with cam gears

Then repeate for exhaust cam except its measured in degrees BTDC?

Am I making any sense? Sorry I have never done this before.

 

In re-reading your post I see the point you're making is that when the follower rides along the base circle of the lobe, you should be reading zero. This is to ensure you have the dial guage setup properly. I got it. Thanks very much for the tip.

 

bump! for help on actually how to do this

 

You've got it - no additional comment required.