timing: ignition and cam

jvandyke

jvandyke

True Classic
okay, new thread because it's interesting.
after much distress last year with blown head gaskets I determined my timing marks on the crank are not correct, or, perhaps better stated; the crank indicates 5 degrees behind flywheel.
I was trying to time it off crank marks, 10 BTDC which was really 15ish, spark knock and blown gaskets. Recent fiddling and engine seems knock free at 5 BTDC (flywheel timed, crank shows 0).
I had set my cam according to crank so I imagine my cam is off by 5 also.
Thing is, the car has never run so well, at least in the upper registers, I was coming in today revving into the 6,000 zone and it was singing, prior to this, when running more initial advance, it never seemed very happy up there, power drop and general "thrashing" about.
I guess I'm wondering if the cam being retarded by 5 and the timing retarded down to 5ish (now) has resulted in a compromise.
I'm thinking I should go back in to set the cam according to the flywheel (trying to verify TDC as best I can without pulling the head again), then revisit ignition timing. This may explain why I didn't seem to have trouble setting the cam after shaving the head (because I wasn't really setting the cam to TDC but rather to 5 degrees BTDC).
It sure seemed really really happy running in today. I'd be happy to leave it be for a while!
 
I think some of our more experienced cam and head guys have posted that when the head is shaved as much as yours has been, it does affect the cam timing. But in order to really know where your cam timing is, I think the next step would be to get an adjustable cam sprocket and then go thru the steps with dial indicators and such to set it up.

In and of itself, installing and tuning an adjustable cam sprocket seems like a lot of expense and bother to me for most likely not much gain over what you have now, which seems to be your best-running period since you've had the car!

OTOH, if you plan on any additional performance mods, like installing a performance cam, then I'd say yep, an adjustable cam sprocket would all of a piece and would make lots of sense.
 
Why bother guessing?

There are several methods to determine TDC with the head on. One simple way that is accurate to a degree or two would be to stick a slender screwdriver down a spark plug hole and rotate the engine (easier with help). You can see the screwdriver "rock" around TDC. I would hold the screwdriver as you do this, so that you can feel when it's at the top, and also to make sure it doesn't get wedged.

Once you know TDC, you can take the valve cover off and watch a cam lobe. It's most accurate with a dial indicator on a base (maybe $30 for a cheap Chinese one) but you can do it visually too. Or bolt a stiff wire to a bolt somewhere, bend it so it sits on top of the bucket, then use a feeler gauge to determine when the bucket starts to move.

Pete
 
in my experience milling the head on a inline overhead cam motor will retard the cam timing since you're adding slop to the belt between the two gears.

I've also noticed in past cam installs, that the sweet spot in the powerband moves up as the cam retards. naturally this is an overstatement, but usually if you look it from say 0 to -5 degrees, that theory holds true.
 
jvandyke said:
I'm thinking I should go back in to set the cam according to the flywheel (trying to verify TDC as best I can without pulling the head again), then revisit ignition timing. This may explain why I didn't seem to have trouble setting the cam after shaving the head (because I wasn't really setting the cam to TDC but rather to 5 degrees BTDC).
Click to expand...
You can pretty much take the flywheel timing marks to the bank; if the flywheel says it's at TDC, that's where it is. It's the crank pulley marks on a 1500 that sometimes lie.

Without an adjustable cam pulley you'll have to move the cam by a full tooth if at all, so you can just put the motor at flywheel TDC and eyeball the cam mark. It' will be pretty clear whether moving a full tooth will get you closer to the timing mark. Of course with your shaved head that timing mark won't be spot on either. If you just want to know what your cam timing really is, Pete's $30 cheapie dial gauge is the way to go.

But....

It sure seemed really really happy running in today. I'd be happy to leave it be for a while!
Click to expand...
That's your answer then. Leave it until the next belt change or valve adjustment.
 
I've heard most cams on these cars like about 2 degree's cam advance. If you have a very shaved head (that retards the timing) and/or a decked block and you move it forward a tooth you might be in that 2 degree advance area with a stock pulley... then again you might not.
 
I will attempt to set the flywheel to TDC and eyeball the cam pointer for fun. I'm not sure yet what, if anything I'll do about since it seems pretty happy right now. It does seem a little slower out of the hole, but I like the revv'n strong on the high side...A LOT!:dance:
 
remember that cams behave generally opposite of ignition in regards to advancing / retarding and the impact on low and high rpm torque.

Advancing a cam will generally bring the power down towards low end, make it more responsive, and help your "launch"... right up to the point where it opens the intake too soon and your car snorts like hippo sneezing up the carburetor in your face (and sometimes the accompanying fireball).

Many cams have advance already built in.. the only sure way to know anything is to degree the crank to find exact TDC, then degree the cam to see the relationship of the actual cam advance to the cam wheel timing marksl. That is best done out of the x1/9 due to clearance issues with timing discs

In a SOHC you can't change overlap and there are many factors at play and you generally are just searching for the sweet spot that makes the whole system work the best (intake runner length, carb type, exhaust runner length, restriction, etc). you can spend 5-10 pulls on a dyno just playing with cam timing if you want to.

Then tune your ignition timing to complement.
 
bikesandcars said:
Many cams have advance already built in. the only sure way to know anything is to ... degree the cam to see the relationship of the actual cam advance to the cam wheel timing marksl. That is best done out of the x1/9 due to clearance issues with timing discs
Click to expand...

Most of the X1/9 cams floating around are symmetrical - TDC right in the middle of the overlap, intake opens the same number of degrees before TDC as exhaust closes after TDC. It's particularly easy to degree these and find the stock TDC position.
 
EricH said:
Most of the X1/9 cams floating around are symmetrical - TDC right in the middle of the overlap, intake opens the same number of degrees before TDC as exhaust closes after TDC. It's particularly easy to degree these and find the stock TDC position.
Click to expand...

great info! thanks :)
 
bikesandcars said:
I've heard most cams on these cars like about 2 degree's cam advance. If you have a very shaved head (that retards the timing) and/or a decked block and you move it forward a tooth you might be in that 2 degree advance area with a stock pulley... then again you might not.
Click to expand...

actually theres a pretty easy way to tell exactly how many degrees one tooth off will make... count the number of teet on the cam gear and divide 360 by that number. Then you will know what one tooth forward/back advance/retard equals in respect to cam timing.
 
Shaved head & cam box moved my cam timing back:

IMG_8698.jpg


I used the Millers Mule gear to bring it very slightly advanced.

IMG_8704.jpg


BTW - did you switch to the 1300 tensioner to make sure the belt is tensioned properly?

Matt's comments on Cam Timing from my old thread three years ago.
 
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