Well, it's been a year and I have finally finished the rebuild of my sl6. I have one major problem right now. When I have the engine timed off of TDC, and the distributor set, the engine will run fine. The timing mark however, is pointing straight up (from the balencer) stating that the engine would be somewhere is the range of 90deg advanced. I have the bolt on timing marker (it's in the right spot). I tried retarding the timing all the way - that didn't move it nearly enough. I then pulled the distributor and moved it back one tooth - the car won't idle for anything, and runs horribly (backfired and set the underside of the hood on fire).

When I did the rebuild I changed the cam, replaced the rings/bearings and lifters. I did not change any valves or lash because the head had just been done (reed cam). Any help would be greatly appreciated.

cbrunner@nexant.com

It sounds like you may have the wrong crank pulley for the engine. As I recall, there are 3 different ones. Doug can give you more when he chimes in.

Chuck


webmaster@omnipages.com

I Didn't change the crank though - all I changed was the cam - I know that would change timing - but to need a new balencer mark? When I say "timed off of TDC" I mean the timing is set to TDC (as it always is).

Chris

cbrunner@nexant.com

Did you test - check for true TDC when the engine was apart? Are you using the same damper as before?

If the timing mark is confirmed correct to mechanical TDC of the engine, then my guess is that the cam is not installed correctly to a proper "installed centerline". Did you degree the cam or at least check to see if the cam's overlap event is happening directly over TDC Ex.?

If you search for "split overlap degree cam" (All) I bet you will find some good info in messages below.
DD

I have true TDC (ended up testing that a few times as I was re-indexing the distributor after moving it around). I'm using the same damper as before.

I don't think I'm going to like the answer to this question, but what does "a proper installed centerline" mean (shadtree mechanic here)?

Thanks
Chris


cbrunner@nexant.com

I would use a brass piston stop to find true TDC. This screws into the spark plug hole. With the #1 piston at TDC, where is the timing mark on your balancer in relation to the timing pointer? If this checks out O.K., then the next step would be to degree the camshaft or at least do Doug's check for where overlap occurs. I guess this is what you do not want to hear.

Mitch

m5black@aol.com

I used something similar to a brass stop to stop #1. The mark (IIRC) was in the right place (over by the #0 on the timing marker). What does "degree the cam" mean?


cbrunner@nexant.com

To degree a cam, you use a dial indicator and a degree wheel to verify where the valve events occur in relation to the crankshaft's position. For example, you find true TDC and fix a pointer to indicate this on a degree wheel fixed to the crankshaft snout. Then you pull the crank through rotation and using a dial indicator, verify where on the degree wheel the intake valve opens and closes. Compare this to the given specs for the cam. This will tell you if your valve timing (camshaft) is advanced or retarded.

Mitch

m5black@aol.com

Once I find out if the cam is advanced or retarded, how do I use that information in relation to timing the engine? (I'm a real novice at this - but trying to learn). Right now the engine runs excellently when it's advanced - I just don't know if it will ping on hills yet (need to install driveshaft and test transmission first).

Thanks

Chris


cbrunner@nexant.com

I searched-out the message on how to check the cam's position, see the link below.
You really need to check this and correct the cam's installed position before going any further. If the cam is off position, (you could be a tooth off) the engine will not run right under load, even with a bunch of advance cranked-in.
DD



Cam Degree Check

I'am entering this discussion a little late. Please excuse the length of the reply, but I am going to try and make this as basic as I can. When you say you "didn't change the lash," does that mean you haven't even adjusted the valve lash? Though you just bolted on the already done head, you have changed some key players in the valve lash computation; like head gasket(thickness), cam(base circle), and lifters(not to mention mixed-up pushrods). The valve lash needs to be checked and adjusted properly, first. If the lash is too tight, you'd have poor vacuum, poor compression, and a host of other maladies and symptoms, varying in degree to how bad the maladjustment was. If the lash is too loose(as long as it's not horrendously loose), it's no big deal; you just lose some performance. It will feel anemic.
If that is NOT the case, then look to the timing mark on the pulley. The mark can be incorrect for reasons too numerous to mention here. That is why the others want you to confirm that when the crank is physically rotated so that #1 piston is EXACTLY at TDC, the timing tab and the timing mark on the crank pulley line up EXACTLY. This is the first step to 'degreeing a cam', which is a more precise and 'real world' way to check that the cam is in proper phase with the crank. You next need to somehow attach a 'degree wheel' to the crank, or pulley, or dampener. You'll also need a sharp pointing rod to use to make the readings off the degree wheel. Roughly adjust the pointer and the wheel to approximate TDC. Since you're probably 'bucks-down' you'll need a 'positive stop' device to stop the piston. You can make one out of an old spark plug and a sturdy rod. Or you can buy one(probably less than $15). Basically you HAND-CRANK the motor around to very near TDC, then back-off about 20-30 degrees. Screw in the positive stop and adjust the rod until it just contacts the piston top. Note the approximate location on the wheel. Back off another 40-50 degrees and then rotate the crank back toward the place it stopped before. Be careful, you don't want to dent the piston top, and you certainly don't want to break the end off of the positive stop. Note the reading(in degrees). Now crank the engine backwards CAREFULLY until the positive stop does it's stuff, again. Note the reading. Calculate the difference. Divide by half. That should be TDC. Adjust the pointer(and/or wheel), until the readings are the same on each side of TDC, and VOILA,now you know zero is your EXACT TDC. It may take a coupla times to sneak up on it. Remove the 'dead-stop'. Now you can roll the crank over to zero on the wheel(TDC), without fear of crushing something. Compare it to your timing tab/pulley mark. If you need to scribe another mark, do so now. Once you know TDC, you can use a dial indicator to figure the center of the cam's #1 intake lobe, and how many degrees after TDC(ATDC) the centerline of the cam lobe is reached. It varies from cam to cam, but should be in the neighborhood of 112-104. If you don't know what the recommended installed centerline is supposed to be, then Doug's split overlap method is the one to use.
Does anyone have one of those cool 'polar coordinate' diagrams describing cam timing? One of those might be helpful to post, so that you can visually see what we're talking about?

I Didn't change the crank though - all I


fglmopar@aol.com

Great idea on the cam cards, here are a couple I scanned-in. Always keep these cards for the cam(s) you get / put in your engine(s)

There are 2 cam cards shown here.
The bigger "camel hump" graph is for the Clifford 276º mechanical cam, the smaller card I inserted in the left corner is a custom grind I worked up with a local grinder.
Note that the Clifford cam measurments are taken at .050 lift.
Both of these cams are "even pattern" with the overlap event evenly split or centered over TDC Exhaust.
DD


Larger full page view (big file size)

You know I can't recall ever seeing the Cartesian coordinate(camel-hump) graph before. I think it's even easier to understand than the other. Thanks, Doc.


fglmopar@aol.com