HELP CANT GET TIMING RIGHT
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He's referring to Bluf100's problem with it not running right and backfiring through the carb.
If yours runs well the way you did it, then it's correct. And you can get advance/retard no matter where the distributor is located. Just how much you can get, or whether it's in the right range is another thing altogether, but you can advance timing from anywhere as long as there is clearance for the distributor body to be twisted.
But I'd say you also got lucky, unless you knew for sure that you had it on TDC of the compression stroke and not the exhaust stroke. Just using the timing marks without verifying TDC on compression is a 50/50 proposition since the timing marks come around twice per cycle. Hence the phrase "getting the distributor 180 degrees out" that you hear so much when an engine won't work after changing things.
To the OP, did you break in your cam? All of this idling and popping and cranking are not good if you did not.
Since you rebuilt the engine (you did it, or someone else did it?) you're probably familiar with the cam break-in procedure? That's where you get the engine started and immediately rev it to at least 2500 rpm and hold it there for at least 20 minutes.
I like to do it for 30 minutes, and I like to vary the rpm between 2500 and 3000, but ask ten cam manufacturers and you get ten variations on that theme. So I choose to err to the high and long side, and have never had an issue.
But if you can't get it to fire and run immediately then you can possibly damage a new flat-tappet cam.
Sorry if you knew all that, but it usually bears repeating for those that don't.
Paul
If yours runs well the way you did it, then it's correct. And you can get advance/retard no matter where the distributor is located. Just how much you can get, or whether it's in the right range is another thing altogether, but you can advance timing from anywhere as long as there is clearance for the distributor body to be twisted.
But I'd say you also got lucky, unless you knew for sure that you had it on TDC of the compression stroke and not the exhaust stroke. Just using the timing marks without verifying TDC on compression is a 50/50 proposition since the timing marks come around twice per cycle. Hence the phrase "getting the distributor 180 degrees out" that you hear so much when an engine won't work after changing things.
To the OP, did you break in your cam? All of this idling and popping and cranking are not good if you did not.
Since you rebuilt the engine (you did it, or someone else did it?) you're probably familiar with the cam break-in procedure? That's where you get the engine started and immediately rev it to at least 2500 rpm and hold it there for at least 20 minutes.
I like to do it for 30 minutes, and I like to vary the rpm between 2500 and 3000, but ask ten cam manufacturers and you get ten variations on that theme. So I choose to err to the high and long side, and have never had an issue.
But if you can't get it to fire and run immediately then you can possibly damage a new flat-tappet cam.
Sorry if you knew all that, but it usually bears repeating for those that don't.
Paul
Senior User
Joined: Aug 2017
Posts: 199
Likes: 1
From: Berkeley, CA
You also need high-zinc oil if you run a flat tappet cam. You may want to contact your engine builder asap before doing anything else.
You can change our oil...if you see metal it could be your cam lobes wiping.
Lead Driver
Joined: Jul 2017
Posts: 9,591
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From: San Jose, CA
Yes indeed Bluf. Sorry to confirm what SixtyFour said, but the cam break-in procedure is probably the single most important aspect of new engine startup. It's nothing to do with the traditional engine break-in that most of us still follow to an extent, where you drive mildly for the first 500 miles, or whatever.
Cam break-in is during initial setup because the mating of the base of the lifters and the lobes of the camshaft are the most stressed portion of an engine especially so during initial startup when oil is getting run around the engine. Mainly because, while the cam bearings are pressure fed oil like most other important things, the cam lobes are lubricated almost entirely from "splash" where the oil being flung around the crankcase, draining back through the openings in the lifter valley, and some squirting out of the sides of the bearings is all that lubes the lobes.
Hence, no excessive cranking while you try to dial things in, no idling for at least twenty minutes, no sitting there tuning the carb or looking for other stuff to do. If it needs tweaking during that time you shut it down until you've finished tweaking. Then start it right back up and run it up to 2,000-3,000 rpm for the rest of that 20-30 minute break-in.
If it won't start, you need to figure out why without cranking the starter. This is sometimes the hardest part. Especially if you're not a long time engine worker-onner-tuner than can figure that stuff out cold turkey.
So yes, lots of bad things may have happened already. Or maybe you'll be lucky and the assembly lube that was hopefully slathered on will have saved you at least initially. You did say that it would idle at higher rpm, and maybe that 1200 to 1500 was just enough to keep things alive. But the reason this even comes up is that backfiring through the carburetor is, among other things, a classic symptom of a flat cam.
Another question then might be just how long did it take to get it to idle at 1500 rpm? Were you cranking it for a long time, or idling at normal speed for just a short time before you got it at the higher rpm? If so then you may still be ok.
If you were cranking for a long time, or idling for a long time before this, then that might be why you only get a constant backfiring through the carburetor.
It's that classic symptom of either really bad ignition timing (too retarded usually) or a flat cam.
At this point I would still try to get it up and running at a higher speed for at least 15 minutes with a timing light connected. If you can get the timing above 20 degrees you should be ok, but if not then running at higher rpm with too little advance can really heat up the exhaust system to the point you can crack manifolds or burn the paint right off of headers in a couple of minutes.
If you just can't get it to run, then I would pull the easiest valve cover off and rotate things slowly by hand to see if the rockers move their full expected movement. If they are not, they are either not pumped up with oil or they have already been lost.
Can you remove lifters through the head on a 352? Or do you have to remove the entire intake manifold and stuff to access the lifters? If it's easy to do, pull a couple of rockers and lifters to inspect the bases and peek down inside with a light at the cam lobes.
Depending on how long you've actually had it up and running, it might still go either way.
Good luck.
Paul
Cam break-in is during initial setup because the mating of the base of the lifters and the lobes of the camshaft are the most stressed portion of an engine especially so during initial startup when oil is getting run around the engine. Mainly because, while the cam bearings are pressure fed oil like most other important things, the cam lobes are lubricated almost entirely from "splash" where the oil being flung around the crankcase, draining back through the openings in the lifter valley, and some squirting out of the sides of the bearings is all that lubes the lobes.
Hence, no excessive cranking while you try to dial things in, no idling for at least twenty minutes, no sitting there tuning the carb or looking for other stuff to do. If it needs tweaking during that time you shut it down until you've finished tweaking. Then start it right back up and run it up to 2,000-3,000 rpm for the rest of that 20-30 minute break-in.
If it won't start, you need to figure out why without cranking the starter. This is sometimes the hardest part. Especially if you're not a long time engine worker-onner-tuner than can figure that stuff out cold turkey.
So yes, lots of bad things may have happened already. Or maybe you'll be lucky and the assembly lube that was hopefully slathered on will have saved you at least initially. You did say that it would idle at higher rpm, and maybe that 1200 to 1500 was just enough to keep things alive. But the reason this even comes up is that backfiring through the carburetor is, among other things, a classic symptom of a flat cam.
Another question then might be just how long did it take to get it to idle at 1500 rpm? Were you cranking it for a long time, or idling at normal speed for just a short time before you got it at the higher rpm? If so then you may still be ok.
If you were cranking for a long time, or idling for a long time before this, then that might be why you only get a constant backfiring through the carburetor.
It's that classic symptom of either really bad ignition timing (too retarded usually) or a flat cam.
At this point I would still try to get it up and running at a higher speed for at least 15 minutes with a timing light connected. If you can get the timing above 20 degrees you should be ok, but if not then running at higher rpm with too little advance can really heat up the exhaust system to the point you can crack manifolds or burn the paint right off of headers in a couple of minutes.
If you just can't get it to run, then I would pull the easiest valve cover off and rotate things slowly by hand to see if the rockers move their full expected movement. If they are not, they are either not pumped up with oil or they have already been lost.
Can you remove lifters through the head on a 352? Or do you have to remove the entire intake manifold and stuff to access the lifters? If it's easy to do, pull a couple of rockers and lifters to inspect the bases and peek down inside with a light at the cam lobes.
Depending on how long you've actually had it up and running, it might still go either way.
Good luck.
Paul
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Potentially a lot of damage. Do you know if you have a flat tappet cam? Maybe your builder installed a roller cam, if they are available. Roller cams dont have the same break in process...
You also need high-zinc oil if you run a flat tappet cam. You may want to contact your engine builder asap before doing anything else.
You can change our oil...if you see metal it could be your cam lobes wiping.
You also need high-zinc oil if you run a flat tappet cam. You may want to contact your engine builder asap before doing anything else.
You can change our oil...if you see metal it could be your cam lobes wiping.
Senior User
Joined: Aug 2017
Posts: 199
Likes: 1
From: Berkeley, CA
- glitter in the oil.
- a rocker arm(s) that don't move up and down as much as the rest. ...
- valve train noise, sounds like a rocker out of adjustment that you just can't seem to get set right.
- engine pops back through the carb or exhaust when under load.
What I would do:
-change the oil to check for metal/glitter
-remove valve covers and inspect each rocker. Are any abnormally loose? Rotate the engine BY HAND and look for the rocker movement. Look for one or more that isn't moving as far as the others.
Assuming all this checks out....then let's talk next steps. But given you say it's a constant backfire/pops when you are accelerating...i think your cam is toast.
Lead Driver
Joined: Aug 2003
Posts: 6,305
Likes: 18
From: Boulder Creek, Ca
IMO carb and timing are inter-linked? On my 65 with the 352/390 I do not have a timing arm so I found the best way of tuning when not certain I remove #1 plug, place finger in the opening and as soon as compression forced it out of the opening I immediately stopped and checked the position of the rotor as it related to the cylinder if off I lift the dizzy and rotate the rotor to # 1 cylinder. I have a Holley 650 which operates off a secondary vacuum which is a metered port. This is just a method I have used over the many years to get in the ballpark, once the engine is running I can then fine-tune by adjusting the idle mixture by gently tightening each idle mixture screws then back them out approx. 1 1/2 turns. I would then adjust the timing at around 10 BTC keeping in mind any change in timing I would go back and adjust the idle mixture and vise-versa.
** When I went to Duraspark ll ignition I re-gaped the plug to around .045.
Anyhow, when this old-time has a senior moment and resort to my back yard mechanic approach in setting the timing it has worked for me??
Anyhow food for thought??
** When I went to Duraspark ll ignition I re-gaped the plug to around .045.
Anyhow, when this old-time has a senior moment and resort to my back yard mechanic approach in setting the timing it has worked for me??
Anyhow food for thought??
Senior User
Joined: Aug 2017
Posts: 199
Likes: 1
From: Berkeley, CA
IMO carb and timing are inter-linked? On my 65 with the 352/390 I do not have a timing arm so I found the best way of tuning when not certain I remove #1 plug, place finger in the opening and as soon as compression forced it out of the opening I immediately stopped and checked the position of the rotor as it related to the cylinder if off I lift the dizzy and rotate the rotor to # 1 cylinder. I have a Holley 650 which operates off a secondary vacuum which is a metered port. This is just a method I have used over the many years to get in the ballpark, once the engine is running I can then fine-tune by adjusting the idle mixture by gently tightening each idle mixture screws then back them out approx. 1 1/2 turns. I would then adjust the timing at around 10 BTC keeping in mind any change in timing I would go back and adjust the idle mixture and vise-versa.
But I think our PO has larger issues right now.
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