at a loss - rebuilt engine won't start!!!
 

I've rebuilt this engine this more times than I can remember, but this is a new occurrence for me.

I just finished a top end rebuild and the motor won't run. I will crank it time and time again, but it will never "catch" to where it even tries to go. I've checked and all spark plugs are getting a spark according to my inductive pickup timing light. The distributor is hooked up (wasn't disturbed in the first place) and wired to the correct cylinders. It's definitely getting fuel, as the carbs stink of gas, and when I inspect the plugs they are soaked in gas.

When I crank the engine for a long time, every so often (1 time every 20 seconds or so) it will backfire and according to my wife, shoot some flame out the rear pipes (I told her it's up upgraded setup!!! Just kidding)

What the heck is up??????

I thought maybe the battery was not up to par providing enough spark, but it is fully charged, and I even hooked up another car to jump it to rule that one out.

The points are set correctly, rotor and cap are same that were on before (no problems before).

It seems the plugs are not firing, or firing at the right time??? I just can't figure this one out; so I am hoping someone might have a tip to steer me in the right direction.

The ignition uses a Delta MarkTen CD unit and it was working fine before the rebuild, and I even press the bypass button and still get no go. I've put all new components : points, condensor, rotor, cap and even swapped back on the originals that worked before, yet no go.

Any ideas...???

Thank you.:(

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The delta mk10 is an antique ( like the old Bosch CD boxes )........we had them in our boat in the early '70s, and since you are using the mk10's bypass to no avail..maybe if all the other ducks are in a row... look for a new ignition box?

no expert in rebuild but a few questions:

As we know, you need fuel, spark and air for acar to run. You have described you are getting everything but maybe in the wrong order?

If you spray starting fluid, will it run?

Are you sure the cams are timed correctly?

If they are 180 off, this may explain it.

From your description I am also guessing that either the cams or distributor are incorrectly timed.

Assuming you set your rotor at TDC it could be likely that you positioned your rotor at the wrong TDC point.

Not only must the engine have air, it must be compressed at the correct time. Remove #1 spark plug, insert a compression tester hose and rotate the engine manually to feel for compression between BDC and TDC. If you have compression, look elsewhere, like ignition timing or fuel. If you don't, find out why. Could be the cam timing is off as 350HP930 and HarryD suggest.

Sherwood Lee
http://members.rennlist.org/911pcars

I was so proud of my cam timing, getting both sides right on. But, sounds like I need to check them. I am sure, though, it was set right. The dot on the cams is up to start, the crank rotated 360 degrees so the dot on the cam is now down, and that's where the timing is set. That is correct, right??? That's how I've always remembered to do it....

By the way, how can you time the cams so they're 180 degrees off?? Isn't there only one way to time them since during the next 360 degrees there is no lift occurring?? I guess you'd have to start with the cams in the wrong orientation, right??

I double checked my distributor and the rotor is for sure pointing at the cylinder #1 mark...

Now that the battery is so run down, would that make a difference?? I'll try again tomorrow when it's charged, but I figure that should not make a difference.

Motors are very very very simple. rember that. compression, fuel , spark and it will run, if all is in the right order.


Back to the basics.

valve covers off. turn engine to tdc, both intake and exhaust are closed on one of two cycles? right? next check number 4 for valve closure on the opposite cycle. Don't worry about exact degrees at this point. Next check the distributor. with the valve covers still off, does the rotor line up with number one with tdc and the valves closed? If so all is good so far. Next is there gas squirting out the accelerator pumps? If so you probably got gas and it most likely will start with minor timing adjustments. If you have soaked the plugs with gas you will need to bake them out first. the safe way is to use a propane torch on the end of each plug. get it just hot enough to smoke a little, its now dry.

If you made thru all t he basic checks ok it will probably will start. If you found a basic porblem, correct it,, eg cam timing out or disributor out. you should be able to detect it with this crude check. IN the unlikely event that the cam timeing is out a little or somthign like this good luck you may neeed it.

Thanks guys for the input; I'll keep you all posted as I'll try to start it after work!!!

when you put the hose in #1 and rotate the engine until you feel some compression with your finger over the end, look at the distributor rotor and be sure it's coming up to #1 also. sounds like timing 180° out more than anything else. or if not 180, then on the wrong cylinder. it also has to be advanced enough to catch and run well.

I'll second these guys, sounds like cams or distributor to me...

Ok, which one of you pelican-heads came over and rotated my distributor?? Huh???

It was in fact my distributor - all of you were correct. I think this is a testament to working too long in the garage without a break for rest or meals (or making my wife feel loved!). I spent about 12 hours on Saturday putting it all back together, following a previous 10 hours on friday... I must have left my thinking cap in bed or something. When I set the cams to time them, the distributor WAS indeed at cylinder #4, not #1 (doesn't that mean it was "pointing" to cylinder #1 literally as opposed to the notch on the distributor body??!). That would do it!!!

My little 911 is running again!!!

Thank you to all of you for your input. When it's sunny out I'll take some pics to share. Thanks again everyone; your expertise is appreciated and I have learned a good lesson from it all.

it's in and running great!

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Looks nice. I'm glad to hear our advice helped you to get it on the road.

This is a common problem - typically when the engine won't start with these symptoms, 99% of the time it is an ignition timing issue. It's not typically a camshaft timing issue, because if the cams were off, you'd have other problems (like pistons smacking valves, etc.)...

-Wayne