75 400 timing showing 20 deg AFTER tdc

D

dewitz

New member
Joined
Mar 23, 2015
Messages
5
Reaction score
0
Points
0
Hi,
75 pontiac 400, 6x heads, performance distributor (http://performancedistributors.com/) set up for this engine, medium comp cam, fast ez-efi fuel injection (throttle body carb style fuel injection) . Compression around 8.5 to 1. I went to set/check the timing this spring, and couldn't find the mark. Figured I hooked to the wrong wire. Nope, left front is cylinder 1. The mark showed (I'm guessing) 40 deg AFTER tdc. OK, figured the distributor wasn't tight enough last year and it was way off. As I turn it back (vacuum unhooked, 1000 rpm, it won't even hardly run as I approach 0. I set it as far ahead as I can, but then it won't start. Acts like it is 20 deg BTDC and firing before the piston gets over the top. I have to back it off to (I'm guessing because there are no marks) at least 20 deg (judging by the light gun) after TDC to get it to start. It feels and acts like the timing marks are off. I got another timing gun, and it shows the same spot. I definitely have cylinder 1. Is there any way the timing mark could be off? I guess my next step is to pull no1 plug and find TDC with the piston and see if the timing mark is right, but this just doesn't make any sense to me. I am 99% sure when I timed it before (several times, when I put in the distributor, the efi, and regular maintenance) that it was at least in the ballpark of where it was supposed to be. Even if the timing chain jumped, the crank should still align correctly and it sure wouldn't run as good as it does. I'd appreciate any help or thoughts. Thanks.
 
the rubber holding the outer ring of the balancer has deteriorated and the ring has slipped. Do as you suggested and get #1 at TDC and see if the groove in the damper is lined up with the zero on the timing tab. Is the wire going to #1 in the cap tower listed in this link?
http://pontiacformula.free.fr/en/allumage.php
 
timing

That's kind of what I was thinking, but I wasn't sure if that could actually happen. I'll check out TDC and go from there. Thanks!
 
timing

And yes, the first thing I did when it was off was to pull the chiltons and double check I was on cylinder 1 and wires were correct.
______________________________
 
You are sure it is After TDC not Before TDC. If Before TDC you could also check the advance weights in the distributor for sticking at full advance. You are checking timing with any vacuum advance to the distributor disconnected?
 
timing

I know, I thought I was an idiot too. But yeah, it shows after. The timing cover marks go from 16 btdc -> 0 -> way farther up where the mark lights the spot on the flywheel. Couldn't even see it at first, almost straight up. Ordered a street one from butler performance. I can't blame the balancer, it has 350k miles on it. That's a lot of revolutions.
 
so you have determined that the ring slipped?
 
You must log in or register to reply here.

Share this page

Back
Top