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engine starts and runs better when I can't see the timing mark, when its set to 8 deg btdc it back fires and runs like crap. Engine was rebuilt and bored 30 thousands
with about 500 miles on rebuild so I don't think it jumped time.Is the timing changed on a engine that is bored out?, is there a way to test the distributor and see if thats my problem? HEI distributor , wires are correct.
Did they maybe re-use the old balancer and it has slipped? Find TDC again and make sure your timing mark lines up, check to ensure your distributor is not 180 off and that your wires are correct.
Bring your engine to TDC for cylinder 1 on the compression stroke. The rotor should be pointing towards cylinder 1 and your timing mark on the balancer should be at zero, or close to it.. If not, either the distributor is off, or the chain has jumped. This is assuming you balancer is OK.
pull 1 valve cover. as you are cranking the motor, cyls 1 and 6 have exh just closing and intake just opening right at tdc. so watching exhaust vakve opening, then stop cranking and bump the engine with the key or turn it with a wrench on balancer. right at the point that both valves are moving you should see the TDC mark right at 0. if so, your timing chain and balancer are bothwhere they belong. and when #6 valves moving, firing on 1. and when #1 moving, firing on 6. also, are you looking at timing with the vacuum advance still hooked up? if so, your timing is more like 8 to 10 AFTER TDC. no setback timing light? you need a 30 BTDC mark on your balancer. put TDC mark on balancer at 15 degrees. now paint a mark at 0 with white out or similar. move that mark to 15 degrees BTDC. now paint another mark at 0. now you can see your all-in timing that is supposed to be at 36 degrees with vacuum unhooked and revved up until centrif stops advancing. usually around 3000 rpm.
Last edited by derekderek; Apr 16, 2022 at 01:20 PM.
To find TDC go to cylinder #6, get the intake and exhaust rockers so that one moves when you turn engine. That is if you turn engine one way the intake moves, if you turn the other way the exhaust moves. That is TDC for #1 cyl.
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by Mr D.
Read the attached .pdf file.
Don't download or use any of my papers you find on the internet. They are either fake/altered papers, or grossly outdated, and they should not be used. Use only papers you obtain directly from me via e-mail request.
Originally Posted by kendix6
engine starts and runs better when I can't see the timing mark, when its set to 8 deg btdc it back fires and runs like crap.
You need to do an accurate TDC verification to verify that your balancer has not slipped and that the timing marks are in the correct location. E-mail me for a copy of my "How to Determine TDC" tech paper and check your engine. Once you verify actual TDC, you can request my "How to set Timing" tech paper and set the timing up correctly, too.
The rotor should be pointing towards cylinder 1...
I always find this troublesome advice. I believe the statement should be amended to say that the rotor should correspond with the #1 spark plug tower, but whether it actually points to the front driver area of the engine depends on what engine is installed, how the wires are oriented on the cap and how the distributor is rotated for timing.
From: At my Bar drinking and wrenching in Lafayette Colorado
The rotor position, and the spark plug wire clocking in the cap also depends on whether this is a points-type distributor or an HEI. On the points distributors, the #1 tower in the cap is the forward passenger side tower. On HEI, it's the forward driver's side tower. For a complete paper with photos on how to install the distributor in the correct orientation, with correct clocking of the wires and rotor, just send me an e-mail request.
This is the correct, standard Chevy installation for a points distributor showing the location of the #1 plug wire tower and the correct position of the rotor in the #1 firing position:
This is the correct, standard Chevy installation for an HEI distributor showing the location of the #1 plug wire tower and the correct position of the rotor in the #1 firing position:
Due to the proximity of the tach drive cable to the firewall on the C3 Corvettes, a Technical Service Bulletin (TSB) was issued in 1968 which required the distributor housing to be rotated 90 degrees clockwise to straighten the tach cable out. The plug wires were then shifted 1 position counter-clockwise in the cap, thus keeping the relative position of the plug wires in the engine compartment unchanged. This TSB was in effect through 1974. The change rotated the distributor housing, but the relative position of the plug wires in the engine compartment remained unchanged by moving the wires over 1 position: The #1 tower/wire remained in the forward passenger side location in the cap, and the rotor position, therefore, also remained unchanged. All Chevy V8 engines up through 1974 have the distributor installed in the position shown above, whether small block or big block, with the only exception being the Corvettes modified per the TSB. After 1975, all Chevy V8 engines with HEI had the distributors installed and clocked as shown above with no exceptions.
Lars
I always find this troublesome advice. I believe the statement should be amended to say that the rotor should correspond with the #1 spark plug tower, but whether it actually points to the front driver area of the engine depends on what engine is installed, how the wires are oriented on the cap and how the distributor is rotated for timing.
Since there was no specific details about what we're dealing with, I believe in most cases my advice is correct. Besides, it should be common sense that wiring firing order is correct, and that would be the first item that someone should verify. And if someone custom routed spark plug wires or installed the distributor "off the book", then all bets are off. Thanks for your advice.
Since there was no specific details about what we're dealing with, I believe in most cases my advice is correct. Besides, it should be common sense that wiring firing order is correct, and that would be the first item that someone should verify. And if someone custom routed spark plug wires or installed the distributor "off the book", then all bets are off. Thanks for your advice.
In replying, I am not seeking an argument but want to respond to "off the book".
"Off the book" implies there is only one official way GM oriented distributors and wires, and that is just not the case. The "book" provided variations depending on: small block, big block, a TSB modification for '68 (and I'd assume at least carried forward to '69), and as Lars illustrated above differences for points or HEI.
You can clearly see in the Chevrolet diagram below that aiming the rotor at #1 cylinder will send your #1 TDC spark to towers 2 or 7. I agree that details may be lacking but making a blanket statement can cause much grief in figuring out what went awry. That's why I think it better to advise that the rotor align with the tower connected to #1's spark plug.
In replying, I am not seeking an argument but want to respond to "off the book".
"Off the book" implies there is only one official way GM oriented distributors and wires, and that is just not the case. The "book" provided variations depending on: small block, big block, a TSB modification for '68 (and I'd assume at least carried forward to '69), and as Lars illustrated above differences for points or HEI.
You can clearly see in the Chevrolet diagram below that aiming the rotor at #1 cylinder will send your #1 TDC spark to towers 2 or 7. I agree that details may be lacking but making a blanket statement can cause much grief in figuring out what went awry.
So you don't even know what the specific application may be, but you want to debate the subject? Have a nice day!
balancer may be old so I see the post of how the balancer should line up with the key way. That will be my first check,wires are correct .Thanks for your input.
From: At my Bar drinking and wrenching in Lafayette Colorado
Even with a new balancer, it's still a good idea to do a TDC verification to make sure the timing line is in the right location in relationship to the timing tab. Aftermarket parts are often not precise, and you never know what someone has done with timing tabs and timing chain covers on an old 50 year old antique car. Check everything. Especially when installing new parts.
Lars
balancer may be old so I see the post of how the balancer should line up with the key way. That will be my first check,wires are correct .Thanks for your input.
The balancer keyway doesn't line up with the timing mark, the timing mark is positioned 10 deg to the left of the keyway looking at the front of the balancer. Picture in post #4 is a brand new balancer.
Even with a new balancer, it's still a good idea to do a TDC verification to make sure the timing line is in the right location in relationship to the timing tab. Aftermarket parts are often not precise, and you never know what someone has done with timing tabs and timing chain covers on an old 50 year old antique car. Check everything. Especially when installing new parts.
Lars
This! This falls under "good practice"......
And #1 on the distributor cap can be anywhere you want it.......you just phase the rotor to correspond with it.
The old "point toward #1" was done to give the average dude/dudette a place to start......
timing problem on 350
