Timing adjustment on 75 L48
Thread Starter
Racer
Joined: Dec 2011
Posts: 284
Likes: 4
From: Philadelphia Pennsylvania
Timing adjustment on 75 L48
I wanted to try the recommended timing adjustment and my adjustable timing gun just arrived. But I'm getting stuck at the most basic part...I can't find the timing marks on my engine. I've had somebody crank the engine/kill it/check for mark dozens of times and I think I just can't see it. I understand it is a groove in the metal that can be painted white but I can't find the groove. I read around here about rubbing the area with a crayon but unless it is while the engine is running it seems like it would take forever as I can only access a small area at a time. Is there an easy way to manually turn the engine without it running? It doesn't look safe to reach down that far with the radiator fan and belts going while it runs. Do I need to remove something for better access?
Drifting
Joined: Sep 2010
Posts: 1,412
Likes: 50
From: Laguna Niguel California
There's a bolt inside the crank pulley. Use a long handled ratchet or breaker bar with the correct socket to turn it over. There is a cut line in the damper but its probably covered with 40 years of dirt and rust.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
It's there. Just cold-crank bit-by-bit with ignition key and with coil wire disconnected and you will find it. And clean off that degree plate so you can see the marks. The large indent is 0*. BFTDC is upwards of that.
Last edited by Paul L; Aug 8, 2014 at 03:59 PM.
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
Be careful if you decide to use the harmonic balancer bolt to turn the engine, personally I wouldn't unless the spark plugs are removed as I have heard of people stripping the threads in the crankshaft nose (on my engine I found that the bolt only threaded into the crank maybe 8 threads so I replaced it with one slightly longer). You can make a tool to fit into the other slots to turn the engine, I'm not sure if you can buy them. A remote starting button that can be connected directly to the starter motor solenoid comes in very handy for inching the motor round and makes it a one person job.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
Be careful if you decide to use the harmonic balancer bolt to turn the engine, personally I wouldn't unless the spark plugs are removed as I have heard of people stripping the threads in the crankshaft nose (on my engine I found that the bolt only threaded into the crank maybe 8 threads so I replaced it with one slightly longer). You can make a tool to fit into the other slots to turn the engine, I'm not sure if you can buy them. A remote starting button that can be connected directly to the starter motor solenoid comes in very handy for inching the motor round and makes it a one person job.
Racer
Joined: Jan 2014
Posts: 334
Likes: 6
Don't worry you will find it! This pic shows mine before and after removing some paint and painting the timing mark with some white-out:
It definitely helps when the sun is shining bright outside!
I turned the dampener with a socket, but in hindsight it would have been way smarter if I had either removed some plugs or used a remote starter as mentioned above.
I have a '75 L48 as well (an older "built-up" L48 anyway) the same color as yours so holler if any questions.
It definitely helps when the sun is shining bright outside!
I turned the dampener with a socket, but in hindsight it would have been way smarter if I had either removed some plugs or used a remote starter as mentioned above.
I have a '75 L48 as well (an older "built-up" L48 anyway) the same color as yours so holler if any questions.
Last edited by C3Hawk; Aug 8, 2014 at 06:42 PM.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Just "bump" the starter with a quick twist and release of the key, then check for the timing mark. If it's not visible, give it another "bump". The engine should not start. It should only take a few bumps to find the mark. Then you can 'highlight' it so it will easily show up with your timing light.
P.S. It's easiest to do this in a darkened garage or at dusk when the sun doesn't bleach out the visibility of the timing light.
P.S. It's easiest to do this in a darkened garage or at dusk when the sun doesn't bleach out the visibility of the timing light.
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Thread Starter
Racer
Joined: Dec 2011
Posts: 284
Likes: 4
From: Philadelphia Pennsylvania
I found it. I did the single bump of the starter repeatedly, cleaning the visible area of the damper(?) off with a wire brush. After a little while I found it clear as day. It is obvious. This means I was so unlucky yesterday when randomly spinning the engine that it just didn't happen to be it in the visible area. I just calculated the chance of me never seeing it with 1/8th of the damper visible over 24 tries is only 4.6%!
Anyway, I marked it using some appliance paint on the tip of a nail, and I will try the adjustment soon. Thanks guys.
Anyway, I marked it using some appliance paint on the tip of a nail, and I will try the adjustment soon. Thanks guys.
Thread Starter
Racer
Joined: Dec 2011
Posts: 284
Likes: 4
From: Philadelphia Pennsylvania
removed hei distributor cap
removed advance cover and rubber-banded centrifugal advance
put distributor cover & cap back on and hooked up timing light
light seems to indicate 8 degrees before top dead center
removed advance cover and rubber-banded centrifugal advance
put distributor cover & cap back on and hooked up timing light
light seems to indicate 8 degrees before top dead center
Thread Starter
Racer
Joined: Dec 2011
Posts: 284
Likes: 4
From: Philadelphia Pennsylvania
I took the rubber bands off and tried it again. Having somebody rev the engine, it settles at 33 degrees advance. I forgot to check which RPM. So I want to adjust to 36 and drive it and see if it pings, right? And then adjust down to 34 or so until it stops?
Thread Starter
Racer
Joined: Dec 2011
Posts: 284
Likes: 4
From: Philadelphia Pennsylvania
After adjusting the distributor until it was 36BTC all-in (~2400rpm) the idle advance is about 0BTC! That can't be right. I just checked it twice, too. Any idea what might be the issue here?
So I'm setting my variable timing light to 36, having somebody rev until it stops increasing, slowly twist the distributor until the lighted line is at 0BTC, tighten the distributor lock down bolt, re-verify 36 at RPM, let RPMs drop to idle, adjust timing gun until the lighted line is at 0 on the balancer indicator dial. It leaves the light gun set at just under 2BTC.
I'm gonna try it again later but I'm obviously doing something wrong.
So I'm setting my variable timing light to 36, having somebody rev until it stops increasing, slowly twist the distributor until the lighted line is at 0BTC, tighten the distributor lock down bolt, re-verify 36 at RPM, let RPMs drop to idle, adjust timing gun until the lighted line is at 0 on the balancer indicator dial. It leaves the light gun set at just under 2BTC.
I'm gonna try it again later but I'm obviously doing something wrong.
Last edited by brianPA; Aug 9, 2014 at 04:46 PM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
After adjusting the distributor until it was 36BTC all-in (~2400rpm) the idle advance is about 0BTC! That can't be right. I just checked it twice, too. Any idea what might be the issue here?
So I'm setting my variable timing light to 36, having somebody rev until it stops increasing, slowly twist the distributor until the lighted line is at 0BTC, tighten the distributor lock down bolt, re-verify 36 at RPM, let RPMs drop to idle, adjust timing gun until the lighted line is at 0 on the balancer indicator dial. It leaves the light gun set at just under 2BTC.
I'm gonna try it again later but I'm obviously doing something wrong.
So I'm setting my variable timing light to 36, having somebody rev until it stops increasing, slowly twist the distributor until the lighted line is at 0BTC, tighten the distributor lock down bolt, re-verify 36 at RPM, let RPMs drop to idle, adjust timing gun until the lighted line is at 0 on the balancer indicator dial. It leaves the light gun set at just under 2BTC.
I'm gonna try it again later but I'm obviously doing something wrong.
You really need to put an MSD 8985 timing tape on the balancer and try again with a straight up strobe light.
Get a Mr. Gasket curve kit for the centrifugal advance.....you want to be all in by 3000 rpm.....
12 degrees initial and 36 degrees total is a very good setting for a mild low-comp 350......
Good Luck!
Jebby
Melting Slicks
Joined: Oct 2012
Posts: 2,156
Likes: 273
From: Dunedin NZ.
Did you disconnect the vacuum advance? Disconnect vac advance and plug hose, take bands off weights and try and see if reaching 36 deg before 3000 rpm, if yes, all good check idle timing and note idle figure for later reference. If wont reach 36 deg before 3000 remove one of the advance springs and try again, you need to establish what the total is, have a read of Lars papers on timing if you have to start changing the advance springs or adjusting the vac advance.
Thread Starter
Racer
Joined: Dec 2011
Posts: 284
Likes: 4
From: Philadelphia Pennsylvania
No I hadn't disconnected the vacuum hose, maybe that is it. I drove it around at the current 2BTC idle/36BTC@3000 rpm and it feels sluggish especially at low RPMs.
Dumb question... which end of the vacuum needs to be plugged? The hose itself or the vacuum bulb on the distributor?
Dumb question... which end of the vacuum needs to be plugged? The hose itself or the vacuum bulb on the distributor?
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
No I hadn't disconnected the vacuum hose, maybe that is it. I drove it around at the current 2BTC idle/36BTC@3000 rpm and it feels sluggish especially at low RPMs.
Dumb question... which end of the vacuum needs to be plugged? The hose itself or the vacuum bulb on the distributor?
Dumb question... which end of the vacuum needs to be plugged? The hose itself or the vacuum bulb on the distributor?
I suspect the total number is wrong.......
Readjust to 12-15 initial....drive it around the block....if it
is MUCH better then.....go get a timing tape and a use a basic
inductive strobe light (no dial)
Jebby