1993 Sea Ray/ Mercruiser 4.3/ Thunderbolt IV ignition timing

[440roadrunner]

Can someone tell me for certain what the initial timing is on a 93 Merc V6 4.3/ Thunderbolt IV ignition? I've searched........there is nothing to unplug like some of the later modules......

And before you get off the track this does not appear to be a V or VI. It has the small module mounted on the dist outside, with trigger inside.

Dist is worn clear out and we have new one on the way. I'll need to know where to set it. I have a good automotive knowledge and have no trouble setting it in "close" to fire.

A word or two about the markings on the timing tab would help, although I can check it with a "dial up" light which I dislike.

This is my neighbor's boat, I'm trying to help him out.

 

[alldodge]

TB-4 for 1993 V6 in manual 18 list 8* BTDC

 

[440roadrunner]

Hi I don't know what you mean TB-4 or manual 18 but anyway looks like 8BTDC I assume that you just set this at low idle? I can find nothing on this system that seems to be a disconnect for the advance in the unit
Thanks for the reply

 

[San_Diego_SeaRay]

Hi I don't know what you mean TB-4 or manual 18 but anyway looks like 8BTDC I assume that you just set this at low idle? I can find nothing on this system that seems to be a disconnect for the advance in the unit
Thanks for the reply

TB-4 = Thunderbolt IV, which is what you have. Manual 18 = Mercruiser Service Manual #18, which is the manual that covers your engine. I just read the timing excerpt from Manual 18 and I agree, there seems to be nothing to disconnect on the distributor to set to "base timing" the way there is on V8 engines. I've attached the Ignition section of Manual 18.

 

[alldodge]

Agree, TB4 is point and shoot, no base timing mode. 650 RPM

 

[achris]

... there seems to be nothing to disconnect on the distributor to set to "base timing" the way there is on V8 engines....

It's nothing to do with V8 vs V6... It's to do with the ignition system. Thunderbolt IV is a basic system with an advance curve programmed into the module. Modules have different curves, as denoted by the module number, for different engines. To time the engine, set the engine running at 650rpm and adjust the timing as you would any other engine.

Thunderbolt V is the same sort of system, but with a lot more smarts inside. Among other things, it will adjust the timing to keep the idle speed steadier, and at the preset speed. You need to set the module into 'base mode' to get the right set on the initial timing because of this.

If you'd like to know more about the systems, -> HOW THUNDERBOLT IGNITION WORKS

Chris.......

 

[San_Diego_SeaRay]

It's nothing to do with V8 vs V6... It's to do with the ignition system. Thunderbolt IV is a basic system with an advance curve programmed into the module. Modules have different curves, as denoted by the module number, for different engines. To time the engine, set the engine running at 650rpm and adjust the timing as you would any other engine.

Thunderbolt V is the same sort of system, but with a lot more smarts inside. Among other things, it will adjust the timing to keep the idle speed steadier, and at the preset speed. You need to set the module into 'base mode' to get the right set on the initial timing because of this.

If you'd like to know more about the systems, -> HOW THUNDERBOLT IGNITION WORKS

Chris.......

Ah, I see. That clarifies things. Thank you Chris.

 

[440roadrunner]

Thanks you guys, I had found that "how it works" article before I posted this.

I've used a number of 4 pin HEI modules to convert ignitions on non--marine stuff. LOL I once had a 20R Toyota in a Cletrac dozer- Toyota dist driving a GM 4 pin HEI. My Dart when it was together used a Mopar breakerless distributor driving an HEI 4 pin

In any case looks like I'm on the right track

 

[Jeepmike]

Does anybody have a pic of the the timing marks? My paint is worn off and it's hard to set exactly. Thanks

 

[San_Diego_SeaRay]

Does anybody have a pic of the the timing marks? My paint is worn off and it's hard to set exactly. Thanks

My timing marks are worn off as well. What didn't wear off is the deep groove that runs across the harmonic balancer. When that is lined up with the "arrow", then you are at 0 degree Top Dead Center. The entire circumference of the balancer is 360 degrees. If you need to be at 10 degrees before top dead center, then you're "mark" should be at 1/36th the circumference of the balancer away from the grove. I'm sure if you measured the diameter of the balancer and use pi you could figure out the math to get the exact mark distance from the grove. Truth be told, I just eyeballed mine. Said "that looks like 1/36th the circumference to me and the engine sounds good, so it's Miller Time." Otherwise you can also buy an cheap aftermarket timing mark and install it. You'd want one for whatever engine you have...350, 454, etc.

EDIT: Actually I should add, that if you buy or rent a good digital timing light, they will actually do the work for you. You just line up the arrow with the grove to be 0 degrees and then set the timing light to be 10 degrees BTDC. You'll see the mark shift and the you turn the distributor until the arrow and grove are lined up again and you're at 10 degrees BTDC. By the way I'm just using 10 degrees as an example. Not sure what your engine calls for.

 

[Jeepmike]

My timing marks are worn off as well. What didn't wear off is the deep groove that runs across the harmonic balancer. When that is lined up with the "arrow", then you are at 0 degree Top Dead Center. The entire circumference of the balancer is 360 degrees. If you need to be at 10 degrees before top dead center, then you're "mark" should be at 1/36th the circumference of the balancer away from the grove. I'm sure if you measured the diameter of the balancer and use pi you could figure out the math to get the exact mark distance from the grove. Truth be told, I just eyeballed mine. Said "that looks like 1/36th the circumference to me and the engine sounds good, so it's Miller Time." Otherwise you can also buy an cheap aftermarket timing mark and install it. You'd want one for whatever engine you have...350, 454, etc.

EDIT: Actually I should add, that if you buy or rent a good digital timing light, they will actually do the work for you. You just line up the arrow with the grove to be 0 degrees and then set the timing light to be 10 degrees BTDC. You'll see the mark shift and the you turn the distributor until the arrow and grove are lined up again and you're at 10 degrees BTDC. By the way I'm just using 10 degrees as an example. Not sure what your engine calls for.

My timing marks are worn off as well. What didn't wear off is the deep groove that runs across the harmonic balancer. When that is lined up with the "arrow", then you are at 0 degree Top Dead Center. The entire circumference of the balancer is 360 degrees. If you need to be at 10 degrees before top dead center, then you're "mark" should be at 1/36th the circumference of the balancer away from the grove. I'm sure if you measured the diameter of the balancer and use pi you could figure out the math to get the exact mark distance from the grove. Truth be told, I just eyeballed mine. Said "that looks like 1/36th the circumference to me and the engine sounds good, so it's Miller Time." Otherwise you can also buy an cheap aftermarket timing mark and install it. You'd want one for whatever engine you have...350, 454, etc.

EDIT: Actually I should add, that if you buy or rent a good digital timing light, they will actually do the work for you. You just line up the arrow with the grove to be 0 degrees and then set the timing light to be 10 degrees BTDC. You'll see the mark shift and the you turn the distributor until the arrow and grove are lined up again and you're at 10 degrees BTDC. By the way I'm just using 10 degrees as an example. Not sure what your engine calls for.

Ok thanks. I'll include the pic on my timing mark on my TBiv 4.3. I'd say I'm 6° too advanced...does that look correct?

 

[San_Diego_SeaRay]

Ok thanks. I'll include the pic on my timing mark on my TBiv 4.3. I'd say I'm 6° too advanced...does that look correct?

How are you doing this with a screenshot from a cell phone? Was the engine turning when you took this picture? If it was and you just captured a video frame and this is indeed when the #1 cylinder fired, then it looks to me like you're about 1 or 2 degrees advanced BTC. I think I can make out an "8" and the increments are 2 degrees. If your engine calls for 10 degrees and you're firing at 2 degrees, then you're 8 degrees retarded, not advanced. Again, I'm not sure what your engine calls for at idle just using 10 degrees as an example.

 

[Jeepmike]

How are you doing this with a screenshot from a cell phone? Was the engine turning when you took this picture?

Ya. It was a video I paused to get a shot of the indicator.

 

[Jeepmike]

I'll see if I can attach the video.