Great question! So technically, there's nothing wrong with a vacuum gauge to set timing. In fact, there's a reasonable argument to be made that with bits of the engine not necessarily being as they came from the factory, and with fuel being different than it was when the car was built, the spec in the shop manual isn't really meaningful. That said.... just because it's not the same timing mark as what you should use doesn't make it useless. It's a good starting point, and then you can advance a few degrees to compensate for the fuel (ethanol burns slower than pure gasoline, so you want the spark to start just slightly sooner). The other thing (and this is why I specifically don't use only a vacuum gauge to check timing) is that a vacuum gauge has no way to tell you if the advance mechanism in the distributor is working properly. In other words, it'll only help you set timing at idle. If the weights in your distributor are sticking and it's not retarding all the way, you'll happily set the timing at idle and then find it's wrong for the rest of the RPM range. A timing light is a good way to verify it's working properly, so you can diagnose other issues. I guess in my case, I have a Sun distributor test machine, so I can check the advance and use a vacuum gauge.... but that's just me showing off, and is more work anyway. Long story short: can you do it with a vacuum gauge? Absolutely. Just be aware that it's limited to checking timing at idle. A vacuum gauge is a fantastic tool though. It can prompt you to check timing, but can also identify potential issues from sticking valves to improper mixture to a timing chain that's skipped a tooth. If you have one special diagnostic tool to go with the average wrenches and screwdrivers, a combination vacuum / fuel pressure gauge should be it.
Another Outstanding video and presentation.
Thanks again!
Had to watch again. Great video! Part two is great too.
Thank you!
So good to hear! Thank you!
What are your thoughts on setting the timing using a vacuum gauge? Thats how ive been do8ng it on my TR6.
Great question! So technically, there's nothing wrong with a vacuum gauge to set timing. In fact, there's a reasonable argument to be made that with bits of the engine not necessarily being as they came from the factory, and with fuel being different than it was when the car was built, the spec in the shop manual isn't really meaningful. That said.... just because it's not the same timing mark as what you should use doesn't make it useless. It's a good starting point, and then you can advance a few degrees to compensate for the fuel (ethanol burns slower than pure gasoline, so you want the spark to start just slightly sooner).
The other thing (and this is why I specifically don't use only a vacuum gauge to check timing) is that a vacuum gauge has no way to tell you if the advance mechanism in the distributor is working properly. In other words, it'll only help you set timing at idle. If the weights in your distributor are sticking and it's not retarding all the way, you'll happily set the timing at idle and then find it's wrong for the rest of the RPM range. A timing light is a good way to verify it's working properly, so you can diagnose other issues. I guess in my case, I have a Sun distributor test machine, so I can check the advance and use a vacuum gauge.... but that's just me showing off, and is more work anyway.
Long story short: can you do it with a vacuum gauge? Absolutely. Just be aware that it's limited to checking timing at idle. A vacuum gauge is a fantastic tool though. It can prompt you to check timing, but can also identify potential issues from sticking valves to improper mixture to a timing chain that's skipped a tooth. If you have one special diagnostic tool to go with the average wrenches and screwdrivers, a combination vacuum / fuel pressure gauge should be it.