Timing using vacuum

[pomester]

I've seen a couple of references to using a vacuum gauge to set engine timing. I've got a TO35 with the small timing hole hiding behind the tie rods and radius rods which makes being able to illuminate and observe with a timing light difficult. If I could use a vacuum gauge at the 1/8"npt plug at the manifold it would be much easier.

I've heard maximizing vacuum is the strategy. At idle? At PTO speed?

Any experience or tips?

Thanks
David

 

[Jim L WA]

I have no experience with that. What would timing have to do with how much vacuum is present at the manifold? I do agree with you on the difficulty of trying to see into that silly timing hole with a timing light.
I just timed my TO-20 by ear. Got it running, and then advanced the distributor until the engine didn't like it. It will become obvious. The backed it off a little and locked it down. It runs well, starts easy and doesn't kick the starter.

 

[pomester]

I have no experience with that. What would timing have to do with how much vacuum is present at the manifold? I do agree with you on the difficulty of trying to see into that silly timing hole with a timing light.
I just timed my TO-20 by ear. Got it running, and then advanced the distributor until the engine didn't like it. It will become obvious. The backed it off a little and locked it down. It runs well, starts easy and doesn't kick the starter.

That's about where I have it now. It's a brand new engine and I'd like to fine tune it. There's marks on the front engine cover and I put a notch in the front pulley while I could see #1 piston, but again the angles and sight lines make it practically impossible to time with any accuracy.

The comments I've seen indicate that highest(lowest) vacuum corresponds to best engine efficiency. Dunno. I haven't searched the web, thought I'd start here.

 

[Brown David]

What would timing have to do with how much vacuum is present at the manifold?

Try it and see. It could be explained out but I'm sure trying it would be very clear.

 

[pomester]

Try it and see. It could be explained out but I'm sure trying it would be very clear.

Ya, gotta get a vacuum gauge - there's a $20 one in my amazon basket ready for the next order unless I find something I like better. Made in China of course, but cursory googling hasn't shown me anything else compelling.

I may post this over at Ford too, I've got some of them and that community may have some insight also.

 

[Ericp351]

Vacuum can and should be used to check the condition on an engine. You may check any vintage Chiltons, Motor Book, old Auto Shop Text, et cetera for a handy vacuum based trouble shoot-chart. That said, I trust that it is seldom done routinely on these very low specific output classic work horses, save when sticking valves are suspected. You should not really on Vacuum to time! These are specked VERY conservatively (poor fuel tolerant+) , but if you "time by Vacuum" you will be way over advanced. Post Script- Timming Tape is cheap and at any speed shop, if you don't like the view from your plug (works for me/most) Vacuum gauges do have their place! Great for adjusting idel mix, et cetera + trouble shoot. I use them to often to dial in Power Valves on my Holley's. You may have-or can tap- a 1/8" plug by carb. Lastly, sissies with rice burners used to mount them to monitor their "economy Range" driving. Good Luck- Rock on.

 

[Fergster]

Like allready said you absolutely shouldn't use vacuum to set timing. With no load on the engine you will end up with over advanced timing. With 6to1 compression it's probably not as critical as far as engine damage but it won't run correctly and may detonate when its hot. That small hole in the bellhousing is a pain in the rear though. I used a degree wheel and made marks on the crank pulley and timing cover last time I had one apart. You can do basically the same thing by just rotating the crank to the timing spec viewed through that hole and make marks on the pulley to use a timing lite. Timing specs for to20 is 7 deg.btdc @400rpm and 31 at 2100

 

[Destroked 450]

If your still using points there’s a easy way to set timing without even starting the engine
With the distributor cap off roll the engine over till the rotor is nearing #1 position, shine a light in the timing hole and turn the engine until you can see the marks. Align the proper mark in the hole (7 degrees on your model), Loosen the distributor, turn the key on and then move the distributor forward and back very slowly until you see a spark from the points. You may what to do this a couple of times to insure you stop rotating the distributor just as the points spark.
Lock the distributor down and install the cap, your timing will be set at maybe 1-2 degrees advanced which won’t hurt a thing and the engine may actually idle a little better
If your one that has to have perfect timing set the flywheel mark a degree or two slower than spec
I learned this method back in the 70’s when I was wrenching for a living and building my own performance engines

 

[Bruce(OR)]

Using vacuum to set timing might be good way to get too much advance. Then again, set it to highest number, shut off engine and then back off dist so it starts the easiest. Still not the greatest. I did an engine with the timing hole upside down by cheating. line up the timing marks in the hole to either zero id you have an adjustable timing light or 6 (?) degrees if you don't. Get out a clamp. Get a straight edge. I used a 6 inch metal ruler. Clamp the ruler to the front bolster with the ruler about a 1/4 inch away from the front pulley.
Scribe a deep groove on the pulley that lines up with the ruler. White Fingernail polish the scribed line.
Start the engine. NOW use the mark on the pulley to set your timing.

 

[J.Wondergem]

Vacuum can and should be used to check the condition on an engine. You may check any vintage Chiltons, Motor Book, old Auto Shop Text, et cetera for a handy vacuum based trouble shoot-chart. That said, I trust that it is seldom done routinely on these very low specific output classic work horses, save when sticking valves are suspected. You should not really on Vacuum to time! These are specked VERY conservatively (poor fuel tolerant+) , but if you "time by Vacuum" you will be way over advanced. Post Script- Timming Tape is cheap and at any speed shop, if you don't like the view from your plug (works for me/most) Vacuum gauges do have their place! Great for adjusting idel mix, et cetera + trouble shoot. I use them to often to dial in Power Valves on my Holley's. You may have-or can tap- a 1/8" plug by carb. Lastly, sissies with rice burners used to mount them to monitor their "economy Range" driving. Good Luck- Rock on.

This is what I use mine for, never used it for timing.

 

[Mad Farmer]

If your still using points there’s a easy way to set timing without even starting the engine
With the distributor cap off roll the engine over till the rotor is nearing #1 position, shine a light in the timing hole and turn the engine until you can see the marks. Align the proper mark in the hole (7 degrees on your model), Loosen the distributor, turn the key on and then move the distributor forward and back very slowly until you see a spark from the points. You may what to do this a couple of times to insure you stop rotating the distributor just as the points spark.
Lock the distributor down and install the cap, your timing will be set at maybe 1-2 degrees advanced which won’t hurt a thing and the engine may actually idle a little better
If your one that has to have perfect timing set the flywheel mark a degree or two slower than spec
I learned this method back in the 70’s when I was wrenching for a living and building my own performance engines

Need to be sure the advance mech is in good condition (goes back to idle/no advance) to static time. Approach opening not closing the points, as you turn distributor.

You can be more accurate using an ohm meter or test light on the points to tell when they open (ohms go to infinity or light goes out with ign key on).

With new, or points without pits, you can crudely time it with a rolling paper. Put the paper in the points contacts and while tugging on the paper turn dist until the paper just slips/points open. I've done hundreds of old motorcycles and cars/trucks/tractors this way and when later tested with a light were always within 1-2 degrees of being correct.

 

[560Dennis]

Interesting post
I use vacuum gage to set idle mixture to maximum values steady needle warm engine. Got it up to 20 inches on engine with unknown hours . your engine Will vary, important to have steady needle. If not find the cause .
Also found top dead center of number one piston ,remove the spark plug. I will use a forney paint welder stick and mark the damper pulley and the engine referencing. Get my timing lighting light and a 12 battery for power. This way I don’t have to get into or under the tractor in cramped positions to find engine Timing. And make magneto adjustments .
Does your timing light have variable zero settings?