Timing a U20

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marcus550
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Timing a U20

Post by marcus550 »

There are 5 timing marks on my crank pulley. Is the first mark TDC? I've got the dizzy pointing at #1, both valves are closed on #1, piston is at the top of the stroke (but I can't tell EXACTLY where).

For smog-removed U20, what should the timing be?

What is the best method to rotate the engine by hand? I can't get a socket AND ratchet on the crank pulley; there simply isn't enough room. A wrench on the alternator just spins the alternator and nothing else. So, trying to rotate the engine by hand to seek TDC is impossible as far as I can tell.
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Re: Timing a U20

Post by jrusso07 »

First notch (widest notch) is TDC. Each other one 5 degrees (5' ,10, 15' 20)

Smog timing is 0 degrees, non smog is 16 BTDC. But you need to have the non-smog distributor cam and springs. The non smog dizzy cam is marked with 7.5. Some say the springs aren't necessary...thats good because you can't buy them.

I rotate the engine by putting the car in gear (like 2nd) and pushing it forward to move the engine just a bit each time. Use reverse if you can't push it forward. This moves the engine a few degrees at a time. Removing plugs makes this easier...but it isnt that hard. I also bought a socket handle that just has a sliding drive. It is thin enough to get on the crank bolt...sometimes a breaker bar will fit...but you only have a few degrees of range until you hit the fan

At TDC Timing mark on cam gear should be at 3 o'clock looking at it from front. Should line up with a silver link on the chain.
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Re: Timing a U20

Post by notoptoy »

With the car in neutral, I rotate using the fan blade with one hand and by putting tension on the long end of the fan belt with my other hand. Works like a charm, especially if the plugs are out.
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Re: Timing a U20

Post by fj20spl311 »

You have the engine near TDC firing on #1 Plug with the two cam lobes pointing up (see your picture) as compared to them pointing down that would be 360 crank degrees out.

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Re: Timing a U20

Post by bakerjf »

I'm with Joe, but instead of pushing the car, I jack the passenger rear wheel and turn it by hand. Good time to adjust the valves...
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Re: Timing a U20

Post by Gregs672000 »

A timing light will make this a whole lot easier! In the mean time, set the engine to proper timing (17 or 0), switch the key on, rotate the dizz until the point spark, lock her down, you'll be pretty close. BTW, as I think Phil was saying, it looks to me that you're 180 out on the dizzy because on my car (when I ran a dizzy!) I think #1 plug wire was at about 4 o'clock on the cap, and was the furthest forward cylinder. However, it makes NO difference in running since #1 and #4 are interchangeable, so as long as the wire goes to the right plug it will be fine. Clear as mud? Let us know!
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Re: Timing a U20

Post by jamesw »

That looks right.

It doesn't matter where the rotor is pointing as long as you put the #1 plug wire there (based on the picture where both cam lobes for #1 are pointing up).

So - put on the cap, put on the wires (dizzy rotates CC and firing order is 1-3-4-2) and fire it up!

Then use your timing light to set the exact timing.

Wear ear plugs in case you get a backfire.

Good luck!
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Re: Timing a U20

Post by dbrick »

Add a fire extinguisher to the tool list. If the crank mark is on TDC, either #1 or # 4 is in firing position, it's the one with the valves closed. If in doubt about smog or no smog distributor, set it at TDC. You will eventually need a timing light to do it correctly.

If you can't turn the engine with the fan because the fan spins freely, you need to get a new fan and remove the fan clutch :D

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Re: Timing a U20

Post by Down under 311 »

Not wanting to high jack this thread - however has anyone got the issue of needing to put the timing at around 25 btdc ? Had thought wear in dizzy was issue but just placed new one in with new cam and springs and presto still 25 btdc still provides the best result ( ps has Petronix ).
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Re: Timing a U20

Post by Mainer311 »

If you put the transmission in 5th, you will have the best mechanical advantage to turn the engine using the rear wheel method. I somehow shimmy a ratchet and socket onto the pulley nut and turn mine that way.
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Re: Timing a U20

Post by Gregs672000 »

Trying to static time the engine by having to move the crank by pushing the car in gear would be very frustrating without a helper! I assume the fan shroud gets in the way for the ratchet huh? I run a Datsun 310 electric fan etc so mine is more easily accessed. Sometimes a short ratchet works if the plugs are out and you're not fighting compression.
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Re: Timing a U20

Post by JohnnyMac »

I think I had to put the socket on the crank, then put the ratchet handle into the socket.
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Re: Timing a U20

Post by jasmith1975 »

Bringing this thread current as I'm trying to time my '68 U20 w/smog.

I read through Gary Boone's dizzy tech wiki which was helpful in identifying the type of dizzy installed (yes I have the dreaded 17.5 smog version). All other smog components (pump, hoses, connections) are present and appear to be operational. So safe to assume I've got some work ahead to desmog/recurve the dizzy (or pickup an EI more likely). But that's for another day as I'm just looking to get her running reasonably well as is.

Anyway, here's my issue. The car idles from <500-1,500 rpm with an occasional dieseling and light backfire/exhaust pop. I thought the erratic idle might be dizzy/timing related and decided to do some maintenance. Points were checked and regapped. Lubed dizzy in the usual spots and put back together. Ok all good there. On to time the engine, which I understand for smog U20's is 0 TDC. So when I gunned my timing it was at 32 BTDC. :shock: Now this was with vac advanced still connected. So I read Keith Williams tech wiki on SU carb tuning that said this:

Where does the vacuum advance from the distributor go?

The roadster uses ported vacuum from the carbs to operate the vacuum advance. This provides no advance at idle, maximum advance off idle and at cruise, and little of no advance at wide open throttle. The 1600 vacuum port is on the bottom of the rear carb. The 2000 vacuum port is usually on the top of the front carb but can sometimes be found on the top of the back carb. The hose barb on the manifold is for emission controls. If this port is used for the distributor vacuum advance the advance will be maximum at idle. This increases the idle speed making setting the carbs difficult.


So I pulled the vac advance hose off the dizzy, plugged the hose with a golf tee and timed it again. Only it was running rough/near stalling. I feathered/locked the throttle to hover around 1k rpm to get a good timing number. Now timing was around 17ish BTDC. Something still seems off.

Forgive the noob-ness of my question(s):
i) Should I time the car to 0 TDC with vac advance connected or no? If no, can I just plug the hose with a golf tee or do I need to plug the vac advance on the dizzy?
ii) Why would the car be running 32 degrees advance at idle? Shouldn't total advance be around 3-3,500 rpm?
iii) Any other things to check before killing more brain cells?
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Re: Timing a U20

Post by SLOroadster »

You should time it at 0 degrees advance on the stand (because it has 17.5 degrees built in with the smog distributor cam) at idle. At 3500 rpm, all the advance should be in, and you should see about 34 degrees advance.

Off throttle crackle is common with the U20. If it diesels at shutdown, its too lean, and/or has a vacuum leak, likely at the throttle shafts.

Funky idle could be poorly balanced carbs, or a hung choke causing one carb to be correct, the other very rich. Make sure both the jets on the bottom of the carbs snap all the way up with the choke off.

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Re: Timing a U20

Post by jasmith1975 »

SLOroadster wrote: Tue Jun 15, 2021 2:42 pm You should time it at 0 degrees advance on the stand (because it has 17.5 degrees built in with the smog distributor cam) at idle. At 3500 rpm, all the advance should be in, and you should see about 34 degrees advance.

Off throttle crackle is common with the U20. If it diesels at shutdown, its too lean, and/or has a vacuum leak, likely at the throttle shafts.

Funky idle could be poorly balanced carbs, or a hung choke causing one carb to be correct, the other very rich. Make sure both the jets on the bottom of the carbs snap all the way up with the choke off.

Will
Thanks this is helpful. I set timing to 17.5 BTDC (previously 32) with vac advance on. Seemed reasonably happy so I tinkered with the carbs/idles and got them synced. Ok all good. Hooked throttle springs back on and fired her up to an awful stumbling, coughing sound. Forgot to tighten the dizzy :roll: Ok, checked timing again and it was off, so tried moving it to 0 TDC now that carbs were synced. That seemed good and I tightened down the dizzy. After turning car off and on, somehow the carbs are way off with the rear hissing sharply and sucking much more air than the front.

Checked jets and they're fully seated. Sounds like I have to tinker with the idles again. :oops: