Datsun l20b cam timing

[Sergio146]

Hello, for the truck that I am working on, the 1980 720 (l20b block with u67 head), should the cam dowel be set on #2 or #1 since when I removed the timing chain, it was originally set on #1. Reason I say it was original, is because it had an oem japanese timing chain kit considering that it has 188k on it currently. This also makes me curious as to if the timing is advanced since the distributor is slightly moved over to one side when adjusting the timing. Is it recommended to place the cam dowel to #2 to achieve the proper adjustments for my carburetor? 

[banzai510(hainz)]

L20s were set to number 2 from the factory more for emissions.  Power come on sooner. Can one tell who knows. Its also used to adjust out timming chain wear.

 

the dist should be timed close to say 10 or what ever your manual tells you. with alot of movement still left in the distrbutor slot to adjust timming to say 0-25dbtc.

 

if you have to crank it all to one side to get 10degs tthen the dist spindal is most like off. but if it was off a tooth I think you would notice and loose power in the top end

 

 

Edited May 27, 2022 by banzai510(hainz)

[Stoffregen Motorsports]

Without getting into which dowel to use, L motors like a little bit of advance in the cam timing. I set cam timing with a dial indicator on the valve tip to get it just right.

 

Ignition timing should be around 12 at idle and no more than 32-35 at full advance. Sometimes this means disconnecting the vacuum advance and plugging the vacuum source on the intake. Then remove one spring from the distributor cam and see if you can get close to those numbers. Removing the spring allows more timing to come in off idle, which L motors like a lot. Too much too fast can cause pinging.

[datzenmike]

Cam and ignition timing are not in the least connected. One does not affect the other.

 

The '80 720 did not come with a U67 head so either the engine was swapped or the head was so that chain has been off and probably put back on the wrong dowel. #2 is the stock location for an L20B.

 

Set on the #2 dowel and then check the cam timing by setting engine precisely to TDC on the compression stroke of the first cylinder. Now look through the cam sprocket and see where the U or V notch is in relation to the small horizontal etch mark on the cam thrust plat just behind it. It should look like this...

 

 

The notch in the cam sprocket should be directly below or slightly to the right of the etch mark. This relationship governs everything. If you have this it is perfectly timed. This picture is an L16/18 that are set on the #1 dowel but all must have the same notch to etch line relationship.

[Stoffregen Motorsports]

There is a bit of slop in the dowel pin hole on the gear. Before I tighten the cam gear bolt, I back the engine up to push the dowel to the right side or front of the hole, then tighten the bolt.

 

Beware that over the years, the dowel pin holes in many cam gears have been drilled or ground out to give more "adjustment". I've done it a hundred times at least. Chances are slim that you'll find one of those gears still in use, but there is a chance.