Datsun Roadster Forum-311s.org

Hello friends, I finally had the head of my U20 rebuilt with new custom c and c'd valves, seals etc. Im reassembling and need to pick your brains. I have looked through a bunch of info here and on the web in general, but want to make sure I have this right. Pics attached engine TDC crank pointer to 17 degrees before TDC. #1 valves closed, rotor points at cyl #1 on dizzy. Mark on cam gear at 3 o'clock. Play in chain and between Cam to crank is noticable. Thoughts?

More pics

It's not usually timed at 17° BTDC it's timed @TDC ( CAM timed), unless it's a gear that allows adjustment , chain worn ?
Good shape on cam gear teeth ? ( all teeth look the same ) and crank gear ?
Use a long screw driver to apply pressure to fully use tensioner then see where it lines up

that gear shows some "Christmas Tree" wear, I would check the other gears, time for gears and chain?

That gear is both worn and modified to allow CAM timing adjustment (not IGNITION timing). Stock cams don't have two locator pins, and to use an adjustable cam gear you remove the pin in order to allow you to rotate the cam gear independently from the cam and then be locked down with the mounting bolts (I have one). Looks like someone figured out how much adjustment was desired and drilled another locator hole for a pin. We don't know if the cam was advanced or retarded, or how much, and that can make a big difference in where the engine makes power, and how close the piston gets to the open valves.

Normally, you observe the other gears to make sure their timing marks line up, but you can't do that with the front cover on. So, we'll assume those are right and that if you align the far LEFT mark on the crank pully with the pointer on the front cover then those gears should be aligned properly (top dead center). Then the cam should be in a position such that the cam gear (with the pin in the stock hole) with the chain on it slides onto the cam and looks like the attached pic (ignore the chain timing mark... the chain had rotated a tooth, but the bolts and pin position are correct). You may have to move things SLIGHTLY (cam, crank) but it should slide on the pin and remain like the Pic (this is all done with no chain tensioner in place). Once bolted down, spin the engine by hand (no spark plugs) a full rotation or two then align your crank timing mark to TDC again and make sure the bolts are like the picture.

As noted, that gear appears worn and it may be wise to replace it. Cam Timing adjustment is an "advanced" tuning consideration, so using a stock gear is best unless you're messing with non-stock cams or looking to modify your powerband. We also don't know anything about the other gears or the chain, which does stretch. Tell us more about what's been done and we'll offer our best advice as we want you to be successful!
(Ya, damn pic upside down, but select it and it will be right.... someone want to school me on this? )