Input requested RE: cam timing

[Galaxybj]

I am preparing to remove the head on my Z and in setting things to TDC I have found the #1 timing mark on the cam sprocket falls between two chain links, rather than in the middle of a link as photos show and past experience has been. There is no "bright" link in the chain that I have been able to find. I have cleaned it, but not one link stands out from the others. The notch on the camshaft sprocket is just to the right of the line on the locating plate as it should be. The crank pulley TDC mark is lined up with the timing pointer. Rotor in the distributor is on #1. Cam lobes for #1 are at 10 and 2. So it is on TDC. Any ideas? Any reason to be concerned as long as I have a paint dot on the chain opposite the #1 mark on the sprocket? I have not not run across this before.

I have read previous posts on similar subjects and so there are no questions/comments as to my resources and abilities, I do have the Datsun factory service manuals for the 240Z (originals from 1971), a service manual from Henley Press (1971) and a Haynes manual. (was in this Z when I bought it). I have also rebuilt a couple of Datsun 4 cylinders for a 610 coupe and 620 pu. Though I am no professional, I do have some experience and knowledge, though not as much as some of you and that is why I am asking for assistance here.

Any input is greatly appreciated.

-Bill-

[Curtis240Z]

Sounds like your cam timing is correct. Either someone previously removed your chain and didn't line up the marked/bright chain link or you just need to rotate the engine a few more times until the chain links line up. The chain links don't line up with the spocket every time TDC comes up so you just need to rotate it again and check. The older chains I've seen only have a dimple mark on them instead of being bright.

[Galaxybj]

Ok, I cycled through TDC 10 times, never did the #1 sprocket mark align with the center of a link, nor did a marked or bright link appear. It was consistent with aligning between links. On the 10th cycle it aligned with the paint mark I had put on the chain. Maybe as long as I have the chain marked it won't make a difference. Any other thoughts?

[beandip]

There are two professional engine builders on this web site. Phred and Paul aka burrap . Not to say curtus240 isn't correct here . Gary

[Curtis240Z]

I've seen "mechanics" install the chain backwards with the marked/bright link is on the back side. If your Z is running fine just make sure you put the spocket back on the same link that you took it off of and you should be good. Another thing to check when you remove the spocket bolt is to note which of the three holes in the cam the spocket is indexed to. When the chain is installed correctly, the indexed hole, the spocket tooth and marked/bright link all are consistent.

Another check would be to remove the spocket bolt to see what hole the spocket is indexed to. If it is #2 or #3 you should be looking for the corresponding #2 or #3 on the spocket teeth to line up with the marked/bright link. Make sure you put the bolt back on before you rotate the motor so the spocket doesn't fall off.

[Galaxybj]

Curtis240Z, the #1 hole on the sprocket is the one aligned with the cam pin. SO everything indicates the cam is timed to #1 mark. My real question now would be why does the sprocket mark line up between links and not centered on a link as all photos show and my past experience has been? It appears I can proceed as long as I mark the chain next to the #1 mark on the sprocket, which I had previously done, unless someone has other input. I had wondered as you, maybe the chain was on backwards, but I did not see a mark or bright link on the backside either. -Bill-

[Curtis240Z]

The joys of buying a used car.....too bad we were to young to drive/buy them when these cars came out. :cheeky:

[Carl Beck]

Who is "we"?.... GalaxyBJ and I had them when they were new<http://www.classiczcars.com/forums/images/smilies/icon_smile_lachuh.gif>

Carl B.

Teeth and chain line up on the half link when the head has been milled (too far?) or if the cam tower shims are too thick?... You may know more once you get the head to a good machine shop and have it checked... No bright link, an aftermarket chain... or repairs done in a z shop with lots of spare used parts..

[Phred]

Galaxybj,

Don't worry about the shinny link. Its probably an aftermarket chain,and most of those didn't have marked links. The shinny link is really only usefull when the front cover is off, and you can see the dot on the crank gear. Then its just a visual check, with the one shinny link on the crank dot, and the other on the cam dot. Just be sure the crank is at TDC, the rotor aligned, and the notch in back of the cam gear is resonably lined up with the mark on the cam thrust plate. If the gear notch is trailing the mark on the thrust plate, the cam is slightly retarded, due to surfacing or chain stretch.Try the #2 setting, which will advance the cam 4 degrees.

Phred

[Curtis240Z]

Who is "we"?.... GalaxyBJ and I had them when they were new

Carl B.

Ahh...the lucky few.

[Galaxybj]

As Carl said we had Z's as new. I bought my first one in July 1971 after returning from the Phillipines, 5/71 production. Unfortunately I sold it in 1984.

Carl and Phred, thanks for the info. At this time I am only planning on taking care of the head gasket, as long as that is all I find wrong once I lift the head off. I will get it checked by a machine shop while it is off though. The notch on the cam sprocket is on the right side of the mark on the plate, so it should be ok. Especially since it is still set on the #1 mark.