Timing chain out of time

[Randog]

Howdy,

My father and I have been changing the head gasket on a 1973 Datsun 620. Neither of us has ever worked with an over head cam engine before, so, not knowing any better, when we took the camshaft off we made the mistake off letting the timing chain loose, and unfortunately, in our effort to get it back up, we lost the timing for the camshaft. I've read that in order to correct that, you need to take the front engine cover off. Is that true? It looks like it would be time consuming. Isn't there a way to time it by finding top dead center?

[Laecaon]

No, and here is why.

 

By letting the chain drop you have let the spring tensioner pop out. It is impossible to put back without taking the front cover off.

 

It is not that terrible to do.

 

Good luck!

[hang_510]

welcome.

 

true.

also true.

if it wasnt @ TDC when you pulled the head the first time, you can set it @ TDC when its off the second time.

[Laecaon]

Well once the front cover is off, might as well set TDC on head and block. Also dont put the front cover on until the chain is on. Just in case of any more chain drops.

 

Just turn the block over til pistons 1&4 are up.

 

Turn head over til the v notch in the cam gear lines up with dash on the cam. Like this:

[Skib]

whats your location?

[620fever]

I'm pretty green when it comes to engine work and I've slowly been doing this project, it really isn't very hard there's a video:

 

 

And I found the How to Rebuild your Datsun book very helpful. With all the correct tools and parts this could have been a fairly quick job.

[Randog]

But...what does the tensioner have to do with whether the top and bottom sprocket are in time with each other?

 

Well, anyway, so the oil pump, distributor, and oil pan all have to come off, is that right? My manifolds are already off. Does anything else have to come out? Keep in mind, have haven't pulled the engine, its still inside the engine compartment.

[banzai510(hainz)]

You dont have to take the oil pan off just loosen the bolts so it drops a little to help get the front cover back on w/o tearing the oil pan gasket. Unless the tesioner fell in oil pan. Put even then its not going to get sucked up(i dont think)

[Bleach]

But...what does the tensioner have to do with whether the top and bottom sprocket are in time with each other?

The tensioner must be pressed in all the way to allow the chain to fit up and over the upper sprocket. With it fallen out like it has now you will not be able to assemble the upper sprocket. If you did assemble the upper sprocket then the chain must be really relaxed and the tensioner fell all the way out and is likely resting in the oil pan or down by the lower sprocket.

Well, anyway, so the oil pump, distributor, and oil pan all have to come off, is that right? My manifolds are already off. Does anything else have to come out? Keep in mind, have haven't pulled the engine, its still inside the engine compartment.

You will likely want to remove the radiator to get yourself some room to work. Take the alternator off the engine too, the radiator fan, and front pullys obviously...

[ggzilla]

The tensioner has nothing to do with whether the top and bottom sprocket are in time with each other. But the cover needs to come off to put the tensioner in.

[Randog]

Alright. Its all apart and parts are ordered. Thanks a million!

[banzai510(hainz)]

key is having the 4 hole cam sprocket(so you can see the V on back thru the hole when installed) and the nice jap chain with the brite links!

[Laecaon]

key is having the 4 hole cam sprocket(so you can see the V on back thru the hole when installed) and the nice jap chain with the brite links!

 

I decided the bright links are nice, but not necessary. On my friends motor I tried just setting the crank at TDC and the head there too. Set the chain on (there were no bright links...) and then counted to make sure. Sure enough lined right up. I would say though when setting the head to TDC remember what hole you used for the cam dowel.

[banzai510(hainz)]

Brite links are good for the new Datsun guys. But I notice chains with no brite links are made in Taiwan

 

But like you did just go with the marks on the dash up top and the crank Zero. it will get you there unless you have the Made in USA cam sprocket them youll never know if its truly lined up as you wont be able to the the V and the dash.(Melling ,Cloyes kit has these spockets) Dont tget those.