Just bought a 521

[mainer311]

I could be wrong, but the rocker ratio on this seems backwards.

[banzai510(hainz)]

yeah I know it seems backwards. but maybe what we been reading was backward all these years. anyway the drawing is correct for the smaller or taller pads to get it in the center wear pad.

These Ford Pinto guys should know what they doing anyways.

 

I always read closer to the pivot point will increase the lift but your on the down ward side of the hump so I dont get it. going by this statement I could just lower my pivot post down a little to get more lift!!!! Ha or on a datsun raise the pivot post. who knows. To me its going to be TDC on that high point either way

Edited February 10, 2021 by banzai510(hainz)

[datzenmike]

It's cantilever with the pivot point at the adjustment then the cam and then the valve, unlike say a GM where the pivot point is between the push rod and the valve. Measure between pivot and cam and cam to valve. The cam to valve should be 1.48 times longer than the pivot to cam.

[mainer311]

7 minutes ago, datzenmike said:

It's cantilever with the pivot point at the adjustment then the cam and then the valve, unlike say a GM where the pivot point is between the push rod and the valve. Measure between pivot and cam and cam to valve. The cam to valve should be 1.48 times longer than the pivot to cam.

Right, I tried looking up rocker ratio stuff and all I get is SBC crap with push rods. Apparently, cam-on-rocker-arm (CORA) is such that the rocker ratio actually changes depending on where in the cycle it is.

[datzenmike]

Yup. As the lobe comes round it's closer to the valve so the rocker ratio is slightly decreased and only hits 1.48 when at full lift and centered on the rocker pad. As the lobe rotates the ratio increases as it closes. Talk about asymmetric.

[datzenmike]

Mainer!!! Did you say some of your replacement valves were a hair longer than the original ones?????

 

Diameter

intake...... 42mm

exhaust... 35mm

[mainer311]

8 minutes ago, datzenmike said:

Mainer!!! Did you say some of your replacement valves were a hair longer than the original ones?????

 

Diameter

intake...... 42mm

exhaust... 35mm

 

Nope, exactly the same. I measured a set that I pulled out of the head, and they were exactly the same as the SI stainless valves that I got:

 

Exhaust: 4.620"

Intake: 4.580"

 

I went 1mm over on the intake valves, so 43mm. Exhaust is the same at 35mm. Exhaust seats were cleaned up, and intake seats were re-cut to center the seat on the 43mm valve.

 

You can tell that the intake valves are shorter when you look at the heights of the pivot ball. The pivots are higher to get the same lash, which makes sense.

Edited February 11, 2021 by mainer311

[datzenmike]

Sorry I may have confused things. I meant length stood up. Same length as the original valves? Also intake and exhaust should be the same length.

[banzai510(hainz)]

2 hours ago, mainer311 said:

Exhaust: 4.620"

Intake: 4.580"

I think this is the lengths

[mainer311]

18 minutes ago, datzenmike said:

Sorry I may have confused things. I meant length stood up. Same length as the original valves? Also intake and exhaust should be the same length.

New and old valves are the same lengths, but intake and exhaust are not.

 

The valves that I pulled out have the Nissan symbols on them and they’re not the same between I and E.

Edited February 11, 2021 by mainer311

[datzenmike]

God damn the intake are a mm or so shorter.

[mainer311]

1 minute ago, datzenmike said:

God damn the intake are a mm or so shorter.

 

Yep.

[banzai510(hainz)]

cant you wack the top off if longer to make them same size?

[mainer311]

Why would I want to? The longer valves make my situation better. Plus, the tops of valves are usually case hardened, so best not to mess with that.

[banzai510(hainz)]

2 hours ago, mainer311 said:

Why would I want to? The longer valves make my situation better. Plus, the tops of valves are usually case hardened, so best not to mess with that.

keep lash pads same size if all the seats are the same

 

im not getting the longer part as it goes back the Rocker arm center wear pad. you either screw up the rocket pivot post and then put the correct lash pad in

Edited February 11, 2021 by banzai510(hainz)

[mainer311]

Longer valves means I can get away with thinner pads.

 

Now that I think about, Nissan used different valve heights because they needed more spring preload on the larger diameter intake valves.

Edited February 11, 2021 by mainer311

[datzenmike]

Check out the Z series valves. They are slightly longer.

 

 

Z24

 

Intakes........ 4.8858 to 4.8976"

Exhaust....... 4.9252 to 4.9370"

 

They uses a different retainer too.

[mainer311]

I'm replacing my timing chain oiler peg in the front of the block because the one that's currently in there is worn away by the chain on one side. 

 

Does anyone know the correct orientation? I'm not convinced the one that's in there is correct. Are they just press fit into the block?

[datzenmike]

They press in and that's not the chain oiler, though some might get on it. The chain oil is from a small oil hole on the front cam tower. Look and you'll find it. The oiler peg is for the worm gear on the crankshaft that drives the oil pump and distributor spindle.

 

Below you can see it's not aimed at the chain.....

[banzai510(hainz)]

30 minutes ago, datzenmike said:

The oiler peg is for the worm gear on the crankshaft that drives the oil pump and distributor spindle.

I didnt know that!!!!!!!!!

 

some said the Z car motors or the Z series didnt even have these oilers

[datzenmike]

I was looking at the front cam tower one day and saw this oil hole and wondered why they would have two for the same job. You can see the bottom one doesn't aim at the chain at all but shoots out at the drive spindle that is diagonally across the front of it.

 

The chain tensioner is also oil fed and some would get on the chain.

[mainer311]

Interesting. I did notice the hole in the front cam tower the other night. As for my front peg, it’s definitely shooting at the 4 o’clock position, so wrong. Glad I ordered another one.

[datzenmike]

Not like the picture?

[mainer311]

1 hour ago, datzenmike said:

Not like the picture?

Nope. The dimple on the top is always opposite the hole. Here’s what mine looks like currently:

 

[mainer311]

My MD Machine front gear cover came today. Has an integrated spark plug wire loom for routing across the front.