86 720 z24 having issues after setting timing

[TimmyG]

18 minutes ago, datzenmike said:

100K is nothing. Invest $30 on a NAPA gasket and go from there. If the gasket IS bad, $30 is cheap fix. A blown gasket is not a good reason for rebuilding it. 

 

I don't think he's planning on doing more than just replacing the head gasket when he says "overhaul." At this point he could have a leaking intake gasket only, but most likely just the head gasket based on my experience. That one motor I tore apart that appeared to have only a leaking intake gasket was probably a fluke. I'm not convinced the head gasket was leaking on that one, but there was a milkshake on the valve train and a crankcase full of coolant ☠ 

[Riceboy12]

29 minutes ago, datzenmike said:

100K is nothing. Invest $30 on a NAPA gasket and go from there. If the gasket IS bad, $30 is cheap fix. A blown gasket is not a good reason for rebuilding it. 

I already have the head gasket kit. I’m not overhauling the whole engine just the head gasket. 

[Charlie69]

Buy the correct timing chain set.  Throw the one on it in the scap pile.

[TimmyG]

Well, he sent me some pics of the cam sprocket today because I suspected if it was the wrong sprocket (hardbody style with the keyed section) it could have slipped cam timing.... since the 720 cam has a dowel and the HB cam has a keyed section on the cam. 

 

Turns out he has a single tooth sprocket that has a dowel pin...what the... 

 

Maybe they did this on the early Hardbody trucks with the z24i ? His looks like this kit I found on ebay.

 

 

 

Anyways, the cam sprocket definitely did not slip because its on the dowel pin. Thinking head gasket at this point unless some ignition component crapped out randomly at WOT. Maybe a coil or the distributor. I offered to lend him a spare distributor and coil to test out. 

 

He says he can see the head gasket material blown out looking down into the timing cover. Wasn't able to get a clear pic from him of that one. 

[datzenmike]

OK.

 

All 720 Z24 use the dual chain, guides, tensioner and top and bottom sprockets.

 

The Z24i in the D21 Hardbody and the WD21 Pathfinder use the same st up till January '88. From January '88 till the end of the Z24i in August '89 a single cam sprocket and chain was used...... however the bottom sprocket, chain guides and tensioner were the same as the dual chain.

 

The cam dowel easily fits the single cam sprocket slot.

 

I did not know this. Had to look it up.

[TimmyG]

15 minutes ago, datzenmike said:

OK.

 

All 720 Z24 use the dual chain, guides, tensioner and top and bottom sprockets.

 

The Z24i in the D21 Hardbody and the WD21 Pathfinder use the same st up till January '88. From January '88 till the end of the Z24i in August '89 a single cam sprocket and chain was used...... however the bottom sprocket, chain guides and tensioner were the same as the dual chain.

 

The cam dowel easily fits the single cam sprocket slot.

 

I did not know this. Had to look it up.

 

Haha! Someone definitely bought a timing chain kit for that and bolted it into his z24. I was surprised when I first saw it, then even more surprised when I saw the cam sprocket had a dowel hole. Thanks for lookin that up. My hunch was correct. Figured it was from a z24i, just never seen it. So the bottom sprocket on the crank was a dual tooth used with that single tooth chain setup from the factory? Weird. 

Edited September 25, 2019 by TimmyG

[datzenmike]

Dual crank sprocket, same wide tensioner and guides. No sense re-designing it for single chain and it works exactly the same. These chains NEVER break, the sprockets would be worn down smooth first and it wouldn't happen without you hearing a commotion. Ever since the L16 they've been using the dual chain. The L series was incredibly over engineered.

 

Here is a main bearing from an L (yes on the left) and  KA which produced at least 50% more power than an L20B and twice what an L16 makes...

 

 

L and Z series, incredibly durable and long lasting.

 

 

Nissan just wanted to save some money I think.

[TimmyG]

35 minutes ago, datzenmike said:

Dual crank sprocket, same wide tensioner and guides. No sense re-designing it for single chain and it works exactly the same. These chains NEVER break, the sprockets would be worn down smooth first and it wouldn't happen without you hearing a commotion. Ever since the L16 they've been using the dual chain. The L series was incredibly over engineered.

 

Here is a main bearing from an L (yes on the left) and  KA which produced at least 50% more power than an L20B and twice what an L16 makes...

 

 

L and Z series, incredibly durable and long lasting.

 

 

Nissan just wanted to save some money I think.

 

Damn! That's cool. I have always thought the dual chains were too stout to ever break. Is it worth replacing them due to stretch? Just good practice to replace them with new sprockets after high mileage? Those L bearings are stout, too!

Edited September 26, 2019 by TimmyG

[datzenmike]

On the L series there was a mark you could check the position of to gauge stretch, and if found out of whack you could move the cam to the next dowel hole to adjust it. It's most helpful if you plane the head enough to throw the timing out. On the Z series this wasn't done nor is there anything in the FSM about any stretch or adjustment though the sprockets still had the extra holes. Maybe stretch doesn't happen and they discontinued any adjustments. I think it's true on the KA series also with the single slot... no adjustment is possible. 

[TimmyG]

5 minutes ago, datzenmike said:

On the L series there was a mark you could check the position of to gauge stretch, and if found out of whack you could move the cam to the next dowel hole to adjust it. It's most helpful if you plane the head enough to throw the timing out. On the Z series this wasn't done nor is there anything in the FSM about any stretch or adjustment though the sprockets still had the extra holes. Maybe stretch doesn't happen and they discontinued any adjustments. I think it's true on the KA series also with the single slot... no adjustment is possible. 

 

Interesting. So in theory the dual link chain lasts the life of the motor. 

[datzenmike]

I would think so. Many people change everything but it's the plastic guides and tensioner that show all the wear. The guides are plastic covered and when the chain rattles against the metal ... "Oh shit! The chains worn out"

 

 

On the L series when you can't get the V notch adjusted under or just slightly to the right of the horizontal etch mark above it on the cam thrust plate, it's considered stretched or the sprockets worn out, or both, and is replaced. The above is an L16/18 which comes from the factory on the #1 hole (so there's two more adjustments available for it) L20Bs are on the #2 hole.

[TimmyG]

11 minutes ago, datzenmike said:

I would think so. Many people change everything but it's the plastic guides and tensioner that show all the wear. The guides are plastic covered and when the chain rattles against the metal ... "Oh shit! The chains worn out"

 

 

On the L series when you can't get the V notch adjusted under or just slightly to the right of the horizontal etch mark above it on the cam thrust plate, it's considered stretched or the sprockets worn out, or both, and is replaced. The above is an L16/18 which comes from the factory on the #1 hole (so there's two more adjustments available for it) L20Bs are on the #2 hole.

 

How long did you work for Datsun? Lol. I like this type of info. Cool stuff...how things work.

[datzenmike]

2 hours ago, datzenmike said:

 

I did not know this. Had to look it up.

 

 Learned something today. Always assumed the Z24i had a dual chain.