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86 720 z24 having issues after setting timing


Riceboy12

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So we re set the timing on my engine and it was running good for about 10 minutes. We noticed that it wouldn’t idle when we came to a stop. It got worse as we got back to the house. As I left the stop light we heard a clatter that sounded like valves so I took it easy back to the house. It died in the driveway and after starting it back it up it had a misfire. We found that the timing was off a little so we re set it agian and still runs like garbage. Could I have a blown gasket somewhere? No smoke and I don’t see any leaks. However there is this metallic gold flakes in my coolant reservoir. Truck run great up until this point. Oil still looks good. Also this z 24 has one timing chain compared to our other z24s that have two. This engine isent the original one. It was swapped in by previous owner. 

 

Here is a pic of the metallic flakes on drop box 

https://www.dropbox.com/s/ai9jmfu3r6pgkf5/Photo Sep 14%2C 12 39 18 PM.jpg?dl=0

 

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So far so good.

 

What was the timing set at? Should be about 30 BTDC

 

Why was the timing set?

 

 

 

Very common to blow the Z24 head gasket. Try a compression test. If two adjacent cylinders are low expect the gasket is blown between them.

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Like extremely off. Also wouldn’t it be smoking if it was head gasket? One of the neighbors thinks it could have been possible to have a loss of oil pressure. But I don’t think that would cause it to rough extremely rough like it does right? It would have died on before I got home I would have thought. If it’s just the head gasket, I’ll be happy.

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We set the timing because I knew it was probably off when I saw this...VSCDXpR.jpg 

He had complained a few times that the truck was a dog with no power. I knew he'd tuned the truck up with plugs, wires, cap, rotor, and made carb adjustments. So I asked him to send me a pic of his distributor bracket. This was the pic. Mine was set more towards the middle at 3 degrees so I figured his was off....

 

We marked the crank pulley timing mark with a silver sharpie for visibility, pulled the vaccuum line off the distributor,  and check the timing with a light.... it was so far off it wasn't even reading on the bracket. It was maybe 10 degrees to the right of zero...so 10 degrees after TDC. 

 

We set it to about 3 degrees BTDC. Put the vacuum line on. Adjusted the idle and mixture screw. It idled noticable better and sounded better. We drove it around the block maybe 2 miles with liberal skinny pedal. I had ridden in the truck before, but now it ripped! Way more power. 

 

We got to a stop sign and it tried to die on us. At the next light same thing, except when he took off it had major valve clatter. It was suddenly running very rough and clattering, with no power. 

 

Check the distributor and noticed it was still loose enough to turn by hand due to having one stripped out bolt (yes one, not two). I watched him tighten it, so I'm assuming he didnt realize it was stripped out as I was telling him careful not to overtighten it.

 

The distributor didnt appear to have moved during our test run. We put another bolt in the distributor from my parts truck,  rechecked the timing at 3 degrees BTDC, and tightened it down. Truck was idling poorly with a noticable miss. 

 

At this point I was trying to figure our of his head gasket took a shit since we got her firing better than ever then gave her hell for 2 miles. Yes, the engine was warm and it had plenty of oil and coolant. 

 

We took off the valve cover just to take a look and I noticed he had a single link chain, not dual link like all the z24 I've seen. His block says z24 and the engine has 8 plugs. Maybe someone used a KA24E timing chain kit? Anyway, nothing looked wrong under there. I'm really not sure why the motor is pissed. 

5DBzXKr.jpg

The rotor button is still in tact under dist cover. The truck started and ran the same when I put the  intake coil distributor wire onto the exhaust coil (left off the exhaust coil dist wire). So I guess the coil is still good. 

 

Truck doesn't smoke. There is gold flakes in his coolant for some reason. Not sure if that's gasket material? I'm still thinking his head gasket is leaking coolant into a cylinder, or maybe the intake gasket if he's lucky. 

 

 

Edited by TimmyG
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I was also thinking the cam sprocket might have slipped timing...but this sprocket I'm not familiar with like the normal z24 sprocket with 3 holes for the cam dowel. Is there a way we can check if this cam sprocket has moved? Seems likely this could cause all these issues suddenly. 

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Compression check will rule out the blown headgasket. There is a lot of guessing and speculation going on in different directions here. The jumping sprocket is pretty rare. A leakdown test is even better and will help find where the lack of compression is going IF that is the problem. Check that first then if good you have a spark or fuel problem. Keep it simple!

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Looks like a KA24E chain and sprocket. If it is I didn't know they were the same lengths.

 

My L, Z and KA24E cam sprockets. The KA on the right is thin and has no adjustment for chain stretch. I guess Nissan went this way to save a buck.

9pcybV1.jpg

 

I just went out and measured center of cam down to the bottom of the head on a Z24 and KA24E head. Both are withing 5mm or half a cent of each other, so a KA timing kit could theoretically work on a Z24 if the guides allow it.

 

I don't think there is near enough chain slack for it to jump a tooth but it could have been put on incorrectly on the rebuild. There appear to be no cam timing marks on the sprocket so about all you could do is wedge the chain so the timing chain tensioner can't fall out and move it one ahead and one behind what it is now and see if it improves.

 

A leak down test is much more definitive for where any lost compression went. Compression tests are unreliable, you may just have a low cylinder. It can point towards a blown gasket once badly blown out but not rule it out.

 

1 hour ago, TimmyG said:

 

He had complained a few times that the truck was a dog with no power....

 

....It was maybe 10 degrees to the right of zero...so 10 degrees after TDC. 

 

We set it to about 3 degrees BTDC. Put the vacuum line on. Adjusted the idle and mixture screw. It idled noticable better and sounded better. We drove it around the block maybe 2 miles with liberal skinny pedal. I had ridden in the truck before, but now it ripped! Way more power. 

 

 

 

Likely the gasket was failing and with the power so low from retarded timing it limped by, but as soon as it improved it blew out.

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31 minutes ago, datzenmike said:

Looks like a KA24E chain and sprocket. If it is I didn't know they were the same lengths.

 

My L, Z and KA24E cam sprockets. The KA on the right is thin and has no adjustment for chain stretch. I guess Nissan went this way to save a buck.

9pcybV1.jpg

 

I just went out and measured center of cam down to the bottom of the head on a Z24 and KA24E head. Both are withing 5mm or half a cent of each other, so a KA timing kit could theoretically work on a Z24 if the guides allow it.

 

I don't think there is near enough chain slack for it to jump a tooth but it could have been put on incorrectly on the rebuild. There appear to be no cam timing marks on the sprocket so about all you could do is wedge the chain so the timing chain tensioner can't fall out and move it one ahead and one behind what it is now and see if it improves.

 

A leak down test is much more definitive for where any lost compression went. Compression tests are unreliable, you may just have a low cylinder. It can point towards a blown gasket once badly blown out but not rule it out.

 

 

Likely the gasket was failing and with the power so low from retarded timing it limped by, but as soon as it improved it blew out.

Interesting to see all the cam sprockets. And yeah, I was thinking his sudden rough running condition curiously reminded me of my first 720s head gasket demise. That truck ran totally fine until one day it suddenly ran very poorly. I cranked it and with no warning it was missing badly and sounded like a diesel. Of course being 16 years old I went and promptly floored it on the highway and POOF. A giant white cloud was born when my engine died. LOL. 

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The thinnest spot is between cylinders but usually this widens to include one of the small coolant holes drilled between the cylinder walls. It can also just blow sideways into the water jacket. Compression leaks into the cooling system over pressurizing and expelling coolant into the coolant recovery bottle. Coolant can reverse into the cylinder after shut off.  Exhaust smells sweet from the antifreeze and if bad enough or cold enough produce a steamy cloud. Coolant can't get into the oil through the head gasket but it can be pushed down past the rings and accumulate in the oil pan.

 

Watch for unexplained coolant loss and top ups. Milky or cloudy oil. Steamy or sweet smelling exhaust.

 

 

On a Z24 that is known for head gasket failures every 100k or so it's advised to re-torque the head bolts at least once a year to prevent gasket failure. Do this on a cold engine. Loosen one bolt several turns at a time and tighten to 60 ft lbs before moving to the next. Do one bolt at a time and you can do in any order you like and no chance of coolant escaping. Re-torquing keeps the gasket evenly crushed. I've removed some Z24 head bolts that were noticeably less tight than the others.

 

 

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12 hours ago, datzenmike said:

The thinnest spot is between cylinders but usually this widens to include one of the small coolant holes drilled between the cylinder walls. It can also just blow sideways into the water jacket.

 

Yep, this is what mine did. Leaked from water jacket near on rear drivers side into cyl 4. Eventually blew out the compression seal at the thinner point between cyl 4 and 3. That's when she gave up the ghost.

 

12 hours ago, datzenmike said:

Re-torquing keeps the gasket evenly crushed. I've removed some Z24 head bolts that were noticeably less tight than the others.

 

 

Yes, I've noticed this also. Reminds me I should re-torque mine soon. 

 

 

He had some gold glitter flakes floating in his coolant under the radiator cap and same gold coating in the overflow tank. Exact same stuff that was in my radiator from the truck with coolant in the crankcase. Here's my radiator for reference. Ignore the finger swipe inside. What is this stuff?

 

odgqFAY.jpg

 

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Yepppp. When I saw that copper flake I was thinking gasket material, but now it makes sense. Before I was wondering what part of a head gasket or intake gasket was possibly copper. This explains it. 

 

Well, that short trip around the block was fun! Looks like his z24 is probably getting open heart surgery now. 😂

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If you have never taken this or an L series head off before, it's imperative that the timing chain tensioner be blocked from falling out when the cam sprocket is removed and the chain goes slack.

 

You need one of these...

 

V4gFyD8.jpg

 

Or this happens....

 

TPKjY2V.jpg

 

And EVERYTHING has to come off the front of the engine to get at and fix. Maybe 4-6 extra hours plus timing chain cover and water pump gasket and front seal at least.

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Don't go pulling the head until you verify the gasket is bad.  there are 2 ways: 

compression test

block tester: its a contraption you put over the radiator and run the engine.  It checks the coolant for carbon monoxide and the fluid changes form blue to yellow if there is exhaust gas in the coolant.  Napa sells and loans them.  

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6 hours ago, distributorguy said:

Don't go pulling the head until you verify the gasket is bad.  there are 2 ways: 

compression test

block tester: its a contraption you put over the radiator and run the engine.  It checks the coolant for carbon monoxide and the fluid changes form blue to yellow if there is exhaust gas in the coolant.  Napa sells and loans them.  

 

I've never even heard of a block tester. Kind of surprised. 

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6 hours ago, distributorguy said:

Don't go pulling the head until you verify the gasket is bad.  there are 2 ways: 

compression test

block tester: its a contraption you put over the radiator and run the engine.  It checks the coolant for carbon monoxide and the fluid changes form blue to yellow if there is exhaust gas in the coolant.  Napa sells and loans them.  

I’ll head to Napa after work tomorrow and ask them about the tester. I’m about 80% that it’s head gasket. Engine needs an overhaul anyways. Unknown mileage on the engine. I believe the previous owner said it had about 100k miles or more.

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