rebuilt z24 pinging

[jilo860]

So I've had this truck for about two years now, brought it back from the dead not
once but twice and its really being a pain now. The engine (z24) is running a Weber 32/36 with no emissions equipment, ka24e pistons, and a ported head.
The head gasket recently went between cylinder 1 and 2, so I had the head and block cut, installed new rod and main bearings, and all new gaskets. I also upped the compression with ka pistons, and cleaned up the ports in the head. The valves were also ground. Basically the engine is fully rebuilt.
My problem is this. The engine knocks/pings when on load.it will also smoke through the dash if you gas it enough while its knocking I really don't want to crack a piston on a brand new engine. The knock is directly related to throttle opening and doesn't happen at idle. My next step is to pull the head back off and start looking around. Any ideas would be greatly appreciated.

[Saudade]

Try some higher octane gas or some octane booster to see if it's detonation.

[jilo860]

Going from 87 to 93 has negligable effects. I'm fairly convinced its oil but I'm still stumped.

[seang]

What do you mean by oil? Like oil contaminating the air/fuel mix and lowering the octane rating?

Do you know what the compression ratio is now with the KA pistons? Are they DE pistons or E pistons? If I am not mistaken, the z24 combustion chamber is closer in size to a DE (45cc?) than an E, which if I remember correctly is about 65cc.

[longtooth]

If you have access to a diagnosit vac gauge I would reconmend using it.

[jilo860]

Compression ratio is around 9.5-1, and yea the oil contamination is exactly what I'm talking about. I keep thinking that because I put the new head gasket on dry, that it may be leaking.

Yesterday I went and got some new plugs, both in a colder heat range and from reading them they seem to be a better choice. I did find out that the engine is running lean, the electrodes are white. The next step after that was replacing the base gasket for the Carb which I'm still in the process of doing. I decided to drill and tap the manifold so the base plate can bolt on using four studs insted of the s*** Allen bolts that the redline kit came with.

Next step today is going to be pulling the jets and emulsion tubes out of the Carb, writing them down and trying to get some more fuel in there.

Also, for the diagnostic vacuum gauge, what would I be looking for as a reading? What's your theory on what's going on? Vacuum leaknof some sort or bent valve maybe?

[jilo860]

I forgot to mention the pistons are. 020 oversized ka24e pistons late model -2.8cc dish

[seang]

Next step today is going to be pulling the jets and emulsion tubes out of the Carb, and trying to get some more fuel in there.

That is a pretty good next step, since rich is safer than lean. Here is some great information from the Datsun Trucks forum on tuning Weber carbs: jetting-and-tuning-weber-carbs-all-you- ... 76139.html

[jilo860]

Affter doing a lot of reading on jetting my Carb, I've come to find out that redline shipped my Carb with main jets smaller than normal. Also, I failed to think about the fact that my head has been cut twice and my block has also been cut. Cam timing is inevitably off and my compression may be around 10:1 sooo that spells out a few issues to be resolved first.

[RT22]

Yep sounds like lean and higher compression is making it pre denonate higher octane rich up the mixture and adjust timing as all 3 lead to pre detonation.

[longtooth]

Compression ratio is around 9.5-1, and yea the oil contamination is exactly what I'm talking about. I keep thinking that because I put the new head gasket on dry, that it may be leaking.

Yesterday I went and got some new plugs, both in a colder heat range and from reading them they seem to be a better choice. I did find out that the engine is running lean, the electrodes are white. The next step after that was replacing the base gasket for the Carb which I'm still in the process of doing. I decided to drill and tap the manifold so the base plate can bolt on using four studs insted of the s*** Allen bolts that the redline kit came with.

Next step today is going to be pulling the jets and emulsion tubes out of the Carb, writing them down and trying to get some more fuel in there.

Also, for the diagnostic vacuum gauge, what would I be looking for as a reading? What's your theory on what's going on? Vacuum leaknof some sort or bent valve maybe?

A engine vac diagnostic gauge can tell you if your ignition timming is off and if your camshaft is out of time.

[jilo860]

Ok so today I got the Carb bolted back on and correctly sealed. the rear throttle shaft seal is leaking but at the moment that's the least of my problems. Cam is timed correctly and the ignition timing is correct. The problem I have found is that the lean condition that makes the engine knock has burnt an exhaust valve. No fluctuation of vacuum in the intake manifold, but there is vacuum in the exhaust pulses. Doodoo. So tomorrows task will be to pull the head and take a look around. Hopefully my new pistons aren't damaged by much.

So all of that aside, does anyone have any jetting suggestions? I have 135 mains in my Weber 32/36 and I'm sure that's waay too small. I'm thinking of buying some 145's but I'm not sure if that's too much. At least being a bit over rich is safer than way over lean.

[jilo860]

I forgot to post my vacuum readings. At idle I get around 20mm HG and while the engine is on decel from being revved it gets near 30mmHg. So one would think that the intake valves are sealing well. I also have 210 psi on all four cyl. Number three gave an initially lower reading of. 190 but when I tried again it got 210. That cylinder is the one with the burnt valve also as the valve stem tip is discolored.

[jilo860]

So I've got four ugly looking exhaust valves. Time for new valves and guides

[seang]

Please update! I want to see if you get it running right or not.

[jilo860]

Oh trust me ill get it running right. There's no way I'm quitting now. Hell if I wasn't posting from my phone I'd put up pictures for you guys, I've got tons.

[kenturtles671]

Sounds like its running lean and could use better fuel.

[jilo860]

So ive got an update. I've got two valves leaking that I just couldn't get to seal no matter how much I tried. I lapped them a few times but no luck, so I dropped the head off at a local machine shop to see if he can get them to seal. Hopefully all goes well.

[jilo860]

Update. I put everything back together and the truck is running again. No leaking valves either. To start getting rid of the knock, I went and put three gallons of 93 in it and sat in my driveway playing with jet sizes. Since I can't really afford to just randomly start buying jets, I drilled them. I've got a set of really nice bits that go up in size from about .3mm to 1.8mm. I take my dial caliper, measure them and team out the hole.

My idles are now at 80 primary 70 secondary. My mains are both 155s and my air correcters are 170 primary and 100 secondary (what came with the carb, makes no sense to be that small).

Going up all these sizes hasn't done s*** for the knock. Power has changed but not the knock.
Anyone ever had an exhaust leak or rattle that sounded like detonation? I'm getting really stumped here. I've never heard a leak sound like this but anythings possible I suppose.

I'm going to post a video and some pics later on today to help.

[seang]

I wonder if the dual-plug setup is speeding up combustion too much for you. I thought the secondary plugs cut off and just the primaries fire under full throttle, but how does your engine know when you are at full throttle? Is there a throttle position sensor on your Weber carb, or is there a vacuum/rpm sensor? Does your engine even have an ECU? I must say I am not completely familiar with how that sytem works but I am trying to understand it better.

[jilo860]

i hear ya, the plugs are supposed to fire intake first and then exhaust a few degrees later. ive run the engine on one bank of plugs without a difference. i love my truck and i love the oldness of this engine but im getting ready to take it out and put a ka24de in it. it would have been a better choice to do that than rebuild this boat anchor.
hell, ive been talking to a nissa failure analysist on justanswer.com and ive got this guy completely stumped. im a tech of 8 years and this guy is a tech of 30 years and neither can figure this thing out, and if it does get fixed the thing is never going to have more than 120hp/140tq. stock a kade is better than that. looks like i tried polishing a turd and it didnt buff out.