new member need help z24 rebuild

[Jaredcd7]

 I recently purchased a 1985 720 2wd truck and have sank way to much money into it at this point to let it go to the scrapyard. I just completed a complete rebuild of the Z24 which was my 1st rebuild completely alone. I've only worked on 1 other rebuild of an American V8 about 20 years ago. Everything went fine up until couldn't get it to fire over. I had spark and fuel both of which I confirmed multiple times. I installed new piston's, rings, bearings, oil pump, timing chain, complete clutch system , all front suspension, whole front and rear brakes system, cap ,rotor , plugs, fuel pump "electric" with filers on both sides all brand new. With of coarse new gaskets and seals. I believe that its a timing issue caused by possibly wrist pin to piston deck height being different from the stock pistons. The kit I bought from Northern Auto parts seemed to have all name brand parts ITM "std" pistons. At the I did not check the pin to deck measurement I mentioned above. Mostly because I thought they were stock replacements. I'm fairly ignorant when it comes to engine internals, but I went by the factory service manual and measured everything twice. In the "book" it gives a max. that can be machined off the engine deck and head but I'm not sure how much has been removed in the last 150,000 miles on the truck. Is there any way to check engine deck height as well as the height of a cylinder head. I found some info on a Datsun U.K. site with a measurement from center of crank to top of engine deck but nothing on the head height. Is this something I should be worried about? I put #2 on timing chain on match mark with cam .The number on the chain was just as the book showed. After the rebuild and before tryin to start I manually turned engine over lots of times as well as looked with borescope for interference, but all looked good. The truck did run previous to the rebuild but was driven about 10 miles with oil pump not pumping before I purchased it. I put at least 200 miles on er before I decided to give er an overhaul. Any advice I would surely appreciate.  Only after priming oil pump with plugs out and checking with gauge while cranking. Did I attempt to start, never got er to fire though. after about 2 hours trying out of frustration I gave er a shot of ether well starting fluid to be exact. Only once and only 1 shot as soon as I turned er over it sounded and kinda looked like possibly a piston hit a valve, but upon removing the head with the wooden wedge there's no evidence of interference, but there was evidence that combustion had occurred by a blackened # 2 cylinder. I'm Stumped and could use some advice what to do next. Engine is installed in the truck and head is not I removed the valves and springs and was going to replace them since they are about the only parts I haven't yet. I would rather not spend the money until I am able to confirm what's going on. Thanks in advance for any info you could provide.

[datzenmike]

If the engine was set to TDC compression stroke before taking the head off....

 

Remove the distributor and look down the hole...

 

 

The drive spindle that turns the distributor should look like above. Tang is at about 11:25 although I would say 11:28. If you have this then the distributor is properly positioned to point the rotor # the #1 cylinder.

 

The deck height for a 2.4 z series engine is 246.55mm. That's from the center line of the crankshaft to the head gasket surface.

I don't have a head thickness. Regardless, As long as the head and block surfaces are flat it's fine. 

 

You have the head off and I assume you are at TDC look at the #1 and #4 pistons. They should be fully up and 2 and 3 down. So are there any valve imprints on the tops of the pistons?

[Jaredcd7]

Yes your photo is the main info I used for timing #1 & #4 are at the top of their stroke and #2 &#3 at the bottom of there's. As far as imprints only the factory imprints or reliefs. If there was any interference it was a tap. I read on L-series engine specs on New Zealand Datsun Club that piston top to deck height was -0.45 below engine deck can you confirm the measurement? That was based on 34.00mm pin height? I'm sure you've read this article before datzenmike most of the info taken or written by Jason Gray? He mentions a Federal Mogul piston with a slightly different pin to piston deck measurement. If I were to get a copper head saver shim that is 0.020plus gasket would timing have to advance or retard? If I tried that what all would be involved? Would it change my timing marks on cam sprocket and chain? I have read almost all your posts datzenmike you already given me tons of knowledge. I love your photo under your screen name she's smokin.

[datzenmike]

You have plenty of clearance between valve and piston tops. At TDC on the compression stroke the #1 valves are closed. On the #4 piston you are on the overlap between exhaust and intake stroke and the exhaust is just about closed and the intake has just started to open. Look at the two valves in the #4 combustion chamber. Both will be just open a hair. Neither will be open higher than the head gasket surface. You have the head gasket thickness which is about 1.2mm and if you look at the piston tops they have a huge 15cc dish that is likely 4-5mm deep.  Tons of clearance.

 

IF, the head was milled down in the past maybe 0.005"-0.007" cut off that's only .130mm or two thicknesses of writing paper. Nothing at all.

 

Extremely unlikely the block was decked as there is no reason for it to warp in the first place. It would only be done to raise the compression and there are easier ways to do this. If the piston is at TDC measure down from the block surface to the top outer edge of the piston to confirm the 0.45mm pin or compression height. 0.45mm is close to 0.020".

 

The piston tops having no evidence of striking a valve, also confirms that they clear.

 

You do not need a copper 'head saver' shim in addition to the head gasket.

 

The Federal Mogul pin height difference is shorter than the stock pin height by 0.2mm or 0.007" an besides it's shorter.... so farther away from the head, so even more clearance.

 

 

[ShutterMeShort]

Oil pump phasing and distributor timing.  Check it 100 times.  Really easy to get the pump 180 degrees off making the distributor 180 degrees off.  TDC compression or you will be 180 off.  Valves on #1 should be closed.