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Hi all--

I bought my Frontier in rough shape...it was running, and I was told it needed timing chains, but really, it had been run low on oil. I took the motor out, tore it down, and started rebuilding it. The crank, rods, and block were sent to a machine shop for grinding, working, and honing. My father and I took the head apart and lapped the valves and put new valve stem seals in it.

Upon reassembly, all ring gaps and bearing tolerances in the bottom end were carefully measured and were in factory specs. The head was installed and torqued to factory specs in the correct sequence (I'd never seen where you have to torque a bolt, remove it, and retorque it, but I did as it said). Here are the brands of the parts in case anyone has experienced an issue with any of them.
Main and Rod bearings: Clevite
Rings: Engine Tech
Head gasket: Victor Reinz
Head bolts: Victor Reinz
Timing kit: ITM (including all new sprockets, tensioners, and chains)

Here's where it gets a little hairy:
The cams look identical, and they weren't marked on disassembly. Both have a casting that say 53F, one has a 2 in it, and one look like a 3, maybe a 5, but I can't really make out what it is. The lift/duration looks to be about the same, but the dowel that the cam sprocket lines up is different between the two. I made a best guess based on some info I found on line about the 2 and 3 markings cast in the cam, and lined all the timing marks up. I turned the motor over by hand a couple of times, nothing hit, so I figured I was good.

Once the motor was back together, it didn't start.

I pulled the valve cover back off, did some more reading and was able to find when the intake cam was supposed to open/close within the rotation, and figured that they were backwards. By some stroke of luck, the marks lined back up between the cam sprockets, so I pulled the cams out, swapped them, put the chain back on, and everything looked to be rotating in the order that it should (the "ears" of the cams are pointing so the tips of the teardrops are facing at about 9:30 and 2:30).

After a series of pulling the oil pump out and re-aligning the shaft that drives it and the distributor, I finally got the motor to putter, but not start. I feel I'm within range on the ignition timing, I have fuel and spark, and it doesn't run on ether either.

I did a compression test: 40 - 87 - 85 - 90. (15*F outside, motor has never run, all plugs out, WOT, 6-7 cranks)

Those results led me to pulling the timing covers back off to make sure I wasn't off. I wasn't.

Summary:
I'm 99.9% certain the bottom end is solid
I don't hear anything in the valvetrain, and the motor turns over by hand, so I don't think it's valves
I feel it may be a timing issue, but all the sprockets are keyed, and marked, and the chains are marked, and marks on the chains/sprockets match up.

I plan to do a leak down test, and I'm going to try and put a scope down in the cylinder to see if I can see if the valves touched hard enough to leave a mark in the piston.

What could I be missing?


Thanks in advance for any insight.
 

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My father and I took the head apart and lapped the valves and put new valve stem seals in it...I did a compression test: 40 - 87 - 85 - 90. (15*F outside, motor has never run, all plugs out, WOT, 6-7 cranks).
FSM:

4. Using a feeler gauge, measure clearance between valve lifter and camshaft.
Record any valve clearance measurements which are out of specification. They will be used later to determine the required replacement adjusting shim.​
Valve clearance (Hot):
Intake
0.31 - 0.39 mm (0.012 - 0.015 in)​
Exhaust
0.33 - 0.41 mm (0.013 - 0.016 in).​
 

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From a 240SX forum:
Re: How to identify KA24DE cams? (with out markings)

...ok so i called Jim Wolf and asked how to identify the difference between the intake and exhaust cams. They said that both have the alignment dowel on the front, for the sprocket.... the intake cam will have the dowel straight inline with the first lobe. On the exhaust, if the dowel is at 12'o clock the first lobe will be at 2'o clock ish.
Do a web search on KA24DE cam identification–there are other forum posts on this.
 
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