Driver Side Head has NO Compression

Nissan 300ZX technical discussion forum: Maintenance, performance, installations, modifications, how-to's and troubleshooting.
GranAutismo
Posts: 10
Joined: Thu Aug 01, 2019 8:38 pm
Car: 1991 Nissan 300ZX N/A

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So I dropped my NA motor in after repainting my engine bay. While the motor was out, I replaced:
All 4 Cam Seals
Front and Rear Main Seal
Rebuilt Lifter
VTC O-Ring
Oil Tree O-Ring
Timing Belt
Belt Tensioner

Before all this, my car ran. 180 on all cylinders except cylinder 6 (130psi). Drove it to work for a couple days before I decided to take it out to paint the bay.

Since the motor is in, cylinders 1,3, and 5 fire, but have a low compression of 90PSI. The cylinders 2, 4, and 6 have NO compression. I checked the CAS, injectors click after every turn. Injectors on the driver head read 12.2-12.4ohms. I have all new Sparkplugs and Coils so I did confirm I had Spark and Fuel. Injector connectors read 11.8v in ON position. The car turns on and stays on, but with only the passenger side head doing all the work. When the car is running (stays on for awhile before it dies) the left bank sounds as if it’s smacking the valves, so I removed the timing covers to expose the timing belt BUT everything lines up perfectly. The timing marks on the cam gears and even on the crank. I even counted the teeth in between each gear. The Intake Valves are straight, and the Exhaust Valves seem good too (bought an endoscope and fed it through the manifolds).
I have yet to do a leak down test since I don’t have the proper tool to do so, but I’m sure that’ll help. The last thing I can think of is maybe I put the exhaust cam wrong when I rebuilt the lifter or either the dowel broke, causing the exhaust cam to stay stationary while the gear moves freely with the timing belt BUT isn’t there a bolt that’s torqued down to 90ft-lbs under the VTC Cover? The dowel is just there to align it with the gear? If timing is correct, then should my valves be bent? If so, why do I have 90PSI on the right head?

If you guys know anything, please let me know. The last thing I’ll do is send it to @SZRpro, a shop that specializes in this chassis

If you’re interested on how it sounds, my IG is (3oozx.na). Yes, those are the letters “o” instead of “0”


itsa300zx
Posts: 1243
Joined: Sun May 31, 2009 9:39 am
Car: 1990 300zx NA W/TT swap
2011 Nissan Rouge S
2008 Highlander SR5
Location: up North

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The only two items that can affect compression (that I can see)on your list are timing belt position or the lifters are stuck. Do your leak down test should narrow down the issues.

GranAutismo
Posts: 10
Joined: Thu Aug 01, 2019 8:38 pm
Car: 1991 Nissan 300ZX N/A

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I went ahead and counted all the cogs again (24-45-24-59) and everything lined up. Cylinder 1 is at TDC too. Cams rotate when I tune the crank so I crossed that out. Went ahead and put everything back together. Since timing was spot on even before I took the covers off, I know the valves aren’t bent. So, I’m going to recheck compression and wiring. I did rent a compression tester for autozone but knowing those tools, you never know if people actually took care of them. Maybe it gave me an inaccurate reading. Last thing I can think of is maybe the FPR is malfunctioning or like you said, something is wrong with the valve-train. Will do the leak down test after all this (Will end up buying my own gauges/tools)

itsa300zx
Posts: 1243
Joined: Sun May 31, 2009 9:39 am
Car: 1990 300zx NA W/TT swap
2011 Nissan Rouge S
2008 Highlander SR5
Location: up North

Post

Wiring and FPR will not affect compression in any way. Compression is purely mechanical seals of the cylinder.

Maybe the tool is somewhat defective; one thing to make sure is a good seal into the spark plug holes. This hose is only hand tightened and seals with the o ring in the plug threads. Our plugs are really deep in there so getting a bit of torque on the adapter hose is sometimes difficult.

I've done some tests where is was low but with a quick 1/4 turn of the compression hose, the numbers were normal.

User avatar
NolimitZ32
Posts: 7112
Joined: Fri Jun 27, 2008 9:07 am
Car: 91 AG2 2+0 TTMT swap/E39 BMW 540i6/E53 4.6is Dinan S3
Location: Houston, TX

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^This, the autozone gauges are garbage.

GranAutismo
Posts: 10
Joined: Thu Aug 01, 2019 8:38 pm
Car: 1991 Nissan 300ZX N/A

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:wtf2: Sorry for the late update. Right Side compression is 170PSI across all cylinders (1,3,5). On the left side, that read in between 0-20PSI. Recently I was rebuilding my old lifters for back-up or to sell (the lifters that are in my Z rn, I got from the junkyard and rebuilt those as they where in WAY better condition) and as I was reading the rebuild forum, I noticed that I had to remove ALL the air from where the check valve sits so it doesn’t compress whenever you press on it. I remember that when I put my rebuilt lifter in, most of them where “spongy”. I’m guessing that the air stuck in the lifters is pushing the valves out, thus not creating a seal during the combustion phase. Funny enough, all the lifters where like that yet the right side has great compression. Should I just pull the trigger and dissemble everything and rebuild the lifters on the left bank? Or rebuild all 24?


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