Engine Vibration after rebuild

[LEMHEAD16]

Hi all, I'm at the end of my rope with this issue.

I recently had the bottom end of my Z rebuilt with:

Eagle Rods
CP pistons
Crank ground 10 under
cometic head gaskets
arp head studs


After rebuild and install I have a wicked vibration from 1500-2300 RPM. It shakes the whole car when I rev it. I replaced all the external rotating components. New OEM crank pulley, new pressure plate, clutch, and flywheel. It vibrates in neutral and in gear with clutch in or out. I've checked and rechecked that the timing belt is not off by a tooth. I have verified timing is 15 degrees at 750 RPM.

It does not feel like a misfire as the engine revs freely from idle to 5000 rpm.

I'm at a loss for what else it could be, I'm open to any ideas before i blow this thing up.

[LEMHEAD16]

Also the engine mounts are brand new and the trans mount was fine when I installed it,

[z.Leinbach]

could be a defective crank pulley. or maybe a dead cylinder, or maybe a defective mount.. i have a dead cylinder on my z due to a bad head (still drivable) and at times the idle feels like its lopey and the whole car idles very rouch below 1000rpms

[LEMHEAD16]

I doubt it's a bad pulley, I had an underdrive pulley on it first and thought that might be it so I bought a brand new oem pulley and there was no change. All the cylinders are firing normally and compression checks out on all cylinders.

[z.Leinbach]

does it have any weird smells when its running?

[LEMHEAD16]

no weird smells

[z.Leinbach]

have you double checked the mounts?? could possibly be the crank outof ballance?

[itsa300zx]

Hi all, I'm at the end of my rope with this issue.

I recently had the bottom end of my Z rebuilt with:

Eagle Rods
CP pistons
Crank ground 10 under
cometic head gaskets
arp head studs


After rebuild and install I have a wicked vibration from 1500-2300 RPM. It shakes the whole car when I rev it. I replaced all the external rotating components. New OEM crank pulley, new pressure plate, clutch, and flywheel. It vibrates in neutral and in gear with clutch in or out. I've checked and rechecked that the timing belt is not off by a tooth. I have verified timing is 15 degrees at 750 RPM.

It does not feel like a misfire as the engine revs freely from idle to 5000 rpm.

I'm at a loss for what else it could be, I'm open to any ideas before i blow this thing up.

This doesn't answer your vibration question but, I hope you got the crank re nitrided after the 0.010" grind.

These crank journals are nitrided and the effective wear resistance layer is only about 0.010" deep, for a nitrided surface.

[LEMHEAD16]

I did check the mounts they look fine, there is no abnormal play in them.

Is there supposed to be a dowel pin between the crank and flywheel? I read some TSBs about it but I don't think the fidanza flywheel had any provision for a dowel pin but I think the crank butt does.

As far as nitriding goes I'd have to check with the shop that built the bottom end. I don't see any charge for that on the invoice though so I doubt it. What kind of trouble would that cause down the line?

Do Eagle rods and pistons need to be balanced before install? The last and worst case scenario I can think of is the piston/rod combo is out of balance.

[itsa300zx]

no dowel pins for the crank to flywheel, just the 8 bolts and the center hub of the rear crank face.

much faster crank wear.

yes should be balanced as a whole rotating assembly, especially with AM parts and a regrind. stock is balanced with oem pistons and rods.

[nissanfreak12]

As far as aftermarket parts being balanced, if you get them from a reputable source, eagle, you should be just fine with the balance. If it was an internal balance issue, it would get much worse at 5k rpms not better.

Have you looked at your injectors? Are you sure you didn't mixup two adjacent cylinders(put 3in cylinder 4) for the injectors? WHat type of spark plugs are you using? If its a TT the gap could be too wide and blowing out the spark. NA could be fouled up or a weak plug, TT same thing. I would look more toward electronics vs rotating mass just because the engine smooths out at higher rpm's.

I had an injector die on me, new style, it would act like a miss at idle and have a wicked vibration randomly, but would always smooth out in the higher rpms. It tested good, it even passed the click test, but when I moved the injector to a different cylinder, it followed. Test your injectors(10-14 ohms), pull your plugs and see what they look like. Are some wet? are they dry and what color do they have? Are you using the correct plugs for the engine?

BTW an unbalanced rotating assembly will feel fine in the lower rpms, and worse in the higher rpms. Think of an unbalanced tired, will feel fine at the lower speeds, but you will notice a shimmy at about 40mph, will probably smooth out at 50 and come back hard at 65+.

[nissanfreak12]

Another thing to try, remove all the belts that runs the accessories, that will definitely rule out water pump, fan, alt, ac, power steering. I remember I also had a vibration when I first installed my TT engine. Granted it didn't last up to 5k rpms, but it got worse. I dealt with it until I really got on the engine, got about 4500 and water pump busted open.

Apparently the water pump that I left on the engine was bad. I later found out it was involved in a front end collision which somehow bent the part that attaches the pulley and fan. Couldnt tell when idling, but after 1500 rpms I noticed a vibration and it got worse the higher it went. Just a thought.

Your car will run for a short time as long as the battery is fully charged, but this will rule out all accessories.

[LEMHEAD16]

Thanks for all the input!

I have checked everything and still have a vibration.

Plugs all look normal and I used my borescope to check for any leaking fuel injectors.
Injectors all test around 12.4. I compared the wiring to the engine diagram to insure the were connected to the correct cylinder.
Coil packs ohm test checks out
I have removed all accessory belts

I did a power balance test using Nistune and the vibration remains when each cylinder is deactivated.

I don't know what else to check