L28 Low Speed Vibration

[jamunm90]

Hello

I hope someone out there has had a similar experience that might be able to give me some advice.

 

The first question probably should be, do these engines have a vibration common to all L6 series at low rpm?

 

Here's the background...I have a 1980 280ZX. At about 90K miles, the N/A engine developed a small but noticeable vibration at 1200 to 1500 rpm...I can describe it almost as a lope, similar to an engine with a mild cam. Never could figure out what it was, it was a little irritating but it wasn't bad enough to pull the engine....It was small but noticeable at idle, but disappeared above 1700 rpm or so. At 400K miles, I rebuild another L28 engine, this time a turbo motor from another car. Rebuilt the entire engine and put it together, dropped it into the car, and the same vibration is present...This happens in neutral so I know the drive train is not part of the problem.

 

Now there are NO parts that were shared between these two engines. I then pulled the flywheel and clutch, had it re-surfaced and re-balanced since it was from another donor car that I was not familiar with. It was within spec but had it done anyway...I understand these engine parts almost never need to be rebalanced. Also, I know all valves are straight and seal well, cam lobes, cylinder pressure, crank runout and connecting rods are all within spec and straight as I rebuilt the engine, and I checked all of these again during reassembly. Motor mounts looked OK so I didn't bother replace them, as well as the harmonic balancer. Valve timing and clearances are in spec. Fuel injector spray pattern was checked and looked ok...This is a stock engine using the stock ECCS FI.

 

Could this be something common to L series engines or should I be looking at something else? I've run out of ideas but I'm probably overlooking something simple…

 

Thanks all!!

Edited May 23, 2011 by jamunm90

[johnc]

Probably normal. Try replacing your engine and trans mounts.