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2008 Altima Balance Shaft Trouble

Maintenance/Repairs
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#1

I have a 2008 Nissan Altima 2.5SL with 85K miles. It has a strong vibration around 1800RPM. I have had all motor and transmission mounts checked, transaxle assembly and the transmission replaced (under warranty) with no improvement. The dealer is telling me it is a balance shaft and that I need to replace the engine for $6000.00

Does this diagnosis sound correct? Could it be anything else? Is there anything I can do to correct this without replacing the engine? If not is there a cheaper source for an engine replacement. Finally if I continue to drive it with this problem will it damage the engine further and eventually fail?

#2

The balance shaft, two of them actually, are solid pieces of steel that are driven by a chain from the crank sprocket, so I am wondering what the dealer thinks is wrong with them. Maybe the bearings? Maybe the chain broke? If the chain broke, I would think that it would make a lot of noise and possibly tear up teh oil pump.

Have you had this car since new?

If it is a recent purchase, is there any evidence that the engine may have had some “performance” improvements done? I.e. large exhaust, cold air intake (CAI). Often after the CAI and fart can exhaust, the next modification on this engine is to remove the balance shafts, that frees up about 11hp.

Is this a manual transmission? Another mod that will make it run rough at this RPM is an aluminum flywheel. The stock flywheel is a dual mass flywheel and it is possible that it is worn out too but I’m not sure how that would affect the vibration, it does make using the clutch much more difficult. NA with an automatic transmission.

If it is the balance shaft, you do not need a new engine. Your dealer may not want to do the disassembly on this engine, but it can be done. It can even be done with the engine in place but its no fun. In a shop, I would pull the engine out first. There is a lot of disassembly involved. The balance shafts are located in the upper oil pan, so that means the valve covers have to come off, then the lower oil pan, then the upper oil pan and finally the timing chain cover/oil pump has to come off. The timing chain has to be removed and then the balance shaft assembly can come out for replacement.

This is at least an all day job for one mechanic, maybe more so the labor cost is going to be high. For that reason, I would like to know why he suspects the balance shafts in the first place.

#3

Why did ur warranty only cover trans replace but not cover motor work? Sounds like ur trans replace was a waste of time/money?

#4

Stoveguyy
Nissan covers the CVT transmissions for 120K miles since they have had so many issues with them. Only cover the engine for 60K. Replacment was only a waste of time!!

Kieth

Have had the car since new. Is an auto transmission. From what I can tell they came up with a balance shaft problem because they couldn’t find anything else wrong with the car after 3 attemps to fix it. They said they got the advice from Nissan Tech Line.

#5

I agree with Keith. Balance shafts are very much like small camshafts that are spun by the crankshaft to counteract the vibration inherant in the engine. They are solely counterweights, and I don’t see them as a likely cause, although a bad counter balance shaft could cause vibration. And if a balance shaft somehow went bad, that would not justify replaceing the entire engine.

Exactly what has the dealer done so far?
Has he checked for inconsistant compression?
Did he check for uneven compression? Dd be check vacuum?
Did he check the sparkplugs for signs of uneven compression?
Did he check the harmonic dampener?
Did he put a scope on the ignition system to look at the spark pulses?

#6

Has the dealer run the engine with the accessory belt removed. Any rotating component can cause a vibration. The dealer seems to be punting out on first down.

#7

Does this vibration exist only when the vehicle is in motion at 1800 RPM or can it be felt in neutral with elevated RPMs? The balance shaft diagnosis is a shaky one IMO.

#8

I’m not much informed on balance shafts, or what can go wrong with them, but it seems to me that replacing the engine may be the most practical solution to get you back on the road. It might be possible for an experienced mechanic to diagnose and fix whatever is wrong w/the existing engine, but it appears they’ve done a lot already, and it ain’t fixed yet. $6000 (installed) seems fairly reasonable for a new engine. Here’s some info.

"Other manufacturers having produced engines with one or two balance shafts include:

Nissan 2.5L (QR25DE) four-cylinder engine"

#9

Fine car! Fix for vibration is new trans! Huh? That didn’t work. Ok, let’s replace motor? And that is reasonable? You are a fool.

#10

Replaceing the engine for a vibration is extremely premature, and IMHO any shop making such a recommendation should be walked away from. You do not fix a vibration by replacing the entire engine.

Before even considering such a thing you need to figure out WHY it’s vibrating. Since the dealership won’t cover the fix under warranty anyway, try a reputable independantly owned and operated shop. There are countless diagnostic protocols that can be done to determine where the vibration is coming from, and you should have them done.

See my earlier post for some ideas on what tests can be done. Add to that such things as the use of linear accelerometers (vibration sensors).

#11

Does the vibration occur at engine speeds above 1800 rpm or is this just where it starts? When did this start happening? Does this occur in neutral or park when you rev the engine? Is this 1800 rpm vibration occurring in all gears ratios, that is you take off with a heavy foot so that the engine quickly rises to 1800 RPM and then holding that engine speed as the car accelerates, does the vibration remain constant?

This is a lot of questions but it will help to isolate the vibration to the engine and not to something else like an axle or hub assembly.

One more question that might help, is the vibration constant when you are accelerating, decelerating and cruising or does it change with each of these scenarios.

#12

Keith

The vibration starts at about 1400 - 1500 RPM and is noticable until you hit >2000RPM. Only feel it when the car is in gear. Nothing in park or neutral. The vibration remains constant regardless of the gear the tranny is in. You can feel the vibration when accelerating or decelerating as long as it goes through the 1800 RPM area.

Thanks for the inputs

#13

I’m on the way out right now but will be back later this evening to hopefully offer some insight on the problem.
Based on what you just related I’m not buying the balance shaft diagnosis at all because if a problem existed with a balance shaft then it should be noticeable in both park and neutral.

#14

The way linear accelerometers work is that they’re stuck (via a wax) to various key spots on an engine and drivetrain and send signals to an analyzer that converts the signals to “traces”, like on an oscilloscope. Numerous traces can be run simultaneously. Using this technique, the source of a vibration can usually be isolated and definitively diagnosed. Any good shop should have this equipment.

Since it only vibrates when in gear, it’s a good bet that the vibration is somewhere in the drivetrain. Since it vibrates no matter what gear it’s in, and I assume (correct me if I’m wrong) that means regardless of the car’s speed, it sounds like a resonance somewhere in or attached to the engine, but one that requires the engine to be under load. Some things are different on an engine under load than an engine not under load. Isolating those things suggests perhaps a bad Exhaust Gas Recirculation system, That system allows a bit of inert (already burned" exhaust gas to be recirculated back into the engine when under load in order to keep cylinder temps from getting too high and causing preignition.

Items that oerate differently under load:
fuel delivery and metering
combustion
egr system
valve timing
antiknock system

Items that react solely to engine RPMs without regard to load:
counterbalance shafts
harmonic damper

items that react to car’s speed:
axles
CV joints (part of axles)
anything in the drivetrain or rolling stock past the flywheel

I think it’s safe to start with the assumption based on the description that the problem lies somewhere in the first category. Couterbalance shafts would react to engine rpm regardless of whether the engine were under load or not. The differential, drivetrain, etc. would react to the car’s speed. As I stated, I don’t think proper analysis has yet been done. A different shop might be a good idea. The tools do exist to diagnose the problem.

#15

I believe that the vibration caused by balance shafts will not go away above 2000 rpm, but their frequency could increase to the point that they are less noticeable. They would go from a shaking to a buzz kind of feeling. The motor mounts might absorb the buzz.

The serpentine belt goes around the outside of the harmonic balancer so there would be other issues if that were the problem.

Has this always been a problem with the car or is this recent? Was the transmission change because of this or other reasons and if this is recent, did it start with the new transmission?

If it has always been there, then it is quite possible that the balance shafts were not timed correctly when the engine was assembled. If so, and you complained about this to the dealer while it was under warrantee, they are still responsible for its resolution at no cost to you. If it started when the transmission was installed or shortly there after, I’d be inclined to check the flex plate for cracks, which requires removal of the transmission. A cracked flex plate would do all this.

#16

One more thing, this engine has a vibration dampener that is located under the throttle body. It goes from the top of the block to the firewall and looks like a miniature shock absorber. Has anyone checked it?

#17

The problem started this summer. The transmission was replaced in an effort to fix this problem. I don’t know if the vibration dampener has been checked. From everyone’s input I am thinking I need to take this for a second opinion / another dealer.

#18

If you put the transmission in low gear does it vibrate at the same engine rpm or the same road speed? How about reverse?

#19

I can see a case for the balance shafts, but only for a broken chain. My son has this engine in his Sentra spec V and a neighbor who was helping him put in the Nismo S cams, dropped a tiny bolt down into the timing chain cover.

We did not even start the engine, just rotated it a few degrees and it locked up. That tiny bolt, 4mm could not fit around the timing chain at the bottom of the cover, there is no room. That is why I would find it hard to believe that this engine can run with that chain broken, and run without making a lot of noise.

We had to go through the procedures I described in that order because of he way this engine is put together. We did it with the engine in the car but it was a lot of work and there isn’t much room. If I had known at the start how hard it was going to be, I would have gotten out the cherry picker and pulled the engine. To pull this engine, you have to buy a kit that costs about $50 because the factory does not leave the hoist points attached to the engine.

BTW, that little tiny bolt, with only a little hand pressure to turn the engine actually broke the inside of the timing chain cover, which also houses the oil pump, so my son had to get a new cover/oil pump.

#20

Honestly, I think those guy pulled the “balamce shaft” diagnosis (and I use the term “diagnosis” loosely…VERY loosely) out of their…hats. I’m being polite.

Although I’ve never actuallly seen a balance shaft not timed correctly, in theory one would creat an oscillation at the lower end of the rpm spectrum that would increase in both amplitude and in frequency over the operating spectrum. Until it shook the engine apart. It’s input would couple with the input that it’s supposed to counterac, out of phase, t…and the results would not be pretty.