Post track engine vibration
 

Hello all,

A while back I attended a club sprint meeting with my S2. Apart from a spin, the day went well until I drove home. I do not remember any over revving.

While driving the car experienced an engine vibration between 3500 and 4000 rpm approx. vibration not apparent on track post spin.

Car was carefully driven home, parked and not started or driven since. Some forum searching has indicated the likely causes as either the balance shaft system or the engine mounts.

The left hand engine mount has previously been identified as needing replacement (part on hand), however, I decided to inspect the engine belts.

On removing the lower belt cover, the balance shaft belt was found to be loose, ie able to twist the belt beyond 90 degrees. There is also evidence of rub marks from this belt on the water pump pulley.

Both belts look to be in good condition.

Without a timing inspection at this stage, is it likely that the balance belt make have jumped a tooth or two?

If so, is it safe to drive to a repair venue?

Cheers and thanks

Greg

Greg

The balance belt is surprisingly loose when tensioned correctly. Check the marks on the balance pulleys line up with the marks on the rear covers when the cam gear as at tdc. If they line up then it is right (might be out by half a tooth).

There are lots of possible vibration causes, cv joints (if under load), torque tube bearings, engine mount, clutch, even spark plug leads not seated on plugs properly (had this once and it vibrated only at some revs).

balance belt should be able to spin 180* when tight.

Thanks all,

Am in process of checking balance timing. On turning the engine to find TDC the belt tension has increased.

Will report as more info comes to hand

Greg

Was the spin on course? If so, possibly flat spots on the tires.

it is not uncommon for the balance belt to hit the water pump, especially if the lower eccentric was spun to the wrong side. it changes the placement of the belt, and puts it too close to the water pump.

that being said, where is the vibration? is it in the engine, or in the suspension? is it different at any particular rpm? is it different at any particular road speed?

if the belt was loose enough, you may have jumped a tooth or two on the balance belt

if you feel it more at one road speed than another, you may have thrown a balance weight on a wheel, or flat-spotted a tire. if you went off-road, you may merely have picked up some dirt in the wheel.

Push the car in neutral with the clutch in and rev it to 3500-4000. If you don't hear the noise anymore it is your torque tube bearings. If you still hear it, you can eliminate that from your list.

Thanks guys. Will check

Hmmmm,

Got the car on stands today to check timing.

Looking underneath, says I "that bush shouldn't be there!". One of the sway bar bushes has split in half with none remaining in place.

I start the car, warm it up.. and no engine vibration in the 3500-4000 rpm range. I now suspect the sway bar is vibrating in that range.

Off to confirm timing and change the engine mount regardless.

Cheers
Greg

Found TDC, cam alignment ok, top balance shaft ok.

Cannot get lower belt cover off. Retaining bolts have seized and captive nuts are spinning. It's never easy is it? Any suggestions as to how to fix this?

Will find my inspection mirror (or buy a new one) tomorrow and see if I can confirm the lower timing.

Cheers

Greg

You can drill a small hole through the plastic into the side of the captive nut to pin it as you remove the bolt.

Thanks Eric,

Greg

Great tip.

Hi all,

Eric, I am afraid your method has not been successful in this instance.

I did borrow a boroscope from a work colleague, after several checks, re confirmation that the engine was at TDC, it appears that the lower shaft is out by one (1) tooth. Clark's guide talks about re doing the timing at this point. Thoughts?

I tried to eliminate parallax as an issue, it's so close to being in(let's say 0.75 to 1 tooth out).

Would it be a case of backing the tension off, rotating the lower gear around 1 tooth and re tensioning?

Cheers
Greg

Replaced the sway bar bushes and went for a drive......

Great, no vibrations throughout the rev range.. Down to refuel, vibration has returned. What the......?

Can give some specifics; only appears at 3800-3950 and only appears sometimes....less of an engine vibration than a a vibrating sound that sounds like it's coming from the passenger side.

A quick peak underneath has found nothing loose, I do want to dive underneath properly tomorrow to check a little better. Am thinking a heat shield or so etching may be loose.

It was fun to drive though, first time since March, the M030 package is great.

Greg

Ps: my passenger side is your drivers side