Engine Vibration

[turbora28]

Hi all, I wanted to start a thread to discuss about how my 3T-GTE powered RA28 gets some seriously annoying vibrations over 3500rpm.

Originally I was suspecting drivetrain and lately have been mucking around with different tailshafts etc.

Anyhow.. After more testing it definately isn't drivetrain related as if the car is stationary, foot on or off the clutch, soon as you hit around 3500rpm all the way to redline there is a vibration you can feel.

Everything that isn't bolted down tightly rattles and shakes, you can feel it through the seat and especially the accelerator peddal.

Its a very fine vibration though and not like a big lumpy one.

Engine has been balanced including flywheel, pulley etc around 30,000 km ago now.

Wanted to start this thread to get some suggestions as its really starting to piss me off to the point of wanting to pull the engine out and fit something else. I basically change gear now before it hits 3500rpm so I don't have to put up with it. But a turbo engine under 3500 is a bit average!

The 4AGE engine in AE86 I have you can basically cruise along at 6500rpm and its smooth as silk. I want something like this!

Can the turbocharger itself cause vibrations? I'm wondering if that is out of balance.. Just seems such a hard thing to track down as its the 'whole' engine that seems to vibrate and very hard to know where exactly its coming from.

Well thanks all for any suggestions and putting up with this rant

Cheers
Joel

[thaphatty]

maybe a engine mount is on the way out, or not secured properly.

[RedMist]

I'd suspect that even though the engine was balanced the flywheel or cover plate has been put on in a different direction. I'd most certainly check engine balancing again.
By balancing, you don't mean that the flywheel was neutrally balanced? They are supposed to be balanced against crank weights and cover plate.

[Adamal]

How many K's has the engine done?

[badidas]

turbo cant put the engine out of ballance lol
try another flyswheel on it on that hasnt been machined
mabey another clutch too id be looking at your engine balancing
explain it to the person who did it and see if they can shed some light on the subject

and dont drive it what if it spits a crank seal or something big time pulling the crank out for that

good luck

[sleeektoy]

did you get the clutch pressure plate balanced with the rest of it?

was the fltwheel marked with a direction for mounting it onto the crank as it has 5 other positions it could go in!!

Early T and R series engines always have had vibrations between 3-4000 rpm dads 18R-G has an extremely bad engine vibration between 3100-3200rpm. Which happens to be 100kph in 5th!!

[turbora28]

Hi all, thanks for the ideas and suggestions..

To answer a few questions -

Originally I did get the pulley, crank, flywheel, pressure plate all balanced as a rotating assembly. This was around 30,000km ago.

Engine mounts are brand new, changed around 1 month ago.

It's interesting someone has mentioned was the flywheel marked with what direction to go. Since pulling it off I've found out it was indeed marked, along with the pressure plate but i'm not sure if when the guy who built it for me knew of this.

So possibly it was assembled without the flywheel and pressure plate in the correct position for the balancing.

I took the flywheel and pressure plate to the machine shop this morning who originally did all the work. They seemed to think it would have vibrated from day 1 if something was wrong, and the fact its started now is points to something other than flywheel.

But they are going to balance it and the new pressure plate I got again and will see how we go from there.

There has been some mention of engine harmonics with the new turbo and manifold. Maybe not enough bracing? Does anyone know about this sorta stuff?

Cheers
Joel

[RedMist]

Again, your attempting to get the flywheel and coverplate neutrally balanced. Unless your crank is also very well neutrally balanced you'll still have a problem. You should have your crank balanced against your flywheel and again against your coverplate. I've never had this done without removing the crank, however I'm no expert it may be possible. Every time I remove a flywheel I mark the crank to the flywheel so that it may be put on in the same direction.
If you do pull your crank you'll also want to balance the rods and pistons.

[turbora28]

Yeah I was talking to the machine shop about this but they said because the crank has already been balanced they can balance the flywheel and it'll all be good. also they showed me the mark they put on it when they originally balanced it. so I can put the flywheel on how it was meant to be.

But i dont think its going to be the flywheel as the problem started after a few years of driving, and like the shop said the flywheel doesn't really change.

They seem to think its engine harmonics due to the new exhaust/turbo and plenum.

[sleeektoy]

Clutch pressure plates can crack or rivets come loose if they get a hammering. could be the cause of the balance problem coming on after a while

[turbora28]

Just a bit of an update...

I took the flywheel along with a new pressure plate and my pulley to Graham Wilkins and had it all balanced up again.

He said the flywheel was perfect, the old pressure plate was rooted and the new pressure plate all balanced up.

Now I thought great problem will be solved as old pressure plate was no good.

Put it all back together on the weekend but the vibration is still there!

Not all was a waste though as I had problems with the clutch picking up right on the floor, now with new pressure plate that problem is fixed.. So not total waste of time.

But back to the vibration problem... spent some time with a screwdriver testing each area of the engine to get an idea where it might be most noticable.

The vibration is definately coming from around the throttle body/front of plenum area.

The plenum is a custom front facing one. Even at the back of the plenum its not as noticeable. But the front is a shocker.

If you try and hold your hand on it almost hurts from the way its vibrating.

There is a rubber bend on the front of the throttle body and then the intercooler piping. There is NO vibration in the intercooler piping.

So whats everyone think? The plenum/runners more so is already braced to the block with the factory brace. Maybe I need another brace around the throttle body? Or is it possibly the throttle body itself, maybe the butteryfly vibrating around?

Or, is the vibration traveling from someone else and just becoming apparant at the throttle body?

Very confused

Any ideas?

THanks
Joel

[4ageturbs]

I aint a mechanic but have you removed your vibration dampners

[86 Power]

I would say the intake manifold and therefore throttle body are connected directly to the head and therefore just exagerating a vibration from the engine. Have you checked all the pulleys etc?

So now you have an engine that has been fully balanced in combination with the clutch?

What else can you tell us - has it got oversized bearings? All parts from original engine or mixed and matched?

[turbora28]

Yeah engine is all balanced, which it already was but had the flywheel and new new pressure plate re-done.

Umm what else can I say about engine..

It has .5mm oversized forged pistons
Heavy duty valve springs..

Bearings are not oversized as far as Im aware.

So thats internally.. Externally it has a custom made turbo manifold and a custom made forward facing plenum.

Running after market autronic ecu. direct fire ignition.

[turbora28]

Sorry should also mention rods and crank and everything are the original items..

Also just wanted to mention again the problem only just occured, never happened when engine was first built.

[jondee86]

When you have several different rotating masses linked together, as in an engine, you can get resonance occuring at various frequencies. This would typically give you some buzzing at certain engine speeds, for example, between 3000 and 3200 rpm. Above or below that speed the engine would run smoothly. There can be several resonant frequencies of different strengths.

A single out of balance rotating part would give you more and more vibration as the engine speed went up, and eventually the engine would poop itself.

Intake (or exhaust) resonance also typically occurs at a specific rpm range, related to the valve opening/closing frequency and the length of the intake runners. Above or below the resonant frequency, the noise/vibration disappears.

Does your vibration simply "go away" at certain revs ??

Did you change anything at about the time the vibration first became noticable... for example, a new exhaust ??

Are your new engine mounts made from harder material than stock ??

Alter the engine timing ??

Cheers

jondee86

[86 Power]

Ok heres the thing... have you installed a new spigot bearing?

My clutch plate sheared off all it's bolts and jammed against the bellhousing, which i thought was a seized engine, but turned out wasn't.

I figure it was due to the vibrations caused from not having the input shaft of the gearbox supported. Random.