strange vibrations

[cedwards]

Also be unlikely gearbox if as you say does it with clutch in.. I would think that meant
More likely as you said flywheel or other rotating mass, engine mounts all good?
Can you be more specific about noise, has it always been there? Or is it something that has popped up suddenly?
If sitting with car stationary and revving to 4k does it do it then? Clutch in and out? Car in gear and out with clutch in? If so I'd be pretty sure you can eliminate gearbox.
If taking it through to 6k and taking foot off gas does it do it as engine slowing down back through 4k then stopping too? Help to eliminate missing etc.. (bit vague though)
Yes also try without all belts (just remember no cooling don't wanna warp the head)

[l1ttle_d3vil]

If the vibration only occurs between 4000 and 6000 rpm, I'd be looking for some non-rotating part that can vibrate. Something that runs real close to some other part, loose brackets, shagged centre bearing, exhaust touching the floor...

a few people have said if it was the flywheel, it could still drive through it.
exhaust doesn't touch, engine mounts are fine etc etc. center bearing = spigot bearing? if so, thats brand new.

Can you be more specific about noise, has it always been there? Or is it something that has popped up suddenly?

fairly sure it has always been there, can't remember if it was doing it on the dyno or not. it will do it with car stationary and revving to 4k, clutch in or clutch out. will also do it while revs going up or down/coasting off gas. it is pretty severe though, vibrates the whole car - can't see much clearly in the rear view mirror, steering wheel vibrates etc, not really worse in any particular place.
a couple of people who've felt it have said it can't be anything "small" that would cause it to vibrate this bad - would have to be a decent mass like the flywheel. i've pulled it off this afternoon to get balanced anyway, as a start.

only other thought i've had is the bellhousing is a custom made (picture below), something might not be centered 100% or allow a bit of movement which might cause a vibration. but if something isn't lined up the gearbox isn't likely to fit the clutch/spigot bearing nicely, and it does all slide together easily when bolting them up.

[Dunny]

Ah - I think you might be onto something now with mentioning it's a custom made bellhousing, this is now sounding very similar to my problem and we are leaning towards the bellhousing being the issue (mines custom made upright k-t bellhousing).

My problem only started when we fitted the T50 (which had a brand new gearkit), custom bellhousing, and a different driveshaft. D/shaft has been elimitaed by having the new one made which only made things worse, pretty sure the gearbox is fine but we will try a standrd box to eliminate the whole box, if it still vibrates the only thing left is the bellhousing.

I'm sure a very small misalignment could cause the issue, so the box still may fit fine.

[NOLAW]

just back stepping to the pulleys, will my alloy gilmer pulleys be an issue on my 4agte?

[l1ttle_d3vil]

I'm sure a very small misalignment could cause the issue, so the box still may fit fine.

mentioned this to someone else, who pointed out that it still vibrates with the clutch in, when the gearbox wouldn't be moving at all. im sending the flywheel away tomorrow to be balanced, once I get it back I'll fit it all up with just the bellhousing so I can start it up. if its fine I'll fit the gearbox back up and see what happens.

morgan - i'd imagine they would cause problems seeing as they are solid alloy with no harmonic dampener.

[NOLAW]

S**t! if im wanting to run over 1bar - 19psi of boost and get 200+kw atw, how soon will it be before these pulleys give me problems?

[l1ttle_d3vil]

S**t! if im wanting to run over 1bar - 19psi of boost and get 200+kw atw, how soon will it be before these pulleys give me problems?

AceSniper has run into allsorts of problem with his engine after around 20,000km, but seems everyone has different results - could happen alot sooner. Im getting rid of mine now just to be sure.

your cars gonna be a handful on 19psi!!!

[Boosted_162]

Just to throw a completely different idea in there...

Is your external wastegate plumbed back?? I had mine done recently and the car gained a wierd vibration that only happens at 2200rpm...

[l1ttle_d3vil]

im running standard internal gate, but interesting to know... haven't paid any attention to if its boost-related but will keep an eye on it.

[l1ttle_d3vil]

ok bit of an update...

flywheel and clutch setup has been off, balanced and marked. it was out slightly but he didn't think enough to cause a severe vibration, theres only one small hole drilled on one side and a skim taken off the edge of the pressure plate. put it all back on with just the bellhousing and no gearbox (just incase the gearbox was causing problems from misalignment), still vibrating slightly right through but no severe vibration at 4 - 6000rpm, could've been because the engine was only bolted in by its mounts, no support from the gearbox etc.

have now put everything back together and found the bellhousing is extremely close to the tunnel and gearbox was actually touching the tunnel on one side - sledgehammer fixed most of that. there is only a minor vibration right throughout now, and possibly on de-acceleration, but I can actually hear the vibration on the tunnel itself so must be the gearbox or something still touching from the mass torque

looks like i'll have to save up and get a niteparts bellhousing, and do some more massaging on my tunnel. either way, its good enough to take to the drags like it is so bring on winter!!