AAZ rattling noise

[Al Housman]

Put a good AAZ engine in my Doka earlier this year. It runs well and pulls well even when loaded. No smoke to speak of. There is quite a distinct chattering rattle when accelerating. There is a slight knocking when at standstill but problem is most obvious when crawling up a hill in 2nd. Of course it may not be a problem in the engine.

My thoughts are:

hydraulic tappets. Could there be a problem with these?
broken clutch spring(s)
CV joints dry
gearbox (but no probs getting through the gears)

I'm open to any suggestions. Did discuss possibility of difflock being stuck on with Aidan but that's not it.

It almost sounds like something is loose and rattling only at higher revs. You can't really hear much once cruising(!) along except when I drive past brick walls with the window open it's really obvious.

Thanks
Al

[marlinowner]

Loose baffle in silencer?

[Al Housman]

Thanks.That's one I haven't tried.

It is getting worse so may be easier to diagnose. I just hope I can do so before something nasty happens!!

I wonder if a broken shock spring in the clutch would cause a loud rattle.?

[Paul Weeding]

Hit the silencer with a rubber mallet... Any rattling and that's the culprit

[Al Housman]

Thanks.I'll try anything at the moment!!

[phil_b]

Hi, I've had a similar issue on my AAZ conversion, rattle/chatter/vibration not engine speed related only occurred under load, sometimes worse when driving through bends. After checking all the usual I had finally concluded it was most likely a gearbox issue, but turned out to be much simpler. On my conversion the high pressure inlet pipe from turbo to inlet manifold has two rubber elbows joined by a rigid steel pipe, this runs very close to the engine mounting bar on that side. When under load/boost there was enough give in the rubber elbows for the pipe to move over and touch the engine bar, made worse when cornering as the engine would rock slightly more to that side. Slight easing of the rigid boost pipe has now given me 6mm+ of clearance and noise completely gone.
Hope yours is equally easy/cheap to resolve, although it took me a many weeks to track this down.
Cheers Phil

[Al Housman]

You know, that sounds like it's well worth checking. Thanks.

Must admit I'm pretty sure the noise is related to engine speed rather than road speed. It virtually disappeared when I removed the prop shaft (it's a syncro) but that seems good and no obviously excessive play around the front diff, universal joints (prop was fully serviced about 18 months ago) or nose end of gearbox. I'm guessing the prop is amplifying the sound.

Aidan kindly had a listen yesterday and confirmed that I wasn't hearing things but we couldn't really pinpoint source since it's only really noticeable when driving along.

I'll certainly investigate turbo pipe since it sounds like I have a similar set up to you and it does sit close to the bodywork.

[Al Housman]

Just in case it happens to you!!!!

The mysterious rattling continued until about 1 month ago. I'd put it down to a dry CV joint and vowed to sort it when the weather improved.

Then on our way to a job the noise became worryingly loud. We turned round and got near home accompanied by a trail of engine oil and horrendous banging.

Stripped the engine down last week to find a cracked sump (hence the oil leak) and a broken main bearing housing, along with two sheared off high tensile bolts and two mangled halves of main bearing.

What I guess must have happened is that the lower bearing housing had snapped in two and the pressure on the crank resulted in the pins snapping.

Bottom end is u/s so have another engine on its way. I can then decide whether or not to combine the top end of this engine with the decent bottom end from the engine I replaced this time last year!!

If anyone has any theories I'd love to read them.........

[silverbullet]

Pics or it didnt happen...

[scimdiesel]

mine had the bells !... basically it would resonate the heat guard between the inlet and exhaust manifolds and ring like a bell!.. Took ages to find because it only did it at at the right load. The AAz is not the most refined so it might just be your expectations. It could just be just be fuel timing. Has yours a fuel advance electric solinoid on the pump. connect it and it will be more advanced and noisier. leave it unconnected it will smoke a bit more when cold. mine was on a timer.

[silverbullet]

He has already said that it's broken a main bearing cap

[Al Housman]

Haha!

With or without pix it's definitely happened, however I'll try to post some.

Have a replacement engine on its way and am determined to rule out any possible overheating/oil pressure problems, though I'm sure the oil situation was ok on this one.

Wish me luck!

[silverbullet]

Its a rare occurance for any engine to fracture a cap. Putting any bias aside, I would say that it boils down to an assembly error (undertorqued cap bolts working loose) or a fatigue failure of the iron bearing cap (engine design has finite operating hours)

[Al Housman]

Yes, I'm inclined towards your second diagnosis since the bolts have definitely sheared.

As you suggest unusual since those caps are pretty chunky but the break between the two halves is not clean metal which suggests it's been like that for a while.

I don't think this kind of thing can happen very often!

[silverbullet]

Any sign of a casting flaw in the cap i.e. an inclusion or porosity?