Butchering the dogbone (engine brace), and aural enhancement...

[johnl]

The 'dogbone' engine brace has two rubber bushings to absorb vibration. Unfortunately these also allow some engine rocking to occur, especially if either of the bushes is in any way knackered. Both of mine were, so engine movement was somewhat excessive, causing an 'elastic' feeling to the manner in which power was transferred from the engine to the wheels. This was a minor annoyance that could be felt taking off from rest, when changing gear, and with any transition between on / off throttle.

First problem with this (dogbone brace) was when I discovered that the rubber bush - the one pressed into the aluminium casting attached to the engine - was broken. The sensible thing to do was buy a new one, but I thought it could be rescued without spending any cash. The bush has a deep annular groove on each side of the rubber, intended to make the bush more compliant. The thinner rubber between the grooves had failed, and the centre section could be easily removed (once the bolt and brace had been removed).

I found some steel tube into which the central part of the separated bush could be pressed (in a vice using plenty of rubber grease), so this now resembled a 'silentbloc' bush (with the original inner steel crush tube, then rubber, then an outer thinner walled steel tube). Next I cut another piece of the same tubing to the same length, and hack sawed a longitudinal cut along its length. I then spread the tube open a bit so that I could force it over the first piece of tube, in effect doubling the thickness of tube wall. Using more rubber grease and a large pair of adjustable jaw pliers I forced this assembly into what remained of the rubber still attached to the bush in the aluminium casting.

Result; less engine rocking and the 'elastic' feeling is decreased. I think this 'repaired' bush is now significantly stiffer than a new bush would be, because of the tubular 'inserts' taking up the space where the two annular grooves once were, and because the force needed to assemble the bits compressed the rubber to some degree. Still felt a bit 'soft' though, because the bush at the chassis end of the 'dogbone' was also not the best (though not nearly as bad as the one at the engine end).

Anyway, the other day I stumbled across an old 1/2" spherical rod end that used to belong to my Nota (google will give you some idea what a Nota is), the kind commonly seen in racing car suspensions. It crossed my mind that instead of replacing the dogbone (and its integral bush) it should be easy enough to adapt the dogbone to fit the rod end in place of the bush. So, I cut the bush off, leaving just the 'U' and the tube welded to it. Next I welded a suitable nut to the cut end of the dogbone tube (1/2" UNF, not kosher for an Alfa I know, but that's what the rod end is...), so that the rod end could be attached to the tube (replacing the rubber bush). Next I sprayed it black. Next I fitted it to the car. I used two largish nuts each side of the rod end eye to act as spacers so that the chassis bolt could clamp it all in place.

Result, well good, but also a bit surprising. Of course there is much less movement in the dogbone brace now, with zero movement at the chassis end and less at the engine end, so the unwanted 'elastic' feeling is much improved, the engine now feels more 'connected' to the chassis. There is also a noticeable increase in engine vibration transferred into the chassis, which occurs mostly at low rpm when taking off from rest, and driving at low speed just above idle (much less so at higher rpm). This was expected, but not nearly as bad as I feared it might be, IMO easy to live with, though others mightn't like it.

The surprise though is just how much more engine noise is now transferred into the chassis, and hence into the cabin. I did expect some increase, but thought that since one of the bushes was still basically rubber it would likely be minimal, but it's a bit more than that.

I like it, though others may not. There is significantly more induction noise, especially at wider throttle opening. There is also an increase in the 'mechanical' noise that the engine makes (not that the engine actually makes more noise, it's just more easily heard). There is now a faint whine that could not previously be heard (and I suspect might be the power steering pump). The increase in noise isn't all that much when just cruising, but it is somewhat louder.
Anyway, the engine is now enhanced with some aural character, whereas before it was (IMO) way too quiet (and bland, for an Alfa). I can now easily hear the engine, so rev matching for heel / toe is much easier, resulting in more consistent down changes. It's now more tempting to rev the engine out just to hear it sing, so fuel economy is likely to be worse, at least until the novelty wears off (if it does, but I suspect it may not...).

Anyway, this was a very quick and easy modification. If anyone tries it and doesn't like it, very easy to 'undo', just fit a new stock dogbone brace.

Regards,
John.

[johnl]

Seems like no-one is all that interested in this, but I'll update anyway.

With further familiarization, the increase in engine vibration that can be felt through the chassis is very minor. I can feel it momentarily as I let the clutch out from rest, and less so when the car is rolling in gear at idle speed or only just over.

What I think I'm feeling is each firing stroke as it occurs. That's two 'pulses' of momentarily increased crank speed per crank rotation, with each increase in crank speed trying to rotate the engine backward and (as per Newtons' third law of motion) reacting through the brace against the uncushioned rod end, and thus against the chassis. It smooths right out as soon as the rpm start to increase. Assuming this is a correct analysis (i.e. hunch), then I would expect it to be a stronger effect with (say) a lighter flywheel because a lighter flywheel would damp such crank speed oscillation less effectively(?).

It's a non issue compared to the reduction in unwanted drivetrain 'elasticity', the smile inducing acoustic enhancement, greater ease of judging rpm for downshift heel / toe, and I'm now convinced that the general quality of gearshifting has improved, at least a bit. Oh, fuel economy is definitely worse, hard to resist revving the engine, sounds great...

Regards,
John.

[johnl]

I'm finding that the engine sounds significantly louder (and better) in the coolth of the night than in the warmth of the day (though it's still sounds a lot better than stock even when it's warm outside). My best guess is that the remaining rubber bush (the one attached to the engine) isn't, and doesn't get, as warm in colder ambient temperature, therefore is and remains somewhat harder and so conducts a bit more noise...? Either that, or the cooler air is denser, and this has some effect...??

Anyway, it's still all good, I'm still enjoying it. It's nice that I don't just get an increase in induction noise, but also can more clearly hear some of the mechanical sounds as well. It does add character.

I don't yet know if the increase in sonic communication will become wearing say after a few hundred km on the highway. I suspect I might possibly find an increased desire for a sixth gear. IMO it's a pity Alfa didn't fit one anyway, or at least a taller fifth gear, or maybe just a tad taller diff ratio (I don't think the car needs such a very low first gear, and if first gear were a bit higher then the rest could be slightly taller too).

Regards,
John.

[cc]

is interesting!

[johnl]

is interesting!

I'm now wondering if the reason why the engine noise(s) are more pronounced (inside the car) at some times and less so at others might not be due to intermittent metal to metal contact between one of the internal side faces of the 'U' section of the brace, and the side of the aluminium casting (in which the engine bush is located). Of course with the spherical rod end (aka 'Rose joint' or 'Heim joint', depending on whether you are American or European) there is now effectively a metal / metal contact at one end of the 'dogbone' brace (it's actually metal / teflon / metal, but the teflon insert is very thin and quite hard). The remaining rubber bush (attached to the engine) should still act as a vibration isolator, reducing noise transferred through the brace to the chassis, but, if any bit of metal directly attached to the engine were to be in even fairly light contact with any metal part of the brace, then a lot more noise would transfer through the brace...

One of the inside faces of the 'U' section of the brace is very close (about 1mm) to the side of the casting, and sometimes might move sideways because the engine bush has some lateral movement in it (remember that the rubber itself is actually broken with some short pieces of steel tube wedged in there to take up any radial slack, so the 'inner' part could move sideways relative to the 'outer' part of the bush, or just flexure in the rubber may allow it). This might or might not happen , and might (or might not) be affected by warmth or coolth? If so then this might explain why the engine noise is louder when the ambient temperature is lower, as well as why it's louder at the beginning of a journey but seems to decrease somewhat after a period of driving.

I'm intending to experiment with making a rubber disc that would gently push one side of the brace 'U' section into constant contact the aluminium casting. Theory suggests this should increase conducted vibration and thus noise, and might make it more consistent, we'll see.

Regards,
John.

[johnl]

Further fiddling with this in an attempt to make the increase in engine noise more consistent.

I lightly wedged some 1mm thick aluminium sheeting (small piece, 25mm X 50mm-ish) between the inner side-face of the 'U' and the aluminium casting, this to ensure metal / metal contact between the braces 'U' and the casting. I was going to use some rubber to push the 'U' of the brace over a little so that metal to metal contact was made, but it was just easier to insert the metal 'shim'. I've ensured the shim can't drop out by leaving 'tabs' on the shim and bending them around the 'U'. This is so the tab can't (if it fell out) potentially fall onto the auxiliary belt (I have earlier removed the plastic belt cover so that it is easier to monitor the condition of the belt).

This seems to have done the trick, so far. The engine is easily heard inside the cabin, just a bit more than before - and sounds very nice, very much more like a 'sports' car engine should sound (IMO). The test drive today wasn't in very warm weather, so I'm still not 100% sure what might happen on a properly hot day, but I suspect heat will have less muting effect...

Another known unknown is whether or not the shim will wear significantly quickly (and lose contact), there is still some movement in the rubber bush that will cause a degree of rubbing.

Regards,
John.

[johnl]

As more than half expected, the aluminium shim did wear and become a bit loose, a bit more quickly than I thought likely. I've replaced it with a steel one, and installed it with a little grease where it rubs against the casting. Should be OK for a much longer time, probably...

I'm still enjoying the ripping engine sound that now emanates into the cabin, it hasn't gotten old yet. The engine is now sonically entertaining in a manner somewhat reminiscent of the Alfetta I once owned, with its dual twin choke Dellortos and minimal attempt at sound insulation. I've clearly undone a lot of dedicated work done by the earnest NVH engineers at Alfa Romeo, which IMO is a good thing, i.e. I think they were too successful in muting this car to the point of sounding much like any four cylinder shopping trolley (which it isn't).

There is more of an induction 'roar' as the throttle is increasingly opened and the rpm increase, but it's the multiple 'mechanical' noises that really make it sound interesting, e.g. I can now hear some cam whine as the rpm rises, along with other engaging but harder to describe notes. It's quite 'hi-fi', in that I can clearly hear any change in what the engine is doing, and every large or small variation in throttle opening.

I'm pretty sure that if the engine were ever to significantly 'ping' it would be easy to hear straight away. The variator noise is very obvious upon start up, just for a few seconds until it pumps up. At very low rpm I can hear what I think is probably the power steering pump, though I don't think there is anything wrong with it, just that PS pumps do make some noise. At any rate this sound is quickly lost among the others as rpm rise.

And, it's also very discreet. Unlike a noisy exhaust it's not significantly louder outside the car, only inside, so no unwanted attention is drawn. I want to feel like a boy racer, but not heard to be one...

As I said earlier, because the engine can be clearly heard it's easier to rev match for downshifts without getting it a bit wrong. It's also easier to make cleaner upshifts because I can more easily judge backing off the throttle for just the right amount of time before I depress the clutch for the gear change, so the rpm 'hang' (that seems ubiquitous with modern cars, for reasons associated with emissions control) doesn't mean the rpm are still too high when the pedal is released and the clutch engages. So it's easier to make clean gear shifts both up and down the box, which makes me feel like I'm a better driver...

Regards,
John.

[Bobulon]

John which car have you done this to? I'm not familiar with which flavour of Alfa you own

[johnl]

Bob,
it's a 147 TS (MY03).

I'm still happy with having done this, the increase in engine sound volume isn't enough to become irritating (to me, I can't vouch for other peoples thresholds...). There must be some additional vibration transferred into the chassis as well, but I've found it to be minimal to the point that I can't say as I have noticed a significant increase in engine vibration.

The sound transmitted into the cabin (through the 'solid' spherical rod end) varies with temperature, i.e. in cooler weather the sound is noticeably louder, in hotter weather less loud. This is also apparent as the engine is somewhat louder (as heard from within the cabin) at the beginning of a journey, but becomes less loud after a long enough period of driving that the engine bay temperature has risen for some time. I assume that the remaining rubber bush (at the engine end of the 'bone') is harder when it's colder and softer when it's hotter, causing more sound dampening when the bush is hotter. 

I'd like to try a stiffer bush at the engine end of the 'dogbone', which ought to raise the in cabin volume a bit more. I think the only practical way to do this would be to use a poly bushing.

PS, I find that ambient temperature also has a noticeable affect on the hardness of the bushes (seemingly) in the lower wishbone and the rear lateral control arms. In cold weather the steering is sharper and more accurate, but becomes a bit 'doughy' as the temperature climbs. This also manifests as an increase in the tendency for directional stability to deteriorate noticeably in warmer weather, especially when braking, causing the car to veer from side to side (not badly, but enough to be annoying, especially as it is significantly less of an issue in cold weather). The rear end also becomes a bit laterally 'squishy' on hotter days, which adversely affects turn in and change of direction in general.

I'd like to fit hard bushes in the front lower wishbones and the rear lateral control arms. I'm fairly sure this would significantly improve the temperature sensitivity of the steering and handling that I am encountering. However, new bushes will have to wait until after I've paid out for some good front dampers (i.e. Bilstein B6), the almost new 'stock' front dampers being particularly useless in hot weather, and I'm desperate to get rid of them (but funds are limited...). The weird thing is that the rear 'stock' dampers are not nearly so bad...?

Regards,
John.