Scary bonnet opening at speed
Discussion
Since owning my 1996 Chimaera 500 (March 2002) the bonnet has always flapped about at speed on the passenger side. On the way down to Le Mans it had raised some 4-5 inches at speed (although I think it was more like 10-12 inches, but I would 
) and my passenger could clearly see into the engine bay. We did the McDs stop at Caen, took the roof off and headed down the dual carriageway. Bonnet still flapping away, but as I overtook two lorries at 130mph the bonnet actually popped open. Cue swearing and pulling into the hard shoulder!
Over the weekend I spoke to a few other owners and lovely French lady and her husband told me that the spoiler under the front bumper prevented the bonnet movement, I checked my car and I didn't have it, any thoughts either way on this one? Or any ideas on a cure? Has this happened to anyone else?
Many thanks.
Jonathan
) and my passenger could clearly see into the engine bay. We did the McDs stop at Caen, took the roof off and headed down the dual carriageway. Bonnet still flapping away, but as I overtook two lorries at 130mph the bonnet actually popped open. Cue swearing and pulling into the hard shoulder! Over the weekend I spoke to a few other owners and lovely French lady and her husband told me that the spoiler under the front bumper prevented the bonnet movement, I checked my car and I didn't have it, any thoughts either way on this one? Or any ideas on a cure? Has this happened to anyone else?
Many thanks.
Jonathan
another possibility is the catch on the bonnet not always lining up and so not propperly engaged - even when you think it is.
My bonnet has a piece of clear plastic tubing on the peg that fits into the catch. This tube has a nick out of each side so that it bites in the catch correctly. I have found that this tube can twist round a bit so that these nicks are not lined up with the sides of the catch. The result is that when the bonnet shuts it seems like the catch is locked but the bolt + tubing isn't really home far enough. Hence the bonnet can spring up when there is sufficient pressure - eg at high speeds.
My bonnet has a piece of clear plastic tubing on the peg that fits into the catch. This tube has a nick out of each side so that it bites in the catch correctly. I have found that this tube can twist round a bit so that these nicks are not lined up with the sides of the catch. The result is that when the bonnet shuts it seems like the catch is locked but the bolt + tubing isn't really home far enough. Hence the bonnet can spring up when there is sufficient pressure - eg at high speeds.
quote:I don't have a spoiler on mine and haven't had any problems. Depends how fast you go though as one of the discussions on splitters on these boards suggested that their effect only comes in to play at 120mph or above (although recently someone said they noticed a difference at 80 mph but may have been tyre condition pressure etc). So IMO No!!
Anyone got any thoughts on the spoiler under the front bumper - I can't find a "yes" or "no"?
How do you close your bonnet? Presume you check it's secure before setting off. The guy I bought my car off use to shut it by slamming it on to the catch whereas the guys at the TVR dealers place it on to the catch then apply pressure to shut it. I prefer the second method.
MC
I do the "close it" and then "push it" locked technique too, that day I had been driving up to 150mph, sitting about 130mph for many miles on the empty foreign roads so it had been flapping about like a flappy thing from flapland for ages.
In answer to the question about the cross stays, they are both attached and connected and the bonnet catch seems okay too - I am not so worried about the bonnet catch / opening more how to stop the thing lifting at speed as that was definitely the cause of the bonnet popping open.
In answer to the question about the cross stays, they are both attached and connected and the bonnet catch seems okay too - I am not so worried about the bonnet catch / opening more how to stop the thing lifting at speed as that was definitely the cause of the bonnet popping open.
) I experienced the bonnet problem on my way down to Le Mans as well. In fact I was a passenger at the time and when I noticed the thing rising up at 120+ I asked my co-driver to slow down. I asked him if the same thing had been happening when I was driving and he said yes (I hadn't noticed from the drivers side and he being a bike racer probably does not scare as easy as me!). Anyway a bit of a worry,
so I'm sure there would be a market for a commercial solution.
so I'm sure there would be a market for a commercial solution.Spoiler stopping movement... Hmmmmmm
Well some people say that the spoiler helps increase air movement through the rad and it is this air movement that helps cause the bonnet to flap.
If you don't have the spoiler, this movement doesn't happen so the bonnet shouldn't flap so much. This goes against the French advice so...
To get the bonnet rigid enough to stop moving you need a wedge grade bonnet which weighs in at some 30-40 Kg which is roughly equivalent to reducing the engine bhp by 11 for a 500 car. Aprt from making sure it is locked down, I wouldn't worry about it.
The 520's bonnet is made from a single weave grp cloth, with a hint of resin. Along with the front spoiler and bumber, came to around 4 kg. It doesn't moove that much as there is a 3 foot by 1 foot ish vent to prevent air presuure in the engine bay which is the cause of most bonnet distortion. Again a bit extreme for a Chimpari and soda...
Who knows? I don't think the spoiler does anything except increase aluminioum sales anyway...
Steve
Well some people say that the spoiler helps increase air movement through the rad and it is this air movement that helps cause the bonnet to flap.
If you don't have the spoiler, this movement doesn't happen so the bonnet shouldn't flap so much. This goes against the French advice so...
To get the bonnet rigid enough to stop moving you need a wedge grade bonnet which weighs in at some 30-40 Kg which is roughly equivalent to reducing the engine bhp by 11 for a 500 car. Aprt from making sure it is locked down, I wouldn't worry about it.
The 520's bonnet is made from a single weave grp cloth, with a hint of resin. Along with the front spoiler and bumber, came to around 4 kg. It doesn't moove that much as there is a 3 foot by 1 foot ish vent to prevent air presuure in the engine bay which is the cause of most bonnet distortion. Again a bit extreme for a Chimpari and soda...
Who knows? I don't think the spoiler does anything except increase aluminioum sales anyway...
Steve
Can I suggest that both the mid-point rests are checked as providing some support as it is closed. This would put some pre-load in to the bonnet.
The logic being that as there is only one catch the bonnet would flex (or bounce) from a nett upward pressure, particulary on the passenger side. Without the small mid-support this flexing would be from the front hinge.
I note that the bonnet that popped open did not fly off.
There is an internal pressure (for cooling) but this is vented through the bonnet slots.
IMO there is a nett external pressure because of the shape of the bonnet and the effect from the windscreen.
If there was a nett uplift (an aero wing) two bonnet fixings would be advisable.
>> Edited by dlewis on Friday 5th July 15:01
>> Edited by dlewis on Friday 5th July 15:03
The logic being that as there is only one catch the bonnet would flex (or bounce) from a nett upward pressure, particulary on the passenger side. Without the small mid-support this flexing would be from the front hinge.
I note that the bonnet that popped open did not fly off.
There is an internal pressure (for cooling) but this is vented through the bonnet slots.
IMO there is a nett external pressure because of the shape of the bonnet and the effect from the windscreen.
If there was a nett uplift (an aero wing) two bonnet fixings would be advisable.
>> Edited by dlewis on Friday 5th July 15:01
>> Edited by dlewis on Friday 5th July 15:03
The bonnet came open but didn't come off and it seemed to lock okay once more when I stopped, Dave Batty at The Garage has now got me a spoiler so I will get that fitted and report back whether that's done the trick or not. If not I too would be interested in a second catch.
Jonathan
Jonathan
I have now had the front spoiler added to my Chimaera and the bonnet hardly moves at all (had it up to 140mph on the Autobahn), I also got the bonnet release cable changed too as this had become frayed with the continual bouncing of the bonnet. Well worth doing if you don't have that spoiler and drive over the ton.
Spoiler fully discussed here, albeit on Griffith:
www.pistonheads.com/gassing/topic.asp?t=13101&f=9&h=0&hw=spoiler
www.pistonheads.com/gassing/topic.asp?t=13101&f=9&h=0&hw=spoiler
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