Lotus Elan

knocking sound on take-off/stromberg airbox

PostPost by: bengalcharlie » Mon Jan 28, 2008 8:43 am

Hi all,

After I have just solved my run-on problem by adding some Wynn's engine cleaner to the fuel tank I am on my last?? fault that I have had for a while but not cured yet. Although I am pretty sure I know what it is.
On take-off and reversing the engine torque tilts the engine over that the airbox of my stromberg engine hits the inner fender.
I suspect that it hits just in the crease of the fender where the cap between the box and the fender is only about 10-15mm at the most.
I have checked all the mounts and they are all Ok.
the engine sits absolutely 100 level across and lenghtways.
On the exhaust side I put some spacers of about 10-12mm in place in order to clear the exhaust/chassis and if I look at the back of the engine I have an even gap for the gearbox bellhousing on either side.
It all looks OK. I have been thinking of tilting the engine towards the carb side but the engine would not sit level anymore ( do weber engines sit level??) and secondly the carbs themselves might hit the bonnet.
I run the car at present with a K&N cane filter directly mounted to the GRP airbox and I have noticed that there is already some slight rubbing going on on the tip of the filter so raising is not an option.
So I am thinking of cutting a piece out of my beautifull reglassed and 2 pot painted box to make some more room between fender and airbox.Bugger!!
Any suggestions or comments are welcome. I researched the site but could not find a satisfactory answer to my problem so that is why I decided create a new topic.
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PostPost by: CBUEB1771 » Mon Jan 28, 2008 1:17 pm

Unfortunately this is a normal problem. There is little clearance under the standard airbox to the inner fender well. Mine does not knock audibly but marks are evident on the fenderwell from sporadic contact by the airbox. In a +2 the engine is mounted straight up and down. The spacers on the exhaust side seem a bit odd. I presume you mean the four cylindrical spacers between the engine block and the mount on that side. The standard length for these spacers is 1 1/8 inch (31.8 mm).
Russ Newton
Elan +2S (1971)
Elite S2 (1962)
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PostPost by: 1964 S1 » Tue Jan 29, 2008 12:34 am

I have this problem to a mild degree on my S1. It didn't occur until after I had to replace a broken engine mount on the exhaust side. (yes I think I installed it correctly) I chalked it up to being an inferior new mount made of softer rubber. Perhaps you can load test your car to see if you're getting engine torque twist, indicating a weak mount.
My Weber engine is very slightly tilted upwards on the carb side.
An extremely wise car guy I know, Rallye Ralph, thinks it's a great idea to go from one end to the other on classic British cars, every few years, tightening all nuts, bolts and screws you come across. Not a bad idea, and now that I think about your (our) problem here, what about the bolts that hold the body to the chassis, if a few come loose the body could "rise" creating less clearance? I know it's a stretch but, time to check mine,,,
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PostPost by: bengalcharlie » Tue Jan 29, 2008 2:53 am

thanks for your replies and I am sort of happy to hear I am not the only one suffering from this but that it is a common problem.
Russ, yes I do mean the cylinder shaped spacers for the exhaust side so that should be fine.
I have to admit that the point made by the the other reply ( sorry forgot your username) is a very valid one and that is the rise of the body .
I should check the bolts again because I remeber now that I tighted one of the bolts in the front RH footwell on my RHD car and that actually made a difference although it was not enough.
I will check this over again and then make a decision how to go forward because I will get rid of it! It drives me nuts and it is not good for the carbs either.
Many thanks again
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