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modifiedv8engines

V8 Cam Belts

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Hi All,

Reading through the service notes on cam belt change it looks as though the only way of measuring the tension is to use a Clavis gauge which I assume measures frequency ?

Has anyone got one or is there another method for checking tension ??

Engine is to be removed to sort out some other issues ( several ) and cam belt repalcemnt looks to be fairly straightforward if you fabricate a slotted dowl for the crank position and say a some 4mm twist drills for holding or checking the camshaft position.

Gather that the 3 bearings (expenisive @ £70 each) are also worth replacing as well as the belts .......another £140 ish

Cheers

Paul

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Plenty of threads on checking/adjusting tension on the belts, however I suppose for simplicity I will post here as well. Alternative tensioning devices can be found on the internet. Basically the clavis gauge that Lotus recommends is a frequency meter. Some on here have gone the "cheap" way and used a high quality mic and guitar or piano tuning software (TuneIt! comes to mind) as well as a laptop for portability. The particular program mentioned will give a fairly accurate Hz reading that some have said is quite close to the $1200US clavis gauge for a fraction of the cost.

As for the guide pulleys and tensioners, I'd examine them closely, and if you are unsure on any of them, I'd suggest replacement. It's cheap insurance and much much easier to replace with the engine on a stand rather than installed with a couple inches of working space between the engine and passenger compartment.

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Hi Paul,

As suggested there are a number of threads here on that very subject.

If you´ve got the engine out, then you should check and consider replacing not only the tensioners and steady idlers, but also the intermediate shaft roller bearings - in block and front cover. The intermediate shaft has something of a touch time and this could represent a good opportunity to refresh those rollers.

Cheers,

Mike S

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Thanks for the advice Mike/Blake

Will certainly check out the bearings as suggested.

Just for interest really .............came across this description/explanation which has probably already been posted but enables the job to be carried out with a spring balance, scales and a calculator

The question of how to convert pounds tension into Hz. is perhaps one of the most often asked questions from people outside of Europe. (In Europe the major manufacturers are now supplying diagrams of belt drives on with the HZ figures attached, so that it is easy!).

Below is a practical approach which does not depend on having any manufacturers data. Manufacturers data will give you both belt length, weight and also often the mass per unit length of the belt.

Stage 1.

The required tension has to converted from lbs to units of Newtons by multiplying by 4.45. As an example for the exercise let us say that the tension is specified at 100lbs. The required tension in newtons is therefore 445.

Stage 2.

The CLAVIS gauge should be used on the longest span of the belt. You need to measure the span length. This is the distance from where the belt leaves one pulley to where it makes contact with the other pulley. You should measure this distance in millimetres. Let us assume for example it is 200mm. which is 0.2 metres.

Stage 3.

You now need to weigh the belt. You should use postal scales or perhaps electronic cooking scales. The weight for a typical automotive timing belt is around 0.1 Kilogrammes (100 grammes) which is only around 3 ozs. So for accuracy it is important that you use sensitive scales. We recommend scales for measuring the weight of letters which can read to 1 gramme. Finally the total length of the belt should be measured. This can be done by laying a flexible tape measure around the outer face of the belt. The belt length for a typical timing belt is around 1200 millimetres or 1.2 metres.

At this point we calculate the mass per unit length of the belt in units of kg/metre, (ie. divide the weight of the belt by the length of the belt)

0.1/1.2 = 0.08 kg/m

Stage 4.

We now have all the information to calculate what the frequency reading should be on the CLAVIS gauge at the correct tension value.

The formula is;

T=4ml2f2

Where;

T is your required tension, in our case 100 lbs, or 445 Newton.

m is the mass per unit length, which we have calculated at 0.08 kg/m

l is the span distance (in metres) which is 0.2 m.

Therefore;

445 = 4 x 0.08 x 0.2 x 0.2 x f2

f2 = 445/4 x 0.08 x 0.2 x 0.2

f2 = 445/0.0128

f2 = 34,765

f= 186Hz

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