CAM BELT Run out

[Rowge]

Hi All, Just did a top end rebuild on my 1987 Excel SA, details can be found by searching for tapping noise, anyway started up, engine sounds awesome and quiet on tickover, BUT cam belt moving from side to side on the cam pulleys by 1 to 2 mm, also belt was about 2mm nearer the front of the Aux pulley, and on the edge of the inlet pulley, but worst of all on the exhaust pully the belt stuck out more than the pulley by around 1mm, the belt was a genuine unopened Lotus belt with RED Lettering but of unknown age as it came with the car, new tensioner bearing, all pulleys look good. Anyway removed the crank v pulley again to check the cam belt pulley, I then realised the error of my ways, the belt pulley has a boss on its rear that the large washer SHOULD FIT OVER, mine was not hence the pulley was a few mm too far forward. I was enable to assemble the pulley and washer and fit to crankshaft as the casing with the timing marks on sticks out to far, so after cleaning up the washer centre so it was a nice fit onto pulley boss, I replaced the washer followed by the pulley, making sure the washer is sitting on the pulley boss before fitting the crank shaft v pulley, result belt still runs to the front of the aux and cam puleys but very close to the previous belt position. The belt is still moving in and out, maybe the belt is at fault, Tensioner adjusted anti clockwise to read 50 lbs on my Krikit 1, sounds good, when engine is warm Krikit reads 70 lbs.

[mkelite]

thats very interesting. had loads of nightmares replacing the cambelt on our Excel SA too...........after the car had been left in the garage for ages after previous cam belt shed teeth and everyone told me the valves would be bent etc. put new belt on, full compression on all cylinders! trouble then was a vrrr noise which increased with revs. replaced cam belt tensioner bearing, crankshaft drive sprocket and tested belt tightness with a Borroughs gauge to the letter as in the Lotus manual. still had a noise! so now very p'd off - i loosened the belt a little and the noise significantly reduced. still a bit there but im not loosening it any more, what would be the point of using the gauge............. still gotta get my new road springs and shocks on tho! regards all.DC.

[robertverhey]

Sorry to sound like a Krikit sceptic, but I'd be checking the twist-ability of the belt by hand as well...85 degrees with reasonable twisting force

Then with regard to the movement of the belt laterally on the wheels, I'd be double checking the placement of washers, spacers etc on each wheel against the exploded parts diagram. This shouldn't happen, these motors are built to close tolerances.

Robert

[chrisw2811]

I echo Robert's comments. The line-up across all pulleys should be very tight - sub-millimetre, and in the centre of the pulley front-to-back. Could the crank pulley still be projecting further forward than it should?

[Rowge]

Checked the cambelt wobble/run out with a DTI, the belt actually wobbles/runs out by 0.25mm or 0.10'' in old money, this was measured between aux pulley and inlet and between inlet and exhaust pulley, the run out position on the belt was the same so it seems like the belt is faulty, also the belt runs in the centre of the Auxilary pulley but is approx 2mm from the front edge of inlet and exhaust pulley. I placed a straight edge on the back of the inlet pulley and measaured the gap between the edge of the auxilary pulley and the straight edge, sure enough I have about 1.5mm, so if I use a 1.5/2.0mm packer behind my inlet and exhaust pulleys, the belt should run centrally, I do not have any packers/washers behind my inlet or exhaust pulleys, does anyone else have them, or heard of the need to do this?