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907 cambelt change, who's done theirs recently? - Engine & Ancilliaries/Gearbox - The Lotus Forums Jump to content
CharlieCroker

907 cambelt change, who's done theirs recently?

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I'd like to change mine just to be sure, especially as I intend to drive the car a lot this summer and it hasn't been done for a while. Who can give me a step by step guide, how do you lock the cams and stop any movement, what do I need to do to make it as easy as possible?

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Hi Charlie, her's a little sneaky one I used a few years back.

Sharp Stanley knife and cut the belt in half round it's circumference, the let of a little tension and slip off half of the belt, slip the new belt onto the pulleys then cut through the remaining half of the old belt, push the new belt fully on and heyho. Now adjust the tension. Done this a couple of times on and old Elite long time ago and on pinto engines. Just make sure you have the belt far enough on the pulleys so that it does not turn in on itself. 

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Interesting technique, not sure I would be brave enough to cut the belt in situ!

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I normally mark the old belt and pulley wheels and sprockets with a tyre pen before removing the belt and then transfer the marks to the new belt before refitting, it ensures that it stays the same.

Regards Dan

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To start with, I'd focus on making sure the proper timing marks - the bumps on the cam pulleys etc, - all line up as the manual says they should.  If they do, then it is straight forward to reset everything whatever happens.  All these random marks people Tipex in seem to invite errors - as per mine car when I got it, which was a cog out on the exhaust timing.

 

I found  the hardest thing regarding the cambelt when rebuilding my engine was pinning the tensioner pulley, which is why johnpwalsh'es technique has an appeal if you can get it work.  

 

There is so much myth around these belts, I was scared before doing it.  But actually it really isn't that hard.  Just measure twice, cut once.

 

Your final problem is belt tensioning, given you can't get the old-school gauges Lotus used.  There are various recommendations on amount of twist on the forum elsewhere if you search.  

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Thanks Herc, I have had so many people say my method will not work but provided you do the norm and line everything up properly, just in case then there is no issue, and as you say measure twice, cut once.

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I did mine when I got it and I remember the job being refreshingly straight forward with the only odd bits being having to drain down the coolant and pull the upper radiator hose and maybe keeping the distributor timed.  I

 

What I remember about the job...

 

I pulled the hood which gave great access to the front of the engine.

 

I'm sure I didn't clamp the cam sprockets in any way.  Usually the cams stay put if the marks are lined up properly.  Be warned though, if you have them in the marked position and you move them several degrees in one direction or the other, the spring pressure from the valves will snap the cam to the next low spring pressure position, possibly knocking a valve into a piston.  If you are not clamping the cam sprockets, be sure not to rotate them at all.

 

I put a dab of white paint on the cam timing marks and the crank pulley some times though in the case of the 907 the crank pulley mark was very visible.

 

If the bearings on the tensioner are anything other than perfect, replace them.  It is a simple matter to press in the bearings (on the tensioner with replaceable bearings) and a seized tensioner bearing will destroy a timing belt in short order.

 

I didn't look at the video tony referenced above, but I'm sure it has as a penultimate step to rotate the engine over until the timing marks line up again to make sure everything is good before attempting to start the motor.

 

Don't be in a hurry to get done, and you should be fine.

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I had a quick look at changing the belt yesterday evening and moved everything into the correct position and marked all the correct alignment. Everything seems ready to go, slackened off the tensioner and was hoping to get the crankshaft pully off. So how does this come off without braking anything, in the video above the guy says put the car into 4th with the handbrake on then socket on the nut and away you go?

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Crankshaft pulley removal - undo then nut, then use a puller. But then I had the engine out.  Might be a bit of a fiddle in-situ.

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I've managed to get the thing off, the nut was the barsteward, I did what the guy said in the video, handbrake on and in 4th gear. Used a breaker bar on my ratchet and it came off. The pully came off without a fight. My tensioner bearing seems a bit grainy/noisy when spinning, think I'm going to change that while I'm in there.

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