Timing belt. Have I b@llsed up??

[Trev G]

Decided to fit new a timing belt on my R500 tonight.I lined up marks on pulleys,cracked the crank bolt, inserted cam locking tool, loosened off tensioner and removed old belt. So far so good! BUT when I tried to fit new belt it was either too slack between the cam pulleys and tight everywhere else or the belt teeth would sit on top of pulley teeth when I tried to get a more even tension.With the cam locking tool still in place using a 17 mm socket I very gently turned both cams just a fraction to allow the belt to fall into the teeth.I then tightened up the tensioner.Problem is the cam locking tool now wont come out and I may be paranoid but the marks on the pulleys look to be out by a fraction.Should I have turned the cams or should I have fitted the belt less tight between the cams? .HELP PLEASE

[oilyhands]

That is quite common.. either the line up will be right or it will be a complete tooth out, slight misalignment is not a problem. Often the cams will move a little once the belt is off in response to valve spring pressure, even with the locking tool in place, re-aligning perfectly without stressing the cam locking tool is quite hard to do, if you rock the pulleys a little you should be able to extract the locking device.

 

Oily

[Willie.]

Hello there,

 

Don't let the slack belt between the pulleys fool you. You just want to make sure nothing has turned (Cams are in the correct position relative to crank), which should be the case if you've kept the cam locking tool in.

 

I triple check that all 3 pulleys are in the correct position, then roughly tension the belt. Remove the locking tool and turn it over by hand. At some stages the belt my go loose between the pulleys...this is ok, so long as you've the belt nice and tight on the long run from exhaust cam to crank.

 

The reason the belt goes slack between the pulleys when you're timing it, is simply because of how the cams are rocking on springs etc. When its running, the cranking is constantly pulling the belt down...which pulls the exhuast cam...which pulls the inlet cam...and so there is never any slack when running.

 

I had the same panic.

 

If you're in any doubt that the pulleys are not in the right position, stop. And start again.

 

Just my 2p.

 

Willie

[Trev G]

Many thanks Oily and Willie .

[Sheds Moderator]

As Oily says it will be either right or a tooth out. Rock the cams a bit to get the locking tool out, then turn it over a few times by hand and recheck the timing. IF it's out you will see, if correct then happy days. Verniers should be fitted to the R5 (I thinhk), if you haven't disturbed the crank pulley then the exact timing should still be right. I'm not sure though if manufacturing tolerances on the belt might mean a *slight* difference in timing that you could/should correct on the verniers. This is not enough to bugger anything up though, simply a nice to have and you can reassemble it and recheck the cam timing with dial gauges when you like without removing the cambelt cover.

[Peter Carmichael]

It is worth double checking before you go any further.

 

The two cam pulleys are spaced apart by an exact amount, designed into the machining of the cylinder head. This means that with a taut belt run between the two pulleys, the cams should be exactly on their marks, in line with the centre line of the two cam pulley bolts.

 

The distance from the crank to the cam pulleys may be affected by the head previously having been skimmed. Also, the timing mark is much more difficult to view. There are all sorts of possibilities for getting the crank one tooth out....

 

... however, you will be much less in a muddle if you are 100% certain that the cams are on their marks and are correctly positioned relative to each other, with a taut belt run between them.

 

Here is how I do it:

 

1. Starting with a slack belt and everything approximately on their marks with the cam locking tool in place

2. The cam locking tool interlocks the two cam pulleys so that if you turn one pulley slightly it will tend to turn the other pulley in the opposite direction. By nudging each pulley by turn (inlet clockwise/exhaust anti clockwise) you will get a pulley position where the belt will go on with a bit of slack between the two pulleys, but once the pulleys are relaxed back onto their marks it will go tight.

3. Keeping the crank on its mark is a pointless and futile exercise. Again... nudge the crankshaft anticlockwise by the half tooth needed to get the belt to engage.

4. Keeping the belt from slipping on the cam pulleys, fit the tensioner and jiggle the belt to a fit on the crank timing gear.

5. Apply initial tension to the belt and this will tend to rotate the crank and bring it onto its mark.

 

Just as you have found, this may rotate the cam pulleys slightly, jamming the cam locking tool.

 

6. Nudge the crank gently in the direction required to bring the cams back onto their marks. The cam locking tool will now be loose - if it isn't, it means you have cocked up on step 2. Remember we are looking for perfect alignment against the cam itiming marks and we are happy that the crankshaft may be slightly off its mark.

7. Check where the crank is now, relative to its mark. It should, if anything, be slightly clockwise from its mark.

[Stationary M25 Traveller]

As a cambelt change virgin, due to do mine soon, the above looks so very useful. To be printed and kept handy for the Big Day.

 

7 related photos

[Trev G]

Thanks all for the advice.I took the belt off again last night (cam locking tool would not come out ).I refitted the way it was the 1st time (ie more slack between the cam pulleys),tightened everything up and turned over a couple times and all the marks appear to be lined up.Fingers crossed.Cheers.