What can cause the Cam belt to jump 20+degree

[hissyfizzy]

On a serious inspection of the car it has been found that the belt has jump somewhere in region of 20+ degree advance ie it's jumped past the entire length of the timing marks which is 20 something degrees. Might explain some of the timing problems distributor has been found to be faulty.

What could cause this ?


Hissyfizzy
avidly awaiting the distributor

 

[frank]

not tight enough ?

 

[superls]

has it slipped or has it been replaced incorrectly?

 

[hissyfizzy]

Jump 20 degree

not tight enough ?

I can't see how but it's possible as it was measured @1mm deflection, it seems to have done it all of a sudden

has it slipped or has it been replaced incorrectly?

It was replaced correctly

 

[frank]

hissyfizzy

i dont understand the "1mm deflection" ?

 

[hissyfizzy]

according to the manual it states there is supposed to be 1mm if you press the belt down on the longest side of the belt

 

[frank]

-hissyfizzy

ye see what you mean, mine says 2mm/1lb of force, i used to set it so you could twang it, but not megga tight
in theory it would slip "retarded" is it 1 tooth out ?

 

[hissyfizzy]

No it was far further than that if you look at the timing cover see the timing marks 10, 0 etc mine was totally advanced by more than the timing marks 5+ teeth out at the crank not cam

 

[frank]

hissyfizzy

so your saying, the points are starting to open at 20 odd btdc ?

 

[hissyfizzy]

It seems on the down stroke atdc, if that's possible, there is a lot of tapping noises with the car running

 

[frank]

hissyfizzy

i think you best reset the cam belt timing, mr piston is probably kissing mr valve !

 

[hissyfizzy]

Possibly!! Hopefully not!!!!!!! It's being reset tomorrow hopefully not too much damage has been done

 

[Ed]

One tooth out on the top is a huge amount at the bottom 2:1 ratio. So one tooth may be enough to move it nearly 20 deg.

 

[frank]

hissyfizzy

i would hazzard a guess, that the tensioner has let go !

 

[hissyfizzy]

Ok I'll have that changed tomorrow. If the worst has happened and valves have bent anyone got any idea on how much a new set is?

 

[frank]

hissyfizzy

i doubt that its bent the valves if it was ticking over

 

[slyboogie]

i don't know, but my brothers rover cot about £450 with all new valves fitted (he sourced the valves i believe) and a new head gasket and cambelt, tensioner and waterpump (he had it all done then). It could be quite costly! Another engine would probably be cheaper?

 

[SammoHung]

tentioner is usuallt fairly reliable as this part of the engine is mostly grime free....

tentionner should be locked back out of the way while fitting , then when the belt is in place, the tentionner should be slackened off so that the spring on the tentionner tightenes pulley against the belt....then the tentionner should be nipped up again....

...then after all this and a couple of by-hand turns of the engine the tention should be measured.....

2mm at center of longest run with a forceof 500 'somthing or others' IIR

 

[hissyfizzy]

Cam belt 20+

tentioner is usuallt fairly reliable as this part of the engine is mostly grime free....

tentionner should be locked back out of the way while fitting , then when the belt is in place, the tentionner should be slackened off so that the spring on the tentionner tightenes pulley against the belt....then the tentionner should be nipped up again....

...then after all this and a couple of by-hand turns of the engine the tention should be measured.....

2mm at center of longest run with a forceof 500 'somthing or others' IIR

Belt refitted to the correct timing marks Engine now running again. Distributor arrived today thanks. To fit the electronic dissy to the early engine do I simply plug up the existing earth and one of the other two wires and leave the third blank or do I connect both wires to the coil, the haynes isn't very clear on this it shows one wire going no where so im guessing you double connect it.