ZX Cambelt Questions

the_weaver · Post by **the_weaver** » 19 Aug 2010, 18:54

John

I'm sure a lot of people just tighten it up as far as they can. I expect a lot of mechanics who use windy guns just do it up with the gun. Having tried to use a torque angle gauge I can see why people don't bother with them.

Richard

Thanks for the useful tips. I was thinking of putting spots of Tippex on the pulley but I never thought of using the nut corners as a guide. I was going to measure 50 degrees with a protractor.

The belt makes it's way to a position of about 1mm off the edge of the pump sprocket within a few turns of the engine (by hand) and stays there. It doesn't continue moving outward more than the 1 mm. I'm hoping it is the crank pulley that is the cause. I think it's inside edge acts as a guide for the belt. It's a taper fit on the shaft and I haven't torqued it down properly yet. Hopefully, if the pulley moves down the shaft a bit then the belt will move inwards on the pump sprocket as well. The water pump is brand new. I bought the one with the protector for the sprocket by mistake but I don't think that's got anything to do with the problem.

Is the crankshaft pulley bolt a stretch bolt? If so, then the stretch calculation might not work for the second or third time. So maybe normal torquing is better if you're re-using the bolt. I have bought a new bolt but I'm keeping it until I know everything works ok.

Paul

the_weaver · Post by **the_weaver** » 22 Aug 2010, 23:06

I've now torqued and angle-torqued the crankshaft pulley bolt down fully and the problem with the cambelt hanging slightly off the edge of the pump sprocket is still there. What is strange is that the belt is on the cam sprocket by quite a bit. If there was a problem with the belt I would have expected the belt to be off the edge of both sprockets but for some reason it's only the pump sprocket that's affected. I've got my suspicions that the garage may have been messing about with the pump sprocket to "adjust" the timing. I would pull the pump sprocket off and re-seat it on the shaft if I could, but the threaded holes in the pump sprocket are M7 and I haven't got any long M7 bolts to make a puller.

Paul

the_weaver · Post by **the_weaver** » 23 Aug 2010, 00:07

I've noticed that the belt runs to one side on the crankshaft sprocket. It's running close to (or touching?) the back of the crankshaft pulley. There is a gap on the other (engine) side of the crankshaft sprocket between the belt and the raised inner edge of the crankshaft sprocket. Is this normal?

Paul

the_weaver · Post by **the_weaver** » 23 Aug 2010, 13:31

Does anybody know whether the crankshaft sprocket (behind the pulley) is a taper fit or not? I've replaced the old crankshaft sprocket with a new one. I'm wondering if the new, less worn sprocket sits further out on a tapered shaft and holds the crankshaft pulley further out from the engine.

When I was fitting the new idler I noticed that the idler is not a precise fit on the large circular locating dowel. I could slide the idler around quite a bit and effectively get some "adjustment" on the cambelt tension. I think this could affect the final position of the tensioner adjustment bolt in the slot and the amount of tension produced by the auto-tensioner. If the idler position is set so that the belt is fairly loose initially then the tensioner will have to take up more slack, the spring and plunger will have to come out more and the spring tension will be weaker and the cambelt tension will be less.

Paul

the_weaver · Post by **the_weaver** » 24 Aug 2010, 16:02

I've done some alignment checking using a steel rule. Not easy due to lack of space.

Using a steel rule on the flat face of the cam sprocket and taking the rule over to the pump sprocket I can see that the outer face of the cam sprocket is slightly further away from the engine than the face of the pump sprocket. I would estimate the difference at 1 or 2 mm. Is this normal?

Using a steel rule on the flat(ish) face of the tensioner roller and taking the rule over to the idler roller I can see that the tensioner roller is slightly further away from the engine. As before, the difference appears to be 1 or 2 mm. Is this normal?

I can't think of any way of checking the water pump to see if it's sitting flat. One thing I've noticed is that the garage, who fitted the water pump recently, seem to have used a sealant between the water pump and the engine. It was a brand new pump with a gasket so I don't know why they did this. I can see the sealant where it's come out at the side of the pump and it's black and rubbery. Obviously it was liquid when they put it on and now it's set. Would this be enough to skew the water pump over and cause the cambelt to run 1 mm over the edge of the pump sprocket?

Paul

spider · Post by **spider** » 24 Aug 2010, 16:12

I think the sealant around the pump is just the usual mechanics 'belt and braces' approach, as its horrible to fit something build it up and have it leak. They don't leak with a new gasket (unless you are very unlucky) , although the sealant is highly unlikely to cause the effect you mention, I know why you asked though. If you think about the bolts being tightened up, it will only mostly by virtue of hydraulic pressure squeeze the sealant out anyway, so I would not worry about that myself.

Regarding the pump sprocket vs cam sprocket, off hand I am not that sure, it does not sound wrong to be honest, I cannot really see how either of these two could be out, assuming their actual central bolts are tight, as its not practical for anyone to space them out with washers etc.

Sorry that's not a lot of help though.

the_weaver · Post by **the_weaver** » 24 Aug 2010, 20:14

Andy

Thanks for the reply. With regard to the diesel pump sprocket being slightly closer to the engine than the cam sprocket, I was wondering whether somebody in the garage might have removed the diesel pump sprocket and tightened the nut back up too tight, causing it to sit too far down on the tapered shaft. I was also wondering if somebody might have removed the Woodruff key to make the sprocket "adjustable". The chap mentioned something about adjusting the pump timing. If he meant moving the belt a notch then fine but if he was playing with the sprocket then it's not good. I was going to remove the nut on the diesel pump to check that the Woodruff key is still there but there's no room to get a torque wrench in to tighten it back up again and you need a tool to hold the sprocket.

Paul

spider · Post by **spider** » 24 Aug 2010, 21:03

I see.

You need a tool to pull the sprocket off really anyway it should not come loose. Either from another pump or a special tool, I dare say it can be done with a couple of bolts and a piece of straight bar.

I highly doubt they took the key out to get a little bit of movement on the pump, that's really bad idea to be honest, DW8's have vernier (sp?) adjustments and slotted holes if memory serves (not look at many as when this engine appeared I had almost left!) and mainly I did small servicing and things so by the time the later engines were at belt change time, I had gone.

I don't think you can actually force the sprocket further up the shaft than it should go really, can't say I've heard of it though.

The sprocket holding tool is so you do not turn the pump when attempting to tighten it up, a 'Y' shaped bracket, I dare say a 'good' strap wrench (material one obviously!) would hold it still too.

the_weaver · Post by **the_weaver** » 24 Aug 2010, 21:33

Andy

I'll assume they haven't messed about with the sprockets then, as it's too much of a pain to remove them just to have a look if the Woodruff key is missing.

I've got the old style cambelt covers. There's a thin metal backplate behind the sprockets inbetween the tensioner etc and the block. There could well be rubbish down there getting inbetween the tensioner and the block. It seems difficult to remove the plate as you have to remove both sprockets, the tensioner and possibly the engine mount as well. Not a good idea at all. I wonder if that's why they changed the design.

Paul