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mg_tf
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Discussion Starter #1
IHello all-
I'm in the middle of replacing the timing belt on a ZT120.
New water pump in place and about to fit the new belt, but find the teeth on the belt aren't fitting properly on the gears.

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The belt also doesn't want to pull tight on the driven side (towards the front of the car), but feels too loose.
Locking tool went in (with difficulty) before the old belt was removed and hasn't been out.
I haven't done one of these before, but it seems like the gear on the right needs to be rotated a few degrees anti-clockwise to both take up the slack on the driven side and allow the teeth to mesh on the other cam.
But, as I understand it, the cams shouldn't be moved with the off?
When trying to time her up I did also find that if I had the lower timing mark correct, the gears were slightly off.
Any suggestions on correcting the timing very welcome.
Cheers!
 

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rover_400_95_99
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It may be the camera angle, but the locking tool appears to be incorrectly fitted. The middle ridge should be in line with the arrows on the timing gears. This is probably why you had difficulty fitting the tool.
 

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mg_tf
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Discussion Starter #3
Thanks Xanb
Picture is looking down- the lock tool is fitted with the central rib in line with the timing mark.
Somehow I've let something move just enough to stop th ebelt slipping home. Left it today before doing something stupid.
Things far worse get fixed- I'll read a bit more and go back with fresh eyes tomorrow.
Thanks again!
 

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Trophy Blue MG ZT
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Hi, you definitely did the right thing stopping because it didn't feel right.

Good instinct.

First off I'd check the crank hasn't moved.

2 dots either side of the rib which is roughly at the 1 o'clock position.

Or with the lower timing cover and pulley back on, the small line on the pulley and the far right most mark on the cover. Ignoring the timing and TDC marks.

Next make sure all the marks on the cams line up perfectly (Exhaust - In - Exhaust - In) use a ruler if you need to. They do want to move when you take the old belt off. Inlet cam will try to move anticlockwise and the exhaust clockwise due to valve spring pressure.

Next check the belts teeth are actually sitting in the teeth of the crankshaft, you'd be amazed especially when the lower cover is on.

The rest you know already by the looks.

Just a tip when all done manually crank a good few times and check the tensioner hasn't moved.

Have fun and take care.

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mg_tf
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Discussion Starter #5
Thanks, DeathDog.
Car too nice to kill by wrecking the valves so decided to take advice. She's been off the road for 7 years, another 24 hours wasn't going to hurt.
Much clearer on what I need to do, so when our first rain in weeks stops I'll have another go at timing her properly.
Cheers!
 

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I changed my ZS 120 cam belt last week for first time and had the same problem initially with the alignment. The locking tool fitted in very easily. I tried to re-fit the original belt but it no longer meshed either so my conclusion was that the cam gears had moved very slightly when the original belt was removed with the locking tool in place. I put a spanner on the cam gear bolts and there was sufficient 'wiggle' movement for the belt to drop into place correctly.

Locking tool removed, turned the engine over manually and everything checked out fine.
 

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mg_tf
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Discussion Starter #7
Good Morning Martin.
Yes, something shifted just enough to stop the belt meshing properly. For folk who've done this a few times they will have seen it before. I'm happier now to tweak the cam positions until the timing marks are bang on, then try again.
The access on the ZT is pretty good, with excellent visibility. Now glad I didn't try the TF for my first attempt.
Cheers,
Colin
 

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mg_tf
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Discussion Starter #8
Lovely (but cold) evening so went back to this.
Tweaked crank and cam positions. Put a metal straight edge across the cams as a guide and got all the timing marks exactly right, then locked in place.
Had a coffee, came back and double checked. Yup, all timing mark exactly right.
Belt on (LN100560), bottom crank first, then front cam, but it will not sit correctly on the second cam.
I tensioned it anyway to see what would happen, and sure enough the timing marks on the cams move out of step by about 3/4 of tooth. Just a little frustrating. I didn't rotate the engine, so no harm done.
Watching Technozen's video on youtube
I can see the belt mesh neatly with the cam teeth at about 4.20 in the video. Mine doesn't seem to wannt to play ball.
Tomorrow we'll have the belt off and look again.
Cheers everyone!
 

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mg_tf
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It sounds as if you have done all you can to check and double check that the timing marks are exactly where they should be.
I would now ask:-
Can you refit the old belt keeping the marks where they should be?
Make of new belt?
Have you changed the water pump, and if so what make?
Kind regards,
Austin.
 

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mg_tf
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Discussion Starter #10
That's an idea- might have a go at putting the old belt back in just to see if it actually fits.
Old and new belts carry the same markings- Gates Powerband, new one came in a kit from Rimmers. Belt, water pump and tensioner.
All boxed as 'MG Rover Parts'.
All good fun!!
 

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'06 MG ZR +120 (HQM) '04 MG ZR 105 (IAB)
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Gates PowerGrip were the original factory fit belt for the K, so you won't get any better a belt than that :).

I have found the easiest way to get the run from crank sprocket to exhaust cam sprocket tight is to turn the exhaust cam sprocket clockwise one tooth, fit the belt over it (with the crank sprocket marks aligned), and then turn the exhaust cam sprocket back to align the EX mark with the IN mark on the inlet cam, and only then insert the locking tool. That side of the belt should then be tight.

It may be due to pin-cushion distortion by your camera lens, but in your photo, it does appear that the cam sprocket timing marks are looking slightly 'uphill' at one another. They do need to align absolutely horizontally pointing at one another.
 

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I fitted a timing belt to a R25 a couple of weekends ago. I had the same type of problem as you. Belt was really tight on the pulleys, so started with it part way on, slipping it back when in position. With the locking-tool in it sat nicely in the front pulley, but not in the back pulley, and it was hard to get on the tensioner. With it fitted, I rotated the engine a few times and the locking-tool did’t fit with the marks aligned, it did fit with 1 tooth out. I tried again fitting without the locking-tool and got it on correctly, rotating the engine a few times to check. Some seem to go on easier than others...
 

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mg_tf
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Discussion Starter #13
Thanks Gents:
Man in the car- sorry about duff photo. I laid a metal straight edge across the cams to make sure the timing marks line up with the index line inside the rear cover. In that position the belt sits on the front cam fine, but on the rear cam I seem to get 'tooth to tooth' contact rather than 'tooth to notch'.
There are a lot of cars out there running around with properly timed K engines- I know this can be done, I'm just making an @rse of it somehow.
Thanks for all the advice.
I'll try and post a couple of decent pictures showing all the timing marks aligned. Got to go and work now unfortunately.
Cheers all!
 

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mg_tf
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Discussion Starter #14
For all hints and suggestions, thank you very much indeed everyone.
Belt now on.
For anyone else trying their first ever belt:
Importantly, make really sure the timing mark on the crank is exactly right. Then you can just forget about the bottom of the engine.
What I didn't really grasp (Duhhh . . .) was that with the belt off the crank and the cams are no longer linked- you can't turn the engine over as the pistons would hit some valve or other. But, there's nothing to stop you turning the cams. When I tried to fit the belt it was way too loose across the cams. Got the belt in place, with a bit of hose under the bottom of the belt to hold it on the crank. Then, I took the lock tool out. I put a spanner on the end and by rotating the cams just a little the belt then meshed with the teeth on the cam gears. Having the belt on the teeth stops the cams springing back, even without the lock tool. Just use your third right hand to guide the tensioner into place while holding the belt on the gears and sliding the belt round the water pump
With belt and tensioner in place the upper timing marks on mine looked a tiny bit out, but presto- two rotations of the engine and both upper and lower marks all fell perfectly together.
Tighten the tensioner bolt almost fully- you still need to be able to turn the tensioner anticlockwise to tension the belt without it just springing back when you let go.
If it doesn't look right, stop and have a coffee. It's better to take the belt back off, re-time the cams, and try again, rather than kill the car. I ended up having four attempts at fitting the belt: Awful, 3/4 of a tooth out, nearly right, then correct.
Haynes is good, but I didn't really understand this properly until I got into it.
Once again,
Thanks Team!
 

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Trophy Blue MG ZT
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Well done!

I bet you feel like you've been on a bit of a journey.

Mikey

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mg_tf
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Discussion Starter #16
Hi Mikey-
I knew my car was just like every other 75/ZT, so all the bits had to go back together. It's very satisfying when the engine fires up and doesn't miss a beat.
I'd do it again in half the time now I understand what's actually going on, but I take my hat off to some of the folk on here who are doing a head gasket change in half a day, never mind just the belts.
Cheers!
 
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