Cambelt alignment

[tomward]

I’m having difficulty fitting the cambelt. As far as I can tell all the marks are lined up correctly, I’ve even done a dummy fit once before and it all went fine.

This time with the cover on the back I cannot get enough tension in the long run from the right side cam gear down to the crank pulley. Putting the belt over the teeth leaves it too slack, any tension I put into the belt leaves me half a tooth out. I can’t mess with the position of the gears and trying to fit it with the run a bit slack is impossible.

I’ve wasted two days on this and I really don’t know what is wrong, it must be quite fundamental

[Tipper]

My thoughts are:-
1 Which engine is it?
2 Do you have the correct cambelt? There is a difference between that for the 1.6i/1.8i and VVC. Compare the number of teeth with the one you took off.
3 Are you setting it up using the correct timing marks for the safe position?
4 If you place the belt on the longest run and then around the other pulleys/tensioner and finally tension the belt it should be in the right position. I find that the cam pulley locking tool sometimes didn't help the process and I had to remove it and adjust the belt a little to get it all in-line.
5 You say 'with the cover on the back'. Do you mean the back half of the cambelt cover?

[Reckless Rat]

Sometimes when fitting a new belt it is necessary to "ease" the crankshaft slightly to get the belt to slide over the exhaust cam wheel and the crank. Don't remove the cam locking tool, just turn the crank back (anticlockwise) a tiny amount making sure the two dots are still either side of the casting mark, and it should slide home:

[Gavin207]

I agree with Reckless, the gear position sometimes need easing, I had the same problem when I recently changed my head gasket. With the crankshaft locked I adjusted the cam shafts to get it to fit, first time after turning the engine over by hand they were one tooth out, so I had to take it off and try again, second time was ok. My preference would to be to adjust the cam shafts rather than the crank shaft, one of the advantages of the K series is that the engine is timed with the Pistons mid bore, so with the crankshaft locked for timing there is no risk of pistons hitting valves when turning the cam shafts.

[RobboMC]

+1 to Gavin,

I have done by cam belt twice and both times ended up half a tooth out. My diy solution is to leave the belt properly tensioned for a week,
then come back and reset it again. The new belts are very hard to get on with enough tension on the exhaust run.

I also adjusted the cam shafts rather than the crank for the second adjustment.

Turning the engine by hand seems OK, just don;t hit the starter key until you are 100% certain it's all timed up correctly.

[Rob Bell]

I have to say I've not encountered this on the engines where I've changed the belts (at least, not yet). I wonder why this is a problem on some engines and not on others? A heavy skim will alter the relationship between the cam and crank - but so much as to be that far out I would doubt...

[Gavin207]

I think the issue is a combination of the cam locking tool allowing a small but significant amount of movement of the cam shafts, and the difficulty of checking that the timing marks on the cam shafts are in line with the engine in the car, even with the help of a mirror, resulting in the marks being slightly below or above the horizontal, which enables the belt to be installed one tooth out.

[Reckless Rat]

Whilst moving the cam wheels with the crank in it's safe position (ie all pistons half way up their bores between TDC & BDC) isn't dangerous, the cam followers are spring loaded and if you move the cam the pressure from one of them will cause the cam to rotate off the cam follower. It's far easier to leave both cams in the locked position with the tool in place and make a slight adjustment of the crank to allow the new belt to slide onto the exhaust cam and the crankshaft. That run should still be tight. If it isn't then you've moved the crank too much and you'll be a tooth out. However, look at the photo I posted earlier. The two dots on the crank wheel are still either side of the casting mark although the right hand dot is slightly closer. It's only a matter of moving the crank a tiny bit anti clockwise to allow things to fit. Once the belt is on, sort the tensioner and then rotate the crankshaft twice by hand to ensure that everything still lines up. If you're happy then you can put everything back together and fire it up.

[Rob Bell]

Ensuring that everything still lines up after two rotations of the crank is the key here - and so long as you achieve this then how you get there doesn’t matter too much... lol

Just ensure you torque up the crank pulley retaining bolt/screw thingy - it needs to be very tight!!!

[tomward]

I didn't provide an update. The cambelt is on and tensioned. I couldn't move the crank because it was already up against the lock in the starter motor hole - technical term - and trying to bring it a smidge anti clockwise just undid the bolt. I gave both cams a full 360 degree rotation and lined it all up again. Looking at it with a mirror there is a tiny difference in the alignment of the cam gears but there was no other way of feeding the belt onto them and it might have just been the angle of the mirror. I've turned the engine twice, reset the tensioner turned it twice more and I'm reasonably happy it's going to be OK.

Half a tooth (if that) isn't going to make the pistons hit the valves is it? It's more likely it will just run a bit rough??

The next fun part is this weekend, trying to connect all of the pipes, electrical connections and hoses - I wish I'd stripped it myself in the first place

[Rob Bell]

No, half a tooth won't cause valve/cylinder contact. But the engine won't run as well as you'd hope it would... Any pictures? After two rotations, the cams should still return to their alignment positions.

[RobboMC]

Found this when doing a bit of googling:

It's from http://www.timguydesign.f2s.com/pics/MG ... cement.pdf

about how to change the head gasket on a 160.

Roughly align the engine into its service position aligning the
crank pulley with the 90o ATDC mark on the belt cover.

Loosen the crank pulley bolt. (I used a quality windy gun) and
nip it up again. If you don’t have an impact tool, you will need to
lock the engine. The best way is with a locking tool that engages
on the flywheel starter ring gear through the starter motor hole.
You need to take the starter motor off to use this though. Others
have trusted to luck, put the car into 4th gear and got someone to
stand on the brakes whilst they attack the crankshaft pulley bolt
with a breaker bar. I’m personally not especially in favour of this
method; it puts a lot of strain through the system.

Accurately position the engine to its service position.

Check the cam pulley timing marks are pointing at each


This is something I've not been doing. It's probable that when undoing such a tight bolt that everything flexes and moves.

So Tim's method was to loosen the bolt from it's initial torque, then nip it up enough to rotate the engine
( which isn't much as we all know ) and then position the crank accurately.
I'll be trying it this way next time, which looks soon from the amount of oil I have floating down the engine.

[Rob Bell]

I've tended to replace the water pump when replacing belts, so that, by accident, is what I have done in the past...