AJP engine (or enginering) expert required!

[itiejim]

I have recently removed the engine (4.5) from my car as I had a noise that I suspected was timing chain related. Brief symptoms were a ticking noise like a loose valve clearance which was more pronounced when on a trailing throttle.

I have got the engine on a stand, removed the timing chain cover and am using a piece of bar attached to the front pulley to turn the crank.

Doing this I have noticed that, when looking at the chain in the middle of the V the chain goes cycles through tight and loose spots. The tight spots are very tight indeed - so much so that you can feel the stiction through the lever on the crank. At the end of the tight period the chain becomes slack all of a sudden - twice per revolution of the crank. This causes the chain to drop down onto the plastic chain carrier and, I suspect, is the root of my noise.

I have excluded the chain as being the culprit as the repetition is too regular given the length of the chain. I have noticed that the idler gear in the middle of the V is a bit worn - sharp teeth, but the other gears appear OK. However, the problem seems more linked to the bottom pulley rather than the top one.

So, two questions really:

1) Any ideas as to the culprit here?

2) How can I mark up the various pulleys to ensure that I can remove the chain and get the timing right again without removal of the heads?

Thanks!!

[stuthemong]

You sure tightness isn't just you opening up valves (i.e. fighting against the valve springs)?

If so you'd be working the lobes against some hefty springs. Then when the valve has gone over the peak lobe position, the springs will help rotate the valves which would propgate through cams through timing chain -> therefore getting easy again for a moment?

I'd defo take cam covers off and work out if the cam position isn't 'in sync' with the effect you mention.

Stu
EDIT
Also, chain hitting the tensioner when 'let off' - I know not how tight the chain should be, but that sounds very slack - you sure it's tensioned properly?

Also2. Timing. Can you not whap a dial guage down a spark plug bore to measure TDC of a piston (at least on most cars you can)? If you can get a spark plug out and see into the bore easily enough I'd probably retime it that way, then you know you are bang on. Also, assuming the cam pulleys have adjustment (vernier pullies) you could use this as an opportunity to totally dial in the timing more accurately than "which tooth" mechanism you are currently shooting for. This would only be a good thing if you can give it the time. (obviously you'd need to tension the chain properly first before going all out on a micron timing session!)

Read this: http://www.mgf.ultimatemg.com/group2/engines/tunin...
That's for DOHC, if I'm not being a 'tard there is only 1 cam on the cerb per bank, so it would be easier to do aswell (although you have to do it twice!)

Edited by stuthemong on Wednesday 26th August 17:57

Edited by stuthemong on Wednesday 26th August 18:27

[itiejim]

Stu,

I don't think this isn't the case. It goes loose (or tight) for the whole length of the chain between the cams (4 times per revolution of the cam).

I'll go and have another look though

[nemasis]

sounds like a loose tappet and is more pronounced on throttle over run!!!!!! i think you have a little end gone.

[ridds]

Not looked at the front of an AJP for a while but isn't the chain tensioner built into the front cover?

If so how have you retained tension in the chain?

[itiejim]

stuthemong said:

Also, chain hitting the tensioner when 'let off' - I know not how tight the chain should be, but that sounds very slack - you sure it's tensioned properly?

Also2. Timing. Can you not whap a dial guage down a spark plug bore to measure TDC of a piston (at least on most cars you can)? If you can get a spark plug out and see into the bore easily enough I'd probably retime it that way, then you know you are bang on.

Stu, the chain tensioner is part of the cam chain cover, so as soon as you take it off you lose the original tension. I've jury rigged something to keep reasonable tension.

I guess I could get a dial gauge down there - won't be easy though...

sounds like a loose tappet and is more pronounced on throttle over run!!!!!! i think you have a little end gone.

I wondered this as well. However, when the engine was running the noise was worse when hot - not what I'd expect for a little end, plus this whole timing chain thing looks wrong to me...

[itiejim]

Ridds - quite right - I've put a bolt in the front of the engine and used another bolt with a spacer on to maintain tension at something like what it should be.

[stuthemong]

OK, well I was a bit of a moron earlier but managed to edit it before anyone rightly lambasted me!

The camshaft performs 1 rotation for 2 rotations of the crank.

In 2 crank rotations you will have 1 inlet open/close and 1 exhaust open/close per bank.

This doesnt explain why you feel it go tight twice per rev UNLESS the opposite bank is out of phase.... which thinking about it, it must be, because you have a flat plane crank and a 75deg V, so when a piston is TDC in one bank, none can be in the other (one is 75 deg off, the other 105) Yeah. So you would expect the tight/soft/tight/soft to be the open/close of the inlets and exhausts on both banks, and that would give you 2 'tight' sections per crank rev.

If you look at the valve trains you'll see when some are pushing, and some pulling. As one cam is driven by the chain before the other (crank->left hand cam -> right hand cam -> tensioner) if the left hand cam is 'resisting' and the right hand is 'assisting' then the middle would go slack. The only way it wouldn't is if the chain was correctly tensioned such that the tensioner is stronger than the springing forces of the valvesprings (otherwise the valvesprings will just displace the tensioner spring and the chain would go slack)

It's like a bike derailer. If you pedal and push on the chain between the crank and rear casette, it's very firm. If you push underneath to the bottom chain, it's very soft, as you just make the derailer spring spring. I think you have something similar going on here to be honest.

Edited by stuthemong on Wednesday 26th August 18:43

[FarmyardPants]

itiejim said:

Stu,

I don't think this isn't the case. It goes loose (or tight) for the whole length of the chain between the cams (4 times per revolution of the cam).

I'll go and have another look though

If it's not a stretched chain then the only other possibility is the distance the chain has to span is changing (no st Sherlock) which could only be bent cam(s) or off-centre cam sprockets . Seeing as cams have broken in the past at the front (albeit a rare occurrence), presumably it is possible for it to bend there prior to failing(?). If you take the plugs out and turn it over faster with a handle style bar can you see the cam sprocket centre(s) move as it's turned over?

[stuthemong]

Farmyard, I have really talked myself into a 'valvespring stronger than his makeshift tensioner' argument. I think that is more likely than bent camsprokets.

A test of my theory would be to loosen the tensioner when the midspan is 'slack' and see if it gets even more 'slack' with the adjustment. And vice versa (tightening tensioner tighten midspan).

Of course, the only bad news is this doesnt explain the underlying tappet noise problem. It's just what it would be supposed to do. Little ends etc. I know nothing of diaging from noise, but if a trailing throttle would give rise to the sound you mention, then it seems a likely culprit to me. Certainly worth more investitgation

Edited by stuthemong on Wednesday 26th August 18:47

Edited by stuthemong on Wednesday 26th August 18:48

[ridds]

It sounds like you somehow have incorrect timing between cams. You have a large amount of slack in the V portion of the timing chain, if it was all timed and tensioned correctly then there should be no slack there even with the loading from valves opening/closing.

Are you sure you've applied the correct tension on the tensioning blade?

You'll struggle to GTI for TDC due to the plug bore angle.

[ridds]

Robbed Clivef's pic here

[stuthemong]

ridds, why would timing affect slackness?

The seperate banks operate 75 degrees out of phase to eachother, so the cams will be 75deg (or 105) out of phase of eachother. If the timing was slightly off you'd still have your 2 'spring/unspring' cycles per crank rev?

[ridds]

Thinking about it, it wouldn't

It's chain tension that's the problem. How else can the chain get "slack" Chains will go through tight and slack phases when working against the valves springs just whether this is the slackness that is being seen here or not.

[FarmyardPants]

stuthemong said:

Farmyard, I have really talked myself into a 'valvespring stronger than his makeshift tensioner' argument. I think that is more likely than bent camsprokets.

A test of my theory would be to loosen the tensioner when the midspan is 'slack' and see if it gets even more 'slack' with the adjustment. And vice versa (tightening tensioner tighten midspan).

Of course, the only bad news is this doesnt explain the underlying tappet noise problem. It's just what it would be supposed to do. Little ends etc. I know nothing of diaging from noise, but if a trailing throttle would give rise to the sound you mention, then it seems a likely culprit to me. Certainly worth more investitgation

Edited by stuthemong on Wednesday 26th August 18:47

Edited by stuthemong on Wednesday 26th August 18:48

You're right, my Sherlock argument is BS, the tension in the V is a function of how difficult it is to turn the left hand cam, which will vary somewhat with the position of the lobes. There should always be some tension, cams won't move by themselves lol, so it all boils down to what 'slack' means and whether the difference in slackness is normal.

[stuthemong]

ridds, thats a great pic of the badger.

Looks to me like the cam sprokets have adjustment capacity for timing on them - how would one find TDC on the AJP then if you can whap a dial guage down? Is there a mark on the crank you can use or something? I doubt that would be accurate enough though for proper timing.

[ridds]

People have created dead stops to find TDC and work the engine back and forth with a timing wheel to find 0.

[itiejim]

I'm fairly sure that the cam tension is not far off.

Also, the reason I took the engine out was because I had witnessed the chain suddenly dropping onto the guide when looking from the top with the cam cover off.

I don't think that the valve springs are enough to effectively turn the cam on their own.

I suspect one of the pulleys is out of true or something (but it's the or something bit that's getting me!)

[jammy_basturd]

What about this:

Slightly bent valve on Bank A, causing a friction spot. As the friction on Bank A reaches its peak, the timing chain uses up all its slack between cam A's sprocket, the makeshift tensioner and cam B, causing any slack to appear in the V.

[ridds]

Valve springs certainly do have enough pressure to turn a cam on it's own.

how much slack have you got, are we talking 1mm deflection of 10mm?