TDC mark doesn't seem to correspond to TDC at piston #1...

[johnl]

147 TS:

So I'm finally doing something about the leaky water pump since the leak has become significantly worse in the last few days (pump seems OK, suspect large OD O ring). So I'm now messing around with the timing belt as it goes back together.

In my messing about I've found that it seems one of the TDC marks on either the the lower belt cover or the pulley is about 5mm off (whatever that might equate to in degrees). When I set the #1 piston to TDC (as carefully 'measured' with rod down plug hole and eye), then the mark on the pulley is 5mm past the mark on the cover. Assuming my observation to be careful enough (I think it is), then this means that if timing were set using the belt cover and pulley marks then the valve timing would be significantly advanced.

Is it common for the pulley / cover marks to be significantly 'off' as seems to be the case here?

Regards,
John.

[Citroënbender]

Bonsoir John,

In my observations to date - three damped pulleys on 147TS motors - two had "spun". 

I use a TDC tool too, but indulged and bought the one Jamie Porter sells - think it's a Laser brand piece. 

[johnl]

Thanks CB,

CorelDraw tells me that a 5mm misalignment between the marks on the pulley and the cam cover equates to near enough 4°. So, divided by 2 at the half speed cam sprockets and the cam timing is very nearly 2° out relative to true TDC. If my visualisation is correct (harder than I thought, I may have it backwards), then using the incorrect timing marks (trap for the unwary) the cam timing will be near enough 2° advanced relative to what it would be if set up relative to true TDC, I think...

My belt had been set using the timing marks (and cam blocks), so I wonder how big an affect this has been having? Whatever, maybe 2° is not very significant, perhaps it is?

I dial indicator would be nice, or a 'positive stop' style TDC tool (screwed into the spark plug hole, stops crank rotatng at X° each side of TDC, with TDC being in the easily measurable middle).

I'm quite confident that I can very closely (as near as will make no signnificant difference) determine TDC using a rod on the piston crown and eyeballing it as it rises and falls. There is a very small rotation in which the rod neither rises nor falls (being piston 'dwell' at TDC), with true TDC being half way crank rotation between the piston ceasing to rise and beginning to fall, or vice versa (I'm sure you know this).

No matter how many times I've checked this, or which direction of rotation I check it from, I'm getting the same result, i.e. true TDC is 5mm past where the stock timing marks say it is. So, true TDC is 4° 'retarded' from where it has been running, so where it has been running is 4° advanced from what it should be, so cam timing has been 2° advanvced. At least I think so, hard to tell with this headache...

Regards,
John.

[Citroënbender]

Hi John,

Being cursed with optimism ("My glass is still almost half full!") I reckon the small discrepancy will probably result in headaches for the most part. Baselining is going to be cumbersome to achieve accurately, but at least you're not in a heavily urban area. 

[johnl]

Baselining and urban driving...?

My headache is due to attempting to visualise whether the existing incorrect timing marks have caused the valve timing to be advanced or retarded, and by how much.

Whatever, I'm sure the timing has been wrong and must have been having some adverse affect. Kind of hoping it's been a big bad effect, it would be nice to get some windfall boost in performance, but a little dissappointing if rectification turns out to make no detectable difference...

Regards,
John.

[Citroënbender]

Normally a balancer ring spins counterclockwise as some accessory loads it up and the slip occurs. It's unlikely it made nearly a full spin bar the last 5mm. 

If the mark is lining up before mechanically determined TDC, the cam events are happening before they're supposed to, so the cam is advanced.

And just to mention an unmentionable. 

The Alloytec range of GM donks, with their two-stage timing chains and all the grief that came with chain stretch and neglect. Eventually they'd get so far out of whack the cam sensor didn't tally with the crank sensor and they'd throw a code.  I don't know how many degrees, but it was well before any physical contact was risked, and from vernacular comments - assuming the variators were OK - well before any degraded performance came to light. 

So you might be looking at a similar risk scenario here; if the ECU feels it can't abide by the exhaust cam timing relative to the crank timing then it would alert you to an engine fault. 

[Cool Jesus]

I've never used the timing mark on the crank pulley. Always used the cam blocks and piston TDC with dial gauge (or rod as you have is OK I guess). Cam blocks aren't expensive if your keen to DIY the timing belt. If the timing is off, the little TS should feel like it could give more (If you k now what I mean). Once I tidied up our TS it went like a scalded cat. You wont find any detriment if you rectify any off timing. Remember,  these TS engines have a variable intake valve for peak performance output. Infact, I even think the intake manifold has adjustable intake runners. I was initially concerned at what you were describing, but you sound like your not new to getting your hands dirty. Don't put too much (or any faith) in the timing mark on the crank pulley. I never have, its all in the TDC of piston 1 on combustion stroke and positioning of piston 1 cam lobes (intake pointing to rear / exhaust to front) The workshop manual doesn't even mention the crank pulley mark. Actually, the pulley is removed to fit the belt!

[bazzbazz]

There is a much easier way to tell when your are top dead centre -

On the crankshaft pulley there is a locating lug for the balance belt pulley and that has a matching locating lug for the accessory belt pulley. When this lug on the crank shaft pulley is at the bottom of the rotation and the #1 piston is up, you have TDC,

Of course the engine is inclined slightly so you have to make sure your lining up the lug with the centreline of the engine, so picture the engine sitting dead vertical, when the lug of the crankshaft is at the centre bottom you have mechanical TDC. the only way this can be out is if you have a bent con-rod.

In this position it is EXACT TDC, no worries about trying to measure dwell ect.

One does pick up a few tricks when you do this as your day job.   

[johnl]

I've never used the timing mark on the crank pulley. Always used the cam blocks and piston TDC with dial gauge (or rod as you have is OK I guess).

I was surprised to find the Alfa marks so far off spec. In the past I've used the external factory marks to locate TDC, mostly because that's what most manuals say to use, and I'm a bit lazy, tending to assume it will be close enough if I'm not building a race engine (which I've only done once, not counting kart engines). Also, with a lot of engines it isn't possible to change the relationship between crank and camshaft rotational positions (with the stock parts). 

A dial indicator may be a tad more accurate, but mostly just makes finding true TDC easier than observing the vertical motion of a rod resting on the piston crown (I wonder whatever happened to the one I had all those years ago). Anyway, with care I think that an adequate 'measurement' of TDC can be achieved with a rod and eyeball.

Even with a dial indicator there is a small degree of crank rotation each side of TDC where the dial needle doesn't move (or piston movement becomes so infintesimal that it doesn't register on the dial). True TDC is half way between when the needle stops moving on the upward stroke and then starts to move again on the downward stroke (which of course is the 'piston dwell'). This is the same as with rod and eye, just easier to observe, and you still need to find the crank rotation point half way between the piston stopping and starting to move. Dwell period varies from engine to engine, depending on stroke and rod length (and weirdly is different at BDC than it is at TDC).

Cam blocks aren't expensive if your keen to DIY the timing belt. If the timing is off, the little TS should feel like it could give more (If you k now what I mean). Once I tidied up our TS it went like a scalded cat. You wont find any detriment if you rectify any off timing.

I used cam blocks. Without them I wouldn't have realised that the timing was so far out (or out at all), unless I 'degreed' the camshafts, which wasn't in danger of happening.

Brief test drive only so far with the 'new' timing, and first impressions are that the engine is now a bit 'torquier' than it was before. More miles required for a better feel of this.

The engine has been running the wrong timing since I bought the car. Shortly after purchase I changed the timing belt, and I checked the timing before I pulled the old belt off. It was set to TDC according to the crank and cover marks (with cam blocks fitted). I had no reason to think I needed to change this, so fitted the new belt as per. Live and learn...

Regards,
John.

[Cool Jesus]

There is a much easier way to tell when your are top dead centre -

On the crankshaft pulley there is a locating lug for the balance belt pulley and that has a matching locating lug for the accessory belt pulley. When this lug on the crank shaft pulley is at the bottom of the rotation and the #1 piston is up, you have TDC,

Bazz, keep giving away these little gems and you'll have no work! Nice... thanks

Actually, now that you've mentioned it, yeah I did notice this notch and the relationship with the piston on the crank on a recent engine rebuild.

[Cool Jesus]

I was surprised to find the Alfa marks so far off spec.

Yeah, I thought I read correctly between the lines on your post. It sounded like you knew what you were doing. I've heard and seen back yarders just rough guess it, no blocks, no TDC, just mark the old belt and cogs, transfer marks to new belt and replace, scary stuff.

Did you remember to loosen the cam gear wheels when adjusting the tensioner? Many forget to do this little bit which can and will leave your timing off slightly.

[johnl]

Did you remember to loosen the cam gear wheels when adjusting the tensioner? Many forget to do this little bit which can and will leave your timing off slightly.

Yes, both camshaft sprockets were loosened when setting the valve timing.

At some previous time with some previous owner, white 'aligning' marks had been painted on the inlet sprocket and variator.  When I first changed the timing belt (shortly after purchase of the car) these marks didn't noticeably change alignment when I loosened the inlet sprocket, but this time they did. I assume the exhaust sprocket also probably changed its' position on its' camshaft, but there are no marks to make this obvious.

This is undoubtedly because the valve timing has been / is set with the camshafts locked at X° and Y° courtesy of the cam blocks, and the crank is now at TDC instead of at 4° BTDC. Previously the incorrect crank positioning meant that the crank was 4° retarded relative to the camshafts, so keeping in mind the two to one rotation difference between crank and camshafts, the valve timing was advanced by 2° relative to the crankshaft, I think...

Anyway, whatever the specifics, the result is noticeably improved engine performance (apparent with more driving beyond the initial test drive). The engine now has a bit more torque, so is happier to pull a higher gear in situations where before it would want a downshift to stay in its' happy place. Throttle response has improved and it generally feels 'peppier'. I haven't really driven it hard (yet), nor revved it out properly, so can't yet comment on any affects on outright performance or how it feels in the upper reaches of rpm.

Power delivery has smoothed out a bit, wherein previously there were some noticeable little 'dips' in power at some points in the rev range, this is no longer noticeable. It seems a bit smoother (i.e. less vibration), but this is hugely subjective and might be no more than a placebo affect. I do think the affects on power and 'driveability' are real, if not then I'm more prone to delusion than I'd like to think...

Regards,
John.

[johnl]

Normally a balancer ring spins counterclockwise as some accessory loads it up and the slip occurs. It's unlikely it made nearly a full spin bar the last 5mm.

Agreed. It hasn't spun 356° (which of course would be impossible without complete failure of the rubber insert...). The damper 'ring' appears to have crept anti-clockwise relative to the pulley centre by 5mm, which equates to 4° (very close to it), or, has been manufactured with the TDC mark 5mm off, or, the TDC mark on the timing cover is incorrectly located, or, a combination thereof.

This does imply some chance that there is an incipient problem with the rubber insert between the harmonic damper ring and the centre section of the pulley assembly. If a misalignment has developed in the pulley / damper (as opposed to being due to a mis-located timing cover mark), then the rubber has at least 'taken a set' in reaction to the forces it is exposed to, which is best case (probable case I think).

Worst case is that the rubber, or its'' attachment to the steel components, has begun to fail. With any suspicion of an issue with a harmonic balancer it would be ideal to replace it, but I'm not about to unless it starts to show visible signs of distress, i.e. cracks appearing in the rubber etc. Were I using this damper on a race engine, or any engine that was going to be used habitually at high rpm, well I wouldn't use it. High rpm places a lot of stress on the rubber insert in harmonic balancers because the forces acting in the rubber become quite 'energetic' as rpm increase. The ring moves significantly in relation to the centre section of the pulley, and this generates quite a bit of heat in the rubber due to cyclic 'squirming' of the insert, which eventually leads to failure. It is my understanding that this is why harmonic dampers are (or should be) a 'lifed' component on high revving race engines (bad things happen if they fail...).

As it is the rubber in my damper appears OK, no cracks etc. and I'm fairly confident it will be fine on my relatively gently driven road car (relative to a race car that is...).

If the mark is lining up before mechanically determined TDC, the cam events are happening before they're supposed to, so the cam is advanced.

Agreed. As I figure this out / visualise it, before correcting the TDC issue at the crank, the valve timing was advanced by about 2°. It should now be where it is supposed to be, or at least a lot nearer than it was...

Regards,
John.

[bazzbazz]

The TDC mark on the plastic belt cover is not intended for setting the timing but to give an approximate position to place the crank before everything is pulled off the engine. If you use it as an initial guide it just makes setting the timing easier as the cam locks pretty well drop into place nicely and the #1 piston is pretty much at TDC and just requires a little tweaking.

(And YES, I DO realise I should have mentioned this at the very beginning, I'm having a bit of a "blonde" moment this week, obviously.  )

[johnl]

When I initially replaced the old belt I did check, i.e. before dismantling anything (other than taking off the upper timing cover), with the cam blocks in place I checked the marks on the pulley and on the lower timing cover. With the cam blocks installed these marks lined up perfectly, so I assumed it must be correct and made sure this is what I had when I fitted the new belt. I discounted possible belt stretch because it is my understanding that timing belts (in general) do not stretch to any significant degree, due to the kevlar (or whatever it is) used to make the belt cords being hugely resistant to stretching (being a major reason why it's used).

One of the factors in leading me to assume that the marks could be trusted was that the belt was apparently changed at 121,297km by Aotomoda in Five Dock, who as I understand are Alfa specialists, and should know. My assumption was, and still is, that the belt which I took off was most probably installed with the now suspect marks in alignment, so I just replicated this.

Anyway, sorted now.

Regards,
John.