Timing chain inspection

[Huib]

You have to add the normal operating valve clearance to your values.

Those clearances are included in the 2,2 mm. So you are pretty close, at least on the exhaust.

The slack in the chain "measured" in the center between the sprocket wheels should be plus and minus 5 mm max. There should be a bit of slack to allow for thermal expansion of the engine but certainly not too much. As as I said above, you have to rotate the engine to a position where valve springs are pushing the sprocket wheels towards each other. Thus a combination of an opening exhaust valve and closing inlet valve and no other valves exerting pressure the other direction. To make sure the latter is not the case it helps to retract the tappet screws which are not involved in the test.

Using a dial gauge is an excellent idea.

I doubt if only the vernier would have done any better. I don't have any camshafts at home to have a look and count the number of holes. I seem to remember that the wheel has 11 holes and the camshaft 12 holes. There are thus 132 positions which means shifting position corresponds to 2,7 camshaft degrees which is 5,4 crankshaft degrees. Shifting the pin one position would change the timing by 5,4 degrees. In rounded off figures 3 degrees late would change into 3 degrees early which you don't want on intake valves.

There is a trick however to get a very accurate setting with the vernier. The sprocket wheel has 38 teeth. The 38 can be factored into 19 and 2. The 2 does not count as 12 (the nr of holes in the camshaft) also has a factor of 2 in it. Thus by jumping teeth on the sprocket wheel the number of different positions is multiplied by 19. You can get down to an accuracy of 5,4 / 19 = 0,3 degrees!!!

[Huib]

I suddenly doubt if pulling the chain at the center is a valid way of testing the chain in standard engines with unmodified tensioner. Even after compensating for all the leverages involved the valve springs are probably a lot stronger than the tensioner spring

[Peter Cripps]

Ah yes Huib, I forgot to include the clearances! As it happens, I've just measured them -- they are pretty close to the desired 0.15 mm intake and 0.25 mm exhaust, making my totals about 1.95 mm intake and 2.15 mm exhaust. Given that we're talking about a degree or two on the camshafts, this seems to me to be 'good enough'.

The amount of chain movement I get between the wheels varies quite a lot. In fact the movement at TDC seems to be more than elsewhere ... in other positions it's much tighter. Since there are no funny rattling noises when the engine is running I think the chain is probably OK for now.

Peter

[P. de R. Leclercq]

Yes that's right: in England we call this "hunting tooth"

Paul

[P. de R. Leclercq]

The way I test the chains is to ensure maximum "wrap" around a wheel and then attempt to lift the chain from the wheel. If there is little or no movement then the chain is good.

Paul

[P. de R. Leclercq]

Peter, in fact your timing is probably near perfect. The factory specified a clearance of 0.4mm for checking the timing - this probably allows for the "clearance ramp" on the camshaft

Paul

[Huib]

Isn't the 0,4 clearance specified obly for checking with a degree disc?

[P. de R. Leclercq]

Huib,

I don't know - you've got me there, but I don't see why it should specifically apply to the use of a degree wheel - and Peter's timing would be almost exact at 0.4!

Rgds

Paul

[Huib]

It is not a belt but a duplex chain, which is a lot safer and it gives you advanced warning as it becomes noisy when you release throttle.

Interval is very difficult to say as it very much depends on quality and driving style. On 1300's a common interval is 70.000 km. On1600's much less if driven agressively.

The ones I have for sale on this site are DID. Click here.
Also very good are Iwis chains. www.iwis.com