Timing chain tensioner and timing

[DavidHill]

I am in the process of rebuilding my series 1 engine and am about to fit the timing chain tensioner and then the head and camshaft.

Two areas that are puzzling me.....

1. In the attached TAV the large spring 38-3307 applies tension to the pivot part 38-3305 which in turn presses the tensioner sprocket 38-3314 against the timing chain.
The large spring is tensioned by part 38-3332.  It looks like the two holes in the circumference of the part can be used to preload the spring with a tool engaged into those holes before the part is pushed down onto the spline of part 38-3330which attaches to the pivoting part 38-3305.  My question is if this is correct - any recommendations on how to construct the tool (with a ground down sprocket perhaps?) and how many turns of the 38-3332 should i make with the tool before locking the spring in tension?

2. A more general question - how should i setup the timing chain wheel which attaches to the camshaft so that the camshaft is in the correct position in relationship to the pistons?

[simonandjuliet]

If no one else can answer this, give me a couple of days (I'm away at the moment) and I'll get back to you

[DavidHill]

Thanks Simon,

I have now bought a tool that does the job nicely (from Toolstation!  a universal adjustable angle grinder spanner - fits nicely

Recommendations on how much tension to put in the spring and how to set the camshaft up correctly still needed,

cheers
David.

[Andrew Cox]

With regard to the timing chain tensioner, I don’t think there is a recorded measured amount of tension that I am aware of. What is important that the tensioner applies enough pressure on the chain to keep it from moving too much while not loading up the bush at the centre of the gear excessively. This might sound a bit vague, but in practice it isn’t too hard to work out. Wear in the bush at the centre of the gear is very common cause of poor oil pressure in the Aprilia, hence it is a really good idea to renew it when doing an an engine rebuild. It is worth noting that the thread on the short splined shaft is left hand

[Andrew Cox]

With regard to how to set the valve timing on the Aprilia, I find the simplest method is as follows.
With the timing chain and gear installed on the camshaft, use a spanner on the crankshaft pulley to rotate the engine until the valve gear is rocking on no 4 (the rearmost cylinder). By this I mean that cam followers are climbing the lobes on both the inlet and exhaust and are an equal distance from the top ( around 10mm?). I would then remove the cam gear and rotate the bottom end until no 1 cylinder ( the front cylinder) has the piston at top dead centre. The distributor points should be about to break with the rotor pointing approximately at no 1 on the distributor cap. I find a piece of wooden dowel inserted into the cylinder via the spark plug hole helps with this job. Then reinstall the tensioned cam gear and chain and check both measurements. If all is OK insert the pin into the cam gear ( it will only fit into one of the holes) and fit the large nut and retaining washer to front of the gear and camshaft. The job should be then be complete. There will be cleverer and more exact methods, but the above works reliably for me.

[DavidHill]

That's very helpful, thanks Andrew!  I had to remove the short splined shaft as some of the splines were slightly damaged, and discovered the LH thread then!  You refer to the bush at the centre of the gear...do you mean part no. 383320 in the Tav diagram above?

[Andrew Cox]

Yes, the bush I referred to is part number 383320. I have seen a conversion with the bush removed and replaced with a modern sealed bearing. This would involved machining the centre out of the gear and would not be a job for the faint hearted, but well worth considering for a long term solution to a common problem.

[DavidHill]

Many thanks Andrew...I hope to get time to fit the tensioner and set up the valve timing this weekend.  Ref the tensioner part 383320, i think the bush is ok...out of interest how would the worn bush cause poor oil pressure?

Also thinking about attaching the chain to the cam wheel and setting timing etc ...is it best to set up the tensioner with tension before assembling the chain over the camwheel or is it best to assemble all with the chain slack, set the timing etc and then as a final step put tension in the tensioner by winding up the spring?

[simonandjuliet]

I wrote this up a while ago - hopefully it makes sense !

[Kari]

I was following the descriptions further up and the input of Simon and thought finding the right the position of the camshaft to the crankshaft is a bit vague. I compared the original text in the handbooks of both the Augusta and the Aprilia, the description is quite similar, but it seems there is room for improvement.

Some time ago, the late Andrew Maclagan issued a description how to adjust the valve timing on the Augusta more accurate. I wonder if the method for the Augusta could be adapted for the Aprilia, both the 1350 cc and the 1500 cc engine. I look forward hearing from Aprilia owners opinions about the improved procedure.


MIND THE GAP, by Andrew Maclagan

When setting the valve timing on an Augusta engine following work on the cylinder head I have in the past always referred to the
usual instructions. These tell you to adjust the tappets of the inlet and exhaust valves of what Lancia
ingeniously calls number one cylinder (corresponding to the second crankpin from the front, who would ever have guessed it?)
to 0.45 mm instead of the standard 0.25 mm. You then rotate the camshaft until the one valve is 'just' opening and the other
'nearly' closed. In this position and with the corresponding piston at top dead centre (i.e. flywheel at 1 /3), you fit the camshaft
sprocket to the camshaft. This works well enough, but there is an element of doubt as to the
exact point at which the desired position is reached, using just this visual check

Recently John Millham told me of a more accurate method which he remembered John Maltby using many years ago. It may be
old hat to the experts, but I had not heard of it before. It works a treat.

Instead of 0.45 mm you set the two tappets to an even wider
gap. Then at the point of `balance' you insert a feeler gauge at each tappet in turn and rotate the
camshaft back and forth until the point where the resistance felt at both gaps is the same. With the
two gaps set to 0.70 mm I found a 0.20 mm feeler was a tight fit and it was easy to compare the resistance
when withdrawing it at each tappet until this felt exactly the same for each one.

This method enables you to find the exact point you are looking for with absolute certainty, rather than relying on the visual check outlined in the book of words.

Karl

[Spider2]

That is the method described as to how to time the Appia engine. Differences of course are 2 cam shafts and the "false" clearance is set to 1mm and a .03 mm feeler is used to find exact point of opening (and closing for the other). Worked well for me.

[DavidHill]

Thanks to Simon and Andrew and Kari for descriptions of setting the timing.

My plan of approach is as below:

Fit head gasket(composite) and head and torque down to spec (58lbft)
fit cam and tappet followers etc to the head
put the timing chain around the cam wheel (with no tension on the tensioner)
put a medium amount of tension on the timing chain tensioner
follow the valve timing instructions and set the timing correctly and lock the vernier in position
reset the timing chain tensioner to the correct tension (still not sure what that should be - but guess it will be clear from how taught the chain is?)

does that sound the correct sequence?

[Spider2]

My gut feeling is put more than a medium amount of tension on the chain to avoid too much lash. Again going back to the Appia, the whole processhas has to be done with the tensioner in place.

[Andrew Cox]

Re the oil pressure issue, the arm that carries the tensioner gear has an oil passage within it and the bushes on the arm are drilled to allow the passage of the oil. The arm is part of the oil gallery hence wear in the bushes can cause noticeable oil pressure loss.

[DavidHill]

Major progress to report...the head is now on, the timing chain fitted, valves timed and valve clearances set...so the engine is finally complete.  Thank you to all who helped with advice.  Will post my next question about fitting the gearbox on a separate thread!