Difficult starting / No power following cam belt change 5J BNV built Mar 2009

[16csvt]

This was starting and running fine before I broke it.

Following routine cambelt /idlers/pump change, it is very difficult to start, and lacks power. At idle, when the fan kicks in, it almost stalls.

Having tried to take the usual greatest care regarding locking off cam and crank, I am not totally convinced the belt timing is awry.

 

Before starting, I took the precaution of turning it over with a spanner 4 crank turns, two complete cycles and nothing touched.

I am a diesel bloke of the 'Old school', and have just had a very steep learning curve for the PD type fuel systems.

I was convinced from the sounds at starting that there is / was air in the system somewhere, it would start with coughing and knocking, then clean up to an idle.

Although it will rev to well up the gauge, it is sluggish and lacks the previous 'willingness'.

I have introduced a transparent piece to the tandem pump return pipe, and although I have seen a couple of tiny tiny bubbles, there was nothing to write home about.

When the pipe is disconnected at one end while running, the tank pump delivers at a very respectable rate out of one open pipe, and there is return from the tandem pump, but not as much, out the other end.

Putting ones thumb on the end of the (open) return pipe produces a proper hosepipe type squirting.

I am fairly sure that the tandem pump is in order. There was nothing wrong with it before, and it seems to perform now.

 

Back to the timing.

 

The book of lies does not instruct how to establish Crank TDC from first principles.

It assumes the timing is correct, and derives locking off positions from the peg in the cam pulley.

 

I think I probably need to prove the timing is correct.

The big question.   How can I derive the proper crank locking position from first principals, without reference to the cam?

 

The top belt cover is easily removed to access the locking hole.

Are there any tricks to avoid stripping the bottom for access?

 

[Paws4Thot]

@16csvt Did you count teeth between adjacent pulleys before and after the belt change? Have you reset the electronic fuel timing?

[sepulchrave]

https://www.asttools.co.uk/diesel-pumpe duse-commonrail-enginesettinglocking-balancershaft-belt-replacement-ast4840a-vag-1.2-1.4-1.6-1.8-2.0

 

All VW engines of that era have a tiny triangle mark on the crank sprocket which you will see has been highlighted in white on the photo in the link above, this must line up in the vertical plane of the block which is at about one o'clock due to the slight slant forwards of the engine.

[16csvt]

Last things first.

 

Reset timing.

                        No, have been meaning to get a vcds but somehow have never got a round tuit.

                        Had this vain hope that if mechanically it went back together at the same timing as it came off then it oughtn't to need change.

Teeth counting.

                         I confess I am not up on this technique. Have you a link to the detail so I ( and prob others in the future) can see the method?

                         I hadn't counted before, so it is probably pointless to count now?

                         In the past I've been fortunate to have engines with a peg through the block into the flywheel and a pegged cam (similar to this one).

 

Regards

16csvt

[sepulchrave]

Ok, do this:

 

Find the tiny triangle or mark on the crank sprocket and turn it to one o'clock, now try inserting the cam locking pin, rock the crank back and forth until it goes in, now loosen all three cam locking bolts slightly so you can turn the crank to the correct position and insert the crank locking tool, now tighten the three cam bolts and torque correctly. Whip out the locks and restart the engine. Better?

[J.R.]

Having done the first principles procedure outlined by Sepulchrave there is also the possibility of the (not) vernier pulley adjustment being needed for the new belt, VCDS can report something called Torsion Angle (I think) which is how many degrees from the optimal the injector timing is, this can make a big big difference.

 

My way to retain the existing crank & cam pulley alignments is to slice the old belt in half circumferentially then back off the tensioner just enough to persuade the new belt half way on, retension a little if needed then cut off the old half belt which will have kept the timing alignment for you, slide the new belt into its correct running position then adjust the tensioner as it should be.

 

On a PD engine I would then check the Torsion angle figure from VCDS and adjust if need be, that has pitfalls of its own so please ask if its indicated that you need to adjust it, also beware, a zero figure is far more likely to mean the angle is outside measurable limits than it is spot on, especially given how rough your engine runs.

[16csvt]

This time I put the peg in the cam and put paint dabs where the timing tabs are and on the backpeice.

Armed with the knowledge of the little mark on the sprocket,

I've knocked the crank pulley off, used the correct tool  (choice 2) with the correct corresponding mark very near the peg (per photo)

and lo and behold, cam is one whole tooth retarded w.r.t. crank. Easy done. (My excuse anyway).

It's easy when you know how, innit.

 

I shall be on with it, and report back the outcome.

Many thanks for the replies so far.

This Torsion Angle malarky looks interesting, but thats a job for when the mechanicals are in the right place.

 

16csvt

 

 

[Paws4Thot]

4 hours ago, 16csvt said:

cam is one whole tooth retarded w.r.t. crank

I wondered, but tooth counting is the only way to prove that either way...

[J.R.]

Excellent news and well done on avoiding valve/piston contact.

 

I have bought a few cars cheap in the past that in hindsight had been sold after cam belt or cylinder head gasket jobs and the owners complained of power loss to be told by the garage everything is correct.

 

They have all felt a little wheezy to me but hard to be sure if you did not know the engine, on the Suzuki Jeep I had already owned one so was pretty sure the cam timing was out.

 

They were all (3 vehicles) transformed by correct valve timing, on all of them the marks on the camshaft(s) fell either side of the fixed mark dependant on whether you advanced or retarded the cam, that is to say for the mechanic it was a 50/50 choice and he would not know which one to choose, I used a timing disc and dial guage to find the max lift ATDC point but it was very difficult to get the figure from the manufacturers, in the absence of it I would choose the mid point between max lift BTDC and ATDC for the inlet and exhaust cams.

[J.R.]

If someone had been mucking around with the torsion angle in the past its quite possible that the timing marks would never line up correctly without moving the cam(s) relative to the pulley and you would be faced with the 50/50 choice.

 

I got the cam timing wrong on my MK1 Octavia when I changed the belt, the problem was my neighbour who was watching the flywheel TDC mark while I was looking at the cam timing marks, he had twice as many functioning eyes than me but was looking at something other than the engraved line.

Edited 6 October, 2023 by J.R.

[16csvt]

Power and willingness restored!

In case the link to the picture of the timing marks breaks at some time in the future, here is one I prepared a short time ago.

The mark on the sprocket was originally a tiny rectangular dint, roughly the size of the light mark.

Notice that it had originally been picked out in BLACK!

One could just about see it with a mirror from above if one knew it was there somewhere.

The triangle mark on the tool (now blobbed white)  was hidden by the removal knob, now removed itself.

Once again, many thanks to those who responded.