Request for camshaft module photos, timing belt failure.

[lateski]

Hello!

I'm in the middle of a cylinder head repair of a 2019 T6 with a CXHA engine. It has a teethless timing belt(~1,5 years/75k km driven) resulting to valve and camshaft module damage.

I already had the head refurbished with new valves and before I fitted the new camshaft module it seemed to be far too different from the old one, so it made me unsure about quality of the new part.

The old module is 04L 109 071 E and it was supersede with 04L 103 044 AG, so I ordered the later module.

To the matter itself. Here is a picture of the modules. Old on the left and new on the right. Both are set around the TDC and all of the exhaust camlobes are misaligned with eachother, but the intake camlobes are identical in each module with the G40 trigger wheel, but the shaft itself is 180° off with eachother.



In the old module cylinders 2 and 3 had clearly spun cam lobes and those had also two broken rocker arms.



Do I have a case of spun exhaust cam lobes and a spun gears between shafts? Could the exhaust cam lobes spin each one equally as much? What do you think?

By looking at the new module the camlobe positions seems to be in place thinking about the engine work cycle, but I'm really uncertain about this situation. It's my first cylinder head repair to this generation engine and I have earlier worked around cast camshafts.

I'd like to have pictures of a known good camshaft module, if you have some, to make sure that the new module is good to fit the engine.

 

[Pauly]

Cant see how a revised head would have different timing to that extent !
If they fit on the same block then the firing order ect has to be the same surely ?

 

[lateski]

It shouldn't have. That's why I'd like to be sure and compare the new module to a known good one.

It's just beyond my comprehension, that could all eight exhaust cam lobes have spun around ~90° excluding those two on cylinders 2 and 3 and cam gear sprockets around ~180° degrees at the same time.

If I rotate the new module in working direction cylinder 1 opens exhaust valves and cylinder 4 intake valves as it should. Duty cycle should be ok on the new module. Am I just incredibly unlucky with the old module, that the exhaust cam lobes have all spun the same amount?

I bought the car from auction, so I don't know the conditions of the timing belt failure. Engine load, speed etc.

 

[Podge]

If I rotate the new module in working direction cylinder 1 opens exhaust valves and cylinder 4 intake valves as it should.

That's not right. If the exhaust valves are open on number 1 cylinder (exhaust stroke) then number 4 cylinder will be on the compression stroke so the valves on number 4 should be closed and that cylinder will be about to fire. I've seen a few piston to valve collisions over the years some have smashed holes in pistons or broken valve guides and wrecked tappets but I have never personally seen lobes spun. Although that cam looks well capable of it.

 

[lateski]

Maybe I wrote it a little wrong. Here is a picture around when cam should be able to lock with timing tool. Cylinder 1 should be firing around here and cylinder 4 intake valves are about to open.


On this second photo cam is turned 180° and intake valves are about open on cylinder 1 and exhaust valves have just been closed.



Exhaust cam is driven by timing belt, rotating clockwise and intake cam is driven by gear rotating anti-clockwise.

I think the work cycle should be ok, but failure of the old module is messing with my mind.

 

[Podge]

It is weird but I can't see anything else for it but lobes on the old cams have spun in a very similar way. Your new setup looks fine to me. Obviously you will be turning the engine at least two full revolutions of the crank with a spanner to check that nothing is catching before starting up. Don't forget to follow the rules for first starting with a new cam.

 

[lateski]

Update, I received photos from a friend of mine and new camshaft module looks like it should. Picture is taken from a dealer workshop of a known good used head.



In the meantime I disassembled the old module with angle grinder, cut the lobes off the camshaft and took the gears off. Lobes had little marks of turning and the gears also.

I'll post next update when I get the engine running, but finding time to go to the garage to finish the head rebuild during my parental leave is difficult sometimes.

 

[gjw5670]

I take it when the pin is in at TDC all the valves are closed? I think my cam wheel has spun on the shaft because number one is on inlet and number four is on exhaust.

The alternator bet shredded and got caught up in the cam belt ! It didnt bend any valves but I cant rotate the cams when the crankshaft is at TDC.

 

[lateski]

When camshaft is locked by pin exhaust valves on cylinder 2 are partially open, if I looked at it correctly.

If cylinders 1 and 4 are at TDC, you shouldn't be able to rotate the cam, because intake valves on cyl 4 are about to open next. If you rotate crank about 90°, you can rotate cams when pistons are in the middle of the cylinders.

Did the alternator belt destroy the timing belt plastic cover?