Lucky escape?

Yeah, that sure was a close one

Holy Sh1t.... Bad luck Lloyd. Hope the cams not to badly scored.....

I would love to know what caused it as I have just replaced my stem seals and wonder if there is something that needs checking....

Hope it's not to bad mate....

Alex

This has happened here in the recent past after a head makeover.
Usually you´d expect the car becoming a fog machine and not only hear ticking with a valve open

The reasoning behind this went so (I am not a technical guy, so it may be close only)

The hydraulic elements being completely empty do not provide the required pressure to the rocker which is installed with some kind of a washer. The washer may shift in the beginning ever so slightly and move the rocker out of its position from where it will eventually topple over.

The tech discovering this is a seasoned 8er wrench and has done quite a few top end refurbs, so he was just as surprised as you are.
He was certain not to have done anything wrong but still it has happened.

Good thing you looked into it by not only guessing

Cheers
Reinhard

I guess this could then be a problem if you don't use your car for a while and the oil drains out of the tappets??

I wouldn´t think so. Else we´d have heard about it many times. There probably is a difference between empty in "drained by standing" compared to "taken out of a box" and installed new.

Lloyd has not told us yet what was required when he did the valve stem seal job...

Cheers
Reinhard

Making the assumption that you refitted the shim on top of the valve stem correctly and had the follower properly aligned in the shim all correctly, then there is no clearance for the shim to pop out or the follower to slide sideways unless there was excessive clearance when the engine was started, and this could only be cause by drained lifters.

After this assembly procedure, I will normally crank the engine to achieve oil delivery to the heads so that I can check both the flow of oil from the spray bar, to settle the shims/followers and to ensure an oil flow in general from both heads.

This would have hopefully been sufficient time to either pump up the followers, or show the follower coming adrift as once the lifter is pressureized, this could not happen.

8Tech.

In that case, you have a lifter fault that has allowed the situation I describe above. The non return valve has failed and allowed the excess clearance.

Yes, replacing the lifter will also replace the NRV. I would also lubricate the cams, and especially the new follower with some cam lube on reassembly. Not only will it protect the cam and followers during initial start up, it is very sticky and will help keep everything in place whilst the oil pressure pumps-up the hydraulic tappets (lifters in US English) and most importantly of all, will help bed-in the new follower.

8Tech.

No, that is the breather non-return valve. The lifter has a NRV built-in which is an integral part of the lifter.

When you start the engine, oil flows into the lifter under engine oil pressure and pressurizes a chamber within the lifter that expands the length of the lifter untill all the slack is taken up, effectively giving zero tappet clearance.

There is a bleed valve on the lifter that then relieves any higher pressures so that the oil pressure does not apply any force on the follower or cam. When you stop, the NRV closes, preventing the oil contained within the lifter from draining back into the engine. Therefore when you restart the engine, the lifter is already "pumped-up" and does not rattle.

If the NRV is not fully sealing, then the lifter drains down again, back into the engine and the tappet will rattle on restart until it is filled up again. This is why an older car with a slightly worn NRV will rattle on start-up with a thinner oil, the thin oil works past the valve whereas the thicker oil does not.

An improvement on this basic design is seen in the roller followers fitted to the M73 engine. This reduces the friction on the cam/follower surface and allows hollow cams due to the reduced load, reducing valve train and general engine mass and the thermal loading on the oil.

A continuation of this explains why the "M" spec non-turbo engines still use manually adjustable tappets rather than the hydraulic types. The high lift radical cams in these cars accelerate the lifters so much faster, and therefore with so much force, it can either damage the NRV mechanism for sealing, or the excess pressure "bleed" valve can leak due to the higher mechanical pressures involved on the lifter.

Going a stage further with the explanation then of the mechanical lifter, early designs (E36 M3) used a shim on top of an inverted bucket on top of the valve between the cam and the valve stem, completely doing away with the "finger style follower", with the cam acting directly atop the valve assembly, vastly reducing valve train mass, and this made adjustment fairly straightforward. However as cam profiles got more radical, the cam lobe would hit the edge of the shim and spit it out like a tiddlywink with usually catastrophic consequencies. To combat this, the buckets were hardened and the shims placed between the bucket and the valve stem (E46 M3), known obviously as "shim under bucket" and this was good for 2 reasons. You could use any cam profile as long as it bore down on the bucket, and the shim could now be smaller and lighter, insert into the upper valve spring retainer and reduce valve train weight allowing higher rpm. With this arrangement, I have built engines with cam profiles (lobes) so huge, I have had to grind metal away from the cam cover to clear the lobes!! (Kawasaki Z1)

Main disadvantage however is that you now have to remove the camshafts to do the tappets, and thats why an "M" car is so expensive to service......the valves are (supposed) to be adjusted during an inspection service. It is not unknown though for the cam cover to be cleaned and a new gasket "booked" on the job sheet/invoice to make it appear they have been done. Doing this can save 3 hours+ for the dealer that you have still paid-for and how can you check it?

Asleep yet????

8Tech.

Zitat von 8Tech;84273

Asleep yet????

8Tech.

Well, at 04:37, when you posted the above, I was most definitely asleep.
Most people probably were at that time

Great job Lloyd. I'm all jealous as mine is quite clattery for a few seconds every morning. I think I'll live with it though...;-)

That's great news, well done!

Great news, and well done, hand shandy - not heard that one before!