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[Martin]

Hi,
Iv'e been driving a year with my repaired head(s) after the crank pulley came loose. I hear a knocking noise at 2500 rpm and it is most noticeble under accelleration from slow speed on on 3rd/4th gear. I wonder if it could be a lifter that does not really work properly? One lifter was a bit stiff when I assembled the heads but i thought if would be ok when it had been pressed down a couple of times.

I have also changed the con rod bearings but there was no difference.
I have listened with my stetoscope and hear no knocking noise at 2500
with no load.

If it is a lifter would you try to fix it with the engine in the car? I've also read about "bilstein engine flush" that should fix various noise problems. Has anyone any experience of such treatments on the boxer?

Thanks,

Martin

[Chris Notsis]

The lifter - if it is sticking, should be louder when the engine is first started. If it was stiff at the time you had it out, it is unlikely that using a crankcase cleaner will make much difference. Certainly it is worth trying, but if it is doing it at the speed you mention, the higher (unloaded) oil pressure is attempting to compress it but the inside of the lifter is contaminated (by oil aromatics that leave a permanent residue on the lifter sleeves), increasing resistance, causing the valve to hammer. In short, it is likely to need replacement.

In fact, the noise relative to speed range suggests the valve has worn the seat and the valve face a bit. The guide is probably ok. You will need to remove the head (again!) the verify there is no physical damage to the valve and seat, as well as replacing the lifter. It would be a good time to check the other lifters.
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Chris Notsis

[Martini]

Thanks for you answer! However, I don't really understand the oil pressure logic you explained.

The engine flush is done with some equipment that is connected to the engine lubrication system like a "engine dialyse". It is marketed to cure tappet noise by an alfa dealer close to where I live. It is not that expensive and maybe worth a try.

Could it also be a timing belt one tooth wrong or a fuel injector that is failing? It feels a little bit lazy and it does 140km/h on 4000rpm (on 5th). Don't know if that is normal.

All the best,
Martin

[Chris Notsis]

Mis-timed belt? One tooth out might cause a drop in power but would be noticeable in all power ranges, as well as unusual idle noise from the exhaust. It would not lead to tappet noise of the type you describe.

Injector? A blockage can usually be heard at idle, but only with a stethoscope - by putting the tip on the same spot for each injector and listening carefully, comparing the noises. If in doubt, then have them removed and ultrasonically cleaned (should be done every 100,000 kms anyway!). When was the fuel filter last changed?

Go ahead and try the cleaning method you mention. They add a concentrated distillate cleaner under high pressure and can sometimes work well (and sometimes not at all, especially if the internal sleeves of the lifter is worn).

Good luck. Let us all know how it goes.
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Chris Notsis

[Martini]

I have booked an engine flush in a couple of weeks. I think it'll cost around £100 including oil.

I'll change fuel filter too because I have no history on that. It's not very easy to remove when the screws are rusty though!

Have to change rear breaks first though, the car is stuck on its spot.

I'll let you know how it goes

/Martin