AAN valve guide shortening

[audi660]

Hi guys, my urs6 just started missing and eventually took the head in as cylinder 2 had no compression. Engineering company said the valve seats were too deep and the seat hit the valve guide and broke the bottom off. I'd like to know if I replace the guides, can I have them machined shorter at the bottom and by how much? Would that work and what is the OEM part number? I know they are 7mm. Thank you

[struikie]

Shouldn't the engineering company have a good solution for this?
It sounds to me that the seats have been worn/ machined too deep after all the years of running.
Does that mean replacing the valve seats and guides all together?

JW

[audi660]

I have no idea, thought replacing all of the guides and shortening them will solve the problem

[struikie]

Shortening might have a negative effect on stability of the valve when fully open.
If this is not the case, shortening the valve guides looks like the easiest fix.

JW

[audi660]

Yes it's the cheapest way as I have 4 valves so I only need to buy guides, then only assembly and valve lapping is needed

[K Simmonds]

The valve seat's on all the 20V five pot engines 7A, 3B, ABY, AAN etc are not supposed to be reground, only lapping is acceptable according to the factory manual.

If the seats are knackered they should be replaced but they normally out last the rest of the engine, how many miles has it done?

[audi660]

It's done 200000 miles

[K Simmonds]

Okay that's quite a few miles, however I've seen plenty of S2's and especially URS4/6 car's do well over that without even having the head removed, let alone need valve work.

I'd expect all ten exhaust valve guides to be getting close to the end of the their life by that sort miles but the seats should only need lapping in again unless the car's been run on very poor quality fuel for a long time which I guess is a possibility in SA.

It's odd for all four valves to be damaged on one cylinder unless it's ingested something, do you know if the head's been worked on before?

While the head's off at that mileage you probably want to replace all ten exhaust guide's and possibly the valves as well unless they've been done previously, it's not a job you want to have to do twice.

There should be plenty of clearance between the back of the valves and the guides unless the seats have been seriously mucked about with and/or new guides installed incorrectly in the past.

I'd try and avoid shortening the new valve guide's if you can, but you probably could take them down by 30 thou or so without issue...Though by right's you shouldn't need to.