Interesting build-up on these Volvo valves...

[Infectus-Guy]

I've recently been given a Volvo V40 2.0T with a snapped cam belt (70mph!), all 8 inlet valves were bent which was no surprise. What was a surprise was the amount of carbon build up on the exhaust valves. I've never seen anything like it! Not the most racey of subjects, but I found it interesting and though maybe some of you might be able to explain why they got this bad. Maybe the engine was run on normal unleaded or has never seen over 4k revs in its life perhaps?
Thanks for any ideas,
Guy

[Guy Croft]

Nor have I!

It's not by any chance a sodium cooled valve that has cracked?

G

[Infectus-Guy]

I don't think so because all 8 were just or almost as bad and they've cleaned up nicely, no signs of damage at all. I'm not sure if they're sodium cooled though, i'll have to find out. The amazing thing is, the car has only done about 95,000 miles!
Guy

[Didi]

Hey!

I've seen something quite similar on VW engines, not that old ones.
The disposal on the inlet valves consisted of sodium and phosphate, but not as much as on your exaust valves.
The reason was water coming in through the carbon canister fresh air inlet. So sodium and phosphate derive from the activated carbon.
If this is not the reason on yours, maybe this hint gives you another direction where to search.

I wonder, that none of the ex valves was bend. Belt probably snapped just because of this massive disposals, how do you guess?
This was the second frequent cause for the engine failures on the VW's - strucking* valves. First one was massive water intrution.

Regards, Didi.


(* sticking? GC)

[Infectus-Guy]

Thanks for the interesting ideas, i hadn't thought of moisture intake. Not that it'll be a problem any more because i'm going to be venting the crankcase gas to atmosphere. The cambelt snap was due to one of the tensioners falling apart.
Guy

[Didi]

Hey Guy,

the crankcase gas has nothing to do with the carbon canister. It's a part of the fuel system, venting the tank to atmosphere.
I guess the Sodium is a part of the process of activating the carbon. So if incoming water mixes with the carbon, engine will suck it in, together
with the fuel vapour and burn it.

Regards, Didi.

[Infectus-Guy]

Ah sorry i'm with you now. yes that sounds like the most likely cause, i will have to inspect it.
Thanks,
Guy