Who here had the pitted exhaust valves??

[gorper]

Can't find the original post...

I was curious about your valve issues, so I showed your pics to some professional race engine builders. The consensus was that water caused the pitting on those valves. Also, two of the guys recommended having that head checked for flatness/have it skimmed.

[TheRedBaron]

Shadowworks, I believe

[ShadowWorks]

LOL that was me, but it was from a donar head, I discovered the reason why the valves got pitted and your racer car friends are correct.

The engine was left idling for over an hour without a working cooling fan by a mechanic who is one of only two Saab mechanics in Glasgow

It basically over heat for over an hour and the high pressure water pushed by the headgasket into the piston chambers and gave the valves a superheated steam clean which damaged the exhaust valves and damage the headgasket as well.

It burnt off more than three litres of water and warped the head badly

No engine likes to be to that hot and the B202 is no different, that was an expensive repair job for the owner of the 900 and it was not even his fault.

You could see the damaged between these valves, the one on top left was screwed and the second from the top left is perfect almost, the centre indentation is gone from the valves that got water in the chamber.



Yeh I messed up my horrible kitchen counter

[idiot_saabvant]

Wow...so my theory on cavitation (due to water temps and surface tension) wasn't so far off.

[grif900]

Originally Posted by ShadowWorks

You could see the damaged between these valves, the one on top left was screwed and the second from the top left is perfect almost, the centre indentation is gone from the valves that got water in the chamber.

it looks to me as if those two valves (in the upper left) have been replaced with a different valve.

[ShadowWorks]

Originally Posted by grif900

it looks to me as if those two valves (in the upper left) have been replaced with a different valve.

You could be right, it does look different but I think the errosion has just eaten so much of the exhaust valve away that the centre looks different and bigger, it has lost alot of thickness which is hard to see from this pictures angle.

Originally Posted by idiot_saabvant

Wow...so my theory on cavitation (due to water temps and surface tension) wasn't so far off.

There you go then

I like to understand or diagnose problems before trying to fix anything, it's the only way to understand how things work and repair them correctly myself for free

[grif900]

but,the depression in exh.valve 7 looks to be a perfect circle,and #8 looks to have whats left of the same circle.very hard to tell from a picture but ,thats what i think i see.