Why got valve clearance small?

Lars S · Post by **Lars S** » Mon Mar 30, 2009 11:06 am

Hello,
Ahead of the 412 season (in my country we dont run these cars from September to April due to salted roads

) I adjusted the valves today (it is some 5000km since), all inlets had stayed on the 0.15mm specified but 3 of the outlets had gone down to some 0.05 mm only.
Is it normal for the exhaust clerance to go down or can it be a petrol/valve seat issue (we have only unleaded fuel in here nowdays)?
The adjustment was done on a cold engine and it is original with 180.000km on it.

/Lars S

Lahti411 · Post by **Lahti411** » Mon Mar 30, 2009 12:14 pm

If the adjusting screw's locking nuts were tight and haven't let the adjusters turn then it's quite possible the valves have stretched. It's common especially for the exhaust valves. If you have never opened the heads, it might be the time for it just now...

raygreenwood · Post by **raygreenwood** » Thu Apr 02, 2009 2:50 pm

Yes...very important!
Change the adjusting screws out and drive for a few days and check them again. If the valves have changed again.....quickly as you can.....have the valve replaced. This is common on original equipment valves with high miles ....especially exhaust valves....to start stretching right before they break a head off....which will destroy the engine

. Been there..several times. Ray

Lars S · Post by **Lars S** » Sat Apr 04, 2009 5:27 am

Yes Ray, I have "been there" myself some times but only on Typ1 engines (cylinder no3) ...did't know this was a weak point also on Type4's ...will definitely keep an eye on this from now on.

/Lars S

raygreenwood · Post by **raygreenwood** » Sun Apr 05, 2009 11:01 am

The early 1700's....were notorious for a weaker valve material on the exhausts. Mostly pre-1972....but I am not 100% sure. They stretched alot when milage got high. Technically your 412 is not an early 1700....but it sounds like the same pattern.
Ray

Lars S · Post by **Lars S** » Sun Apr 05, 2009 11:33 am

Im sure this engine is the original and never opened, checked my service book it was some 6000km (

miles ) since I last did check the valves, does it sound to long ago?

/Lars S

raygreenwood · Post by **raygreenwood** » Sun Apr 05, 2009 12:46 pm

Hmmm...3728 miles. No...thats not too far. Typiclaly I like to adjust at 3000 when I change the oil. I also generally find diferences of .001" here and there.
When I had stock valve adjustmenst screws...I found some to be as much as .0025"...looser...from wear to the screws themselves. When I started using Porsches style adjusters....they never got loose....only tight...and only a little...like .001". This is normal.

When they start getting .002" to .003" tighter every 3000 miles or 6000km or so....especially if its the same valve.....its time. This is most common on the exhaust. They run so much hotter. Ray