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VW Cylinder Head Torque

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sonerainut

sonerainut

Active Member
Joined
Jun 17, 2007
Messages
35
All,

A friend I work with deals with the NTSB abd the FAA related to aircraft accidents. He sent me this .pdf of an FAA SAIB related to an unfortunate Q-2 accident. The VW engine apparently had one very lose cylinder head. The resulting hot exhaust gasses actually melted the head in several areas! I do not believe this was in any way an engine design flaw, but more of a maintenance issue.

Let's all learn from this. Check your cylinder head torques.

Lee
 
Thanks for posting this Pdf...

I never saw such damage before...

must have given some serious warning before it totally failed...

Gaston Dorval
C-GPXD S2L
 
I recently had a similar event happen with my Aerovee 2180. While in flight I noticed the engine begin to run rough. I tried making some adjustments to the mixture but it didn't help. At the same time I began to see some strange readings on the CHT and EGT gauges. The EGT on cylinder #1 started falling while CHTs on other cylinders was rising. I quickly turned for home and by the time I was in the traffic pattern the #1 EGT was down to 300F and it was clear that it was running on three cylinders.

After landing, I pulled the cowl and found that two of the studs holding the #1 cylinder head were broken and the other two were loose. Luckily, I didn't end up with any serious cylinder head damage, but the copper head gasket was completely melted and blown out about half way around.

Charlie
 
Yo Charlie,
Did you figure out the cause of the failure? Do you think the studs were over torqued? I believe there are inserts installed in the block on my AeroVee. Did these pull out of the block on any of the studs? It's been a while since I assembled my engine. I haven't run it yet. I think I'll back all mine off and recheck the torque on mine before it's run. It's hard to only torque them down to only 18 ft/lbs.
L8R
Gary
 
The problem started with one case saver pulling out of the case. I don't know how this happened, but I found it when I did the annual inspection and pulled the cylinder heads for a valve job. I made the decision to reinstall the head and leave one stud untorqued....my rationale was that it had been flying OK like that for a year so would probably be all right. Within 15 hours two other studs on that same cylinder broke and caused the forced landing.

I'm in the process of rebuilding the engine with a new case, now.

Charlie
 
Yo Charlie,
Thanks for the comeback. There isn't a lot of material around those case savers.
L8R
Gary
 
I had the similar problem that radfordc had this weekend. #1 cht climbed to 600 degrees and egt bottomed out. I landed at the nearest airport , trailered the plane home and pulled the heads off the engine. #1 head had the valves seats burned and found 2 loose stud bolts before i pulled the head. So i ordered 2 new heads from hummel engines I'll take a picture of the valves and post tomorrow .From now on at 25 hours, i'll change the oil, filter, check the valve lash and recheck the torque on the bolts.
 
here is a picture of the cylinder head
 

Attachments

  • cylinderhead.JPG
    cylinderhead.JPG
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So with this ,I'll change the oil, filter check the valves and cylinder head bolts every 25 hours now.
 
I have a question that no one has been able to give me a good answer. What is it about the VW engine that makes it so you have to continually re-torque the heads? I mean, all the other air-cooled (and otherwise) flat engines out there don't require it, so why the VW? Is it a design short coming? Undersized bolts? Weak metal? What? You'd think after all these decades it would have been resolved. I can see an initial re-torque, but every 25 hours just seems wrong.
 
In my humble opinion, there is no need to check the head nut torque every 25 hours. The normal recommendation is to retorque once after the original installation. When I install a head, I step torque the nuts up to 18 ft-lbs, and let them rest for several minutes, then torque them again. I do this a couple times, and then finish the engine assembly. I have never had a problem with head nut torque. Let's not get carried away here. If anything, check them at the annual condition inspection.
 
Fred, that makes a lot more sense. But you see so many people, and even some of the engine documentation, that say to re-torque quite often. It makes one wonder why.
 
We all might consider how impossible it is to torque the top four head bolts when the engine is installed in a car. No one I knew ever pulled their engine and stripped off the tin to check the torque on the top head bolts. Those engines seemed to run just fine without head torque issues.
 
do you have a good cht gauge, were you running hot. Also a good even warm up cool down. I have had 3 vw bugs old ones and rebuilt two engines and never had a problem with head studs or burned valves with lots of miles and I did not drive nice.
 
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