Update on my over-rev'ed head...

[fspGTD]

I got the head off my 1.6lTD motor... the one that I damaged by mis-shifting into 1st gear instead of 3rd gear during max acceleration while racing, causing the motor to be drastically over-revved.

The head looks like it won't be rebuildable, but I'm going to take it to my trusted machinist to see what he thinks.  One lifter "bucket" was completely missing from where it should be, and instead there were shattered pieces all over.  And another bucket was damaged and had a missing, shattered adjustment shim.  The cam had some damage on the lobes that had the damaged lifter buckets / shims.  All the intake valves, buckets, and lobes were fine, it was just the exhaust valves that had the damaged parts.  The bores in the head where the lifter buckets rode in were gouged out, some pretty badly.  It's because of that that I think the head may not be re-usable.  I wish I had a digital camera with me earlier today so I could show you guys!  I'll have to take some pics of it soon to show you guys the carnage.

Anyway, I also have some good news to offset the bad.  My dad has a core 1.6lTD solid lifter motor, which we pulled the head off of today.  The bottom end was trashed (melted pistons and every piston had deep recesses from what looked to be a mis-timed exhaust valves hitting them repeatedly) but it looked like the previous owner tried to save the engine by installing a freshened up or maybe even brand new head.  The head looks to be in really good shape.  I'm going to drop it off at my machinist's and have it checked out more closely.

More later on the bottom-end situation...

[type53b_gtd]

The bores in the head where the lifter buckets rode in were gouged out, some pretty badly.  It's because of that that I think the head may not be re-usable.

Ouch.  I've been catching up on reading on the board over the past few days, and I was rather surprised to read about the over-revving incident.  I'm sorry to hear about the damage.

If the lifter bores are messed up, then  you've got a paperweight/conversation piece and not
much more I'm afraid.

Sounds llike your replacement head has potential though - I've got my fingers crossed.

{QUOTE]
More later on the bottom-end situation...[/quote]

Hopefully it's nothing more than a few dented pistons!

I had a solid lifter 1.6TD where the timing jumped and one of the lifters was driven right out of the bore, wehre it ended up getting wedged inbeween the cam lobe and the thin wall of the head casting, cracking it to the point where iit actually bulged out.  Hydraulic lifters seem to sacrifice themselves for the good of the head, but there's nothing to give in the solid lifter engines, and it shows.

Drew

[fspGTD]

I just dropped both heads off at my machinist... he's going to take a look at both and get back to me later.  He actually said there might be hope with the over-revved head - that he might be able to install bushings in the messed up lifter bores.  But one of them is really bad.  It's probably gouged out up to 2-3mm sideways.  That would need to be a pretty thick bushing.  But this machinist is really good... he welded the cracks between valves on that head, and they did not re-appear...  More info later on the bottom end!

[2mn2]

Any idea of what the rpm was, when it let go? Also, what do you think the mechanism of the event was? ie belt stretched/broke, valves lagging etc?

Hope you can get it back together for cheap.


m alexander

[fspGTD]

There is more info about it on this thread:
http://www.vwdiesel.net/phpBB/viewtopic.php?t=223&start=15

I can't really say for sure what the RPMs went up to, but it may have been up to 9000RPM.

The timing belt remained in tact.  In fact I could even turn over the engine with the starter pretty well (must have been murdurous on the cam lobes with the shattered cam followers though :? )

From the engine being wound way farther than it should have been as a result of the mis-shift over-rev, it is likely that the valves floated, and then the pistons which "chase" the exhaust valves hit those exhaust valves, and then I can't really say what happened next.

There was also carbon/soot blown into the intake manifold, which made it's way back to the intercooler outlet!

[QuickTD]

I was a motorcycle mechanic in a previous life... Old Kawasaki KZ900/1000cc engines used to do the same thing when badly over-revved. They used an identical "shim over bucket" type of valve actuation. When these engines floated the valves they generally flicked the adjustment shims out of the buckets. There wasn't enough room in the head for the shim to get clear of the cam so the damage was usually pretty severe. Most drag racers installed shim under bucket lifters and valve spring retainers from the KZ550/750. These carried a smaller shim in the top of the valve spring retainer under the "bucket". A better setup for rev-ability but the cams had to be pulled to set the valve clearance. For the VW maybe hydraulics would work better on a highly revved motor. They might be a bit heavier and float sooner but the consequences of valve float wouldn't be as severe...

[fspGTD]

Yeah... I can see that happening!  somehow, during the over-revving period, when the followers moved away from the cam lobes, the shims may have flown out of their buckets...  and then yes, that could cause the shims and/or the followers to get shattered.

In greg Raven's "water-cooled volkswagen performance handbook", they mention there are the aftermarket solid followers available that do away with the shims (downsides are that adjusting valve clearances requires camshaft removal.  :? )  Benefits according to the text are the weight gets reduced a lot - from 71 grams (stock shim and bucket) down to 43 grams (solid-top follower and lash caps), thus allowing the setup to revv higher without valve float.  Doesn't matter a whole lot for my uses though - my race class don't allow deviations from stock equipment in this area.

[fspGTD]

I got the junk head back from the machinist and took some pics for you guys - note the badly scored exhaust valve cam follower bores:





I also saw the progress of my new head rebuild at the machine shop.  It is is coming along nicely.  I'm having them port-match it to a long-runner A2 gasser intake manifold.  

[lord_verminaard]

I got the junk head back from the machinist and took some pics for you guys - note the badly scored exhaust valve cam follower bores:

Well, I was expecting worse.  How did the combustion chambers look?  There is something to be said for the durability of these heads.  
- A little off topic- any idea if those aftermarket solid followers are avaliable anymore?

I also saw the progress of my new head rebuild at the machine shop.  It is is coming along nicely.  I'm having them port-match it to a long-runner A2 gasser intake manifold.  

Nice.  
It aught to run like a scared... er... Rabbit!  

Brendan
84 Scirocco 8v
00 Camaro L36 M49

[fspGTD]

Combustion chambers looked great - here they are, uncleaned:


The cracks between the valves that the machinist repaired didn't even come back!  He does good work.  

I don't know about those one-piece cam followers.

[fspGTD]

...and here is the long-runner A2 gasser intake:


Installing it will require relocating the turbo, which I don't have quite figured out yet.  (But when I do, this intake will be all cleaned, port-matched, and ready to bolt on.   )

[2mn2]

Jake

How did the short block hold up?


m alexander

[fspGTD]

Oh yeah - forgot to update you guys on that.  Two of the pistons got dents in them.  The dents are a little worse than last time it had piston-valve interference (which was when the timing belt got taken out, leading to bent valves and camshaft being broken into several pieces.)  One piston just has minor and even depression across the entire face of the valve contact.  You can feel it with your fingernail, but not very deep.  The other piston, which got it the worst, got gouged a little more deeply at the side, which sort of looks like maybe the valve head got bent around and the edge dug in a little bit.  I am going to try and smooth out the surface of the pistons (not sure exactly how yet.)  And maybe bolt the rebuilt head and and see how the bearings held up.  This bottom end isn't the first time it's been slammed into valves!  It's amazing how well it held up and how well it ran since last time this happened.  It will be sort of an experiment to see if the bottom end runs well, etc after bolting on the rebuilt head, knowing the RPMs that it's seen.  It should make for an interesting experiment!  If I wanted, I could also slip a set of new rod bearings in.  I'm not sure if I should do that or not, I was going to ask my machinist what he thought.  He said if I bothered to drop the pan and inspect them, I might as well go the whole nine yards and slip in some new rod bearings.  I'm not sure if I'm even going to bother though.  Like I said before, I know it's not seized.  Seems to turn over pretty freely.  And it has alread survived one valve bending eposide and seemed to run fine after that.  What do you guys think, disassemble the oil pan and put new rod bearings in or just bolt the head on as-is and see how it runs?  

[DieselsRcool]

I say measure the piston protrusion to check for anything bent. If all's good, button 'er up! I would'nt even worry about the marks in the piston tops as long as crowns aren't dented bad enough to pinch the rings.

[fspGTD]

Oh, they sure aren't dented that badly!  And it's just in the middle where the valves are.  When I get a new digital camera here soon, maybe I'll take some close-ups.

Good idea on piston protrusion measurements, Larry - I have protrusion measurements saved that were taken before the event, recorded individually for each piston.  I could easily measure them now and see how close they were to before... if something is not close, I know that there would be major trouble (IE: bent rod or crank, or bearing severely squashed or missing...)

Although I'd have more confidence in just replacing those rod bearings, I sort of want to try it without doing anything to the bottom end if I can, just to prove to myself that these bottom ends are capable of taking extreme RPMs and surviving (or if they are not capable of that kind of abuse, finding out about it...)  This current bottom end is totally a stock-spec kind of rebuild - no balancing, blueprinting or anything.  So if that could take a 1st gear overrevv and keep on running well afterward, it would be saying a lot I think.