Mechanical over rev. What did you find when it happened to you?
 

So... I went and did a 1/2/1 shift at 60 mph last weekend. I still can't figure out how I did it since I have a kit installed that creates a 1/2 gate and spring centers the shifter in the 3/4 shift plane... but whatever.

I thought I got away with one since there are no odd mechanical noises coming from the car BUT my #4 cylinder is cold and a bore scope appears to show valve contact with the piston. From research my brother and I have been doing, it appears the top end is the primary concern. The valves, springs etc, being the "sacrificial lamb" in a mechanical over rev situation. Naturally if the valve and piston come into contact repeatedly you'd have piston issues but my bore scope inspection only shows a "half moon" on the side of the piston. I'm going to try to get some decent pics but my bore scope isn't the best out there (Harbor Freight cheapo).

I'm waiting for a extension tube to arrive to perform a leak down test. I'm thinking while I wait for the tube to arrive I'll drain the oil, pull the valve covers and see if there's any visible damage.

I'm curious, since there's seems to be limited info on this site regarding the "money shift" and what exactly happens, what others found when they took things apart. I'm not looking for "I did this while I was in there". I'd like to know what damage you found internally. I'll be posting as I learn more about what happened to my engine. My symptoms so far are cold #4 cylinder and the engine is running lean. I'm in the 15-16 range on AFR at a cold start when I'd typically be in the 13's. The engine runs like I've got the oil cap off.

The worst part of all this is that I had the car for sale! I told my wife I should have been driving it like I was selling it rather than driving it like I stole it. :D Oh well!

Some threads I've found on the "money shift" I'm going to try to make this thread the "one stop" for issues related to the money shift. I probably should have included money shift in the title.
http://forums.pelicanparts.com/911-engine-rebuilding-forum/955607-how-much-damage-5-2-shift.html#post9576075
http://forums.pelicanparts.com/porsche-911-technical-forum/970457-money-shift-woes.html
http://forums.pelicanparts.com/porsche-911-technical-forum/357887-missed-shift-broke-some-rockers-what-else.html
http://forums.pelicanparts.com/porsche-911-technical-forum/1050227-broken-rocker-arm-need-advice.html
http://forums.pelicanparts.com/porsche-911-technical-forum/285304-5-3-miss-shift-3-2-what-we-looking-here.html

A leakdown or compression test should reveal a leaky valve if it's bent. You may also hear the bent valve banging against the seat since it wouldn't be sitting flush anymore. This assumes the rocker is still actuating the valve, i.e. rocker not broken.

Bad overrevs often break the rocker arm. If that cylinder is cold, it could be that the valve isn't moving at all anymore due to the rocker being broken. Pulling a valve cover as you mention will reveal that.

Broken crank pulley…

Leak it. It’s the only way to know...

Cabmando, post this in the engine rebuilding forum. You’re likely to get more people who’ve been through this versus armchair diagnostics.

Good point. I'll ask the mods to move to the rebuild section.

Meanwhile, I'm going to try to pull all the plugs today and get a look at each piston with the bore scope.

Good luck Nick.

Hopefully it's something small like the distibutor/lead/sparkplug.

The valve train is the weakest set of components.
I've seen a broken valve train repaired @ race track and back out the next session

The last time I did it... all the rockers on one bank were broken, cast rockers..

If you have forged rockers, you may find more internal damage.. valves bending and cracking the heads where the valve stem passes because the valve is meeting the top of piston, and the (forged) rocker wont yield. The valve stems looks like odd pasta shapes

No armchair BS .... IRL experience..

Oh, mine and Bills butt cracks were pictured on the cover of the Suncoast Regions Club Racing newsletter a few years ago while we did a engine in top end rebuild, in the sandy dusty Roebling Road infield

Seems the early cars, up to 69, had the forged rockers. Knowing that and from having my engine apart my car had cast rockers. Seems that would make any damage to the bottom end unlikely. As mentioned I can see a smile on my #4 piston. I pulled the plugs and it appears each was kissed with some showing more contact than others. I'm going to drain the oil, pull the valve covers and do a visual inspection while turning the engine over by hand. I figure by the time the extension tube I ordered gets here, I'll no longer need it because I will know if the valves are moving and have some idea if any are bent because if they aren't making full travel, my gap will be wrong.

In one of the threads I linked, it was suggested that the head of the pistons be buffed to remove the imperfection made when the valve met the piston. I have six good pistons at my disposal so I'm thinking I might just put those in if I have to do a teardown.

What usually happens on the 2nd to 1st money shift is one or more exhaust valves hit pistons. What happens next depends on the rocker type and how much you over revved the engine. I have done two 2nd to 1st money shifts and both times the engine was at 8,000 rpm when I made the shift.

My 3.6L race engine has cast rockers. In each incident a single rocker was broken. If you have a spare rocker and the broken piece stays in the valve cover area, you can fix that in 30 minutes. Valves might or might not get bent in this case. Put the new rocker in, adjust the lash, and start the engine up. If she sounds good and runs right, you are probably good to go. I broke a rocker at the start of a race. I replaced the rocker and won the next and final race of the day.

But, other things can go wrong. For example, it would appear that in one over rev incident, the passenger side chain tensioner had a retaining ring come off and it disassembled itself. This caused other valves to get bent. A leak down test will help inform you if any valves are bent.

I have a Rennshift shifter. The spring that pushes the shifter away from the 5th/reverse plane has 3 spacers underneath neath it. This provides the max spring pressure. The spring that pushes the shifter away from the 1st/2nd plane had no spacers underneath it. It still provided a push toward the 3rd/4th plane, but it was not all that it could be. I put two spacers underneath the spring and now the centering pressure is much stronger. I believe this will help prevent the money shift as shifting from 2nd to 1st requires much more effort to overcome the spring and keep the shifter in the 1st/2nd plane.

I have a Seine gate shift kit installed. This is why I can't figure out exactly how I did what I did. I don't grab the shifter coming out of two. I push with my palm out of two to allow the spring to move the shifter into the 3/4 plane.

Leak down test is coming. I just have to wait for the metal extension tube. I want to be sure I've got positive contact and a good seal. I know I could use the rubber hose but I think it will be easier to do the test properly once I've got the metal extension tube. Meanwhile I'll keep playing around and doing any visual inspection I can. Hopefully my mistake will help others in diagnosing if the same thing happens to them.

How did you get it into 1st going 60? G50 or 915 ?
Really sorry about the bad break, and hope you get it sorted

915!! That's what new dog teeth and brake bands and sliders will do for ya I guess :(
I'm really missin my old transmission right now. It would have let me know I was trying to go into 1.

On the inspection front, I drained the oil and removed the valve covers. Nothing fell out so that's a BIG plus. I put the engine at #1 TDC and felt valve play. I then went around as if I was doing a valve adjustment... 6,2,4,3,5. Not sure if it's just in my head but the #4 exhaust valve felt loose. Not enough for an "Ah ha" moment but I'm going to put the feelers in #4 and see what it looks like. I had my son turn the engine by hand while I watched the valves move and everything appears to be moving. Next up is a leak down test but that's gonna be a while unless I just decide to use the normal rubber tube. I'd really like to wait till this metal extension tube arrives because I want to see how much easier it makes the job or whether I waited and wasted $22.

I use 1st in at least one turn at every track I race on.......it's easy to shift into first gear!

I think I did the 1st instead of 3d upshift once, at a track at my 2d DE back when. Subconsciousness I think I was trying to impress my instructor that though my line was pretty bad, I was super good at making quick upshifts. Car ran rough thereafter. Tried to reset/check ignition timing. Was all wacky. Found the crank pulley locating pin had sheared, which explained that. Fixed it. Car started to seem to be running pretty much as before after a while. Two years later, with my lap times much improved, after transmission repair the mechanic, who drove it to be sure he had got things right, said it appeared to be down on power. Oh? I did a test (probably compression), and things didn't look so good. So I pulled the engine, and removed the heads, and gave them to the shop. Got a call - mechanics rolling around on the floor laughing. 6 exhaust valves bent into a sort of S shape.

What had happened is that the valves sawed grooves in the valve guides so the valve heads could seat again fairly well.

Lap times got even better after the engine went back in. Not something I would suggest as a long term fix, though. But one never knows. The head of one of the new valves from the rebuild broke off on track without the benefit of a missed shift, and there had been no such overevs in the interval. This time all sorts of things were destroyed, though the case could be welded up where the rod had sawed a new slot.

Without a broken rocker, my guess would be a bent valve head. That could lead to larger valve lash before anything started to readjust. The leakdown will tell you what is going on. Can you do your own engine removal and teardown and reassembly? Not so hard if you like puttering, and the head goes off to a shop which does that kind of thing.

Oh yeah, that won't be a problem. I've had the engine apart before when I had to do head studs. Waiting on this extension tube is going to feel like an eternity. I think I'm just going to go at it and see what kind of results I get using just the rubber adapter.

Pull the valve covers and check the rockers while you wait.

Hi Matt ..he did post #15......i do this all the time;-)....that i overlook.....

Ivan

You’re right. I scrolled on past when he responded to Suga nuts, and missed his second post.

Once years ago I did this and broke several rockers and bent at least one valve.

I did it a couple of weeks ago while racing ....going for a downshift to 3 on my freshly rebuilt 915 and got 1st. It was oh so brief and it made me **** my pants. So far that is the extent of the damage. I got lucky it seems. I did see some video from the driver behind me. It was a pretty ugly puff of gray smoke that came out of my pipes.

Many years ago when Mike Bruns helped me build my 3.0L, he said we will build the crank connecting rods and valve train to turn 8500rpm. Soo my 8000rpm missed shift didn't do anything and it's been running fine since.

Nick - what do you think is wrong with using a rubber line with an end which screws into the plug hole? That is what most if not all of the leakdown testers come with, isn't it? I wrapped mine with some stiff foam and lots of tape to stiffen it for easier install/removal, and it works fine.

I had made a steel tube line by busting out a spark plug's ceramic and threading its ID to screw a threaded tube in, with an air fitting on the outside end, all to speed up the install/uninstall process. Worked, but because I hadn't gotten the threaded hole fully axial, it wasn't easier to use. Better workmanship ought to do the trick, but again, what's the deal with the rubber? It's not going to expand and give bad readings, is it? Think rubber brake lines.

I got impatient and used the rubber line. I just thought the metal tube would make a positive seal. Story ends with the engine is gonna get dropped. #1 was 90psi/72psi #4 was toast. At this point I'm not sure checking #3 and #5 is necessary since visible inspection with wiggling the rockers indicated that #4 was loose. #6 and #2 were pretty solid at 90/86. The only benefit I can see from finishing is to let Craig know which cylinders to really look at for replacement parts.

Yeah, after my last over rev I did a leak down and found that cylinder 3 had 70% leak down. I stopped there as I knew the heads were coming off and going to Xtreme to be R&R'ed.

Your shop can most likely efficiently remove all the valve springs and valves. Check #1 is to put the valves in a valve grinding machine, or a lathe, and spin them up. If the stem is bent or the head is bent, that shows right up visually. Send them all. Maybe discuss with the shop - odds are decent that the intakes are OK - especially if there are no marks on the pistons showing intake valve contact. You could probably use that approach with the exhausts, but since a couple got dinged, why take the chance?

With the valves out, the shop can test the guide wear better, too.

I'm going to chat with Craig (cgarr) and see what his preference is. I have no problem with taking things apart I just want to be sure what he'll want.

Outstanding choice.

I brought the heads to Craig last Friday. I also brought the cam towers and rockers along. He's going to do a sonic clean on the towers and inspect the rockers.

Meanwhile, I'm debating rod bolts. Seems there's a lot of talk about the rod bolts being the weak link on the bottom end. I've read that rod bolts have caused catastrophic failure but I have yet to see a thread where a person points to faulty rod bolts (other than one where the original bolts were reused in a rebuild) as the reason for bottom end failure. Oil, or lack thereof, seems to be a more common reason behind a catastrophic failure.

I'm doing all the reading and research I can because I don't want to button this thing up and have a problem later down the road. My first inclination is to drop the $250 for bolts and move on.

Check your shift coupler in the tunnel. Mine lost it's bushings and I did the 2nd to 1st shift. Worth checking.

I did the 3\2 money shift. Think I hit 11k RPMs. Valve dropped into the combustion chamber and turned one of the pistons to powder (just gone). Drove it 30 miles home like that. Was an expensive rebuild.

73 911 E

My coupler has brass bushings but I will check my shift rod bushing. Once I get the engine back in, I'm going to play around with the coupler adjustment. I'm thinking I have the coupler adjusted on the jagged edge. I never readjusted the coupler when I went from my old transmission to my refreshed transmission. I just bolted everything together and it shifted well enough. But I think I've got some tweaking to do.

Thanks for the suggestion.

Just shy of three months and it's back together and running! Merry Christmas to me!! Now to find decent days to drive it for break in.

FWIW, I had 3 bent valves. Cgarr did the work and replaced all valves, guides and seals. I did a few "while you're in there" things like new pistons, rings, and rod bolts.

Congrats on the quick turn around.
What was the final bill ?

I haven't done a final tally but with rod bolts, 12 new valves, new piston rings, gasket kit, and machine work, I think I'm in it somewhere in the $1500 range. Not terrible.

Edit: Just ran the numbers and it came in at $1447.00 for everything listed above. This doesn't include brake cleaner purchased by the dozen along with other cleaning supplies, a new torque wrench because none of mine worked well in the 18-20 foot pound range, oil, oil filter, fuel filter. So all in I was probably closer to the $1800 range.

$1500 is extremely cheap. Free labor, I guess.

I drive Ferraris with dog leg shiift gates. You cannot shift back into 1st from 2nd.

Labor other than Cgarr's, which was in the total, work was all me. I dropped the engine, tore the engine down, put the engine back together, and put the engine back in by myself.

The frustrating thing about what happened is that I have a Seine gate shift kit in my shifter. I'm going to look at the spring tension and do some tweaking on the shift coupler.

Yeah and not a single photo!

I was going to post some pics but I figured everyone knows what a disassembled/reassembled 3.2 looks like. I took PLENTY of pics of the entire process.

One pic I didn't take that I should have was checking ring gap for the new piston rings. I bought a ring squaring tool and checked ring gap which is highly recommended when you're putting new rings in your existing cylinders. Outside of that, I think everything else has been covered here multiple times. I could be faulted for not posting the obligatory pic of me standing in my engine bay after dropping the engine.