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Broke THREE 2.7 intake rockers on one side - ?????

Howdy,

Stock 2.7RS engine, low hours, with Webers.

At the Monticello race I was flat out in 4th near 7000 RPM and lost power. Car was running fine till then. Made it in and found all 3 intake rockers broken on the driver's side. Did a leakdown, and valves are not bent!!!

I though I was shifting at or before 7200 in the race, but I did hear my rev limiter kick in a few times which is set to 7500, so now I am thinking my tach may be off. But the engine did not sound like it was revving that high. I think I have the titanium valve spring keepers, noticed a funny color when adjusting the valves. Not sure what valve springs I have.

Had anyone ever seen THREE rockers break like this? I am going to check to see if the cam timing is OK and that the spray bar is working ok. Anything else I should check before installing new rockers? Are stock early rockers best for this engine?

My GT3 cup engine died last year, (again) I just have no luck in the last few years.
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1973 911RS Clone F class, 2008 GT3 cup GTC4
2004 Touareg, 2006 Mini Cooper S, '01 Viper GTS
my racing pages - http://www.analogman.com/911
~^v^~ aNaLoG.MaN ~^v^~ guitar effects LLC www.analogman.com
Old 07-15-2017, 07:08 PM
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Good luck getting this fixed, Mike. I'm curious to see what the consensus is.

I always enjoy seeing you run at the Lime Rock vintage weekend. Is this the car that broke?



Mark
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Old 07-15-2017, 07:36 PM
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Thanks, Mark!!!

Yes that's the same car, with the same engine. It's been good for me, winning the class at this event several times in the last few decades
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Regards, mike AnalogMike at aol.com
1973 911RS Clone F class, 2008 GT3 cup GTC4
2004 Touareg, 2006 Mini Cooper S, '01 Viper GTS
my racing pages - http://www.analogman.com/911
~^v^~ aNaLoG.MaN ~^v^~ guitar effects LLC www.analogman.com
Old 07-15-2017, 07:51 PM
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Interesting that it was the intakes. Stock cams?
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Old 07-15-2017, 08:31 PM
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You got to carefully look at the cams. There are several worthwhile threads in the Engine Rebuilding Forum. Here is my saga....
Cam removal question
Good luck.
Johan
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Old 07-16-2017, 05:20 AM
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I once broke 2 out of 3 rocker arms on one bank (have yet to reach the trifecta thus far). It also bent a couple of valves and broke their respective rockers, but I forget if they were intake or exhaust. And that happened under more or less mundane driving conditions.

Sounds like a classic case of valve and piston contact. Fortunately, your valves seem to have survived, but not your rockers which are, by design or by default, sacrificial components in the 911 valve train.

In my case, it was due to the original subpar rubber chain ramps crumbling due to heat and ageism, broken bits of which end up between chain and sprocket causing the chain to skip and lose critical valve train timing. When valve timing is off, something's gotta give.

In other situations, excessive engine speed can result in valve float, the inability of the valve train to maintain contact with one or more cam lobes due to inertia. Lighter components (valves, retainers, locks, etc.) and heavier springs can delay or reduce the mass and avoid valve float , but all it takes is a missed shift or a sudden unloading of the drive wheels before engine speed momentarily increases beyond red line. Minimum valve-to-piston clearances can exacerbate the situation.

Retest and confirm each of the cylinders are healthy. Even so, without inspecting the pistons, there's always a chance damage was done that may not reveal itself until the next excursion to an unknown engine speed.

Sherwood
Old 07-16-2017, 12:59 PM
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I will be interested in what caused this. The exhaust valves are the ones that are in danger of piston contact. I guess with aftermarket pistons you could have piston to valve contact without bending the valves? Due to the fact that, for example, JE pistons have valve pockets that are square to the valve face?
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Old 07-16-2017, 04:45 PM
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Usually caused by over rev on downshifts.
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Old 07-16-2017, 05:46 PM
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thanks for the replies.

It's a stock 2.7RS with lowish hours. I have not pulled any other valve covers yet but will asap. I think I remember tilting the car to the side to keep oil from coming out of the exhaust valve cover. I just changed the oil, it has about an hour on it so don't want to drain it if the engine is ok. But maybe I should anyway in case some rocker arm fragments got in the oil.

I read the link above about spray bar issues, I don't remember seeing much oil in there.
I think the spray bar shares oil with the chain tensioner, I wonder if the tensioner leaked too much if it could cause a lack of oil to the cam area. I will check the tensioner and cam timing asap.

I have little energy for fixing this as I spent months working on it pulling the powertrain out to get the trans rebuilt, valves adjusted, and several oil leaks fixed. Will post my #8 bearing leak fix solution when I get some time, it seems to be holding.

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1973 911RS Clone F class, 2008 GT3 cup GTC4
2004 Touareg, 2006 Mini Cooper S, '01 Viper GTS
my racing pages - http://www.analogman.com/911
~^v^~ aNaLoG.MaN ~^v^~ guitar effects LLC www.analogman.com
Old 07-16-2017, 06:11 PM
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I would remove the valve springs and check them for seat & open pressures.
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Old 07-17-2017, 07:55 AM
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It looks more like mechanical interference than a lube issue.

Along with Steve's suggestions, check spring installed height. Depending on several factors (component machining, valve stem length, cam profile, valve guide installed height, valve spring shim thickness, etc.), the spring could stack at full lift.

Suggest checking valve-to-piston clearance with modeling clay. Set up a single cylinder (e.g. no. 1) and set cam timing. Set normal rocker arm clearance. Manually rotate engine a couple of revs., disassemble, then inspect and compare with specs.

Just to be sure, confirm the short pin that fixes the cam sprocket timing position is in place. Some folks have assembled engines using just the cam nut/bolt. That only works for awhile ........ or less.

Sherwood
Old 07-17-2017, 08:16 AM
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I am thinking there might be a valve spring issue, I was hearing what I thought was a rev limiter kicking in on the L O N G straight at Monticello, but the revs were a few hundred RPM lower than the limiter. It sounded more like valves floating... never had that issue before. I don't know when I will have time to get back in my garage as I spent a lot of time getting it ready and racing, now real life is in the way. But any suggestions or ideas still welcome.
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1973 911RS Clone F class, 2008 GT3 cup GTC4
2004 Touareg, 2006 Mini Cooper S, '01 Viper GTS
my racing pages - http://www.analogman.com/911
~^v^~ aNaLoG.MaN ~^v^~ guitar effects LLC www.analogman.com
Old 07-17-2017, 09:10 AM
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OK I finally had time to check out the engine at home.

Other rockers are ok, just 1-2-3 intake rockers broke.
While at TDC with the valve cover off, I shook Cylinder 1 exhaust valve and it felt loose, I had just adjusted them and my notes said that one was in spec and not adjusted. But it was quite a bit loose. Odd.

Chain and tensioner seems ok. Spray Bar seems clear though the cam area is quite dry.

But cam timing seems very retarded! I believe it should be vertical at TDC:



Any ideas on how the cam timing could be so far out, if it actually is?
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Regards, mike AnalogMike at aol.com
1973 911RS Clone F class, 2008 GT3 cup GTC4
2004 Touareg, 2006 Mini Cooper S, '01 Viper GTS
my racing pages - http://www.analogman.com/911
~^v^~ aNaLoG.MaN ~^v^~ guitar effects LLC www.analogman.com
Old 07-22-2017, 03:31 PM
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The cam rotates CCW so you're quite advanced. Probably advanced enough to hit the intake valves on the pistons before TDC. You'll be really out of room if you have CIS pistons.
Bent intakes, maybe?
Bruce
Old 07-22-2017, 06:28 PM
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cams turn CCW so advanced, that makes sense that I would have broken the intake rockers. It's a stock 2.7 RS so the cams are S cams. But how does cam timing change?
Old 07-22-2017, 07:42 PM
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Rockers don’t break on their own. Something hit something. Without knowing the cam specs it’s hard to establish what hit what. As suggested it could also be a coil bind issue, but that is something that wouldn’t change from good one day to bad the next. The first thing to do is to check the condition of the engine. If you broke rockers you probably have bent valves. No point guessing what did what as you may now need to disassemble the engine. Checking clearance with bent valves is pointless. Establish the engines condition first.
Old 07-22-2017, 09:11 PM
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I don't see how your cam could advance unless you dieseled on shut down.
You're going to be taking things apart, time to pull the 46mm nut and see that the pin is in place, trying to figure how the cam advances...
Bruce
Old Yesterday, 02:41 AM
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Are we sure it's at TDC firing and not overlap? Maybe it's actually retarded.
Like Bruce said-hard to imagine it advancing.
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Old Today, 03:32 AM
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Though how could that happen without taking out exhaust rockers?
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Old Today, 03:36 AM
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Sorry for the engine trouble ... Sounds like cam timing changed somehow, causing valve-piston interference. Will be very interesting to hear how the cam timing managed to shift ...
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