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Old 06-12-2010, 10:08 PM   #1
DJIMPREZA
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Default Cosworth official answer after their engine`s large valve head failure

Guys

A friend of mine, running his 10 sec sti on a cosworth large valve head/cam kit have lost one of his cylinder number 2 intake valve after 8K miles of street use and some runs at the drag strip, here it is the answer from cosworth, wich makes sense, so you guys running larger valves, next time make sure you use the subaru procedure for installment, and turn the intake and ex LH head cam sprockets in the right direction, and turn them with the less angle possible and do not make them move, wich is difficult, but can be done..

so here it is

"The main issue is that it's difficult to keep the cam gears in the proper position when installing the belt and that you don't open intake and exhaust valves at the same time causing contact. As long as you follow the factory service manual instructions exactly, you will be fine. I've attached a PDF copy of the timing belt procedure. On page 5, they explain the importance of the steps and rotation directions. With +1mm valves and higher lift cams, the danger of valve to valve contact during timing belt installation is even greater.
once the valve is slightly bent, the higher spring rate and constant contact of the valve to the valve seat tries to straighten the valve. Plastic deformation sets in, like bending a paperclip back and forth, and then the valve head falls off causing failure. We inspected a number of these valves and the material showed evidence to support our diagnosis.
It's always number #2 that fails, so we're confident this is the problem. Some people argue about piston to valve contact with the AVCS full advanced or retarded, but we've bolted on a cutaway head and manually clocked the avcs cam to each extreme and never came close to piston to valve contact. If the cam timing is phased properly you don't have to worry about the AVCS.
Hopefully the customer in Venezuela can elaborate.
Thanks"

So be aware with the timing belt on high lift/large valve heads

Cheers

DJ
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Old 06-13-2010, 04:53 PM   #2
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Thanks DJ. I'd like to add some additional insight on this particular type of failure if you don't mind?

The following pictures are of intake valve stems from two different failed engines with cosworth cylinder heads... and guess from which cylinder they're from? Yep, cylinder #2!



Uploaded with ImageShack.us

Notice, first of all, the valve stem is still straight after the failure- which means the failure wasn't a result of piston contact, or foreign debris in the cylinder. If that were the case the valve stems would have bent. Instead what we have here is a clean break, like the valve head said, "later man, I'm outta here", and took a vacation.

Secondly, look at the beach marks on the broken surface of the stem. See how the half-moon lines on the face begin on one side of the stem and get bigger? This is a sign of fatigue, and in this case, plastic deformation. It happens when a slightly bent valve tries to straighten itself out over many miles of operation. And at the weakest point of the stem (in this case where the stem is necked down, just before the radius into valve head begins) a microscopic crack appears then gets bigger and bigger over time. Eventually, POP goes the valve head.

Note this will always happen to the intake valves and not the exhaust due to the thinner (weaker) stem, and the larger head diameter- they bend easier.

Also, if an engine failure such as this happens at a low rpm and the driver shuts the engine off quickly enough (like the examples above), it is likely you will see only one, not both intake valves in cylinder #2 that will look like this because both valve heads will never decide to pop off at the same time, and it is always that first popped valve head that takes out the other intake valve (and everything else for that matter) before it has a chance to do it on it's own. However, a said failure at higher rpms will just obliterate everything, including the chance you'll find a relatively clean valve stem break to look at such as the ones you see above.

When it comes to installing a timing belt, I imagine the common logic of some engine builders/mechanics is to think the cam sprockets should only be rotated in the direction of engine operation, and that you always begin with the intake cam gear first... because after all, the mechanical cycle of engine operation is dictated by the intake valves opening before the exhaust valves do, right? So when it comes to lining up your marks to install the belt, it would make sense to phase the cam gears in the same manner, right?? WRONG WRONG WRONG!! Especially if you are running +1mm over-sized valves, be warned that you WILL bend the intake valves when they come in contact with the exhaust valves, in cylinder #2, on an EJ engine if you adapt this logic.

This is why it is very important to refer to the factory service manual when phasing the cam gears before you install the timing belt. If you don't, you run the risk catastrophic engine failure, and not to mention a very expensive repair.
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Old 06-13-2010, 06:23 PM   #3
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^^^nice write up with very usefull info. Thanks guys^^^^^^^^^^^^^^^^
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Old 06-13-2010, 10:44 PM   #4
DJIMPREZA
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Man, and there has been a list of complaint at cosworth for this, so they made lots of important broken valve material investigation and came with this results, in the manual it is also sai that if you turn a cam sprocket without the timing belts it will ben the valve steam!!!

Keep this sticky!!
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Old 08-09-2010, 08:21 AM   #5
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Quote:
Originally Posted by BallPeenHamr View Post
Thanks DJ. I'd like to add some additional insight on this particular type of failure if you don't mind?

The following pictures are of intake valve stems from two different failed engines with cosworth cylinder heads... and guess from which cylinder they're from? Yep, cylinder #2!



Uploaded with ImageShack.us

Notice, first of all, the valve stem is still straight after the failure- which means the failure wasn't a result of piston contact, or foreign debris in the cylinder. If that were the case the valve stems would have bent. Instead what we have here is a clean break, like the valve head said, "later man, I'm outta here", and took a vacation.

Secondly, look at the beach marks on the broken surface of the stem. See how the half-moon lines on the face begin on one side of the stem and get bigger? This is a sign of fatigue, and in this case, plastic deformation. It happens when a slightly bent valve tries to straighten itself out over many miles of operation. And at the weakest point of the stem (in this case where the stem is necked down, just before the radius into valve head begins) a microscopic crack appears then gets bigger and bigger over time. Eventually, POP goes the valve head.

Note this will always happen to the intake valves and not the exhaust due to the thinner (weaker) stem, and the larger head diameter- they bend easier.

Also, if an engine failure such as this happens at a low rpm and the driver shuts the engine off quickly enough (like the examples above), it is likely you will see only one, not both intake valves in cylinder #2 that will look like this because both valve heads will never decide to pop off at the same time, and it is always that first popped valve head that takes out the other intake valve (and everything else for that matter) before it has a chance to do it on it's own. However, a said failure at higher rpms will just obliterate everything, including the chance you'll find a relatively clean valve stem break to look at such as the ones you see above.

When it comes to installing a timing belt, I imagine the common logic of some engine builders/mechanics is to think the cam sprockets should only be rotated in the direction of engine operation, and that you always begin with the intake cam gear first... because after all, the mechanical cycle of engine operation is dictated by the intake valves opening before the exhaust valves do, right? So when it comes to lining up your marks to install the belt, it would make sense to phase the cam gears in the same manner, right?? WRONG WRONG WRONG!! Especially if you are running +1mm over-sized valves, be warned that you WILL bend the intake valves when they come in contact with the exhaust valves, in cylinder #2, on an EJ engine if you adapt this logic.

This is why it is very important to refer to the factory service manual when phasing the cam gears before you install the timing belt. If you don't, you run the risk catastrophic engine failure, and not to mention a very expensive repair.
If this happens, will the engine start at all at the first startup try? Mine dosent even start! I cant hear any "ticks" from the valves or anything wrong. it just wont start.
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Old 08-09-2010, 10:28 AM   #6
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I would imagine that if you had this happen to you, the engine might lock up? Is it not turning over at all?
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Old 08-09-2010, 11:14 AM   #7
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I kind of think that is an excuse. Building a high performance motor is usually done by someone who KNOWS what they're doing. Everytime I install heads, the rotating assembly is set with the pistons halfway in and crank sprocket in position for the timing belt installation. Heads are installed valves closed. Only ONE camshaft should be turned until it's in position for the timing belt install before the other one is rotated.

I dunno... but it's just me.
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Old 08-09-2010, 03:32 PM   #8
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Quote:
Originally Posted by FuJi K View Post
I kind of think that is an excuse. Building a high performance motor is usually done by someone who KNOWS what they're doing. Everytime I install heads, the rotating assembly is set with the pistons halfway in and crank sprocket in position for the timing belt installation. Heads are installed valves closed. Only ONE camshaft should be turned until it's in position for the timing belt install before the other one is rotated.

I dunno... but it's just me.
Pretty much how I did mine and I have the +1mm valves, but mine hasnt ran yet either. LOL Hopefully this weekend comming up..
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Old 08-09-2010, 06:09 PM   #9
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it just wont start, but it runs fine when i turn the key, no missfires or sounds from the heads.
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Old 08-09-2010, 10:09 PM   #10
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Tat last coment makes no sense.^



Thanks for the info OP
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Old 08-09-2010, 11:32 PM   #11
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Quote:
Originally Posted by bodyshot View Post
it just wont start, but it runs fine when i turn the key, no missfires or sounds from the heads.
I think something is getting lost in the translation..

Perhaps you could post a video on youtube or something of what you are referring to?
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Old 08-09-2010, 11:49 PM   #12
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Quote:
Originally Posted by bodyshot View Post
it just wont start, but it runs fine when i turn the key, no missfires or sounds from the heads.
you probably have something unplugged or the fuel lines wrong. You also probably should not be asking about it in this thread.
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Old 08-10-2010, 01:58 AM   #13
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Sorry guys, my eng sucks when it comes to explaining car/engine parts. Here's my built engine and pics: www.garaget.org/bodyshot click on the blue Impreza.
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Old 08-11-2010, 12:54 PM   #14
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it is not related with the fatory timing procedure, if you obey the instructions as well it will happen again, you will see that.
It is related with AVCS. me and my friends see that issue with cosworth cams many times. in cyl2,cyl4 and also on cyl3 not only on cyl2. I am sure that in all installations mechanics obey the procedure but if you dont close the avcs, it will happen again,again and again.
please when it happen again in future like i say, bump this topic and proof my idea.
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Old 08-12-2010, 05:01 PM   #15
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Funny that we had 3 cars running coswoth valves that dropped valve heads...and none others also running 1mm over valves like manley and BC
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Old 08-13-2010, 06:05 AM   #16
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what are the cams on that 3 car which dropped cosworth valves and what are the cams on the cars with running maley and bc valves with no problem. does all have avcs cams or non avcs?

i am sure that reason is not the valves, reason is cams and the actual reason is avcs, also i am sure that reason is the cam profile. we are running cosworth cams at least since 2006 the first ones doesnt cause any problem but the cams we purchased after 2008 are all have problems. Cosworth denies the problem but me and may people sure about the issue. if needed i can attach many email with cosworth about the issue for both ej207 and ej257.
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Old 08-13-2010, 10:48 AM   #17
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degree your large cams so you know how much avcs advance you have to work with
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Old 08-14-2010, 01:17 PM   #18
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subscribd.
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Old 08-15-2010, 06:35 PM   #19
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the avcs is very weak in terms of real maximun advance sometimes, when running aem and a slighty dirty oil or to much oil weight the target will be off by some miliseconds and can cause the problem

please attach your emails from cossowrth, we have now switch to gsc stage III cams with more agressive profile, so we`ll see what happends to a 15K long block
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Old 09-12-2010, 05:02 PM   #20
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I'm having trouble understanding the implications of this thread.
While your post is informative, it seems like you're trying to point a flaw that's being uncorrected by Cosworth, and I can't tell if you're in

1) disagreement that it's installation related and feel that the valve itself is made of faulty material
2) in disagreement that it's installation related and feel that the camshafts combined with too much avcs advance is to blame.

So if it's 1, then the camshafts are unrelated.
If it's 2, then the valve material is not to blame.

Am I right? I'm trying to understand and there's no sarcasm intended.
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Old 09-14-2010, 02:13 AM   #21
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Valve overlap,
Add bigger valves to decrease overlap clearence and time the cams wrong + slight valve tap = broken valve over time. Anyone worried about this and a quick leak down will tell you whats up. If the motor is pulled and you have no leak down tester. You can also check the valve clearence. I will show a valve seat problem.
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Old 02-19-2011, 07:19 PM   #22
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another valve drop issue from cosworth lomng block, 07 sti!! after 15000 miles!!
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Old 02-19-2011, 07:31 PM   #23
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I think you need to shift 1500 rpms lower.
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Old 04-21-2011, 10:07 PM   #24
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i recently am having a problem with cylinder 1 not having compression with cosworth big port heads. im thinking it is a valve seat problem but i wont know untill i get the head off, its possible its the rings in cyl 1 but this is a brand new short block and start up hasn't really happened fully because it was running on three cylinders after i got it together. the heads were purchased privately so... i keep yous all posted.

gabe
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Old 05-21-2011, 10:18 PM   #25
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hey alaskan

did you find out what happend in your car?
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