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L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

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Old 06-20-2010, 12:06 PM   #21
JAKE
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"Since the cam and springs were upgraded . . ." there-in may lie a clue to the cause of the failure. Geometry/clearance issues?

Jake

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Old 06-20-2010, 12:31 PM   #22
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Quote:
Originally Posted by Churchkey View Post
If the rocker rides the retainer the keepers can pop out.

------------------------------------------------------------
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I agree. The rocker hitting the retainer allowed the keepers to pop out. The head need to come off but it's your car.

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Old 06-20-2010, 01:31 PM   #23
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I have a 94 LT1 with LT4 heads, it was just rebuilt and had less than 300 miles on it when one of my rockers came off just like yours with the same type damage to the rocker, (I have Crane Gold rockers).
I still have no Idea what caused it but my push rod was not bent and after I replaced it I have not had any issues since.
The only thing I can figure is when the shop put the engine back together they did not adjust it properly.
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Old 06-20-2010, 03:24 PM   #24
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Originally Posted by Pete K View Post
Any of the above.
The only way to know is with a full visual assessment on your end.
Keepers are cheap. Replace them all. Replace all rocker studs with arp's and add guideplates before installling new non self aligning rockers.
Lifters did nt likely contribute to your problem, but it is possible. I would change them out, as they are cheap enough.
As far as the valve is concerned, if it passes a visual inspection, have a local shop chuck it up, and kiss it with the stones. If it is bent, it will show up.

If I was a betting man, I would throw a few buck on the likelyhood the installer did an incorrect valvetrain adjustment. If he did not know the valvetrain was different than a typical sbc, he may not have adjusted it as a positive stop set up.
Ok, thanks everybody on the advice. What are "arp's"? When you start talking about replacing parts, I don't know what to buy. What brands, etc. Is there more than one GM Hot cam? Thats what the guy put in it. What lifters, springs, rockers, should I get. I'm going to look for a book on re-building LT4's. What's a good one? I have done a valve job on a '72 sbc LT-1, rebuilt a 350 in a '72 Chyenne, and swapped a couple of engines out, so I'm not totally in the dark. This car has 69,000 miles on it, did run perfect, no smoke, good compression...I just don't want this to happen again. Seems to me to help keep this from happening again I should go with guide plates and non self-aligning rockers. The ones on the car are self-aligning, is that the washers on each side of the rollers to keep it on the valve? I have read the debate on the process to add guide plates, milling the stud mount surfaces down the thickness of the plates? What about shortening the length of the studs since these type rockers tighten down with no adjustment?
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Old 06-20-2010, 07:55 PM   #25
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Quote:
Originally Posted by mcox8051 View Post
Ok, thanks everybody on the advice. What are "arp's"? When you start talking about replacing parts, I don't know what to buy. What brands, etc. Is there more than one GM Hot cam? Thats what the guy put in it. What lifters, springs, rockers, should I get. I'm going to look for a book on re-building LT4's. What's a good one? I have done a valve job on a '72 sbc LT-1, rebuilt a 350 in a '72 Chyenne, and swapped a couple of engines out, so I'm not totally in the dark. This car has 69,000 miles on it, did run perfect, no smoke, good compression...I just don't want this to happen again. Seems to me to help keep this from happening again I should go with guide plates and non self-aligning rockers. The ones on the car are self-aligning, is that the washers on each side of the rollers to keep it on the valve? I have read the debate on the process to add guide plates, milling the stud mount surfaces down the thickness of the plates? What about shortening the length of the studs since these type rochttp://forums.corvetteforum.com/newreply.php?do=newreply&p=1574454286ker s tighten down with no adjustment?
The ARPs they are talking about are the products made by ARP, one of the more respected brands of hardware. http://www.arp-bolts.com/

Give http://www.hitechmotorsport.com/ a call and see what cam the can grind for you and what rockers and studs. They did a fine job for me.
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Old 06-21-2010, 10:27 AM   #26
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Soldierboy609, did you remove the head and check the valve?
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Old 06-21-2010, 11:40 AM   #27
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Quote:
Originally Posted by mcox8051 View Post
Ok, thanks everybody on the advice. What are "arp's"? When you start talking about replacing parts, I don't know what to buy. What brands, etc. Is there more than one GM Hot cam? Thats what the guy put in it. What lifters, springs, rockers, should I get. I'm going to look for a book on re-building LT4's. What's a good one? I have done a valve job on a '72 sbc LT-1, rebuilt a 350 in a '72 Chyenne, and swapped a couple of engines out, so I'm not totally in the dark. This car has 69,000 miles on it, did run perfect, no smoke, good compression...I just don't want this to happen again. Seems to me to help keep this from happening again I should go with guide plates and non self-aligning rockers. The ones on the car are self-aligning, is that the washers on each side of the rollers to keep it on the valve? I have read the debate on the process to add guide plates, milling the stud mount surfaces down the thickness of the plates? What about shortening the length of the studs since these type rockers tighten down with no adjustment?
I'm just curious, but have you checked out the Grandsportregistry website. There was a recall on some of the engines for the rockers. They list the vin #'s of recalled engines. But it may be possible that yours falls into this. If the the recall service was not done to your car perhaps this is why they recalled them. Not sure where you'd stand with GM today, but perhaps they'd fix it under the recall?

There is also a host of useful info on the LT4 there.
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Old 06-21-2010, 02:48 PM   #28
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Quote:
Originally Posted by Churchkey View Post
If the rocker rides the retainer the keepers can pop out.
That's my thought.

If the valve last were mistakenly adjusted with the cam lobe in the wrong position, it could have ended up loose. Then, when the rocker jumped off the valve stem, it started pressing on the retainer -- just like you'd do to install a spring.

Once it jumped off and rode on the spring/retainer, the valve probably wasn't getting actuated either (IOW, it stayed closed). But, the retainer was being pressed (and oscillated so quickly) that the keeper fell out.

That's the scenario where I could see Soldierboy's mishap ending w/o cylinder damage. Hopefully for mcox too!

To avoid pulling the head, couldn't a compression/bleed test be performed (after the rocker was reinstalled)? If the valve kissed the head and was bent/damaged, that cylinder would show a problem holding compression. Don't you think?
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Old 06-21-2010, 04:49 PM   #29
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Quote:
Originally Posted by lt4obsesses View Post
I'm just curious, but have you checked out the Grandsportregistry website. There was a recall on some of the engines for the rockers. They list the vin #'s of recalled engines. But it may be possible that yours falls into this. If the the recall service was not done to your car perhaps this is why they recalled them. Not sure where you'd stand with GM today, but perhaps they'd fix it under the recall?

There is also a host of useful info on the LT4 there.
Yes, this car is actually a Grand Sport Edition and I am a member as of buying this car two months ago. My car was later after those getting re-called, number 616. I have posted this scenario there too but nobody has had this problem.
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Old 06-21-2010, 05:35 PM   #30
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The roller rockers are torque to yield from the factory (no adjustment if using stock LT4 rockers and studs)!
This I am sure of.
If the Cam in your engine is the LT4 Hotcam then this should not have happened.
Everything I have read about the Hotcam for the LT4 is that it will work with Stock factory LT4 springs,pushrods,rockers and studs.
In my opinion: change the stud to a factory LT4 stud, change the valve keepers and retainers, and the rocker arm. Check the Pushrod for not being bent on a piece of glass. If it is bent change it.
I would not pull the head. The valve probably Did Not bend if the rocker tip fell off the valve stem tip.
I had a ZZ3 345hp GM crate engine that destroyed the exhaust valve spring and bent the pushrod, took out the valve seal. I just replaced the broken parts and the car ran fine down the dragstrip. It did it again on a different cylinder same carnage. And I just replaced the broken parts.
The engine was fine after these two mishaps.

Just reread first post on upgraded springs. The LT4 springs are Beehive shaped springs, yours Do Not look like this in the picture. I would take out the aftermarket springs that you have in there and install the original Beehive springs form GM (this is only if you are sure you have a LT4 Hotcam). Maybe the rocker is interfering with the spring!

Last edited by grandspt; 06-21-2010 at 05:45 PM. Reason: Reread his first post about upgraded springs.
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Old 06-21-2010, 06:06 PM   #31
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Quote:
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The roller rockers are torque to yield from the factory (no adjustment if using stock LT4 rockers and studs)!
This I am sure of.
!
Not torque to yield. Torque to 18 Ft/Lbs. There is a large difference.

The oval shape of the wire is subtle and hard to see even holding one in your hand.

Last edited by MK 82; 06-21-2010 at 06:16 PM.
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Old 06-22-2010, 12:35 AM   #32
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I would say that either A) the poly lock backed out and the rocker jumped when it got loose enough, or B) the lifter collapsed.

Those look like the original springs, they are oval wound and not beehive. It was pointed out to me some time ago that the beehive design didn't come for a few years after 96.

From the pic it looks like the rocker took the brunt of the abuse from this. I would replace the rocker, the polylock or whatever it's called on these, the keeper and valve seal. You said the stud looks good and it probably is, but change it too if you want. (if you can find them)

I would also change the oil, run for 30 min and change again. I'm sure there are remnants of that rocker floating around in the oil just waiting to cause more trouble.
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Old 06-22-2010, 03:09 PM   #33
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My bad, torque to yield incorrect. The Beehive was from Competition Cams! I guess GM said they were eliptical shaped.
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Old 06-22-2010, 09:06 PM   #34
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Originally Posted by lt4obsesses View Post
I would say that either A) the poly lock backed out and the rocker jumped when it got loose enough, or B) the lifter collapsed.

Those look like the original springs, they are oval wound and not beehive. It was pointed out to me some time ago that the beehive design didn't come for a few years after 96.

From the pic it looks like the rocker took the brunt of the abuse from this. I would replace the rocker, the polylock or whatever it's called on these, the keeper and valve seal. You said the stud looks good and it probably is, but change it too if you want. (if you can find them)

I would also change the oil, run for 30 min and change again. I'm sure there are remnants of that rocker floating around in the oil just waiting to cause more trouble.
Thanks everybody. I talked to Dale at Tach It Up Motorsports, the guy who is going to fix my other problem: the clashing noise at start up. He suggested a cylinder leak down test to see if the valve is bent and not seated, nobody around here has one so I got one from eBay. In the meantime I thought... let me know what you guys think about this... I used a dial indicator, base mounted, and positioned it on the end of the valve stem - pulled it up, noted the reading, turned slightly, pulled up and noted reading - did this all the way around several times and barely had .001 variance. Do you think this means the valve is ok? I think it shows that. Further, Dale thinks that the retainer on top of the spring more than likely was the culprit. He has found the stock retainers do not hold the keepers correctly and has repaired several of these. Especially if they don't even match the spring, most guys use the stock ones when upgrading the springs. He said get Comp Cams "918" springs (which are beehive shaped, $180 set) and use titanium retainers ($230 set) to match, and use all new GM keepers. Not cheap but anything to help prevent this from happening again. These are not the original springs, the previous owner said he upgraded them. He won't talk to me so I can't find out what springs he used or what the originals were like. Check out tachitupmotorsports.com, Dale is pretty cool.
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Old 06-22-2010, 09:12 PM   #35
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The plan sounds OK except that the titanium retainers are severe overkill.
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Old 06-22-2010, 09:48 PM   #36
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Was this fixed under the LT4 recall?

LT4's had issues with the rockers when they came out.
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Old 06-22-2010, 10:19 PM   #37
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Was this fixed under the LT4 recall?

LT4's had issues with the rockers when they came out.
There was a recall on early LT4's, mine is a later build date. Seems the pin that held the roller on the tip of the rocker was backing out.
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Old 06-22-2010, 10:24 PM   #38
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The plan sounds OK except that the titanium retainers are severe overkill.
I agree, but if using the titanium retainers could guarantee that this doesn't happen again, I'm all for them. The next time I may not be so lucky, and there are 15 more chances for failure. I do not want to lose this engine. Having the original engine in a Corvette is paramount if you want it to be worth anything down the road.
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Old 06-22-2010, 11:48 PM   #39
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Ok, lying in bed I realized how my test doesn't prove anything. If the valve were bent it would still pull up to the same point. What about pushing it down? It is hitting the piston as it sits. Since the piston is not parallel to the valve face it would work, but there are indentations in the piston, I assume for clearance of the valves. And I wonder if those indentations are parallel to the valve face? It is the exhaust valve that the problem happened on. Can't you see the valve through the exhaust port if the headers were off? And possible check for runout? Geez, I hate to pull that head!
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Old 06-23-2010, 07:33 AM   #40
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I would make sure all the parts are the proper ones. Original type 10 mm studs, locks and rockers. Just to make sure someone didn't force 3/8 ploylocks on. I think going with the aftermarket springs are overkill for the Hotcam. Gm sells the proper LT4 springs for like $40. You can also buy new keepers and caps fairly cheap.

Since the rocker chewed up the tip of the valve I would pull the head and have the valve replaced. The new rocker roller tip may get chewed up on the rough tip. This way since it will be apart you can check the lifter, and cam lobe to be sure they were not the problem.


If it were mine I would also replace the non-adjustable rockers with adjustable ones. I never liked the fact of swapping in a cam and not being able to set preload. And as stated you can not use guidplates with self-aligning rockers.
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Old 06-23-2010, 07:33 AM
 
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