Yesterday I went to fire up my car (it was already warm since I had used it earlier in the day) and about 10 seconds after it started I heard a snapping sound followed by it running rough. There was a consistent loud ticking noise which sounded like something hitting the inside of the valve covers. I shut it down and pulled the covers to find out both sides broke a stud clean off right beneath where the rocker mounts. They were not opposing cylinders either. #2 and 3 cyl. Also, FYI, I noticed another rocker was 'loose' on its stud, just kinda flopping around. I extracted a couple bent pushrods too. Here are (what I know of) the engine specs: Pre-'86 small block 355 (casting # 3970010) Iron Vortec heads (casting # 10239906) Comp cams 268H Edelbrock RPM Air-gap intake + #1405 600cfm carb Hooker headers So I'm wondering what the hell happened? And is it worth repairing these studs or swapping on a better set of heads? I didn't build the engine in the first place, so I'm open to any recommendations.
Check for rocker bind in the slots or valve spring bind due to too much lift or too much rocker ratio.
I agree, I have seen many non-pinned studs pull up and or out but not break like yours. Plan on replacing all studs.
The 268H only has .456 lift with the stock rocker ratio so it doesn't seem likely that its excessive lift but you may have a coil bind issue. By the marks on the valve tip it looks like the roller is in the center. How much time is on the motor?
I'm not sure exactly since I bought the car after the motor was rebuilt. However if I had to venture a guess, I would say somewhere around 5000 miles. Thanks.
I see a few issues, one is those are not Vortec springs and retainers, another those are not the original studs, and how are you aligning the rockers with the valves as vortecs require self aligning rockers. With that spring and retainer you might be hitting the seal with the retainer.
those springs look pretty tough to compress It would it be better to go to screw in studs, and 7/16 studs so you can replace easier and find some springs that will do the job for street or at least test the pressure to compress them they appear to have a very large wire diameter also on the tear down check the guides, someone may have did something to your oil or fuel to seize the valves
I agree with the last two...also check retainer-to-guide clearance. If those rockers are 1.5s I wouldn't really expect too many problems, but it is possible with higher ratios. I wouldn't "think" that rocker slot bind would be an issue with those rockers, but anything is possible. Are they marked/stamped with anything? They kind of look like Chinese rockers sold under different brand names, but it's hard to say for sure from here. Some of the Chinese stuff have trunnions that are not concentric...this causes some weird and interesting problems. Also, what is aligning the rockers? I don't see any guideplates and they don't look like self-aligning rockers. It's also somewhat possible that you have insufficient piston-to-valve clearance, either on the face or the edges of the valves. You might also check the pushrod clearance in the cylinder heads throughout the entire travel of the valvetrain cycle. There is nothing in particular wrong with those cylinder heads...but you have valvetrain bind, somewhere, that needs to be addressed.
Stock Vortec heads are limited to .500 valve lift. That's where the retainers touch the valve guides. If those rockers are 1.5's you should be OK, if they're 1.6's you are pushing the envelope. If you don't care to pull the heads down, at least round up a set of stock rockers off a late 90's 5.7 pickup engine. They are good heads for a street engine, if you know how to use em.
Hell, there is nothing I can see that keeps the rockers aligned! In fact, I can wiggle them around with my finger. Here's a couple wider shots: So it seems like a crucial thing missing are guideplates. Is it even worth having new screw in studs installed by a machine shop? How much should that cost? Maybe there are better aftermarket heads for not much more? Tomorrow I will mess with it some more. Turn it over, see if anything is binding, and probably also pull the heads.
I discovered that these heads have screw in studs. I clamped a vicegrip to the stud and voila, I was able to unscrew it from the head. Did any Vortec heads ever come from the factory with screw in studs or was this done by someone after the fact? I'm guessing these are the studs currently installed: http://www.summitracing.com/parts/MRG-1076/?rtype=10 EDIT: Also I found 'MID-LIFT PRO-2024' stamped on the rockers.
Could have been incorrectly heat treated. Or installed incorrectly. I would change them all to a better brand.
Vortecs come with screw-in studs...at least, some/most of them do....there may be some castings that didn't at one point or another. Those appear to be older PA-series Miller Mid-Lift rockers...an unusual part to find in a ordinary mild street 350. Nothing at all wrong with them. You'll either want to use better studs & guideplates, measuring carefully to make sure that the bosses don't need to be trimmed...or, use self-aligning rockers like what was originally installed on Vortec-equipped engines. As noted those aren't Vortec retainers, so I don't know that you can use the self-aligning rockers with them without interference. If you use guideplates, I would also again suggest watching the pushrod travel through the cycle to make sure there's no interference with the head casting. Also, with guideplates, you'll need hardened pushrods.
One thing for sure--you either have to get "self centering" rockers or guide plates (can't have both-it WILL cause a bind) with the large push rod holes some thing has to keep the push rods in line. THATS a costly lesson I learned. BILL RINALDI
Thanks Homespun and Bill, Apparently that's one lesson I just learned too. I'm on the lookout for self-aligning rockers now.
GM 12495490 is a complete self-aligning set with pivot balls & nuts for about $65-70. Again, though, I believe you will have to switch the retainers back to the Vortec type. One thing I forgot to emphasize- with that cam I would make sure to check the retainer-to-guide clearance. You are probably OK- usually about .460 is where you start to worry with Vortecs, with some being "looser" than others- but as long as it's apart ya might as well check it. Since the retainers are different you don't really have a guideline for what clearance is there. The fact that it didn't have any alignment method for the rockers makes me think that the "builder" probably didn't waste much time checking clearances.
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