Nathan Plemons

A certain forum member who I know yet shall remain nameless unless he choses to identify himself had some engine work (heads / cam) done by a shop that shall also remain nameless. The car was modified and it did run fine. The car was dyno tuned and it was driven all the way back home, which I'll just say was a great distance. A few other problems aside this major problem happened many months after the original work was done. Keeping this in mind, please offer your thoughts on this situation.

Forgive me for not having the technical names of the parts involved. It should be very straightforward though for those who have ever worked on a hydraulic roller.

Assume for the sake of argument that an engine (in this case an LT1) had two cam lobes destroyed by lifters turning sideways and grinding down the lobes of the cam. The "spider" that holds down the lifter retainer "dogbones" was actually bent up out of the way thus all hell was allowed to break loose. There were also two broken poly locks. The pushrods were NOT bent.

The question is, what happened? Did a polylock failure result in a rocker that was loose, thus allowing the pushrod to move without back pressure, allowing the lifter to come up too far.

OR

Did the problem with the lifters cause the broken polylocks.

Also, given your answer to the above, why? Was the failure due to faulty parts, bad luck, over-revving the engine, or neglence of the installer.

Corvette Kid

In what way were the poly locks broken? Aside from the obvious damage from the lifter rollers dragging on the cam, was a possible to tell if a roller initially failed, jamming and pushing the dogbone and spider up? This would make sense since it would have only taken the failure of one lifter to start that sequence. Both polys failing simultaneously would seem unlikely.

bogus

Damn. I don't know how that could happen, short of the lifters being installed incorrectly, being the wrong part for the application or, the spider being compromised in some way (incorrectly installed, damaged).

That is nuts.

STL94LT1

Sounds like a bad cam install to me.

REDC4CORVETTE

Were the bolts still in place in the tray?
Did the roller rockers have gouges underneath where the valve runs on the rocker?
Did the top of the stud that the polley lock attaches to have a dent in the stud where the polley lock was tightened?

Pete K

What was/is the spring pressures?

Pete K

The factory cam, lifter,dogbones, and spider are made sort of idiot proof. The dogbones ensure that the lifter is in the correct position. I would check spring tension, open and closed, Also physically check pushrod length. If these check perfect, it eliminates them from the equasion.

aqualung

Thanks for the post Nathan. Sometimes I'm still a little shy about posting my problems mainly because I don't know what the heck I'm talking about half the time.

I called my mechanic friend after I saw your post. I got some of the story wrong. This is what happened:

He took off the intake and noticed 1 of the spider legs on cylinder #4 was bent up. The rest of the legs were in place and the whole assembly was bolted down.

The dogbone on cylinder #4 was loose and got damaged bouncing around. The 2 lifters turned sideways and were lifting up and down but not rolling. The 2 lifters were damaged. One of them fell apart in my friends hands when he took it out. The 2 cam lobes were both visibly damaged.

When he took the RR's off, he noticed 1 polylock was installed so tight it was actually crushed and broken.

My friend feels this is all caused by the installer leaving the spider leg bent up and it has been broken since almost day one.

I will leave the shop nameless because to be honest with you, the heads are fine and they make great power. Also the owner of the shop is a good guy. All the problems were caused by the installer who no longer works there.

Davemc1963-87conv

Just wondering, Did it have roller rocker arms? I'm assuming it might have by the fact that it had poly locks, although they are also fitted by some to std rockers as well. Where they self aligning rockers, or did they use guide plates? Was it inadvertantly fitted with close fitting guide plates and self aligning rockers, causing an alignment conflict? The late 86/87 engines used hardened push rods and guide plates and non self aligning rockers. The 88 on engines only used the guide plates for assembly purposes and self aligning rockers. Just wondering if there was a conflict of parts that eventually failed.??
Were the rocker arm studs just damaged or just the poly locks?
What lift did the cam have? was there enough retainer to guide clearance? If not, when the springs were new, it might have just got away with things, but if it was 'over revved' and/or the springs lost a bit of tension and therefore control, the springs may have floated, causing the retainers to make contact with valve guides. Although you do not mention any damage to push rods or valve guides etc. this sounds unlikely to be the cause.
Not sure about the later engines, but did the LT4 use a metric thread on the rocker studs? (M10) as opposed to 3/8" UNF. Any conflicts there with hardware used?

bogus

This update changes a lot.

And your friend is saying pretty much what I suspected... the spider was bent. That sucks.

As for the polylock, it sounds to me like they screwed the pooch on that one. No way around it.

CFI-EFI

I can't say what all went wrong, but what ever went awry up above should have no bearing on the bent spider leg and turned lifters.

RACE ON!!!

Nathan Plemons

I'll admit that there was a lot of sloppy work that came out of that shop but I really find this hard to believe. If that piece was bent I really can't see the installer putting it back, there were plenty of "junk" engines around to rob parts from.

Also would it survive MANY WOT dyno runs and a trip back to Canada?

That's what I find hard to believe. As for the springs, they're the exact same springs I've been running for quite a while now. They're very stout but not excessive for that application.

Sorry but I don't see how the car could make 360 RWHP on the dyno if the lifters weren't running properly. Seems like that would make just a little bit of noise.

Oh well, I guess we'll never know.

Alvin

I actually had this happen to a mustang I tuned. 2 rockers tore themselves up along with the spiders and dogbones.. This thing was a pretty sick car 3000lbs, 550rwhp, 6500 RPM. The guy who built the engine builds some of the nicest stuff here so we really just put the blame on the parts. Nobody had a real explination..


my point is.. same exact thing happend to us

Zix

I saw that happen here on a relatively stock LT4 Grandsport, it had a HARD over-rev from a missed shift and blew a lifter out of the bore...that destroyed the spider and killed the cam and rocker. Was the car driven hard at all?

Nathan Plemons

That's what I was thinking. I really can't see the car running as long as it did if it was torn up from day one.

tjwong

Was a small base circle cam installed using stock OE style or OE length aftermarket lifters? The reason I ask this is because if a small base circle cam was used. The lifters would be down the bore about .100+ which means that much less lifter guide engagement. I seen a engine come apart due to this a couple years ago, under high RPM things move, just enough that the lifter came out of the alignment dogbone causing the exact damage you described with the bent spider arms and the destroyed cam lobes.

That was all I could see that could have caused it, the guy went back to a standard base circle cam and never had another problem. The cam was purchased from Comp who sold it to him because he told them he had a 383. For some reason them boys sell a small base circle cam to everyone that is doing a 383. Which nine times out of ten isn't necessary, especially if the engine is being built with stroker profiled rods. Another thing to watch out for from Comp if you get a LT1 cam from them, every damn Comp cam I have got for an LT1 had a longer than spec dowel pin. This especially irritates me to no end. Just because I fought a drivability problem for a few days on the dyno just to find out that the dowel pin on a Comp 305 cam was nearly .200 longer!!!

Nathan Plemons

Well it was a comp cam and I think it was a custom grind. It could have been a small base circle, I'm fairly certain they used standard length pushrods but I wouldn't swear to it.

Very interesting indeed.

CFI-EFI

I have been straining to figure out what may have happened, here. The small base circle cam makes perfect sense.

I forget the exact application but I think the long dowel pin is correct for a certain engine. I'm not sure if it's the LT4 or maybe the LS series. With some cams, you can just tap it in to the correct length. With others you have to cut it off. I remember Ski-dwn-it had one hole saw a hole in his timing cover, but he runs L98, Gen I, engines.

RACE ON!!!

Nathan Plemons

Agreed. That allows us to shift the blame from the owner of the car and the shop and over to comp cams :P

tjwong

one thing I forgot to mention about that particular engine. The lifters that didn't blow out of their guides and that were still in place were quite a bit lower in the lifter guide dog bones. If you were to see this, the best way to describe it would be that the lifters were below the top edge of the dog bone by at least .080+ what I remember was it was less than half of the engagement into the dog bone if the lifter was sitting on the cam base circle. If it were me that built the engine, I think I would have slipped in some retrofit lifters with link bars that has long bodies. Crane offers OE style long body lifters just for this application.