I just had a hotcam installed. Runs great except for the usual misfire code due to lopey idle.

So last night I got into a little bit, after having it back since Friday. Not for a long time, and didn't hit the rev limiter. But after pulling off from a light, I hear the dreaded knock. I believe it to be from the bottom end as I have scoped the valve train and they seem normal.

However, the knock doesn't really kick in until about 2500 rpm, then seems to mellow out just over 3000, but still present.

I'm just sick about this. Is there any other thing that I might investigate?

 

Who did the install? How many miles? I'm doing mine myself this weekend. After hearing this I'm glad too. I really cant help you much but I've heard getting any kind of dirt in there or nicking the journals during install can be real bad. Possibly cause a spun bearing? Maybe someone more knowledgeable will respond. Sorry to hear of your troubles. Hopefully it's something else.

 

There are a few threads on here where shortly after installing a cam (HotCam) swap, a spun bearing results. I wonder if it's not a dirt particles or tiny bits of material fall into the oil pan, get picked up and got through the oil pickup screen, and if the oil is cold (thick) pass through the oil filter bypass and end up in the cranks oil galleys and starve rod bearings???

 

If it were mine I would pull it apart and check it out. You could do even more damage if you continue to drive it with a knock. A knocking sound has never been good for me. I would rather pull the motor out inspect the rod and main bearings just to be 100% sure. I hope its something more simple than that but prepare yourself for the worst. Good luck!

 

The previous owner of my car spun a cam bearing which resulted in two spun rod bearings. It was due to a dent in the oil pan though. The oil travels around the outside of the cam bearings and then down to the main bearings and through the crankshaft to the rod bearings. One small hole in the cam bearing delivers oil to the inside of the cam bearing.

If the journals on the hot cam are smaller than the stock cam it would reduce oil pressure to the rod bearings. It could also be an install issue or something else. I'm currious to find out what causes this.

 

My brother did the install of the hotcam at the dealership. Between him and the other techs on his team I have no doubt about the quality of their work.

Took it down today and replaced the oil, went back to 10/30. Yes, I really kind of have to drive it because it's my only ride. Taking back Tuesday to get the pan off. He thinks it coming from #8.

As per causes, well, I did get into it pretty hard. Though I've done it before, I probably should've waited till after the first oil change. This combined with stock tune and related vibration, and even perhaps 75K on th dual mass could have created the "perfect storm" in the crank case. The #8 is the one that my brother didn't check because it requires a few things to come off and all of the others were fine, so the assumption was made it was also. Can't fault him for that. But perhaps it was on it's way out long ago, who knows?

Anyway the hope is that we have caught it early and a simple bearing replacement is all that is needed. For now, driving is only when neccessary and keep the rpms low. I now know why life is so much easier for the "waxers", you can consider me one of those now.

 

Broken valve spring can make a hell of a racket and give the illusion of coming from the bottom of the engine.

You'll also want to double check the damper install. Some (not all) of the LT4 dampers had small balancing weights added. If yours has those pins added, it needs to be installed in the same position it came off. There's no woodruff key, but there is an arrow on the hub (and on the damper). Just make sure the #1 piston is at TDC and the arrow on the hub is at 12 o'clock.

In this pic of my LT4 damper vs my ATI damper, you can see the balancing weights (pins) in a few of the holes around the perimeter...



A friend of mine had a horrible vibration and what I described turned out to be his issue. If it is a bearing issue, you'd hate to repeat the replacement process twice.

 

Hmm... Shortly after I bought my car I hung out with a lot of people who were big into F-bodies. Many of them, and people on their message boards, swore up and down that changing the cam in an LT1 was an instant recipe for spun bearings. Well after changing the cam in mine twice, my friend's once, and watching at least 3 other friends change cams in their LT1 I've come to the conclusion that this is simply not the case.

The people who have problems never seem to mention that some bubba did their cam swap for them in the middle of a dusty old cornfield. If this wasn't the problem, it's because they swapped the cam and then went out and tried to spin the motor to 10k RPM's without trying to break it in at all.

Being a hydraulic roller cam there isn't too much to break in, but I am still sure to put plenty of royal purple assembly lube all over the cam, timing set, etc. When I first start up the engine I'm listening carefully for exhaust leaks, mis-adjusted rockers, etc. It never gets above idle until it's quiet. Once I'm convinced that everything is right, then I can go for the first drive. I do my best to keep it under 3000 RPM's while everything gets up to temp. If, once at operating temp, everything is still quiet and it's still running alright I figure that all the assembly lube is washed down into the pan. I generally recommend driving it this way for about 200 miles and changing the oil again before hammering on it, but I know people who have not and have never had a problem.

If your brother knows his stuff then maybe it's something else. Here's wishing for the best.

 

go to the impalassforum.
same problem.
cam swap = spun bearing.
very common.

I won't touch my motor.

 

I and others have swapped plenty of cams into LTx motors without issue. If the car is used in a manner that requires better than stock oil control (ie baffled pan, accusump, dry sump, etc are options), it won't matter what cam is in there. Plenty of guys have grenaded engines due to oil starvation issues.

Just my opinion, but I think the majority of the spun bearings are directly related to the total number hack wrenches doing the work. Some of these guys post pictures of the....umm..."garage".....they do the work in and the "tools" they use and it's amazing the cars even run again.

It also seems that a lot of them, while the engine is apart, pull a main cap or two off to peek at the bearings. That cap and bearing will never re-seat exactly as it was before the cap was pulled. Add to that the desire to run the thing to redline as soon as the car is off the stands and it's no wonder it goes boom.

Like I said, just my opinion.

 

I grew up with the guy that did the work. He is the tech that all of the other techs come to when they need help. His tool collection is probably worth more than the brand new Excalades he works on. He is a true professional, just so this is understood. The problem might be that I am not a true professional driver, this I could conceed.

Nathan, I have read some of your stuff and respect your knowledge, thank you. The only thing I did differently than what you described was not changing the oil before taking it to 6K. This was the first and only time I did, and it was about 200 miles after the install.

I also appreciate the info about the damper. That is certainly something to double check on. I ask about it. I really don't think it is a spring. Although we didn't pull the covers, both of us scoped the top end pretty well and there was no hint of trouble there.

We'll see next week when she's up and oil pan comes off. Like I said, hopefully a bearing replacement is all it'll need. Although I understand her racing days will be over.

 

If you did spin the bearing I think you'll be looking at a new crank, 2 conecting rods and a bearing kit. I wouldn't put the ol' girl out to pasture just yet she still may have some good runs left in her yet...you just need to keep the RPM under control in the future. Just because the engine keeps pullin' past red line doesn't mean it will take the abuse at that level.

 

The bearing isn't spun yet. The knock appears at 2000-2500 rpm under acceleration. Not really loud yet either. I do believe the crank in the LT4 is a forged steel, correct me if I'm mistaken. So there is a pretty good chance it will be okay.

 

Another possible cause for a spun main/rod bearing is a nicked cam bearing. When removing or installing the cam, if a cam bearing is burred or nicked by a cam lobe. The cam bearing will be a little tight and could spin in the block. This would cover up the oil hole that feeds a main bearing, which also feeds a rod journal. Even a partial blockage of the main bearing oil galley will reduce oil volume. This could explain some of the mystery.

 

I went though this on an engine once. I didn't drive it very far at all when a rod journal began knocking. I pulled the engine, removed the crank, took it to Kelly Gardener whom was doing Patterson Racings cranks at the time. Kelly said the indexing was off. Or that journal had been knocked out of phase several thousandths. He straightened the crank and polished the mains & journals and it was good to go. This was a forged steel crank. I learned from Kelly that rod knocking will bend a crank fairly easy. It might not hurt to have the crank indexed to be sure that journal hasn't been moved. Whatever rod has been knocking, replace that rod, it's not worth the cost of a cracked block.

 

First I want to thank everyone for their input. It's really great to have a place to go know where to look for answers. I don't even know how much money we help eachother save.

So, the #8 rod bearing was spun. Hard to believe considering how much noise it didn't make. The crank was damaged about .0016. Oversized bearings come in either .0010 or .0020. The goal was going to be to fix it w/o removing the engine. However, the rod was worn out of round, elongated, so the rod would have to be replaced. Can't pull the crank and remove the piston this way. Engine has to come out, head has to come off. So, we're just going with a new crank and rod. Man, I wish I had the cash to do a 383.

The real downer is this is taking up what little extra I had for a tune. As well as I was going to start shopping for a place w/ a garage so I could do my own work. If only that bearing could have help out till July. Oh well.

 

Thanks for letting us know what happened.