Problems after cam swap
Thread Starter
Joined: Jun 2007
Posts: 840
Likes: 1
From: Encinal/Kingsville, Texas
Problems after cam swap I drove the car into the shop, and started pulling it apart. Stupid me forgot to disconnect the battery and something arced against the AC line. I disconnected the battery after that and went on with the swap. Pulled the stock cam out and replaced it with an LS1 Hotcam. Lined up the dots on the cam sprocket and crank sprocket and checked to make sure it was right. I changed the springs out for ls6 springs. After making sure the stock push rods were straight I put them in and torqued down the rockers. I got everything back together and tried to crank it. No go... the motor spins over like its In free spin. It doesn't act like its making compression. I get a few pops but other than that nothing. I clear the codes and still nothing. I pulled the pcm out to make sure I didn't fry it and it starts in another car no problem. I checked all of the fuses inside and out and all of them are good.
I tore it back down and found 3 bent push rods. Pulled the plugs to look for impact marks on the pistons and find nothing. The timing chain is still intact also. This is where I am at now. Any suggestions?
I tore it back down and found 3 bent push rods. Pulled the plugs to look for impact marks on the pistons and find nothing. The timing chain is still intact also. This is where I am at now. Any suggestions?
No compression and bent pushrods points towards the pushrods are too long not letting the valves close and opening the valves too much which is why the pushrods are bent.
Why you are having that problem with the Hot cam I don't know. I really wouldn't think you would. The only other think I can think of is you didn't get the pushrods down in the lifter cups.
Why you are having that problem with the Hot cam I don't know. I really wouldn't think you would. The only other think I can think of is you didn't get the pushrods down in the lifter cups.
Thread Starter
Joined: Jun 2007
Posts: 840
Likes: 1
From: Encinal/Kingsville, Texas
I've got a push rod length tool on the way. With the rockers torqued down should there be any play when the lifter is down? I've got .100 gap between the rocker arm and valve tip when its not under load.
TECH Fanatic
Joined: Jun 2011
Posts: 1,343
Likes: 8
From: Katy, TX
so you basically have zero lifter preload? The pushrod needs to be sized to ensure about 0.050 - 0.080" of preload (assuming GM lifters) when the lifter is on the base circle. There should be no "play" in the system at all.
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Yikes!
How did you have the ***** to do that without knowing the proper procedure?
Lol I'm afraid to touch my engine without knowing exactly what the heck I'm doing...
What did you torque the rocker bolts to?
What torque wrench do you have?
Maybe some bolts walked out, that and pushrod length..
How did you have the ***** to do that without knowing the proper procedure?
Lol I'm afraid to touch my engine without knowing exactly what the heck I'm doing...
What did you torque the rocker bolts to?
What torque wrench do you have?
Maybe some bolts walked out, that and pushrod length..
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Verdad Gallardo Thread Starter
Joined: Jun 2007
Posts: 840
Likes: 1
From: Encinal/Kingsville, Texas
This is not my first cam swap. I have done several of them. This is just the first time I have run into a problem like this.
The rocker arm bolts are torqued to 22 ft/lb using a snap on torque wrench.
The rocker arm bolts are torqued to 22 ft/lb using a snap on torque wrench.
Thread Starter
Joined: Jun 2007
Posts: 840
Likes: 1
From: Encinal/Kingsville, Texas
Before the came swap I did some reading on here and more than a few people were using stock length push rods. And I assumed they were correct because this cam came out of my brothers Corvette with ls6 heads and 7.4 push rods. I have done everything the same as every other swap I just can't figure out where this one went wrong.
You need professional help before you cause anymore damage.
My guess is the pushrods were too short. I'd be willing to bet the new cam has a smaller base circle like most which means you should have put in longer pushrods. That "play" is a no-no. If I read your post correctly you have less than 0 preload i.e. with the rocker torqued down you can move the pushrod up and down with your fingers.
I'm not trying to be an A-hole, but an ASA cam and LS6 springs should be the easiest swap in the world. Something is seriously fundamentally wrong for pushrods to have bent.
My guess is (and I hope I'm wrong) that you did not line up the gears dot to dot, the valves hit the pistons causing the pushrods and valves to bend. With the valves bent, they're hung up in the guides, which is why there is a gap now. If you are going to press on yourself, I suggest hooking up some compressed air to the cylinders with the rockers off and make sure you don't have a major leak.
Thread Starter
Joined: Jun 2007
Posts: 840
Likes: 1
From: Encinal/Kingsville, Texas
I pulled all of the plugs and looked in with a bore scope and did not find any contact marks between the piston and valve. The valves do open when the motor is spun over by hand so I'm sure they are not stuck in the guides. I'll try the compressed air when I get home from work.
I don't understand how something so easy could go so wrong.
I don't understand how something so easy could go so wrong.
Thread Starter
Joined: Jun 2007
Posts: 840
Likes: 1
From: Encinal/Kingsville, Texas
Driver front at tdc. Un bolted rockers pulled push rods. Lifters pulled up with pen magnets. Pulled the can put the new one in. Changed valve springs and assembled as it was taken apart.
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From: BFE