Valvetrain noise - Magnum headed LA 360

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racingsnake440

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I recently put together a Magnum headed 360 for my Dart -
bottom end
Summit 6901 hydraulic cam - 0.470" lift (with 1.6 ratio rockers) 218 intake and 228 exhaust duration at 0.05, 276 intake and 286 exhaust advertised duration
Comp Cams lifters with pushrod oiling provision
Mopar Performance conversion pushrods for Magnum heads on LA motors
Mopar Performance thin head gaskets
stock Magnum heads redrilled for LA manifold bolt pattern
Mopar Performance valvesprings with 2.2l retainers
Edelbrock LD340 intake with Carter AVS carb

It runs pretty good but the valvetrain is noisy, not really audible at idle but becoming noticeable at about 1500 rpm and getting progressively noisier - by 4000 rpm the clatter is pretty loud. The motor revs cleanly round to 5500 and will go to 6000 but doesn't seem that enthusiastic about it.

I didn't measure lifter pre load when I assembled the motor but it looked like there was quite a lot of preload - possibly too much. Could too much preload cause valvetrain noise?

Since putting the engine together I've seen reference to blocking off the oilways for the rocker shafts when using Magnum heads - I just bolted the heads on. Doesn't this block the passages sufficiently or is something else required?

thanks
 
My guess would be too much cam, too much valve lift, not enough clearance. My buddy just went thru the same thing. He switching too smaller cam. :( Sorry
 
I'm assuming your using the stock non-adjustable magnum rockers. You need to check preload on any non-stock build. My guess is that either you have not enough preload or you have too much preload which may have ate the cam.

Time to pull the rocker covers.
 
My heads on my magnum/LA hybred are not decked but the block was machined about 0.020" to get the pistons to zero deck and I have a 0.039" thick head gasket.

The threads on the bolts holding on the magnum rockers are 5/16-18 which is 0.055" per revolution of the bolt. When I put mine together from the point that there was no clearance to the point the pedastels bottomed on the head was about 1/2 a turn or about 0.027" of preload on the lifter.

If I had not decked the heads I would have had about 0.007" of preload. I have heard people report that the conversion pushrods are too short so depending on your parts you may not have enough preload. i would pull a valve cover and check a few.
 
I did the swap with the same thin Mopar head gaskets. The cam was already in before the swap with Rhoads lifters. After the swap, the lifters were noisy to the point that it sounded like the rocker arms were loose. I checked preload and it was roughly .040". I swapped to regular lifters, measured roughly the same preload and things quieted down substantially. I would double check the rocker arms and make sure they are still torqued down properly. Some noise is to be expected, or so I am told, with the newer performance cams.
 
In my opinion I don't thing its to much cam for a 360. But it might be to much cam for the compression ratio your running. Did you check the piston type, dish or flatop, how far down in the hole it was? Did you cc the heads? Mopar chamber numbers were not very accurate.
On a conversion motor you must check the valvetrain geometry. My magnum headed 340 will have custom lengnth pushrods.
 
pulled the valvecovers and found I've got a collapsed lifter. I'll replace and check the preload and see what it's like then
 
racingsnake440 said:
pulled the valvecovers and found I've got a collapsed lifter. I'll replace and check the preload and see what it's like then
Click to expand...

Too much preload. Have you or are you going to install adjustable rockers?
 
ramcharger said:
Too much preload. Have you or are you going to install adjustable rockers?
Click to expand...

If you go to adjustable rockers let me know. I'll make you a good deal on the Crane stud kit with guides. Looks like you have to use the rockers they list, I tried a couple of different Chevy rockers and the geometry was way off.
 
yeah, i figured it was probably too much preload - the cam's had it as well so I may pull it and put a big block in instead
 
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