I finally got around to firing my car up (stock short block, 233 .578 113ls cam, 5.3L heads milled .035, 7.35 pushrods, 1 MMS shim on each side) and it makes horrible noises! I only let it run for 10 seconds or so, but the idle seemed rather smooth @ 1000rpm considering. I pulled the valve cover and noticed that when I tighten the rockers all the way down the spring is slightly compressed, seems to indicate too much lifter preload. If the rockers are too tight will the engine run yet make horrible noises? My experience has always been that when the preload is too much the engine just won't make enough compression to run. Any ideas?

Maybe the combustion cycle is leaking in to the exhaust making a racket? Maybe the valves are tagging?

 

really....I think you have too little preload...

who is your cam from?

I know the TR cams (and many others) have a 0.030" smaller base circle than stock....so that right there would have basically cancled out your 0.035" mill on the heads (would have an extra 0.005" preload with stock push rods)....


now...7.400" pushrods are actually 0.020" longer than the stock (stock is 7.380") so those 7.350" are 0.030" shorter than stock....couple that with the extra 0.005" of your mill and your pushrod is 0.025" shorter than it should be....


so here you have 0.025" too short of a pushrod and then you go put a spacer on the rockers to add MORE distance (reduce preload even more).....

how thick is the spacer?

I would start by removing the spacer...that should make it somewhat better....

if you use the 7.350" pushrods you will be 0.025" too short...if you go 7.400" you will be 0.025" too long.....I would rather be too long and be able to space the rockers up from there to remove preload....

hope this helps...

 

oh...one more thing, the engine will have excess noise for a little bit after start up....the lifters need time to pump up....

also...realize that with a faster ramp rate cam and stiffer parts, its going to be louder....

later

 

I tried to take the spacer off one side and it seemed louder... It's an MMS cam, I don't really know what the base circle is. I've had a few cams that are similar to this and I can tell something is pretty wrong, its _really_ loud, I can't even talk over it. It's too loud to be the rockers too loose, but I've never had them too tight (with an engine that would run) so I'm not sure what that would sound like.

 

terry mine did the same thing, every valve was hitting the piston ever so slightly, i thought that the lifter preload was wrong or the lifters need to pump up but when it reved up and the valves floated, boom, lost a block a 2 pistons...hope that isnt your problem but my heads were milled .020 and i had 230/575,111lsa, take it with a grain of salt, keep us updated, iminterested in a solution...

 

The next thing I'm going to try is shorter pushrods, maybe 7.25. Anyone ever run such short pushrods?

 

Have you started up an LS1 before that's been sitting for a long time because you were building it up? It will sound nasty for the first five minutes. The lifters are completely bled down for one.

I'd run your valvetrain geometry by some more folks, it's sounds tight... ie. lot of lift + milled 5.3's.

 

im running 7.25 PRs... but I have adjustable rocker arms...

 

you are running a 233 intake duration cam on 5.3L milled .035 heads?

I think you tagged the pistons on startup. Did you measure PtoV?
Cheers,
Chris

 

John, I haven't.. I guess that could be it.

What does a car that has no PTOV clearance sound like at 1000-2000rpm? Light tapping? Horrible loud racket? I'm hoping that my car is just leaking out the exhaust and intake during the combusion cycle (i.e. valves not closing all the way). What would that sound like?

 

I didn't. On my old setup I ran a 230 duration cam on 5.3L heads milled almost .040 with no ptov problems, so I figured it would be OK. How loud would tagging the valves be?

Maybe I'll throw a couple more shims on each side and try a compression test tonight.

 

PS If I have to take this clunker apart again I'm going to have a lot of parts for sale. =)

 

You had forged pistons with 3-6cc valve reliefs in the old motor right?

It will be an ungodly racket if the valves are smacking.

Bring a piston to TDC and see how the valves look. Check for rocker slop as well. (The rocker will be sloppy where the valves are bent increasing clearance. I bet that is what happened. Pull a pushrod and have a look too. It probably wont be bent but I bet the valves are toast.

Sorry to hear of your troubles man,

Chris

 

The old motor was just my stock shortblock with heads/cam on it. (you're thinking of my 396).

I have all the rockers off that side, I'll try to pressurize the cylinders and see if they leak. If a valve is bent I should hear air whizzing by it right? It's weird one side seemed a lot nosier than the other.

 

Terry, I think Chris is right...... so you didn't check P/V clearance at all with a 233 intake duration? I have LS6 heads only shaved .015 and I barely had clearance with a 230 cam. Those 5.3's are milled quite a bit too.... I'd bet you have some bent valves and some scarred pistons as well. Let us know what you found out. Your old setup may have worked because the other cam was on a different ICL or advanced differently perhaps....

 

yep I bet you have sixteen valve reliefs now in your stock pistons

You need a min of 80 thou on the intake side clearance wise.

Good luck, let us know what happened...

 

Yeah, I mean I'm running a 232 cam now and I only have 75 thou. clearance on the intake side with the same LS6 heads.

 

my money goes on pistion to valve. i heard Kevin's problem first hand, let me tell ya, it was scary. sounds very similar to what your describing. lifter pump up is a slight ticking sound, nothing at all like a horrid noise of p/v contact. i'd definately do a compression test, and if it's not pretty close to nominal (taking new rings into consideration) take the heads back off, check every valve, and start over. better safe than sorry with crap like this. good luck.

 

You guys are probably right, but it just seems unlikely to me that they are hitting. The compression test today will tell all. Worst
case I get a head start on parting my car out.

 

Did it sound almost like a machine gun or a loud snare?