703crewchief

Well, here is another one. Today, bent almost all of the intake pushrods after installing TR224, 114deg. Here is the deal, After installing the bumpstick, dot to dot, the car started with a minor knock, but audible enough to frighten me. We thought maybe the lifters had bled down and were wanting pressure. No dice. I have heard nothing but good about this shaft, is it possible that piston to valve clearance is an issue with a stock flat piston? Here are my two theories. The car the cam was installed in has very high mileage. After debating for sometime, if we were going to change the timing chain or not, we chose not because of the oil pump hassle. This was just going to be a temporary installation, new motor soon. Is it possible that the timing chain would have enough slack to retard timing events in a way to where a valve could meet a piston? I've heard that Thunder has very aggressive ramp rates, and thought it might be possible that the timing chain slop caused contact. Also, is it possible that the heads were milled enough to cause interference. The car was bought with very high mileage and has a mysterious history. The pushrods were stock length, so could this be a problem with heads milled to the maximum allowable specs. Oh yeah and to the other guy, those keepers are a B$%^h, aren't they?

jmd

iTrader: (4)

sounds like you answered your own questions with the decked heads, stock pushrod combo.

DaleMX

iTrader: (4)

Since the ramp and height of the intake and the exhaust are the same, and only the intake pushrods were bent. Sounds like contact.

Raughammer

*sigh* sorry for your misfortune.

Milling heads is a tricky thing aint it? dont go too far or bad things happen. How much were they milled? 40? 30?

Removal of the timing chain and upper sprocket is easy-peazy. Leave the bottom sproket on there but at least change the upper and the worn chain.

Removal of the oil pump is simplicity...

Let us know what you find when you tear it down. Good luck.

AndUAndI

Just bought the TR224 LSA 112 for my 98 LS1. Parts should be here this week. I've been thinking about havinig the (stock) heads milled a little. However, the recent horror stories here have made me change my mind. Kaytech chain and oil pump, and ARP rod bolts comming from TR too (thinking reliability from the beginning of the build).

I'm putting the LS1 into an 1994 Z28.

Trevor @ Texas Speed & Perf.

iTrader: (3)

If you're not buying the heads from the same vendor, then it's always a good idea to call them and ask how much your heads can be decked w/ their cam. I bet Geoff @ Thunder has done one or two of these to know just how much you can shave off of a set of heads and still be safe. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

703crewchief

We have no clue, if the heads have ever been milled or not. We didn't take the heads off the car. Are there marks near the deck surface that will indicate milling? But, after thinking about it, if the pushrods were too long, wouldnt they prevent the valve from closing to the seat when the lobe was on base circle. I pondered this for a while and realized that no matter whats on top of the lifter, it can only push it to the cams actual lift. Pushrod length is important mainly for valve train geometry. But, a milled head will bring the valves closer to the piston and bringing the rocker down to factory specs will make the lifter preload too much. With the lifter preloaded too far, can the oil pressure raise the lift so much as too be dangerous? So now my question is...can the rocker guide/seat be shimmed or are shorter pushrods the best alternative. Also the timing chain slack is still bothering me. Could there be enough retard in a loose timing chain to cause contact? This cam came from a strong running car, so I won't blame manufacturer mis-grind. When it goes back together, the new chain will be installed for sure. But, I would still like opinions on the chain slop being the culprit.

Badazzvette

Depending on what cam was in the car, you may actually need longer pushrods unless those heads were decked and the cam that was in before was getting the V/P clearance very close. You can check lifter pre-load to see how things are there, but you may need to pull the heads and see whats going on in your cylinders. I'm betting you had v/p contact and have some issues there. I wouldn't run the car anymore until you find out how your v/p clearance is. Not knowing if your heads have been decked or milled is definitley an issue as it's important to know for determining your geometry. Try .050 shorter pushrods and see if that makes a difference. How's the power? I don't think a loose chain can give enough slack to cause issues with v/p clearance. If it were that slack, it would jump a tooth or three. Maybe you've done that now with the more aggressive cam, but you would know if it were off one tooth and even more so if it were off more.

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 703crewchief:
<strong>We have no clue, if the heads have ever been milled or not. We didn't take the heads off the car. Are there marks near the deck surface that will indicate milling? But, after thinking about it, if the pushrods were too long, wouldnt they prevent the valve from closing to the seat when the lobe was on base circle. I pondered this for a while and realized that no matter whats on top of the lifter, it can only push it to the cams actual lift. Pushrod length is important mainly for valve train geometry. But, a milled head will bring the valves closer to the piston and bringing the rocker down to factory specs will make the lifter preload too much. With the lifter preloaded too far, can the oil pressure raise the lift so much as too be dangerous? So now my question is...can the rocker guide/seat be shimmed or are shorter pushrods the best alternative. Also the timing chain slack is still bothering me. Could there be enough retard in a loose timing chain to cause contact? This cam came from a strong running car, so I won't blame manufacturer mis-grind. When it goes back together, the new chain will be installed for sure. But, I would still like opinions on the chain slop being the culprit.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">

<small>[ September 08, 2002, 07:25 PM: Message edited by: Badazzvette ]</small>

wrencher

iTrader: (2)

You said it started & ran w/audible knock, I don't think the timing chain is to blame. No way it could run & bend push rods & keep running? You are gonna have to disect this thing & post what you find.

gto69judge

iTrader: (32)

Are you sure it was set up "dot to dot"? It sounds like you advanced the cam sprocket one tooth, which will cause the intakes to hit the pistons. A stretched chain would retard the cam timing, opening the intake valve after top dead center and reduce the contact problem.

You should always replace the chain on an LS1 if it has any miles to speak of. It is a very thin design and stretches quickly. You might check out the new heavy duty GM chain that was just released.

703crewchief

Judge,
You have eased my mind abou the chain itself causing the problem. A cam retarded could hit an exhaust valve, and that was what was going through my head, but I just have intake problems. You are absolutely right. I will find out today whether or not this was my doing or not. The results will be in later.

MNSS

Sounds to me that either the cam was degreed wrong or the heads have been decked and need a 7.350 push rod. compared to the stock 7.4