Argh!! pushrod confusion
Thread Starter
Melting Slicks
Joined: Jan 2007
Posts: 3,333
Likes: 0
From: Athens OH
Argh!! pushrod confusion
I thought I had this answered in another thread, but after more research, i am still confused.
First here is what I have.
243 heads with stainless steel valves(not the hollow)
Comp cams blower cam
GM MLS head gaskets
stock rockers
crane dual springs
I used a pushrod length checker and calculated a pushrod length of 7.350". Stock is 7.400in.
In my research, it appears that comp cams use the same base circle as the LS6 cam, which is .4mm or .0157in smaller than my stock LS1 cam. With the non-hollow valves, which are supposedly longer to make up for the smaller base circle, wouldn't it make sense that I would need a longer pushrod rather than a shorter one as I have calculated?
I used this length checker form Jegs Not the best tool, but I measured the overall length at 7.269, subtracted .017 for gauge length then added .100 for the preload.
First here is what I have.
243 heads with stainless steel valves(not the hollow)
Comp cams blower cam
GM MLS head gaskets
stock rockers
crane dual springs
I used a pushrod length checker and calculated a pushrod length of 7.350". Stock is 7.400in.
In my research, it appears that comp cams use the same base circle as the LS6 cam, which is .4mm or .0157in smaller than my stock LS1 cam. With the non-hollow valves, which are supposedly longer to make up for the smaller base circle, wouldn't it make sense that I would need a longer pushrod rather than a shorter one as I have calculated?
I used this length checker form Jegs Not the best tool, but I measured the overall length at 7.269, subtracted .017 for gauge length then added .100 for the preload.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Does the adjustable have an oil hole in it or is the end completely round? The 0.017" is based on an overall with oil holes.
What overall length are you getting on the stock pushrod?
Check this link for more information: Link
What overall length are you getting on the stock pushrod?
Check this link for more information: Link
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Just went back and re-read your other thread. Did the machine shop do any work on the valve seats? Looks like it in the photo. If they did, and the valves are set deeper, the top of the stem could be higher and hence the shorter pushrod. Also, if they did, you should really check the wipe pattern as well prior to measuring for the pushrod.
Thread Starter
Melting Slicks
Joined: Jan 2007
Posts: 3,333
Likes: 0
From: Athens OH
No, the heads were not decked as far as I know. it was not mentioned when I bought them but at the time, I didn't know to ask. I have to assume that it would have been mentioned if they had been. The tool does not have oiling holes, however, it appears to have a flat spot on top each end that I am guessing is to simulate the holes.
The machine shop shouldn't have done anything other than a basic valve job and replace a few valves. They also noticed that the heads had 2 different sized valves, so I know they inspected stuff pretty well.
I didn't measure the stock rods, but when holding them side by side, there is definitely a difference in length.
Here's a closer pic of the bowl before being cleaned up, and for reference, a pic of the stock LS1 bowl. You can see it had some CNC work there as well. Does that account for anything?
The machine shop shouldn't have done anything other than a basic valve job and replace a few valves. They also noticed that the heads had 2 different sized valves, so I know they inspected stuff pretty well.
I didn't measure the stock rods, but when holding them side by side, there is definitely a difference in length.
Here's a closer pic of the bowl before being cleaned up, and for reference, a pic of the stock LS1 bowl. You can see it had some CNC work there as well. Does that account for anything?
Last edited by AMRAAM; Feb 22, 2008 at 10:47 PM.
Racer
Joined: Sep 2006
Posts: 260
Likes: 1
From: Chesterfield MI
I did pretty much the same thing. I went with 7.425" pushrods and the thing is whisper quiet and the wipe pattern is perfect. You are correct the base circle of the cam is smaller to get the higher profiles and the LS6 hollow/sodium filled valves are longer to compensate. Without the longer valves you either need longer pushrods or adjustable rockers.
Thread Starter
Melting Slicks
Joined: Jan 2007
Posts: 3,333
Likes: 0
From: Athens OH
Thanks for your help guys.
Vettenuts, I hope you don't think I didn't take your word in the other thread. I just thought I had it all figured out then I didn't. Tomorrow, I am going to buy this compcams gauge and hopefully be done with this crap.
http://www.jegs.com/i/Comp%20Cams/249/7702-1/10002/-1
Vettenuts, I hope you don't think I didn't take your word in the other thread. I just thought I had it all figured out then I didn't. Tomorrow, I am going to buy this compcams gauge and hopefully be done with this crap.
http://www.jegs.com/i/Comp%20Cams/249/7702-1/10002/-1
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Thread Starter
Melting Slicks
Joined: Jan 2007
Posts: 3,333
Likes: 0
From: Athens OH
I bought a comp cams hi-tech checker today. I'll get to the garage tomorrow and see what happens. I also went ahead and bought the 7.400 pushrods because that is all that they had in stock. if they are not right I'll order the right ones.
Thanks for the help.
Thanks for the help.
