Measuring Pushrod length. Is this right?
Thread Starter
Racer
Joined: Mar 2006
Posts: 358
Likes: 96
From: Hattiesburg MS
Measuring Pushrod length. Is this right?
I just installed an mild cam in my 04 and I reused everything but springs. I replaced the stock springs with 918’s. Everything is working great with a nice HP pickup. However there is a lot more valve train noise so I think my pushrods are a little short. The noise is coming from both sides of the engine and even front to back. So I bought a pushrod length gauge from Comp Cams and this is what I did.
Bumped the engine around to get #1 to TDC remove the exhaust rocker replace the pushrod with the gauge and reinstalled the rocker torqued to about 10 lbs. Then I tried to extend the gauge but it just spun. So I removed the rocker again and extended the gauge ½ turn then reinstalled the rocker. I repeated this process until there was no lash. Then I retracted the gauge ¼ turn and did a final check. This is what I came up with.
The gauge was 6.8 to 7.8
Final length was extended 10.25 turns or .5125
6.8 plus the .5125 equals 7.3125
7.3125 plus .120 preload equals 7.4325
Does the math look right?
So if I get a set of 7.425 pushrods the valve train noise will go away
Thanks
Bumped the engine around to get #1 to TDC remove the exhaust rocker replace the pushrod with the gauge and reinstalled the rocker torqued to about 10 lbs. Then I tried to extend the gauge but it just spun. So I removed the rocker again and extended the gauge ½ turn then reinstalled the rocker. I repeated this process until there was no lash. Then I retracted the gauge ¼ turn and did a final check. This is what I came up with.
The gauge was 6.8 to 7.8
Final length was extended 10.25 turns or .5125
6.8 plus the .5125 equals 7.3125
7.3125 plus .120 preload equals 7.4325
Does the math look right?
So if I get a set of 7.425 pushrods the valve train noise will go away
Thanks
Racer
Joined: Mar 2006
Posts: 464
Likes: 0
From: silverdale washington
Alot of people are making more power by using a .040 preload. yes your math looks good, however If the lifters were not already pumped up all the way, then they would already be preloaded. and your .120 would not apply. if the lifter were given time to bleed down or they are slighlty worn then they will drop. If nothing except springs has changed then your geometry is exactly the same. they are going to make more noise because you have a stonger spring in their. If you have stock lifters, rockerarms, heads then you will only require stock size pushrods. If you go to big on the pushrods it could be a disaster. I would replace the lifter before I did pushrods if you think they are not seating fully.
Le Mans Master
Joined: Dec 2003
Posts: 5,561
Likes: 448
From: Atlanta metro Ga.
Most folks in the know go with 7.425" rods, as you've calculated, due to the reduced base circle of the aftermarket cam.
It certainly can't do anything but help w/ the valve train noise, may not eliminate it completely (new cam w/ more aggressive ramp rates, different springs, etc. all contribute).
It certainly can't do anything but help w/ the valve train noise, may not eliminate it completely (new cam w/ more aggressive ramp rates, different springs, etc. all contribute).
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Originally Posted by Dan_the_C5_Man
Most folks in the know go with 7.425" rods, as you've calculated, due to the reduced base circle of the aftermarket cam.
It certainly can't do anything but help w/ the valve train noise, may not eliminate it completely (new cam w/ more aggressive ramp rates, different springs, etc. all contribute).
It certainly can't do anything but help w/ the valve train noise, may not eliminate it completely (new cam w/ more aggressive ramp rates, different springs, etc. all contribute).
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
Originally Posted by Cscokd
I didn't think you could accurately measure push rod length unless you used a solid lifter for the measurement because of the hydraulic roller lifter can give inaccurate results?
