Deputy04sierra

Hey everyone sorry if this has been discussed before I had a hard time navigating the site.
I currently just had my deck resurfaced and we took off .005”, I just installed the summit racing sum-8712 cam and I’m getting a little more valve clatter than I did before the install. I’m getting ready to purchase springs and rods but not sure as to what size rods I need to order, I keep seeing a lot of talk about 7.4 but if my head was decked so little will this make any difference. Any insight would be great.

RedXray

It's always best to measure with a pushrod checking tool. If you're using a stock thickness head gasket the factory lifters should easily eat that .005 extra length preload. When you buy off the shelf pushrods they'll vary in length sometimes more than the .005 you took off the heads. What kind of lifters are you running and at what preload? You didn't give any info about the engine in your post. One full turn from zero lash is .050 preload (actually .047) so a quarter turn would be roughly 0.012" extra preload.

You can always ship back a set of pushrods purchased from Summit if the 7.4's don't give you the desired preload (as long as you don't try to run them). The Summit receipt comes with a return shipping label making returns painless. I did this last week when I needed a slightly longer .025 pushrod.

Deputy04sierra

I have a 2004 GMC Sierra 5.3 lm7. I haven’t yet ordered the rods I didn’t know or think that .005” would adversely effect the heads that much as we basically just resurfaced them for a clean slate on the head gasket job. Lifters are stock and so are springs and rods at this point, but like I said I had basically no noise before. It almost sounds as if there is a random tap during the rotation I can hear but my mechanic buddy who’s an LS guy couldn’t. Idk maybe I’m being ocd about this but when you know your truck you know your truck.

Deputy04sierra

Also I don’t know about this preload thing, all I’ve been doing is just torquing the rocker bolts to spec (22ftlbs) and slapping the valve covers back on. Should I be moving past the torque spec to set preload? Sorry I’m new to this.

RedXray

Here are two different methods for measuring pushrod length for proper lifter preload. I use both methods "measure using the $20 Comp Cams adjustable pushrod checker" After I order and receive the correct (or assumed to be correct) pushrods I use the turn method to make sure my calculations were correct, shown in the second video.

Most likely the 7.4's will be the correct length... but this is the correct way for most backyard engine builders. There are other more advanced methods for measuring pushrod length and proper preload but they require a bit more knowledge (like pushrod gauge length vs actual length) and digital measuring tools.


Info starts at 2:30

Deputy04sierra

Awesome thanks!!!! So my truck came stock with 7.318 length rods for the lm7, so between the difference in the base circle from stock to after market cam I was thinking 7.4’s. My buddy just told me he had ordered 7.4 rods also. I was just nervous being I had the heads milled .005” but I guess at the end of the day that’s not much.

RedXray

As a rule of thumb you don't get into base circle change until .600 lift and greater.

I have a like new set of BTR 7.400 that I no longer can use with around 2,000 miles. I went to a set of PRC (Texas Speed) aftermarket heads that required a longer 7.525 pushrod. I have them listed on Craigslist right now for $50 no shipping. If you want them I can do $55 priority mail... let me know.

Deputy04sierra

I sent you a private message I’ll take them

RedXray

Didn't receive...I hit your pm.
I can get them out in the morning and you should have them by the weekend.