How sensitive are cam changes in regards to pushrod length?


My new cam is ground on a 1.050" base circle and I am unsure of the old one. IIRC the old cam card does not specify.
The old cam was one designed for an LT1 application but still cleared everything in my stroker motor.

 

I am uncertain what the "stock" base circle is, but i'm fairly sure you will need different length pushrods. If that base circle is smaller at all (small base circle for a stroker engine right?), then you'll need new pushrods.

 

It almost always is. The cam lobes don't rise up from a standard minimum diameter, they drop down from a standard maximum diameter.

 

true true, otherwise it'd be heck trying to force them through the cam bearings...

 

These will definitely have to be checked then and probably replaced.

I mic'ed up the two base circles horizontally from maximum lift and the new cam is more than a tenth smaller.

I'm also running .080" lash caps as the first guy that helped me assemble the motor suggested.
What would removing these do for the pushrod length? Should I go ahead and remove the anyway? (He was more of a BBC solid roller guy than SBC and uses them to protect the valve tips for his solid rollers)

 

Think about it.
Remove lash caps, now your rocker sits lower (or wants to, to be "flat"). So you need shorter pushrods for that.
Do you have an adjustable pushrod length checker? Use that, with/without lash caps, to see what two lengths would be best.
Then find out which is cheaper/more common, and buy those.

 

No I do not own one or know anyone that does and would hate to buy one. Especially before I buy the correct pushrods from Summit since I have already placed like three orders and am getting sick of their $10 handling charge.


Now lets pray my springs don't bind etc and no valve touched a piston!

 

Unfortunately this is something you have to measure before to make sure you get the right length.

Since you said the old cam was for an LT1 I'm guessing its a roller cam. Stock roller cam pushrod length is 7.200". Your new cam with the different base circle could use 7.150", 7.200" or 7.250" length pushrods.

You could try using your existing pushrods and see how close it is.

And of course I'll recommend Manley pushrods. 25741-16 is 7.150", 25733-16 is 7.200", and 25734-16 is 7.250".

 

camaroRUS, do you live out in the stix? in my town, there's about 2-3 shops that have those checkers on the shelf. They cost about $12 and work like a hot damn. I'd highly recommend it.

 

Nah Sonix, I'm in the city in a pretty big city actually. Louisville, Ky but I don't know where I would find a checker. The O'Rilley's, Autozone's and NAPA don't stock them.

Not many speed shops I know of as they seem to be put out of business by Summit and Jegs.

The pushrods I have now are Trickflow 7.400" with my .080 thick lash caps. They were spot on for the old cam but now I am riding solely on the outermost third of the valve tip.

I'm kind of glad I need new pushrods since I can do away with these lash caps....would hate to see another one get loose and destroy my motor

 

It may be too late. I'd recommend to get an adjustable push rod. I don't know if your engine is out of the bay or not, or if the engine is partially torn down. Pull the rocker arms off the studs, install an adjustable push rod ($11 from summit Trick flow part #9000) put the rockers on (that you plan on using) the #1 cylinder. You'll need to set TDC on cylinder #1 on the intake stroke, and set the intake and exhaust to zero lash, get rid of your spacer, and start with 7.2000 (stock) length. Oh, make sure you use a marker to color in the bottom of the valve stem before putting the rocker/s on. get to zero lash, then turn another 1/2 turn (if you have hydraulic lifters) to set lifter. Once you have your lash set, turn the engine over manually two revolutions. pull the rockers off, and look at the wear pattern on the valve stem. Essentially, you want to see how much of the marker has been removed. the wear pattern should be right in the middle of the valve stem, and the width of the mark should be no more than .800. The ideal amount is .300/.400 but most people don't get it that close. most people don't even check. Good luck. If this doesn't make a lot of sense it's probably because I'm drinking. But the basics are in here, and it's fresh in my mind because I'm going through the same process. This may actually help you establish the procedure to set your valve lash. It's basic and can job your brain, to answer some questions. A couple comments that were made didn't sit right with me, but it's helpful for sure.
http://www.youtube.com/watch?v=89o5rLpbCgI

 

Went with a 7.150" pushrod...first batch I received from Summit were used and had rust in the middle, lots of rust but I am expecting the good set to come in today.

I thought I would have to go much shorter since my heads were slightly milled, the block was decked .015", and I have a very small base circle but it was actually almost a toss up between 7.150" and 7.183".

 

I guess I have an "exception" engine.
I changed the heads and cam among other things. Bought a pushrod length checker from ebay. Found that all I needed was stock length rods. Go figure.

 

Yeah, it all depends. Here's another thing that you wouldn't think would happen, or that you'd need to worry about. I checked one cylinder for valve stem wear pattern (pushrod length verification), and valve to piston clearance. Trick Flow said it was necessary to only check one of the cylinders. Maybe I did this wrong, but I wanted to be sure, and check all 16 valves. I had no clearance issues, but I had different roller wear patterns on the valve stems. nine of the sixteen stem wear patterns look good, but the other seven had different results. Six of the exhaust valve wear patterns show the roller tip favoring the intake side, and only touching 3/4 of the stem. The remaining one (intake) is favoring the exhaust side.

I torqued the heads up, with the head gaskets on. I also set all the valves to zero lash, plus another 1/2 turn. I wanted to set the valvetrain up exactly as it will be when the engine will be running.

Has anyone else experienced these results? Did i do something wrong?