I have an adjustable pushrod. I do I utilize this to check proper pushrod length on my 455 with stock rockers?
First, the following is for a hydraulic lifter...if you're running a solid cam we have more to go over. Heads installed w/gasket and torqued. Rotate cam until the lifter is on the cam's base circle for whatever lobe you're checking. Install adjustable pushrod which has been set at its shortest length. Install rocker assembly. Lengthen the adjustable pushrod until the slack is taken out, i.e. zero lash. Remove adjustable pushrod and measure its length, write it down. Repeat for various lobes on both sides of the engine. Average the lengths measured, add 0.030" for lifter preload. That's the correct pushrod length. Devon
In order to use stock rockers, are custom length pushrods required for pretty much all aftermarket cams?
Unfortunately, it's one of those "it depends" questions. Depends on cam base circle, cylinder head deck machining, block deck machining, head gasket thickness, amount of preload desired, Chevy or Buick lifter plunger depth. Devon
Using hydralic cam and lifters and stock rockers. The only reason I ask is because the heads had .018 taken of and the block was squared resulting in approx .013 off. Combined .030. Shop seems to feel stock length pushrods will be fine. They did not assemble, I did they even they are giving me their disclaimer, but again feel stock length should be okay. I just figured since I have one adjustable rod, might as well check, but confused on how it is done. I shall read the above post Using .040 thick head gaskets. How do you adjust lifter load if non adjustable rockers. Devon, your explanation seems easy enough.
Okay, so I put in a new pushrod from summit that says it is for stock 455. 5/16 length 9.378. When I start to torque down the shaft bolts the pushrod starts to depress the lifter, I guess that means too long. So I swap for the adjustable one. The lifter is on the base circle. I tighten it to zero lash. Measure it, it is 9.250. So if i go like saod above. 9.250 plus .050 preload that should be a length of 9.300. That is .078 shorter than the stock one I bought which was 9.378. Unless I am measuring wrong, way to long. If there is only .030 shaved between heads and block, how can it be that much?? And I missing something?
Does sound a bit odd. Does your length checker have 5/16" diameter ends like the stockers? FYI, the stock length should be 9.350". Devon
Yeah, both 5/16. So the summit ones are longer than stock anyhow. Back to the drawing board. Back to machine shop. Possbly I am measuring inaccurate. How much preload is there suppose to be when on cam base circle
How much preload?? So anywhow if I go my the adjustable one that has zero lash @ 9.250 and I add .030 then I need a length of 9.280. Gotta be more to this then. Cause that would be a .070 deifference from stock. I know less than .050 was removed. Does the angle change, thus effecting length? Damn, shoulda just let the shop build the whole motor
0.030" is pretty much what we shoot for. Factory preload was probably more than this. Not only your mill work, but the cam base circle is an unknown, as is valve stem installed height. If the valve tips are too high, it can make the pushrods seem too long. Devon
This may get an obvious answer, but what is the risk with a little too much preload? Excesive wear on cam? Valves that never close?
The only drawback I've heard of is a bigger potential for lifter "pump up" at higher rpm. Comp Cams suggests no more than 0.040". Devon
Summit must be wrong, if stock length is 9.350, summits are longer and say stock: http://www.summitracing.com/parts/SUM-G6402/
Take their parts descriptions on the web with a grain of salt; I've seen errors there before. I'd go ahead & measure one of your Summit pushrods to see where they're at. Devon
The spec length for pushrods is not measured from tip to tip but from radius of the ball to radius of the ball. I think 5/16 ends result in an additional .020" tip to tip. 9.350 should be radius to radius and 9.375 is tip to tip if I remember correctly. Regardless, sounds like you were setting up ok. There is a world of variables, base circle and valve tip height are biggies. I.e. if they put in seats, what valve source and usually most shops don't put much emphaisis on tip height because Chevies have individual adjustable rockers that can compensate. So with machine work, it is real easy to be .050+ off. The only thing I would do as a gut check is ask yourself how big the camshaft is. Normally, a bigger cam will have a reduced base circle which often offsets most of the machine work. Just follow Devon's steps again and you should be ok.
Good info, Dave. I had forgotten that they're measured in different ways. Some more here: http://www.compcams.com/information/Products/Pushrods/ So that begs the question, if Jay were to decide on custom length pushrods from the TA catalog, should he specify Theoretical, Actual, or Gage length as described in the article? Devon
the easiest way for everyone in this situation is to measure tip to tip and emphasize when ordering that is how you measured. The sales guy @ TA can have someone in (TA's) shop measure one to confirm if necessary. Also, if he is uncomfortable with measuring he can send a properly adjusted one to TA and they will give him an appropriate set. One more thing is that I just remembered to check a couple intake and exhaust. Some shops are known for putting in exhaust seats and those tip heights being different, requiring two different length pushrods for the engine.
Wow, thanks for all the additional info. I was measuring from tip to tip. Did'nt realize there were three different types of measurments, geez. Then if I need different lengths for intake and exhaust, man. I think sending my adjustable one to TA or Greg Gessler might be a very good idea. They can go by the zero lash length and add proper preload length and send me the ones I need. Running TA 284 88h cam, not real big. Shop completely rebuilt the heads so I will have to ask him some of those points tomorrow.
