The heads and block deck on my 303 Olds were milled slightly at the machine shop to true them up. I also have a new hydraulic cam from Ross Racing installed. I understand that I will need new custom length pushrods, since I don't have adjustable rockers. I'm using a new set of 1.8 ratio stock rockers. I ordered this adjustable pushrod length checker to use. What is the correct procedure to measure for the new pushrods with hydraulic lifters. Do I need to prime the engine with oil to pump up the lifters before measuring. Do I adjust the length checker until there is zero lash, with no preload on the lifters. I am ***uming that the measurement should be taken with the lifter on the base circle of the cam. Help me out guys, I've never done this before and don't want to order the wrong length pushrods.
I've fitted adjustable rods and the procedure can't be too different from measuring for custom length pushrods. I think you've got the idea anyway. Dry, base of cam, preloaded to required spec measuring between retaining clip and plunger. Paperclip used as measuring device! This was on bleed down type lifters, so could be different spec, but possibly not. Logic dictates, well to me at least, that there must be some preload as otherwise the lifters would be running on the retaining clip. Chris
Ran adjustable pushrods in an early hemi, but it was solid. I will mention getting a couple wrenches and bending them for easy access was a big help. As said, base circle, you can use a dial indicator to measure lifter preload, and measure the pushrod after setting. Most companies who provide custom length and adjustable pushrods should have instructions. Talking with them to confirm ball end and cup end measurements (don't know what you have) before ordering is important. There is a whole can 'o worms on rocker ratios and travel, often checked in the shop by checking rocker sweep on the valve stem tip. I'd suggest trying to find a supplier who has a good tech line and discussing your build and expectations. If this is a high winding max output build, I'd check all 16. If they are different, I'd find root cause. If it's a street car, checking a single intake and exhaust should get you running. A few tenths difference in preload shouldn't be a problem. Are all the valve installed heights the same? I looked up a pic to visualize the setup.
Thanks for reminding me to check the valve stem heights, they are not the same. The intakes are shorter than the exhaust by .008 to .015. I called Smith Brothers Pushrods and talked to Tony from the tech department, he said to measure the pushrod length without preloading the lifter then add the preload dimension recommended for the lifter. He said that .040 of preload would be ok, does that sound right. Also he recommended that I check all the lengths for the intake pushrods and then take the average of them to get the length of pushrod to order. I'll do the same for the exhaust
Sounds like solid advise.No trying to adjust and read a dial. Just basic addition. 40 sounds good, too. I will say that the first time we ran the valves, it took hours. After a few months we could do it in less than an hour. All that to say, go slow, check, then double check and write it all down as you go. You only have to check 16 once or at most, twice!
With that much variance in the installed height of the valves you might want to consider adjustable push rods. Did that on my Cad 331 due to installed height differences and so far has worked well. I set the pre-load on mine to .032 which was one turn of the adjuster. Regardless, follow the guidance from Smith Brothers and you won't go wrong.
Scored a set of rebuilt Mcgurk rockers and shafts from the boys at Iron Trap for my 303 then had Tony make me a solid roller measured the push rods than gave tony a call he set me up with a set its been a year but he did set me up hopefully some day they will arrive.
I finished measuring the pushrod lengths for all the valves and I was surprised to see how much of a difference there is between some of the cylinders. I measured each twice and made a list, then took the average length of the two measurements. The shortest was 9.150 and the longest was 9.165. The average length of all the measurements is 9.159. Smith Brothers Pushrods recommended that I go with the average length of all the pushrods (9.159) and add .040 for preload. They said a length of 9.200 would be ok and they have them in stock. I ordered 12 pushrods without an oiling hole and 4 with an oiling hole to use on the outer most rockers because I have seen it mentioned that those rockers don't always get enough lube from the rocker arm rail.
Almost Half of them are going to have play/lash with the 9.160 length; Intake 3, 5, 6, and 8, Exhaust 3. 6. 8. Adding 0.040" to the average 9.159 is 9.199". Do they have a 9.200?
Great post. I have yet to figure out the pushrod length for my 324 Olds. We took 0.040 off of the head surfaces and I used a cam and lifters from Tony with non-adjustable 1.8 rockers also. So your data gives me good info for a sanity check.
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