Cam question
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Cruiser
Joined: Oct 2017
Posts: 160
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From: Florida
[QUOTE=AJ88V;18116999]Useful clarification, Agoober. I was sloppy in my language.
The essential point is that the stock pushrods are sized for the stock cams, and the stack-up of any manufacturing tolerances of the entire valve train is taken up by the hydraulic lifter for each of the four pushrods.
The stock pushrods might actually work with a new cam (assuming the head is set up for whatever cam is to be installed! ;-), but there's no guarantee and Harley doesn't control what you may be putting in your engine. The hydraulic lifters have a small range over which they can expand to take up the slack. Too loose and the lifters won't fully open the valves and may induce noise as the cam hammers against the lifter and the rod hammers the rocker. Too tight and the lifter can't loosen up enough, possibly holding the valve off the seat and possibly lifting the valve to the point where it contacts the piston. The adjustable pushrods guarantee you have a pushrod in there that is adjusted to a length where the lifter can operate properly. IIRC, back in 1989 when I built my Sporty, Harley actually offered different length pushrods and maybe they still do, but it's easier to just use the adjustable rods. The cost and performance differences are negligible and it's easier to install the adjustable rods because you can shorten them and install with the rockers installed - no need to open the rocker boxes.
Thanks again for the clarification. Cheers
Road Master
Joined: Aug 2018
Posts: 965
Likes: 297
From: NoVa
[QUOTE=irish44;18117014]
If you are not taking off the rocker boxes, your mechanic will use bolt cutters to cut the stock pushrods and remove them. After installing the cam, you shorten the adjustable pushrods, install them, and then adjust the pushrods and lock them down.
If you are removing the rocker box, you can go ahead and remove the rockers and pull the stock pushrods out the top of the engine without cutting. Then you can install the cam and install the new pushrods and reinstall the rockers. Finally, you'd adjust the pushrods.
It may very well be true that you can reuse the stock rods, but those won't be adjustable. I'd guess the determining item would be the low point on the cam (off lobe). If you mic'd it and it was the same as the stock cam, you'd probably be good to go. If that low point is different in either direction, I'd be concerned using the stock rods. If I had any problems reinstalling the rockers, that might indicate too tight and I'd stop right there and use the adjustables.
Stock rods - free, lighter, maybe stiffer, but have to pull the rockers and maybe not right size for the new cam.
Adjustable - guaranteed to work, don't need to pull the rockers, but heavier (more valve train mass is bad) and cost money.
I think you can pick up Andrews adjustable rods for something like $80 - $100 new on ebay. Easy decision for me.
To the other question, the adjustable pushrods are pretty much set it and forget it. The hydraulic lifter keeps everything in adjustment to compensate for cam and valve train wear. I guess in cases of extreme wear, the adjustables would let you tweak it back up, but by that point, you'd probably want to replace cam, install new valves, and/or replace rockers and lifters.
Useful clarification, Agoober. I was sloppy in my language.
The essential point is that the stock pushrods are sized for the stock cams, and the stack-up of any manufacturing tolerances of the entire valve train is taken up by the hydraulic lifter for each of the four pushrods.
The stock pushrods might actually work with a new cam (assuming the head is set up for whatever cam is to be installed! ;-), but there's no guarantee and Harley doesn't control what you may be putting in your engine. The hydraulic lifters have a small range over which they can expand to take up the slack. Too loose and the lifters won't fully open the valves and may induce noise as the cam hammers against the lifter and the rod hammers the rocker. Too tight and the lifter can't loosen up enough, possibly holding the valve off the seat and possibly lifting the valve to the point where it contacts the piston. The adjustable pushrods guarantee you have a pushrod in there that is adjusted to a length where the lifter can operate properly. IIRC, back in 1989 when I built my Sporty, Harley actually offered different length pushrods and maybe they still do, but it's easier to just use the adjustable rods. The cost and performance differences are negligible and it's easier to install the adjustable rods because you can shorten them and install with the rockers installed - no need to open the rocker boxes.
Thanks again for the clarification. Cheers
Banned
Joined: Jan 2019
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From: Nunya.
Peace.
Last edited by Agoober; Mar 19, 2019 at 11:19 PM.
Banned
Joined: Jan 2019
Posts: 3,036
Likes: 1,013
From: Nunya.
[QUOTE=irish44;18117014]
Make sure you're at TDC when you whip out the rocker gear.
Peace.
Peace.
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