Pushrod question
Road Captain
Joined: Jan 2019
Posts: 607
Likes: 143
From: Hilltown
On base, valves are closed. Closed is closed. I'm trying to figure out why base would be smaller than necessary for valve to rest in it's seat or larger to prevent seating. Please explain.
Seasoned HDF Member
Joined: May 2008
Posts: 21,032
Likes: 12,560
From: South Carolina
Grand HDF Member
Joined: Sep 2017
Posts: 4,359
Likes: 1,219
From: Dubuque, IA
Geezus. So much bs here. Smaller base circles certainly aren't uncommon. Used cams with a smaller base circle on my Sporty build in fact. I would think for all the know it alls here the reason smaller base circles might be used would be obvious. Here's a hint. There's advantages and disadvantages to smaller base circles.
Off the top of my head, the Andrews 57H uses a .020 smaller base circle. I've heard all Andrews cams above 510 lift use smaller base circles but haven't confirmed that personally.
And just beccause smaller base circles are used still doesn't mean adjustable pushrods need to be used. Hydraulic lifters can take up some of it for one and two, decking heads can make up for it.
And adjustable pushrods certainly have a downside. Besides coming loose they've been known to flex, strip, or fall apart. I know more than a few builders wouldn't be caught dead using them.
And yes I'm using them against my better judgement because I was too fkn lazy and yes I had one come loose that was properly torqued. Next time I pull the heads they're coming out. Y'all can run 'em. Just not worth the risk of catastrophic failure.
Solids are lighter, stronger, and more reliable. Not to mention cheaper. It's not that difficult to figure an exact length and have them custom made for desired preload or any changes in valve train geometry.
Off the top of my head, the Andrews 57H uses a .020 smaller base circle. I've heard all Andrews cams above 510 lift use smaller base circles but haven't confirmed that personally.
And just beccause smaller base circles are used still doesn't mean adjustable pushrods need to be used. Hydraulic lifters can take up some of it for one and two, decking heads can make up for it.
And adjustable pushrods certainly have a downside. Besides coming loose they've been known to flex, strip, or fall apart. I know more than a few builders wouldn't be caught dead using them.
And yes I'm using them against my better judgement because I was too fkn lazy and yes I had one come loose that was properly torqued. Next time I pull the heads they're coming out. Y'all can run 'em. Just not worth the risk of catastrophic failure.
Solids are lighter, stronger, and more reliable. Not to mention cheaper. It's not that difficult to figure an exact length and have them custom made for desired preload or any changes in valve train geometry.
Last edited by 60Gunner; Apr 29, 2021 at 01:47 AM.
Seasoned HDF Member
Joined: Dec 2005
Posts: 19,830
Likes: 7,968
From: poway
On twincams, the main reason for smaller base circle was to provide clearance between the main bearing boss and exhaust cam lobes on 99 to 02 tcs. On real high lift cams, they were needed to clear the lifter bosses and with chain driven cams, they were used to keep the cams from colliding with each other. On a M8s it's probably less of a worry about the cam hitting the engine case on taller lifts. When I changed cams on my 17RK, I went with adjustables just so I could replace the lifters without pulling the rockers. Care must be taken when doing M8s as the top tower that hold the rocker shafts can break off if the rocker arm is cocked while cranking the shaft back into place with fixed pushrods. The tower is machined directly into the head so the head will have to be replaced or welded.
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Southpaw Super Glide: A Left-Hand-Drive 1979 Harley FXE Built to Fit the Rider
Verdad Gallardo
Seasoned HDF Member
Joined: Feb 2013
Posts: 24,941
Likes: 19,407
From: New York
The only problems I had with the SE Taper Adjustable PR was their locking nuts cracked. I solved this problems by replacing all the 3/8-24 with 1/2' hex nuts from Smith Brothers Pushrod. https://www.pushrods.net/.