Why use pushrods?
Why use pushrods?
Had a simple procedure done to my eye to correct my vision yesterday (not LASIK, I wish). Anyway, about all I can do is look at the computer cause everything else hurts. So I've put in a lot of hours on this forum and others I'm a part of. After reading across the different boards I came to a question I couldn't find and answer to and don't know enough about engines to explain to myself.
Why does Harley not use overhead cams?
I've noticed that most car manufacturers use them and some of the most powerful ones use DOHC. All I know about cams is that they open and close the valves for intake and exhaust. I think Vic uses OHC and some other bikes as well.
Is there a mechanical advantage to overhead vs pushrods?
Again, may have just spent too much time on the comp, but others may have the same thought. Thanks for the input.
Why does Harley not use overhead cams?
I've noticed that most car manufacturers use them and some of the most powerful ones use DOHC. All I know about cams is that they open and close the valves for intake and exhaust. I think Vic uses OHC and some other bikes as well.
Is there a mechanical advantage to overhead vs pushrods?
Again, may have just spent too much time on the comp, but others may have the same thought. Thanks for the input.
Road Warrior
Joined: May 2009
Posts: 1,945
Likes: 3
From: Victoria, Australia
Switching to OH cams would require a total redesign of (as a minimum) the top end valve train including rocker covers and require a chain drive off the bottom end somewhere.
Regarding mechanical advantage OHC motors can rev higher due to not having to raise lifters, 'push rods' and raise and lower valve rockers.
Google V Rod for more info.. :->>
Regarding mechanical advantage OHC motors can rev higher due to not having to raise lifters, 'push rods' and raise and lower valve rockers.
Google V Rod for more info.. :->>
Cruiser
Joined: Dec 2008
Posts: 214
Likes: 0
From: Peterborough, Canada
Pushrods are perfect for big twins, we don't have 12,000 rpm shift points. The pushrods tubes are classic HD styling. And pushrods keep keep the basic Harley engine simple and air cooled. OHC's are for great for high revving multi valve engines, but they are not advantages in all applications. I love my pushrod V-twin, and would not trade it for any other power plant.
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Seasoned HDF Member
Joined: Sep 2009
Posts: 17,136
Likes: 6,161
From: SE Michigan
A good overview here, but a nice summary at the end (emphasis mine):
"Overhead camshaft engines can produce higher performance but typically cost more to build. Pushrod engines are cheaper to build and work on. Many engines use overhead camshaft designs because the optimum cylinder head design allows for increased fuel economy and performance too. Most high performance vehicles are using overhead camshaft designs but then Corvette comes along again with their pushrod V8. Thirty-five miles per gallon and four hundred horsepower out of a pushrod engine show they can’t be that bad!
"Overhead camshaft engines can produce higher performance but typically cost more to build. Pushrod engines are cheaper to build and work on. Many engines use overhead camshaft designs because the optimum cylinder head design allows for increased fuel economy and performance too. Most high performance vehicles are using overhead camshaft designs but then Corvette comes along again with their pushrod V8. Thirty-five miles per gallon and four hundred horsepower out of a pushrod engine show they can’t be that bad!
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Seasoned HDF Member
Joined: Mar 2010
Posts: 38,295
Likes: 6,322
From: Honah Lee
Because all the reliable metrics used overhead cams and they realized old school (Harleys riders understood pushrods) and they could not go that way. Now the metrics realize to actually sell more the are reverse engineering their v-twin to either be pushrod or at least look like they are. Some run chains in what looks like pushrod tubes. One runs water thru what looks like a pushrod tube. Bet you cannot guess who that is?
Road Master
Joined: May 2008
Posts: 762
Likes: 14
From: Bellevue, NE
Nostalgia. Re-tooling (expensive), cheaper to build, and the bikes still sell pretty well. Would you change, if you were a business like the MoCo? I'm pretty sure I wouldn't. No compelling reason for them to change it up at this point. Harley understands their customer base, and I would expect that until they're forced to change (EPA?) they won't.