Why use pushrods?
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,897
From: Bedford UK
Most mass produced engines that use overhead cams use them for marketting purposes, just as Harley uses pushrods for the same reason. Any engineering considerations are secondary. Auto engines use them to get lightweight valves to reduce parasitic losses, in other words to improve exhaust emissions and economy. Production motorcycles were influenced by factory racing bike design a few decades ago and while sports bikes benefit from OHC the plain fact is that most bike makers use them today for what have become traditional reasons.
Outstanding HDF Member
Joined: Oct 2007
Posts: 2,398
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From: Newport news, Virginia
Not all Chevy V8s were push rod engines....the 1990 Corvette LT5 engine was a DOHC 4 valve per cylinder engine! It was designed by Lotus and built by Mercury Marine. It was produced from 1990 thru 1995.
Road Warrior
Joined: Mar 2009
Posts: 1,317
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From: Idaho
It does make for a simple motor to work on, I can turn a wrench on it BUT something is going to have to give with the EPA locking down. What I can not understand is why they have not upgraded the rocker arms.
Road Master
Joined: Jun 2009
Posts: 1,062
Likes: 18
From: Beautiful SW Missouri Ozark Mountain Country
I have often wondered why someone has come up with a well-timed electronic solenoid to operate the valves. It would take the mechanical load off of the engine. The only potential draw-back would be that electronic solenoid would draw a lot of amps to open and close the valves.
Maybe they stuck with the push rod V-Twin because that much timing chain WILL fail and a failure is catastrophic. No different than a TC chain failure except you can convert to a gear drive on a TC motor. I hate long timing chains.
Road Master
Joined: Jul 2007
Posts: 914
Likes: 1
From: Republic of Texas
Overhead cams are a vastly superior design, which is why it has become the modern industry standard. A brand new 110 ci Harley will make around 80 hp, and only low 90s hp with Stage 1 mods. By comparison, a Honda Goldwing which is 1,800 ccs, (equivalent to 110 cubic inches) will make 118 hp out of the box, no mods.
Reason for Harley's pushrods? Nostalgia and styling. It's what makes a Harley, a "Harley". And Harley Davidson has elevated "nostalgia and styling" to an art form.
Reason for Harley's pushrods? Nostalgia and styling. It's what makes a Harley, a "Harley". And Harley Davidson has elevated "nostalgia and styling" to an art form.
Ok, since someone else brought this up, how do some of the other bike makers get away without OHC and no pushrods. I came from a VTX 1300 and would still love to have a 1800F Spec3. I know the 1800 is an apples to oranges comparison with the 96", but how did my 1300 create the torque numbers it did without the cams (probably should ask this on the VTXOA site)?
I'm playing devil's advocate because if I could only have one bike, I'm going to keep my RK.
I'm playing devil's advocate because if I could only have one bike, I'm going to keep my RK.
Road Warrior
Joined: May 2010
Posts: 1,377
Likes: 20
From: Kafar Hanusi
One item not mentioned here, the engine,
1. the push rods raise oil to the heads to cool them and
2. they never need adjustments.
Why would you want to screw-up a perfectly good design?
Many are bringing up the corvette which uses old-school, proven school, performance design, low r's high torque Vs high r's low torque.
Which pushes you down the road, RPM or TORQUE?
Also high R's means the absolute requirement for water cooling, and with that there goes the Harley air cooled engine with low r's rumble. It's inevitable they will make a pink sportster for the alternate scene.
.
1. the push rods raise oil to the heads to cool them and
2. they never need adjustments.
Why would you want to screw-up a perfectly good design?
Many are bringing up the corvette which uses old-school, proven school, performance design, low r's high torque Vs high r's low torque.
Which pushes you down the road, RPM or TORQUE?
Also high R's means the absolute requirement for water cooling, and with that there goes the Harley air cooled engine with low r's rumble. It's inevitable they will make a pink sportster for the alternate scene.
.
Outstanding HDF Member
Joined: Nov 2010
Posts: 2,627
Likes: 3
From: S.E. Va
First thing, I look at DrPlastic's post and just keep thinking ***!.....sig pic 
OK back to thread, Harley has a signature motor (V Twin), if they change over too fast they will lose customer's, It's the feel/look of an Old School Harley that sells. Sooner or later they will have to go electronic/ computer driven everything and water cooled (sucks) to meet epa standards.
I'll keep my push rod, solid mount EVO as long as they keep selling gas.
OK back to thread, Harley has a signature motor (V Twin), if they change over too fast they will lose customer's, It's the feel/look of an Old School Harley that sells. Sooner or later they will have to go electronic/ computer driven everything and water cooled (sucks) to meet epa standards.
I'll keep my push rod, solid mount EVO as long as they keep selling gas.
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Road Warrior
Joined: May 2009
Posts: 1,945
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From: Victoria, Australia
.. and a radial aircraft engine. I have a work colleague into old aircraft and he has an old Avro radial engine bi-wing. I love to hear that sucker light up!
Road Master
Joined: Apr 2012
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From: San Jose
