Kawasaki Vulcan Forum banner

Engine Theory

3K views 12 replies 6 participants last post by  JerryJ 
#1 ·
Motorcycle engines either have hydralic or solid valve actuation. I like the no adjustment required hydralic valves but not all bikes have these. Thus I must have my valve lash inspected or if needed adjusted with shims or screw and nut every 15,000 miles or there abouts. Why from a design / performance standpoint is one design used over another? Is it because some engines rev higher? My Vulcan 900 is solid actuation vs my son's Sportster 883 is hydralic, both seem to spin up about the same. Also, aren't the older Vulcan 1500 hydralic vs the 900's? Just interested in the engineering design logic here.
 
#2 · (Edited)
Motorcycle engines either have hydralic or solid valve actuation. I like the no adjustment required hydralic valves but not all bikes have these. Thus I must have my valve lash inspected or if needed adjusted with shims or screw and nut every 15,000 miles or there abouts. Why from a design / performance standpoint is one design used over another? Is it because some engines rev higher? My Vulcan 900 is solid actuation vs my son's Sportster 883 is hydralic, both seem to spin up about the same. Also, aren't the older Vulcan 1500 hydralic vs the 900's? Just interested in the engineering design logic here.
jj, you worry too much over something you have no control of. engine design. you can choose yor horse, but you cant bild it.

valve actuation. the higher the rpm, the lighter the valves need to be or they will "float" and not seat. which will diminish performance and burn the valves. which is why most japs use 4 smaller valve heads vs old skool 2 large valves.
SOHC w/rockers and specifically DOHC have less valve train mass. they can spin up faster with less anomalies.

yes, yor v-9 is a SOHC motor as is designed to spin faster than any pushrod motor. it needs to because it utilizes smaller pistons and needs rpm to intake more air/fuel to produce more power. big bore/long stroke motors don't need rpm and it is detrimental to their longevity.
that 883 is just a crippled 1200 is why specs are similar, but it is still a paint shaker even with added rubber mounting.

hydraulic lifters on pushrods are desirable but limited to ~5k rpm. which is fine on big bore long stroke motors which make most power 2k-3k rpm.

screw tappets and shims are not that difficult and only need adjusting when they get to rattling (loose) for wear. they don't impede valve action but you wont get full lift (.005mm loss).

15k miles? what is that 2-3yrs for most folks? if that. If you don't have the desire to open the valve covers on your motor, just pay somebody to do it. silly stuff. I do mine several times each year. on the bikes that have them. not because they need it. because I can. wrench therapy.
 

Attachments

#3 ·
So Ponch, I guess it's all about RPM and HP - sales and marketing. Take these two extremely different motors; a Kawi V17 and a Kawi Vulcan 500, hydraulic vs ohc; the V17 spins slow but much torque and the V5 spins very fast but low torque until a much higher rpm where it gets the HP. Interesting that the V5 puts out about the same HP as my V9.
My son also previously had a '83 Shadow 750 V twin, it had hydraulic valves with respectable HP and Torque and shaft drive.
I wonder how power is affected by valves on my V9 being on the loose side of spec.??
 
#4 ·
So Ponch, I guess it's all about RPM and HP - I wonder how power is affected by valves on my V9 being on the loose side of spec.??
minimum. you wouldn't notice it. if the tappets are making a racket. its time to check em, adjust em.

yor motor is a big air pump. suks in air/fuel. compresses it. ignites it (boom) and then exhaust it. 4 cycle starts all over.

a given size cylinder displacement can only suck in a given volume of air/fuel which = a given amount of power per rpm cycle.
a small displacement motor must spin fast to make small/any power. to spin a motor fast, it needs small lightweight parts that have little mass. the downside is they have little/no inertia and produce little torque (useable power), so they rely upon high rpm hp to do work.. move yor azz down the road.

a bigger motor behaves different. it makes tons of torque (pulling power) at low rpm. ther is no need to spin these motors fast (besides they will self destruct).

the whole key is how much air/fuel can you stuff into a motor how fast and burn it? slow and steady or fast and furry'ous. poncho
 
#9 · (Edited)
The 500 is a parallel twin. The clearances definitely expand with wear, so they need to be reset to the minimum side of the range to allow for that.
watt he said.. btw, only chek em and adjust em when theyr cold. not hot.
 
#11 ·
Crap - I actually wrote the OPPOSITE of what I meant. They need to be set loose, because they wear tighter.
sch'itt happens
 
#12 ·
Believe it or not, on my 900, it got quieter as time went on. The inspection period is 15k and the work isn't that complicated. There's half a dozen threads in the 900 section that go something like this; "Help, I adjusted my valves, and now it's nosier" followed by "Yep, that's what it does" from everyone else. For whatever reason, the 900 seems to get quieter as it wears, and is louder when it's adjusted correctly. Like most Kawasaki's, if the engine is quiet, something is broken.

It's probably COST, ultimately, why some have manual valve adjustment. Hydraulic valve adjustment systems are additional engineering effort that Kawasaki just didn't put into a sub-$10k bike. I did mine every year and it was never a big deal.

The V17 is a SOHC, 4 valve hydraulic adjusted drivetrain. It is nice not to have those adjustments, but they never were a big deal when I did. It's one of those projects that looks daunting but, once you get down and dirty and into it, it's just not a big deal.
 
#13 ·
Interesting thread. I think you're ultimately correct Romans that "cost" is the real factor in engine design. Hydraulic valve train is probably more expensive to manufacture and this would be a new design - more cost. They could do a 900cc with hydraulics but as Poncho says, this could affect performance and possibly lower advertised HP / RPM thus numbers of units sold. I would love to listen in to Kawi's engineering and marketing meetings, still it's all about profit - not what I want to see. Yes, as the 900 engine gets miles without valve lash adjustment it gets quieter, we want some valve lash or the exhaust doesn't close fully thus doesn't cool properly when seated resulting in burnt valves. I've talked to owners with many miles past the recommended inspection with no problems. Do valves (exhaust) really burn, has this happened to anyone?

Thanks for all the interesting comments.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top