Timing belt vs chain (outboard)
Phan...@aol.com
short lived, uneconomical, semi-dependable power, but hoped the new
four cycle trend would offer something approaching the longevity and
dependability of a straight inboard. So I've been window shopping for
115hp 4 cycle outboards. So far, I'm frustrated by what I'm finding.
For instance, only *one* manufacturer is designing their outboards
with a timing "chain" rather than a "belt". What's up with that? Seems
to me the weight difference is insignificant, and the higher initial
cost of a chain is easily justified by lower maintenance expense,
greater durability/longevity and lower risk of failure (and failure of
either belt or chain can mean *extreme* expense).
Google search showed some discussion on this but I never did see a
compelling reason in favor of a belt design. Sales people are no help
either. They just point out the fact that a lot of cars are designed
with belts ... an irrelevant argument as far as I'm concerned. Every
mechanic that I've talked to, when pinned down for an unbiased answer,
would prefer to have chain or gears driving their own personal valve
train.
Besides the weight and initial cost issues, am I wrong in thinking
that there is no real consumer advantage to a timing "belt" design?
Thanks,
Rick
Dazed and Confuzed
1. no need for lubricant, so the belt can be external to the rest of the
motor. THis makes the motor design a bit simpler, more reliablen and
cheaper (fewer gaskets, less machining of mating surfaces, etc..), and
easier to service, as the belt is easier to replace.
2. wear is about the same, except that the belt is much more easily
tensioned, and after the initial stretch (which can be negineered in)
there is little or no change in belt/sheave dimension(until the belt
breaks).
3. Rotating mass is reduced, allowing less wear on bearings, and allowing
faster/better throttle response.
4. less damage when/if the belt breaks vs chain. Less rotating mass, etc.
(of course, this assumes that they engineer valve/piston clearences
correctly)
5. less internal friction
Hope this helps
B
Phan...@aol.com wrote:
--
"They that can give up liberty for safety deserve neither liberty nor
safety." Benjamin Franklin
murphy
they started to appear, but my fears were groundless. It's
good technology.) We run Toyota 4WD's and take them up to
3/400, thousand km. They recommend changing the belts at
100,000 but we have run a couple up to twice that distance.
regards
murphy
"Dazed and Confuzed" <ded...@netnitco.net> wrote in message
news:3CA62B12...@netnitco.net...
Glenn Ashmore
miles I lost. Cost me two pistons, a new head and some mystical machine
shop work.
But then I lost a timing chain on the previous Toyota at 65,000 miles
trying get 10,000 miles out of an oil change. Maybe it is just me.
murphy wrote:
> My thoughts too, B. (I was somewhat dubious about belts when
> they started to appear, but my fears were groundless. It's
> good technology.) We run Toyota 4WD's and take them up to
> 3/400, thousand km. They recommend changing the belts at
> 100,000 but we have run a couple up to twice that distance.
>
> regards
>
murphy
--
Glenn Ashmore
I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
John McCoy
>For instance, only *one* manufacturer is designing their outboards
>with a timing "chain" rather than a "belt". What's up with that?
Performance and cost, mostly. A chain turns out to be a lousy way
to drive a cam (check w/ Smokey Yunick if you want confimation of
that), it stretchs and lets the valve timing wander around, plus it either
needs frequent adjustment or some sort of tensioner. The belt costs
less to start with, doesn't need the cost of the tensioner, stays in
adjustment, and is quieter. It's only disadvantage is needing to be
replaced after a certain length of time.
For ultimate performance, of course, gear drive is best. But it's a
much higher first cost, and they're quite noisy by comparison to a
belt or chain.
John
murphy
"Glenn Ashmore" <gash...@mindspring.com> wrote in message
news:3CA68FA0...@mindspring.com...
> Now THAT I would worry about. I tried it with my Toyota and
at 110,000
> miles I lost. Cost me two pistons, a new head and some
mystical machine
> shop work.
>
> But then I lost a timing chain on the previous Toyota at
65,000 miles
> trying get 10,000 miles out of an oil change. Maybe it is
just me.
>
Or Japan is still exacting it's revenge ;)
regards
murphy
Brian Whatcott
Their resilience helps them damp out the peaks of torque in valve
train drive - which can be big.
Brian W
On Sat, 30 Mar 2002 09:44:49 -0600, Phan...@aol.com wrote:
Brian Whatcott
Altus, OK
Eureka!
Ampdoc
Cams and poppet valves are inefficient anyway.
I don't see why someone doesn't use a rotating valve. Check out
http://www.coatesengine.com
Less moving parts, and think of having a outboard that could turn 14,000
rpm!
Jammy Harbin
"John McCoy" <igo...@ix.netcom.com> wrote in message
news:3ca68ecc....@enews.newsguy.com...
John McCoy
>Cams and poppet valves are inefficient anyway.
>I don't see why someone doesn't use a rotating valve.
Getting the valve to seal reliably has always been the
down fall of various alternatives to poppet valves. The
big advantage poppets have is they take relatively little
machining to get a good seal to the head during the
combustion cycle.
John
Phan...@aol.com
people so far.
I don't disagree with most of your points, but from my point of view I
just don't see the advantages of belt drive overcoming the advantage
of the maintenance free reliability of a chain (asuming a self
adjusting tensioner). But I think it's more a matter of priorities.
For instance, I don't care if a chain makes more noise. It's still
plenty quiet enough for me. Or throttle response. It may be slower
than with a belt, but only by a split second or so (not critical for
me). And weight difference is insignificant especially when you're
used to the weight of an inboard.
My highest priorities are longevity (far more than traditional
outboards), durability, low/no maintenance, and reliability. IOW, the
traditional advantages of an INboard. And that's my whole point. I was
hoping that the new four cycle outboards would come closer to the
advantages (given my priorities) of an inboard. Possibly even
replacing inboards in certain applications.
I may be biased by the fact that, over the years, I've broken so many
v belts, surpentine belts, etc., without warning. Even had water
pump/alternator belts jump off pulleys *without* breaking. And the
only times I've replaced timing chains were during engine rebuilds
(and sometimes not even then).
It's hard to get around the fact that belts need to be checked,
tensioned, and changed fairly frequently. But, with a self adjusting
tensioner, a chain can be practically maintenance free for the life of
the engine. It spends it's life sloshing around in an oil bath ... the
same oil that's required anyway, whether the valve train be chain
drive or belt. And it's safely tucked inside there, protected from any
wayward cables, wires, wrenches, fingers, or whatever, that could
otherwise get caught up in the frey.
Granted it's more expensive initially, but if the motor lasts 15-20-25
years like an inboard, the savings in dollars (and headaches) due to
no belt replacements would more than make up for it. Plus, risk of
failure over the life of the engine is bound to be lower. Not saying
chains don't fail at all, just saying the failure rate is far less.
And, btw, if failure should occur, the rotating mass of flying chain
parts and pieces would be the least of my worries. Main problem being
that they don't design valve/piston clearances wide enough these days
to prevent catastrophic results (otherwise I'd be *much* more swayed
by the pro-belt arguments).
Anyhow, I appreciate the enlightenment. Frankly I hadn't thought of
some of the points you and the other posters brought out. And I'm
still mulling this whole thing over.
Couple of questions:
If, in the future, belt drive really *does* turn out to be a better
idea, do you think it'll eventually be incorporated into engines other
than outboards and smallish cars (i.e. large inboards, trucks, etc.)?
And, how much does an outboard timing belt cost (approximately)?
Thanks again, and thanks to the other posters to the thread.
Rick
Phan...@aol.com
>tried it with my Toyota and at 110,000
>miles I lost. Cost me two pistons, a new head and some mystical machine
>shop work.
>
>But then I lost a timing chain on the previous Toyota at 65,000 miles
>trying get 10,000 miles out of an oil change. Maybe it is just me.
How'd you come out damage-wise when the chain let go?
Rick
Phan...@aol.com
>A chain turns out to be a lousy way
>to drive a cam (check w/ Smokey Yunick
Who he? (and where can I find him)
<snip>
>For ultimate performance, of course, gear drive is best. But it's a
>much higher first cost,
I agree on both counts. Gear drive is the way to go. I assume the
expense is why no manufacturer offers it.
Thing is though, the cheapest throw away engines you can buy (lawn
mower engines) use gear drive <go figger- shrug>.
Rick
Phan...@aol.com
>Their resilience helps them damp out the peaks of torque in valve
>train drive
Sounds like you're saying they're more elastic (like a rubber band)
than chain? Or maybe slip a little on the pulley? <shrug> Can't see
how either would be a good thing ... guess I'm not following you.
Rick
Dazed and Confuzed
7dragoon
who has ridden both Chain & Belt drive motorcycles, which is lower
maintenance & tougher... They'll go with the belt.
<Phan...@aol.com> wrote in message - Snip- .
Dazed and Confuzed
belts (and pulleys) and there is no slip.(until they break)
Phan...@aol.com wrote:
--
Ampdoc
Mr. Coates came up with a method to seal them that looks good on paper,
anyway.
Jammy Harbin
"John McCoy" <igo...@ix.netcom.com> wrote in message
news:3ca7bdc8....@enews.newsguy.com...
John DeShazo
immediately the writer does not know very much about the facts. Large 2
cycle outboards are good for 1500 hours and more. V6 OMC and Mercury 2
cycle outboards should outlast the 4 cycle Hondas of comparable power in
total hours while being cheaper to maintian during their working life. On
top of that, the large V6 2 cycle outboards outperform any 4 cycle unit.
Try it and you will understand. Fact is, the dual outboard offshore fishing
rig has become popular along the coast because they are more reliable than
inboards. With my own eyes, I have seen 30 foot Fountain sport fishermen
with twin stock Mercury V6 outboards running 70 plus miles per hour in a
chop. I have never seen or heard of any 4 cycle outboard (or any inboard or
stern drive sport fisherman with that kind of performance.) It it the same
on lakes. How may of you guys out there have been cruising along thinking
your stern drive or straight inboard is really moving when some guy in a V6
2 cycle outboard bass boat blows by like he is in warp. The problem with
most of this discussin thread is people are presenting knowledge learned
from automobiles. This is a false analogy because marine motors are under
constant load, whereas automobile engines are under constantly variable
loads. Marine engines are in salt water. Automobile engines are protected
by rust inhibitor coolants. Finally, don't give me the fuel ecomomy defense
for 4 cycle engines. To my knowledge, a 4 cycle outboard has never powered
a boat across an ocean, whereas a Tohatsu 2 cycle has done it several times.
Don't give me the tree hugger defense, unless you are willing to document
that crank case oil will never find its way into the environment. Two
cycle v. 4 cycle ... One simply does not compare Lamborginis with lawn
mowers!
Dazed and Confuzed
John DeShazo wrote:
--
George Jefferson
:(of course, this assumes that they engineer valve/piston clearences
:correctly)
compromising the valve design to allow for belt failure is "correct"?
By the way I would not ASSume a belt means the engine is
non interference (or correct as you put it).
Matt Colie
Old George has been trying to sell that in Detroit for about a dozen
years give or take. If it was nearly as good as he thinks, someone
would be manufacturing it by now. I have never heard of anything more
than the rare prototype. History is replete with non-poppet valve
engines, but the current technology makes the historic design real cheap
to produce and assemble.
Personally, I wish him a lot of luck, but uncle Felix built the first of
his motors in 1937 and nobody put it in to production until 1964. I ran
into someone the other day that though his Mazda Rx had a New type of
engine (I think I broke his heart).
Matt Colie A.Sloop "Bonne Ide'e" S2-7.9 #1
Lifelong Waterman, Licensed Mariner and Perpetual Sailor
Dazed and Confuzed
of the drive mechanism (resulting in failure of the timing of the components),
whatever the coupling method, belt, chain, or gears. Unfortunately, this is
often not the case.
George Jefferson wrote:
--
murphy
regards
murphy
"Dazed and Confuzed" <ded...@netnitco.net> wrote in message
news:3CAB80A7...@netnitco.net...
Dazed and Confuzed
Maybe the head. (and it is a chain drive!). THe pistons crash into the
valves. A better design would be to flycut the tops of the pistons to
allow for clearance.
Jean Daugherty
familiarity. A reciprocating engine's crankshaft does not make a single
revolution at the same speed. It moves faster after a cylinder fires, and
slows as another compresses. It jerks its way around. most of this is
smoothed out by a massive clutch plate in a big car engine, but moving mass
balance weights (very complicated, very expensive) are used in aircraft
engines that don't have big flywheels. That keeps the propeller on the
front of the plane for a much longer time. This is a good thing. In
lighter engines such as motorcycles and outboards, these pulsing loads need
to be dealt with differently. The cam shaft needs to turn at a constant
speed, and smoothly. A massive, multilink chain has hardly any damping
qualities and transmits these pulses straight through to the valve train,
while a toothed belt, or a triple groove belt, smoothes things out rather
nicely. It is an elegant engineering solution to a worrisome problem.
While your beloved manufacturer may have had some good engineering reason
for staying with a chain, its probably pretty esoteric, and definitely a
compromise. Everything is.
<Phan...@aol.com> wrote in message
news:i6kfaugj8k0im2m1b...@4ax.com...
murphy
have an example of a successful design -using sound
engineering principles,- that does allow for camshaft drive
failure without damage to the engine in overhead valve
configurations?
Some engines do have partially recessed pistons, but they will
still contact the valves if the timing is out.I suspect that
the reason it isn't taken further, is itself based on sound
engineering principles. - some that come to mind are the
resultant lowering of compression ratio, less efficient
fuel/air mixing and localised burning of the piston in the
recessed areas.
regards
murphy
"Dazed and Confuzed" <ded...@netnitco.net> wrote in message
news:3CABA3BA...@netnitco.net...
Dazed and Confuzed
engine is very carboned up). But they don't damage anything (bent valves
or cracked heads). While close tolerances ar important for combustion
chamber volume and proper "squish" at TDC, there is no reason to have
the tolerances so close that damage will occur when a common failure
occurs. It is called piss poor engineering when you fail to plan for
common failures of components. Many engines aren't "crashers" if/when
the timing belt fails. Many are. I believe that it is not a design issue
as much as a cost issue.
B
John McCoy
>On Sun, 31 Mar 2002 04:26:11 GMT, John McCoy wrote:
>>A chain turns out to be a lousy way
>>to drive a cam (check w/ Smokey Yunick
>
>Who he? (and where can I find him)
Recently deceased engine builder for NASCAR and Indy race cars.
Mostly famous because almost all the rules in both rule books were
written to make his ideas illegal.
However, in this context the important part is some highspeed photography
he did of a timing chain under a transparent cover in the early 60's, which
not only show the chain flailing all over the place, but actually show the cam
rotating backwards a few degrees every so often, then snapping forward
to get caught back up.
You used to be able to find him at the "Best Damn Garage in Town" in
Daytona Beach.
><snip>
>>For ultimate performance, of course, gear drive is best. But it's a
>>much higher first cost,
>
>I agree on both counts. Gear drive is the way to go. I assume the
>expense is why no manufacturer offers it.
Expense, and for most applications the noise (they whine) is an issue.
>Thing is though, the cheapest throw away engines you can buy (lawn
>mower engines) use gear drive <go figger- shrug>.
Those are usually side valve, so you only need one pair of gears.
An OHV engine would typically need a multi-gear train to get to where
the cam needs to be (or, like a Ducati motorcycle, a bevel gear on
each end of a vertical shaft). Factor in that the forces to drive a cam
for a multi-cylinder engine are much higher, and it's not too hard to
figger :-)
John
murphy
you didn't answer the question. You say *many* engines are not
"crashers" with timing belt/chain failure. Name a few.
While damage doesn't necessarily occur in all cases, I can't
think of an overhead valve engine that I've worked on where it
was not possible. (The only ones that come to mind for me are
the sidevalve configurations of yesteryear.)
Whilst marking of the piston is not uncommon in many
instances, particularly in high mileage, poorly maintained
engines, I can assure you that if there is a drive chain/belt
failure in a toyota or a honda, damage can occur.
The close tolerances in today's design are there for a
reason - to allow for high compression, high efficiency
engines. How is it possible to engineer sufficient clearance
to ensure that the piston cannot possibly contact the valve
and yet still maintain efficient compression ratios?
regards
murphy
"Dazed and Confuzed" <ded...@netnitco.net> wrote in message
news:3CABBB6E...@netnitco.net...
Meindert Sprang
news:KoOq8.2642$QC1.2...@bgtnsc04-news.ops.worldnet.att.net...
> It appears your indelible opinions are not grown from actual physical
> familiarity. A reciprocating engine's crankshaft does not make a single
> revolution at the same speed. It moves faster after a cylinder fires, and
> slows as another compresses. It jerks its way around. most of this is
> smoothed out by a massive clutch plate in a big car engine, but moving
mass
> balance weights (very complicated, very expensive) are used in aircraft
> engines that don't have big flywheels. That keeps the propeller on the
> front of the plane for a much longer time. This is a good thing. In
> lighter engines such as motorcycles and outboards, these pulsing loads
need
> to be dealt with differently. The cam shaft needs to turn at a constant
> speed, and smoothly. A massive, multilink chain has hardly any damping
> qualities and transmits these pulses straight through to the valve train,
> while a toothed belt, or a triple groove belt, smoothes things out rather
> nicely. It is an elegant engineering solution to a worrisome problem.
> While your beloved manufacturer may have had some good engineering reason
> for staying with a chain, its probably pretty esoteric, and definitely a
> compromise. Everything is.
Now, I'm not and engine expert, but I find this a bit hard to swallow. It
appears to me that the relation between piston movement and cam shaft
(=opening and closing of the valves) should be a tightly coupled mechanism.
If there is flexibility between the two, the timing of the engine would
suffer from load variations. Apart from that, the rotation of the cam shaft
also seems to induce a pulsed load on the cam shaft, especially with the
'steeper' timed versions, due to the pressure needed to open the valves.
Right?
Meindert
murphy
there are some engines where the piston never occupies the
same space as an extended valve and therefore valve/piston
contact cannot occur.
(1 of 13 Honda engines and 8 of 13 Toyota engines, in the list
I found, among others.)
I'll just have another helping of humble pie ...... and remind
myself yet again that just because I haven't seen it, doesn't
mean it can't exist. : )
regards
murphy
The link below gives a comprehensive list of interference and
non-interference engines.
http://www.howstuffworks.com/framed.htm?parent=camshaft.htm&ur
l=http://www.rovatune.com/tbelt.html
"murphy" <mur...@nospamatallatall.com> wrote in message
news:wiQq8.29025$uR5....@newsfeeds.bigpond.com...
Bill Sheffield
replaced 2 timing belts. One because the customer insisted that it be done.
The other was due to a collision with a barge which broke an inch and a half
section out of the cam pulley, the motor continued to run for 2 weeks on a
water taxi before it broke. There was no valve damage.
I have seen some of these outboards still in operation with over 7000 hours
using synthetic oil.
Bill Sheffield
Jean Daugherty
"Meindert Sprang" <mhsp...@ANTIcustomwareSPAM.nl> wrote in message
news:3cab...@news.nb.nu...
than a Rocket Scientist! (and I'm not...)
> Meindert
>
>
>
Jean Daugherty
fueled by political loyalty and rumor! When the best minds in the world
were debating the number of angels who could dance on the head of a pin, the
guy who insisted on actually looking and counting was excommunicated. You
better watch out!
"Bill Sheffield" <bill...@fdn.com> wrote in message
news:ytYq8.341$Ho1....@news1.fdn.com...
Bray Haven
>than a Rocket Scientist! (and I'm not...)
And a good mechanic is smarter than both of them (together) :o).
Greg Sefton
Dazed and Confuzed
crasher. Have to lok 'em up to give you info on Nissan, Honda and
Toyota, and the rest. Some are crashers, some aren't. If you want a
longer list, then I will provide it. (may take a day or two)......
Dazed and Confuzed
Bill Sheffield wrote:
--
Dazed and Confuzed
B
--
John McCoy
>"Jean Daugherty" <sandyda...@worldnet.att.net> wrote in message
>news:KoOq8.2642$QC1.2...@bgtnsc04-news.ops.worldnet.att.net...
>> It appears your indelible opinions are not grown from actual physical
>> familiarity. A reciprocating engine's crankshaft does not make a single
>> revolution at the same speed. It moves faster after a cylinder fires, and
>> slows as another compresses. It jerks its way around. most of this is
>> smoothed out by a massive clutch plate in a big car engine, but moving
>mass
>> balance weights (very complicated, very expensive) are used in aircraft
>> engines that don't have big flywheels. That keeps the propeller on the
>> front of the plane for a much longer time. This is a good thing. In
>> lighter engines such as motorcycles and outboards, these pulsing loads
>need
>> to be dealt with differently. The cam shaft needs to turn at a constant
>> speed, and smoothly. A massive, multilink chain has hardly any damping
>> qualities and transmits these pulses straight through to the valve train,
>> while a toothed belt, or a triple groove belt, smoothes things out rather
>> nicely. It is an elegant engineering solution to a worrisome problem.
>> While your beloved manufacturer may have had some good engineering reason
>> for staying with a chain, its probably pretty esoteric, and definitely a
>> compromise. Everything is.
>
>Now, I'm not and engine expert, but I find this a bit hard to swallow.
It may be hard to swallow, but Jean is quite accurate in his (her? I'm
assuming him, possibly wrongly, to be French/Canadian) description.
> It
>appears to me that the relation between piston movement and cam shaft
>(=opening and closing of the valves) should be a tightly coupled mechanism.
Quite right, it should be.
>If there is flexibility between the two, the timing of the engine would
>suffer from load variations.
This is also correct.
> Apart from that, the rotation of the cam shaft
>also seems to induce a pulsed load on the cam shaft, especially with the
>'steeper' timed versions, due to the pressure needed to open the valves.
And this, again, is true. The ideal solution, as discussed elsewhere in this
thread, is to drive the cam with a gear train. However, while that solves the
problems you present, it introduces new problems of expense and noise.
The belt drive presents a nice compromise between controlling the valve
motion in a reasonably reliable manner and introducing unwanted costs
to the result.
John
Jean Daugherty
readily as you.
"murphy" <mur...@nospamatallatall.com> wrote in message
news:AdUq8.29178$uR5....@newsfeeds.bigpond.com...
murphy
t...
> Thundering applause! May I have the integrity to admit my
mistakes as
> readily as you.
Thanks Jean,
I'm a fourth generation Aussie and was raised to believe that
it was ok for a man to voice his opinion strongly,
but that if he couldn't admit to being wrong with good grace,
then he was not a man at all.
(the colloquial expression is "copping it sweet.")
regards
murphy
Mark Eckerberg
>revolution at the same speed. It moves faster after a cylinder fires, and
>slows as another compresses. It jerks its way around. most of this is
>smoothed out by a massive clutch plate in a big car engine, but moving mass
Wouldn't this be completely smoothed out when you have multiple
pistons on one crankshaft such as a V-8?
Mark Eckerberg
valves. Tragic. This is one of the most popular/common engines of
all time, known for durability and reliability. I've always heard
that there are performance trade-offs with a non-interference engine.
Mark Eckerberg
problems but then there were breakthoughs in belt technology in the
80's that made belts much more reliable and long lasting. He said the
improvements came from some female chemical engineer. I don't know
about the accuracy of any of this, but it seems resonable, since more
than 20 years ago, belts were more crude than they are today.
On Sun, 31 Mar 2002 21:45:01 -0600, "7dragoon"
<casta...@hotmail.com> wrote:
>Maybe once upon a time... But these aint your old fan belts... Ask anyone
>who has ridden both Chain & Belt drive motorcycles, which is lower
>maintenance & tougher... They'll go with the belt.
>
><Phan...@aol.com> wrote in message - Snip- .
>> For instance, only *one* manufacturer is designing their outboards
>> with a timing "chain" rather than a "belt". What's up with that? Seems
>> to me the weight difference is insignificant, and the higher initial
>> cost of a chain is easily justified by lower maintenance expense,
>> greater durability/longevity and lower risk of failure (and failure of
>> either belt or chain can mean *extreme* expense).
>
>
>