Urethane

From what I`ve been told its possible to use urethane instead of
nitrile-rubber for carburettor intake manifolds. The gains are
longevity, strength and very good resistance to HC`s.

With this in mind I contacted a local specialist in urethane molding
because the original parts just don`t last.

Strength and HC tolerance would be no problem he said, but temperature
might be, as urethane softens when heated above 90 degC (200F +/-).

That was news to me, so I thought it worthwhile to post about it here.

What temperature will the intake manifold of a 2-stroke 500cc liquid
cooled engine typically see? My guess is that it will benefit from the
cooling effect of the air/gas mixture being sucked through.
But to what extent? Has anyone done any empirical tests on this?
How about other types of urethane, i.e. duo/poly?


TH

`96 ZX6R
`86 Maico 500

 

Despite the widespread perception that factory engineers are ignorant
and/or overly controlled by the bean-counters, the OEM manifolds are
probably made out of the best possible material without resorting to
extremely expensive and hard to work with materials.

Are you actually experiencing a performance problem with the stock
manifold? Manifolds for inline-four air cooled bikes can routinely
last for 20 seasons of riding before needing replacement due to age.
I imagine that a liquid-cooled 2-stroke intake would be a relatively
benign environment compared to an air-cooled 4-stroke.

 

Thanks for your input.

Sadly, there is a performance problem with the stock part. It cracks
from vibration and lack of strength. Then air is sucked in through the
cracks, leaning out the mixture and causing the rpm`s to increase.

This is not pleasant on a 500 smoker... Can ruin the engine too. I
replaced the part with a new one in september 2002, yet within less
than a year the problem came back. I have seen it mentioned online in
Maico-forums too, so I know its not just my bike that`s affected.

As to factory engineers; when they get so much right, ignorance is not
what I`d think of just because some minor part fails. Yet budgets need
to balance and compromises are made.
Which in turn fuels the aftermarket industry, and more importantly,
inspires tinkering owners to try their hands on DIY improvements.

I wouldn`t miss it for the world!


TH

`96 ZX6R
`86 Maico 500

 

This sounds like they are asking the manifold to support the carb in a way
that puts too much stress on the manifold. Perhaps adding a reinforcing
brace to the carburetor would be a reasonable way to avoid overstressing
the manifold.

 

While it's true that the rubber boot will be cooled by evaporation of
gasoline during operation, that effect will cease when you park the
motorbike, and the rubber boot will then be baked by the cylinder block
which will probably be about 180 to 212 degrees F...

Maybe higher, I remember that owners of the original Kawasaki 900cc
Ninjas were upset by seeing water temperatures that they thought were
up around 275 degrees F...

But, rather than have expen$ive rubber boots custom made, have you
considered getting some large diameter o-rings that will fit in the
grooves on the carburetor spigots and just use some short pieces of
automotive radiator hose clamped over the o-rings?

I don't mean the corrugated type of hose which is meant to bend around
corners. I'm referring to that other type of smooth rubber/fabric
hose...

 

Say more about these cracks: are they circumferential or axial? Do they
appear in a particular place each time, or are they evenly distributed
about the boot?

Knowing more about your application would also help: what bike is
it-that Maico? Have you modified the intake tract? Is this a known
problem with these bikes?

It's possible that there's something else going on here that's causing
the boots to crack, other than simply bad materials choice or part
design. Knowing more about the circumstances could allow us to help you
more effectively.

Even if the OEM parts aren't up to it, that doesn't mean that the
material itself is the problem: it's possible that a heavier boot, or a
boot reinforced with the proper materials, would do the job. If you're
already talking to someone who does moldings, bring them one of your
failed parts and see if they have some ideas about how to avoid this
problem in the future.

It's also possible that you can find a carb boot from some other bike
that fits and is more robust. This option will require a lot of work,
tracking down similar objects and comparing them to your own.

 

Well... no references to R. Wagner??? Oh well... Anyhow, I did
consider the radiator hose solution, and what backed me off was the
lack of room between carb and reed cage - not to mention that I`d need
to customize a fixing point for said radiator hose on the engine. The
original part is bonded to an aluminium plate which holds the mounting
screws, and furthermore it continues past that to form a directional
tract for the gas flow towards the reed cage. So, I`d have to have a
piece of aluminium machined to perform that role before a rad-hose
even had a hope to enter the equation.
The way I see it I`m left with two evils. Go with the flow and buy
OEM, or go against the grain and make the part out of urethane or some
other material.

Sure, I`ve got the time to experiment; this bike is a pet peeve of
mine. It`ll follow me to my grave. But that`s not to say I`m not in a
hurry. Got any insight into the various kinds of urethane and their
properties? I sure would appreciate it.


TH

`96 ZX6R
`86 Maico 500

 

The cracks are circumferential, not evenly distributed, they do occur
in a haphazard way throuhgout the length of the manifold.

Known prob, yes, as far as it has been mentioned in online forums.
The bike is a 1986 model watercooled 500 MX`er. That`s M-Star in
America - what`s in a name???

Can`t say much more than I already did. I know not to overdo
tightening the clamps... The engine vibrates, but at a steady rate -
like big smokers do.

I did. Suggested solution was to use urethane. The only "if" was
temperature.

Been there....tried that. KTM was a brand I figured had lots of parts
in common with my Maico, but it seems parts for those old katooms is
also hard to find.


TH

`96 ZX6R
`86 Maico 500

 

But then I`d have to buy another frail OEM part. Not to mention that a
brace of some kind most likely would lock the carb solidly in place,
yielding ample room for vibrations to cause fuel-frothing and who
knows what. In short, I think that`d be an ounce of cure, not a pound
of prevention. If I could I`d use fibre to reinforce the original
design, but unfortunately that is not an option. I really hope
urethane is.


TH

`96 ZX6R
`86 Maico 500

 

I'd try reinforcing the entire intake manifold with duct tape. That may
sound like a joke to some, but I think it'll work fine & is surely worth
a try. Duct tape is for *ducts*. I'd try it with two wraps around a
currently cracked manifold to see what sort of service it gives.

-paul

 

Well, thanks, need I say that I tried that? No arrogance intended, but
I`m at my wits end and close to desperation. Besides, chewing gum and
steeeel wire is a "fix" along the same lines. Grumpy? Oh yes, I`m on
my last cigar! Wanna quit before I turn 40.


TH

`96 ZX6R
`86 Maico500

 

I don't know this bike so well. Are the carbs supported entirely by the
carb boots? If so, removing the weight could make your carb rubbers last
longer. I know you don't want to introduce vibrations to the carbs, but
conceivably one could construct a support that is itself isolated from
the vibrations of the engine.

 

The notion of using the original manifold as a "mold" to which stronger
materials can be applied might have merit. Duct tape and the stuff used
for dipping tools handles won't be close to sufficiently heat resistant,
but there might be other alternatives.

One common high-temp rubber is Viton; don't know if it's available in a
form usable for this purpose, but it takes 100 C with no problem and
will survive 200 C for brief periods. If it's available as a latex one
could use simply soak reinforcing fabric in the latex and wind it on
the manifold.

bob prohaska

 

The Viton info page at http://www.dupont-dow.com/Products/Viton/auto.asp
says:

"Application Range -40C to 225C with intermittent exposure to 285C"

I think it might be a pretty good material for this purpose, but getting
a single part made with Viton would be prohibitively expensive.

 

stuff used for dipping tools handles won't be close to >sufficiently
heat resistant, but there might be other alternatives.

We made extensive use of RTV silicon rubber on the Apollo command and
service modules...

The red silicone RTV rubber is very heat resistant, but has low
mechanical strength. Red RTV is commonly available in auto parts stores
and I see people misusing it for gaskets to hold back oil leaks all the
time...

I got ahold of a tube of the white silicone RTV rubber when I worked on
Apollo and used it to encapsulate the coils inside the lighting and
ignition energy transfer magneto on my dirt bike over getting flooded
out on a very wet day motocrossing. Later on, I wanted to disassemble
the magneto and add another ignition primary coil in parallel to the
first to get a really hot spark. I spent all day picking that white RTV
off the coils. It was really tough stuff...

At Lockheed, we used 2-part potting compound to encapsulate electrical
connectors on the F-104G's that we were overhauling for the Luftwaffe.
The engineers wanted to use red RTV instead of the old brown 2-part
stuff. Dunno what it was, but it was very tough, compared to that
crumbly red RTV...

 

Guilty as charged!

I'd forgotten all about RTV silicone; thanks for the reminder!

The self-leveling stuff, mixed with a little chopped fiberglass,
might be just the ticket. Even better, work the white kind into
fiberglass cloth and do a layup over the original manifold. A bit
like the use of prepreg graphite epoxy composite. Maybe it could
be vacuum-bagged before curing

Making the cloth wrap smoothly will take some planning and effort, but
it's far easier than trying to build a die for molding a complete
new part.

bob prohaska

 

but it's far easier than trying to build a die for molding a >complete
new part.

That reminds me of another adhesive we used a lot of on the Apollo
program. 3M weatherstripping cement, the yellow "gorilla snot" that
dirtbikers were so familiar with in the late 1960's, before Loctite was
commonly available...

We needed to secure various small electronic cables to command module
pressure vessel surfaces made of aluminum/honeycomb sandwich. We
couldn't drill holes in the pressure vessel for screws to use regular
electrical clamps, so we used fiberglass tape, impregnated with 3M
weatherstripping cement. When that stuff cured, it stuck to the smooth
aluminum surface like---like---like *glue*!!!

We had to make up test coupons to be pulled apart on the same tensile
strength tester that we used to test the epoxy bonding coupons made
when we patched dings on the floor of the pressure vessel...

So, maybe Torgeir could acquire some fiberglass tape and some 3M
weatherstripping compound and wrap his rubber mainfold with that stuff
and work the glue in. And, as it cured from the 200+ degree
environment, the gorilla snot would get really, really, really *tough*!

I don't know if it would get hard enough to crack and flake off, but,
if it did, no big deal, start over with the white RTV silicone
rubber...

 

Thanks for your original reply, I liked that idea very much. And even
more so now that I`ve gotten a quote on the molding job. Close to 1k
usd for the mold and four manifolds was the price. That could buy me
another old bike. Which I don`t need right now. Nor does the wife,
she`s already having a hard time swallowing the Camel as she most
fondly calls my Maico.
So, I`ll check out the various ways suggested here to reinforce the
original part.

Thanks to everyone for their ideas and comments.


TH

`96 ZX6R
`86 Maico 500

 

And here am I, thinking I`m a crazy booger for merely wanting to make
some molds and such... Thanks for the laugh, thanks again for the
moral support and then for your advice.

BTW, how did that forge work? Were you able to make a structurally
sound part? Any info on the forge, pictures perhaps? I did mention
machining earlier in the thread, yet casting the part - or a part of
it - from metal is a notion that has eluded me. This needs thinking
about.


TH

`96 ZX6R
`86 Maico 500