Flying Pig wrote:
Hi, Ian, and list,

Thanks for the erudition! There's a couple of questions you raise, however,
inline:


"IanM" wrote:

(clip self-layup section; see future post)
However, I'm not convinced that this is a valid repair method. Epoxy is
NOT strong at elevated temperatures and I would be inclined to do the
repair in polyester resin *IF* I could get the muffler clean enough.
I'd lay up the first few layers resin rich with as much glass microbubble
additive as I could use to attempt to provide thermal insulation for the
outer layers then switch to normal laminating, keeping the resin ratio as
low as possible without compromising the layup. It wants to be about 50%
thicker than 'factory' if the restriction is managable as the original was
made under ideal conditions and was probably significantly stronger.

In this, I presume you're speaking of self-layup, not the insertion of the
replacement tube to the muffler? There's not enough left to tell what the
orginal factory thickness was, but the part right next to the "can" feels
like it can't be more than 1/16" thick. What I'm finding is all 1/8" wall,
but if I were concerned, I could spring for the bigger bux, much too long a
piece, in 1/4" wall. So, I'm presuming I'll have a much stronger pipe in
the repair than the original.

You are going to have this job on the bench so measure the wall
thickness at the *other* spigot! If you are buying in the tube, as long
as the wall thickness is similar, and you over-build the fillet
attaching it you should be OK. The body thickness may well be thinner.

I would *expect* bonding problems at the joint so it may be better to make
a flange and bed the replacement spigot on sealant with a ring of self
tappers retaining it. If one is going down that road, and you can get it
made up easily you might as well go stainless.

By "made up" - to what are you referring? Getting a flange with a radius to
match the muffler body? I'm reluctant to be making additional compromises
to the body (4-6 holes in a fibreglass shell prolly wouldn't enhance its
strength, and there's vibration transmitted from the very short hose to the
engine to think about) that attaching a flange would involve, though the SS
pipe certainly would remove dissolution issues, I'd think...
If you have a local stainless worker that's good . . . (quality
stainless work can sometimes be got done in really out of the way
places) OR wrap the muffler in polythene and laminate up a flange.

Don't worry about the strength reduction due to *small* holes drilled in
the GRP, They will be overlapped by the flange that's bedded on an
adhesive sealent.


I presume that you are cruising somewhere undeveloped and can't wait for

Heh. Wilbur can tell you from looking at my SPOT track that I cruised the
interstate highway system for a bit but am back in Saint Simons Island, GA
while I wait for Lydia to tire of the television and other stuff after she
plays Gramma with her (thanks for the thoughts, he's doing fabulously)
grandson who's just had open heart surgery. So, I'm back in friendly
territory for parts, of which I'll need others than just this.

a replacement muffler as fixing it anywhere you can get one within 3 days
is a waste of time and money. You'll probably want to change it next
winter anyway.

Winter is subjective to us, as we have no interest in being somewhere the
daytime temps are under 70 for more than a few days at a time. As,
presuming I find a source (I have a couple; see coming post) for FG pipe, my
repair will involve less than an hour, likely, and a replacement muffler is
some number larger than 1 boatbuck, why would I do that, other things being
equal? (asking, not confronting - the amount isn't backbreaking, so if
there's good enough reason, I would)
Reliability. A faulty exhaust system is potentially lethal if CO fumes
reach the accommodation. It doesn't need to kill you, just impair your
judgement. The clean-up after an exhaust failure is also not fun and you
can take on surprising amount of water via a failed exhause.
How confident are you of the long term durability of your repair? You
can be pretty sure it's good for six months or so then you really should
inspect it thoroughly. What about the rest of the muffler? Is what ate
the spigot eating through it somewhere else?

A few hundred dollars for a replacement *with* a warranty would be a
reasonable investment. If its over $500 that must be a mighty special
muffler! Deduct cost of GRP materials etc. and allow something for your
extra time (when has a one hour boat job *ever* taken only one hour?)
and unless you are paying boutique prices or it will leave your repair
kitty dangerously low, new starts looking quite attractive.

*FIX* the cooling water supply problem that let the exhaust eat the
spigot! (If it hasn't got a water supply problem now, it had one in the
past)

This one is curious to me; in another forum, someone said something about
theirs having gone "porous," or something to that effect, also, making me
wonder if it was a polyester resin issue (like blisters). The cooling water
is, of course, whatever we're in at the time, and the engine runs at
180*-200* all the time once it's warmed up.

So, to your comment, what might make that happen; that is, what sort of
cooling water supply problem might there be?

Often, on temporary or partial loss of cooling water a fibreglass
muffler will 'cook' before the reinforced rubber hose does. Once the
resin has been degraded, you are betting that it still remains resistant
to steam + partially burnt diesel. Sooner or later you loose the bet .
.. . (plastic mufflers are even more vulnerable)
A short hose between it an the engine makes damage more likely and more
severe.

Causes could be weed, plastic debris etc. and the intake cleared itself
before the fresh water side of the cooling system got hot enough to
cause an alarm OR a long term problem with airlocking, fouling of the
intake or a failing raw water pump. You could have reduced raw water
flow and localised exhaust overheating without the engine fresh water
coolant getting much above it's normal maximum.




--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
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