[C38] Transmission

Mon May 14 18:16:30 EDT 2012

Third source of the clunk can be a feathering prop opening when the boat
is put into gear.  

-----Original Message-----
From: listserve-bounces at catalina38.org
[mailto:listserve-bounces at catalina38.org] On Behalf Of
tdtron at earthlink.net
Sent: Monday, May 14, 2012 12:47 PM
To: Catalina 38 forum
Subject: Re: [C38] Transmission

Hello Larry,

I'm no expert on transmissions but I may have some answers for you
anyway.

The "clunk" you refer to is usually caused by two things. The Hurth
transmission uses a spiral input shaft with matching driven plate that
allows the torque of the shaft to engage the drive plates like a nut on
a bolt.  The rotation of the input shaft actually tightens up the drive
plates when you shift gears.  This is how our transmissions shift so
easily when a manual transmission car or truck will have a pressure
plate and throwout bearing and clutch pedal which we don't have.  The
reasons cars and trucks don't use spiral input shafts like our boats do
is because you can't "slip the clutch" with our systems, our systems are
either totally engaged or totally disengaged so they won't work on
street vehicles.

Another source of a clunk sound is the slack in the gears which
increases from wear.  All of these components with slack combine to
cause the clunk but with a good flex plate, this clunk sound should not
be a problem.

As regards to the "sweet spot" your technician was telling you about, it
is the truth.  Every engine has resonant vibrations that are more
pronounced at certain RPMs and less at others.  Having only three
cylinders compounds the problem as does being diesel.  Idling is much
more detrimental than motoring but low speed in either case increases
gear chatter and wear. 
Sometimes speeding up or slowing down  will reduce but not eliminate the
resonant vibrations.

I replaced my Universal flywheel flex plate with the PYI unit and my
engine was noticeably quieter and smoother at all speeds.  Another
extremely important benefit of the PYI flex plate is that the engine
will continue to drive the transmission even if the flex plate fails,
unlike the steel springs Universal unit.  The PYI shaft coupler also
offers this same benefit of positive engagement even with cushion
failure.  I replace both my flex plate and shaft coupler and it was like
I had re-powered to a smoother engine with more cylinders.  The results
were nothing short of incredible.

Universal flex plates have a history of fatigue failure of the cushion
springs which can break like glass after they fatigue leaving your
engine without thrust.  All of those pieces of the steel springs have no
where to go but around and around inside the bell housing causing havoc
to your aluminum bell housing, starter pinion, flywheel and ring gear.

PYI claims their synthetic material isn't prone to fatigue but even if
the cushion material ever did fail, you would still have thrust in both
forward and reverse because the metal dogs are captive with the
synthetic material acting as a cushion between the steel dogs but if the
cushion material somehow magically disappeared, the dogs would still
propel the boat.

One problem I did have with the PYI flex plate was that when I tried to
install it I couldn't get all of the flywheel bolts started without
slightly filing the plate holes with a small rat tail file to help get
the bolts started.  I don't know if the bolt pattern irregularity was
from the flywheel,  the PYI flex plate, or both but the amount of
material I had to remove was only a thousandths or two of an inch so
there was no balance or concentric alignment problem.  

I know money doesn't grow on trees and PYI flex plates and shaft
couplers aren't cheap but the PYI upgrades were some of the best
improvements I ever made to my boat.  With the upgrades we could idle
back to our slip with almost no vibration or noise  and sometimes I
thought the engine had died because it had become so quiet and smooth.

Tom Troncalli

> [Original Message]
> From: Larry Malmberg <Larrypi at roadrunner.com>
> To: Catalina 38 Listserve <listserve at catalina38.org>
> Date: 5/14/2012 12:28:52 PM
> Subject: [C38] Transmission
>
> A very special Thank You to Jay Sorensen for coming through with a 
> used transmission.  Picked it up Sunday and am taking it to the shop 
> today.  A quick question though regarding transmissions.  Does every 
> one with a
Hurth
> transmission get that "clunk" when you put it into gear?  Also, the 
> transmission guy tells me that there is a "sweet spot" for engine rpm 
> when idling, this so called sweet spot causes less wear on the damper 
> and
gears,
> what's your experience with this?  My idle is set at about 900 rpm 
> which apparently is a bit too low?  I'm told the damper was worn from 
> "engine chatter" as well as a few of the gears, the engine chatter is 
> apparently from the idle being set too low.
>
>
>
>
>
> Best regards,
>
> Larry Malmberg
>
> 7231 Boulder Avenue Suite 507
> Highland, CA 92346 PI 15211
> Telephone  909-208-1847
> FAX           909-991-7568
>
> E Mail  Larrypi at roadrunner.com
>
>
>
> ?
> Life is short, Break the rules, Forgive quickly, Kiss slowly, Love 
> truly, Laugh uncontrollably, And never regret anything that made you
smile..
> ?
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> immigration"
>
>
> "Life is not a journey to the grave with the intention of arriving 
> safely
in
> a pretty and well preserved body, but rather to skid in broadside, 
> thoroughly used up, totally worn out, and loudly proclaiming; WOW-- 
> What a Ride!"
>
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