Richard,
We have the 50 hp 4JH (natural aspiration) Yanmar, 1992. Our RPM max is 3600
rpm.

I looked up your engine's rpm rating at
http://www.yanmarmarine.com/products/pdf/JH/4JH3_TE_TechData.pdf. Peak HP
appears to be at 3500 rpm with ability to rev to 3800. The best prop for you
would allow the engine to rev not less than nor more than the 3800 rpm when
you have her at full throttle. All this assumes I pulled the correct stats
off the web.

If you are now reving over the 3800, I would recommend you first check your
variable pitch prop to see if the setting has slipped.

If everything is ok there, you can try cleaning up the turbo and air intake.
The Yanmar shop manual is pretty helpful.

I don't know about the transmission. Yanmar has a couple of models for your
engine. I would call the distributor, Mac Boring in New Jersey. They would
know if it could slip in the way you are describing.

You are right, you do not want to rev the engine above the maximum
recommended number.

Good Luck,

Peter Nucci
S.V. Valerie Arden
Panda 40

-----Original Message-----
From: owner-baba-l@ballreich.net [mailto:owner-baba-l@ballreich.net]On
Behalf Of Richard Cassano
Sent: Thursday, June 29, 2006 3:41 PM
To: Baba-L
Subject: [Baba-L] Engine RPM's increase Problem

Since I have owned our Tashiba 40 the Maximum RPM, while in gear, on the
Yanmar 4JH-TE (turbo) engine has been at its specification of 3500. I
did play with the adjustable pitch MaxProp but ultimately found the
correct setting and maintained the correct max RPM of 3500 when the
throttle lever was full forward. Today while motoring in the harbor I
pushed the throttle to the maximum and the RPM's went all the way to
4000. It seemed like I could have kept going with the RPM increase but I
backed off immediately. I am aware that going over red line is not a
good thing to do.

So... the question is, why has the maximum RPM suddenly increased
dramatically when motoring in gear? My understanding was that setting
the pitch of the prop limits the RPM to what the engine is capable of
and no more. I wonder if the turbo never worked and now suddenly started
contributing boost to the engine resulting in an RPM increase.
Anyone have any ideas what might be going on with this?

By-the-way, I did not hear or feel the transmission come out of gear.
Can the transmission slip in gear without making any funny noises?

Rich Cassano
S/V Gray Eagle, Tashiba 40
Oyster Bay, NY USA

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Received on Thu Jun 29 18:19:06 2006