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Discussion Starter #1 (Edited)
The Yamaha V-Twin engine used in the Star Venture/Eluders was designed so that the alternators are driven by what Yamaha calls a jack shaft, the Star Venture also has duel alternators putting out a total of 700 amps, 350 amps each.

As the engine warms up you can hear what appears to be a knock from the engine, the hotter the engine gets the louder the knock is. The Stratoliner and Roadliner use this same series of engine and have the same sound.

Yamaha determined years ago and issued a service bulletin on this and explained why and what this knocking sound is.

The steel parts and the aluminum case all expand at different rates plus you have the magnetic pulses from the alternator(s) that create a push back on the gears, this all combined together causes this knocking noise. It does not hurt anything or the longevity of the engine/alternator(s).

You can run a 20w-50 weight oil to help dampen the knocking sound if it bothers you.

Some people mistake this knocking sound as a bearing knock, but as Yamaha correctly points out in the service bulletin a bearing knock will not go away and will progressively get worse until it fails altogether.

Yamaha has instructed their service people to explain to the customer what I posted above and to tell them it is a normal sound and will not harm the engine.

I continue to run Redline 10w-40 synthetic oil in my 2018 Star Venture Transcontinental and my Blackstone lab reports on the used oil samples all come back showing excellent wear numbers with much lower wear numbers than the universal averages for this series of Yamaha V-Twin engine. Just as an example my last used oil sample revealed the following after a full 4,000 mile run on the oil:

Aluminum was 3 parts per million universal average 7 parts per million.

Chromium was 0 parts per million universal average 0 parts per million, this engine series does not have issues with ring wear.

Iron 6 parts per million universal average 12 parts per million

Copper 2 parts per million universal average 6 parts per million.

Lead 0 parts per million universal average 1 part per million.

Tin 0 parts per million universal average 1 part per million.

As you can see the Redline 10w-40 oil is providing excellent documented protection in this engine.

My engine has the knocking sound caused by the jack shaft/alternator(s) and it has not effected the engine wear at all.

You can tell this knocking sound because it will come and go with load on the drivetrain. A bearing knock would stay consistent and only get worse, so if you hear this sound don't be concerned as this is a normal sound per Yamaha.
 
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