Hi there, I bought a 42’ trawler as a project, everything was apart of course. Putting the engines back together and they both have velvet drives, one is a 2.10.1, the other is a 1.9.1 I do believe . Does anyone know which one is for port and Stb? I’ve heard different answers to many times, diesel mechanics to shipyards.
Twin Perkins 6.354 help
- Thread starter LCook
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The stbd tranny turns the shaft CW as viewed from aft and the port tranny turns CCW.
I believe the direction of rotation is marked on the case.
I believe the direction of rotation is marked on the case.
STB
Guru
Can you provide the assembly number off of the two transmissions. It'll be something like 10-17-000-007, 10-17-000-008, 10-17-000-009, 10-17-000-010, 10-18-000-005, 10-18-000-006, 10-18-000-007 or 10-18-000-008.
Or, if older, AS3-71C, AS3-71CR, AS7-71C or AS7-71CR or A23-72C, AS13-72CR, AS17-72C, or AS17-72CR?
Or, if older, AS3-71C, AS3-71CR, AS7-71C or AS7-71CR or A23-72C, AS13-72CR, AS17-72C, or AS17-72CR?
STB
Guru
So, an AS3-71C is also known as a 10-17-000-009 and is 2.10:1 standard rotation.
It is normally paired with the same, if one engine is counter-rotating or an AS3-71CR/10-17-000-010 if the transmission is doing the counter rotating, the 71CR reverses the engine rotation.
If that model wasn't available that year in counter rotating, it might also be paired with an AS7-71CR/10-17-000-008, which is the same transmission, also reversing the engine rotation, but in a 1.91:1 ratio.
I'm guessing from what you've written and just guessing, that you've got two standard rotation engines with one 2.10:1 standard rotation transmission and one 1.91:1 reverse rotating transmission.
What are your engine serial numbers? We might can get another data point by decoding them. They often include a build number and a digit, an X, indicating reverse rotation, if they are reverse rotation.
Those transmission can work with normal or reverse rotating engines -- but the internal oil pump needs to be (re)installed indexed into the position corresponding to the engine rotation.
If you DM me with your email, I can send you the manuals for those transmissions and you can see the model chart and how the pump works.
It is normally paired with the same, if one engine is counter-rotating or an AS3-71CR/10-17-000-010 if the transmission is doing the counter rotating, the 71CR reverses the engine rotation.
If that model wasn't available that year in counter rotating, it might also be paired with an AS7-71CR/10-17-000-008, which is the same transmission, also reversing the engine rotation, but in a 1.91:1 ratio.
I'm guessing from what you've written and just guessing, that you've got two standard rotation engines with one 2.10:1 standard rotation transmission and one 1.91:1 reverse rotating transmission.
What are your engine serial numbers? We might can get another data point by decoding them. They often include a build number and a digit, an X, indicating reverse rotation, if they are reverse rotation.
Those transmission can work with normal or reverse rotating engines -- but the internal oil pump needs to be (re)installed indexed into the position corresponding to the engine rotation.
If you DM me with your email, I can send you the manuals for those transmissions and you can see the model chart and how the pump works.
Jeff F
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The 2.10 is the one exception to that rule - they built two versions of the reduction gear, one for CW and one for CCW. There is an arrow showing the necessary rotation. The OP says CCW which makes sense. That one should be mated to a standard rotation motor.
I agree that likely both motors are standard rotation and the 1.91 reverses the rotation.
A common setup. That is exactly what I have. 71C 2.10 and 71CR 1.91
STB
Guru
As you note, it likely doesn't apply to this installation, and the OP isn't rebuilding, so OP should be good.
And, I most certainly dont want to disagree with you, and now that you mention it, I think I saw an earlier thread on TF about that being an exception.
I'm just noting that my 1988 edition service manual covers that gearbox, has a separate section on that gearbox, doesn't show two version of that gearbox, doesnt have two part numbers in the list of configurations, doesn't show two pump versions or two version more generally, and doesn't have that information anywhere that I noticed.
Having said that...I certainly could have missed it, the manual could have neglected it, it could have varied by year or with a design revision, there could have been a problem in the field and a reconfiguration, that could apply post (or even prior) to 1988, etc, etc, etc.
I guess all I'm suggesting is that, if someone is in a bind and needs a transmission swap, they triple check that before losing hope, just because the information available doesn't all confirm that in a universal way.
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STB
Guru
I vaguely remember someone at S&W telling me the 71CR in 2.10:1 was a unicorn, that they'd seen it on paper but rarely if ever in a boat and that the difference in actual use was so small that no human would notice from the helm.
Jeff F
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There was the AS3-71C and the AS3-71CR. But the CR didn't reverse the rotation, it was designed to be used on counter-rotating engines.
I had one that was originally (and correctly) matched to an X version backwards rotation Perkins. I only know all this because I did some research when the unit developed bearing problems after being used for a few years behind a standard rotation Cummins.
I found a good description here:
https://www.kp44.org/ftp/VelvetDriveInstallationManual.pdf
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STB
Guru
That's pretty much clear as day and then some!
Strange the '88 and '94 service manuals don't mention it. For fun, or to show me I missed it, see attached.
STB
Guru
Yeah. I see that in the table with the models.
jleonard
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I also had one in my 1978 Mainship that had a "contra-rotating" engine.
Yes Jeff f, it’s a 76 Bristol. It will take a bit and a lot of money to get it to where we want it but we got it cheap. Actually bought it knowing one engine was seized, so my plan was to haul them out and put in cummins 6bt, but when I was taking the transmission off I noticed the housing was hard up against the flywheel, so the engine spins free lol so we’re up money so far. So we don’t mind putting some extra cash in these engines in transmissions.
