Hello, new owner of 27ft Cherubini

Jun 24, 2018
5
Hunter Cherubini Shell point marina
I recently purchased a 1978 27ft to work on as a family project. I've run into a rough spot, and believe my gearbox needs repair. It's the original SB8 engine and I've having a tough time finding details on rebuilding it. If anyone could provide guidance that would be great.
The main 2 problems are grinding when going into reverse, and no power output in forward. I can see the prop shaft spinning but it's much slower than in reverse, it seems to be slipping pretty badly.
 
Jun 24, 2018
5
Hunter Cherubini Shell point marina
Thanks Will,
I did find that thread but was unsure of the similarities between the gearboxes between the different engine models. I have found that the SB12 and SB8 engines share the same gearbox but don't believe that 3 cylinder engines transmissions are the same, maybe they are similar in functionality though?
 
Oct 19, 2017
7,732
O'Day 19 Littleton, NH
Craibit, I'm afraid I can't really be of any help here. I don't pay any attention to engine questions usually. There are some sailors here with deep and broad knowledge in this area. I can't even tag another member, to call them in, who knows something, because I haven't paid attention to who the experts are in this area. I'm very surprised that no one has picked up your thread yet. @Crazy Dave Condon is the Hunter expert, he might be able to tell you who to ask for help. The '@' symbol in front of a member's name will "tag" them and they will get an alert that they were "tagged" in a post. Help is here, just be patient. If nothing picks up between now and the end of the day tomorrow, I do have automotive class fundamentals from high school, maybe we can work it out together. In the mean time, what is the model and make of your transmission?

Good Luck.

-Will (Dragonfly)
 
May 12, 2004
1,502
Hunter Cherubini 30 New Port Richey
I did find that thread but was unsure of the similarities between the gearboxes between the different engine models. I have found that the SB12 and SB8 engines share the same gearbox but don't believe that 3 cylinder engines transmissions are the same, maybe they are similar in functionality though?
My YSB12 had either gears or plates. I'm not sure. My 3YM20 three cyl. has a tranny with a cone. Hope that helps some.
 
Sep 2, 2011
1,041
Hunter 27 Cherubini Alum Creek State Park
If it's a Kanzaki transmission, it probably has a cone clutch. Instead of having gears that mesh, there are two parts that mate and utilize friction to transfer rotation from the engine output to the prop shaft.

I did this repair 3 yrs ago but unfortunately did not document it in photos.

First, download the engine's shop manual which details how to disassemble and reassemble every part of your engine. Then tear the transmission apart and find the cone and its mating part. Use a very fine grit lapping paste to lap the parts, then replace the bearings and seals and reassemble.
If you don't know what it means to "lap" surfaces, then I would suggest having a diesel mechanic do the work.
I did mine in about a week in my spare time, but you could easily do it in a day if you have the parts and tools ready. After lapping the clutch, my boat easily gets to hull speed where before I couldn't get 3 kts on a glassy lake.

Good luck with your repair.
 
Jun 24, 2018
5
Hunter Cherubini Shell point marina
Thank you for everyone that's responded so far. I did make it down to the marina today and took a few pictures of the transmission as I've been asked a couple times for the model number, but unfortunately there's nothing anywhere on the transmission besides the plate pictured that shows SB8 , the horsepower rating, and the RPMs at crank and prop, as shown in the pictures. I even called a local marine yanmar service center in Tampa and they were unable to tell me what model transmission would go with this SB8 engine. I'm leaving in a few days for vacation and will need to take up this project again after I return on Monday 7/2. If any of these pictures help anyone, and they can lend a hand it would be greatly appreciated. Thank you all!
 

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Jun 24, 2018
5
Hunter Cherubini Shell point marina
One additional note, I tried the Lucas transmission stop slip with hopes I'd at least be able to see some forward movement, but it did not make any difference after pumping out the old fluid and replacing it with a mix of new oil and the Lucas additive.