repowering and running gear upgrade ??

[sandytows]

I am repowering my TJ 28. 6BT to 6LPA. I am also changing all the running gear (increasing shaft size).
I am doing most of the work myself and this project is a little bigger than anything I have done before, but not by too much.

My question is one of timing or procedure. Here is my plan.
Remove old engine. (done)
Dry fit new engine (rework engine beds as necessary) to old running gear.
Rremove old running gear and install new.
Final fit and adjustment.
Done.
My thought is that by leaving the old running gear in it will give me a reference point to work with for lining up the new engine.
The engine is soft mounted so I should be able to adjust for any minor misalignment that creeps in during shaft replacement.

Ok let me have it! Am I going about this the wrong way?

 

[captainlarry84]

I think the big question here is your gear. Do you need a down angle or straight? Next big question is do I go 2:0 or 2:5? If you can swing a 22 to 24 " wheel I would go with a 2:5 gear & 1.75 shafting. If you are max out at a 21" wheel I would go with a 2:0 & 1.5 shafting. Also your gear will be either a ZF63A or KMH50A which both have 8 degree down angle.

 

[sandytows]

22" prop dia. (builder says can swing a 24" but that is tight. I am going 1.75" shaft.
2:1 gear ZF 63a. the old gear was 220a with 10deg down angle. but the old engine was mounted down at the nose so the new gear should allow for a dead level install.

But my real questions is do I rip every thing out and start from scratch or replace engine and then shafting. I am increasing shaft size and going dripless shaft seal.

 

[djmarchand]

Your approach makes sense. The pros use a laser alignment tool in place of the existing prop shaft. But the existing prop shaft should work fine to rough align to.

Curious what speed you are expecting. My Cape Dory 28 gasser which has a similar hull shape and weight would top out at 20+ kts with 275 hp. Yours should do 22-24 kts I would guess.

David

 

[sandytows]

thanks
with the old 210 cummins I got 16kt cruise and 20kt WOT.
I am expecting a 20kt cruise at a load that will allow for long engine life.. WOT means little to me.

I believe the cape dory has more belly and is less flat in the stern.

 

[captainlarry84]

How much longer is your new Yanmar that the old 210 Cummins? The future back the motor the faster & dryer she will run. If you need to push the longer motor forward you may lose a little. Therefore changing your shaft angle a little may also be need to keep the motor back. Is you vessel wet Keeled or wet tube? If it is wet keeled it may be a good time to consider wet tube.

 

[sbmar.com]

The 6LP is noticeably smaller in all dimensions and about 200 lbs lighter than the 6BT.

Set up right. it's a good eng for low annual hour use.. This engine needs to see right at an accurate 4000 RPM with the boat at its working weight.. That way when in a hurry, you can run at 3600 and get decent engine life if all the rest is right.............22" x 22" 4B = 2.5 :1 ??

Tony

 

[captainlarry84]

The 6LP is noticeably smaller in all dimensions and about 200 lbs lighter than the 6BT.

Set up right. it's a good eng for low annual hour use.. This engine needs to see right at an accurate 4000 RPM with the boat at its working weight.. That way when is a hurry, you can run at 3600 and get decent engine life if all the rest is right.............22" x 22" 4B = 2.5 :1 ??

Tony

Good guess on the wheel & gear I concurr

 

[traditions]

Start with a clean slate.You will just end up doing things twice.If you were going to use a gear that was the same configuration ,I would say yes,but to change angles and gears,I would start clean. Put the shaft in and line the engine to it.

 

[sandytows]

So I am pulling all the running gear and swapping that out prior to engine install. I have a standard cutlass bearing and stuffing box. RE Thomas SSB and SB style.
R.E. Thomas Marine Hardware, Inc. Manufacturer of Bronze Marine Hardware

Since I am increasing shaft size they both have to go. The engine will be soft mounted and I want a dripless shaft seal.
What is the smartest way to set this up since I am replacing everything?
Shaft length is 8-8.5' @ 1.75" distance from tranny flange to stuffing box is about 2' The boat is wet keel with no tube. Thanks

 

[captainlarry84]

In reviewing all the facts the boat should really have a 2.5 gear. That will give you a 22 X 22 or maybe even a 22 x 23. 2:0 gear will drop the wheel to about a 22 X 20.

 

[sandytows]

2.5:1 with a 22x22 square is the setup used by the builder behind the smaller yanmar 240. I talked with him and he thinks the 315 will be fine at that ratio with a wheel of 22x20 or 22x22.
I appreciate the feedback, but I am pretty sure I am on the right track.

But can anybody add some feedback about the running gear question.

 

[sandytows]

But can anybody add some feedback about the running gear question.

Anybody help?

 

[lobstercatcher]

"My thought is that by leaving the old running gear in it will give me a reference point to work with for lining up the new engine.
The engine is soft mounted so I should be able to adjust for any minor misalignment that creeps in during shaft replacement.
"

Most of the OP has done checked off so these are the remaining questions in the OP.

The correct answer to putting in the new upgrade is to do it while it is convenient as long as you have the money to do it. You won't gain anything by leaving the old stuff in there when you don't want it in there.

 

[lobstercatcher]

2.5:1 with a 22x22 square is the setup used by the builder behind the smaller yanmar 240. I talked with him and he thinks the 315 will be fine at that ratio with a wheel of 22x20 or 22x22.
I appreciate the feedback, but I am pretty sure I am on the right track.

But can anybody add some feedback about the running gear question.

What is the rpm. You are way under sized 22x20 at a glance. how big of a wheel dia will fit under there


**********I guess I would like to know what is the distance / clearance between the hull and keel/ not the largest diameter someone actually stuck under there.

 

[lobstercatcher]

22" prop dia. (builder says can swing a 24" but that is tight. I am going 1.75" shaft.
2:1 gear ZF 63a. the old gear was 220a with 10deg down angle. but the old engine was mounted down at the nose so the new gear should allow for a dead level install.

But my real questions is do I rip every thing out and start from scratch or replace engine and then shafting. I am increasing shaft size and going dripless shaft seal.

I see the answer to previous post 24 would be nice. Do you have any concerns for slow idle speed? 24 x 22 would probably be about right depending on the boats unknown weight. Builder says its tight or it develops prop knock?

 

[MDI45]

Your not fitting 24" wheel on that boat...unless you like only a inch or so clearance....my friend had one and 22 was Max

 

[lobstercatcher]

Your not fitting 24" wheel on that boat...unless you like only a inch or so clearance....my friend had one and 22 was Max

I think I'd do a 22x 24 then.

 

[petrel]

What are the rpms of that engine? I would think 2.5 to 1 w/ a Yanmar. They turn much faster than a 6BT I would think. Maybe more blade area if you're maxed on diameter. It's a tow boat, right?

 

[eyschulman]

I noticed that Sbmar( Tony Athens ) entered this debate about a week ago. There is a man who has done a few repowers and has had a bit of experience with Yanmar and Cummins being a large volume dealer in both. Located on the West coast so may not be that well known DownEast. Tony for those who don't know(some here do)is the moderator of Boatdiesel.com.