Tahoe 23 engine/transmission

Designs for inboard or outboard power

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TomB
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Tahoe 23 engine/transmission

Post by TomB » Thu Sep 06, 2018 10:53 am

Starting at the transom, I drilled the hole for and dry fit the rudder. Next I measured and measured and found a strut and strut log. Yesterday I began to fit the strut and during the night I imagined putting it in the wrong place since I don’t know/have the engine or transmission.

This morning I started to make a full size drawing of the engine and drivetrain for my Tahoe 23. I have found some schematics including for a 5.7L Mercruiser with a Hurth 63A 8*down angle transmission. The 5.7L sounds right and the 8* down angle sounds right, but by brand I’m less confident. How do I decide which 5.7L and which transmission best suits my objectives (needs to run full power in reverse for starboard helm)? Is the schematic I found “close enough” if I went with the PCM 343? Are there schematics for PCM? Is the difference between Mercruiser and PCM like a heated discussion of the benefits of a Chevy or a GMC?

Where should I get the motor and transmission?

Tom

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Bill Edmundson
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Re: Tahoe 23 engine/transmission

Post by Bill Edmundson » Thu Sep 06, 2018 1:36 pm

Tom

I have the 63A down angle. It seems to work great. If you set it to rotate counter-clock wise it will make a clicking noise at low speed. Just get use to it. The rest I can't answer.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
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TomB
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Re: Tahoe 23 engine/transmission

Post by TomB » Thu Sep 06, 2018 2:38 pm

Thanks Bill...ticking...I've been thinking about a boat name for years...maybe "Time Bomb" :D

Here are a few scans of how the transmission angles, 0*, 8*, and 12* fit in the cross section holding the engine to maintain design CB.

The straight transmission is very close to the KH design with the drain plug on the keel and the spark arrester tight to the engine cover.
scan10002 copy.jpg
The 8* down angle transmission adds more space between oil pan and keel. The engine cover framing would be close.
scan10001 copy.jpg
The 12* tranny has about 4" between oil pan and keel and the engine cover framing is still close.
scan10001 copy.jpg
It looks like I could move the motor (1000 lbs) back a foot and improve the fit while screwing up the CB.

Any suggestions?

Tom

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kens
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Re: Tahoe 23 engine/transmission

Post by kens » Fri Sep 07, 2018 3:27 pm

Hi,
It seems that the 8* tranny, while setting the engine flatter, but it raises the front end of crankshaft about 1 1/2", correct?, compared to a 0* tranny.
I assuming you looked at the ZF63A tranny for the 8* option.

Which tranny did you look at for the 12* item? Twin Disc?
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

TomB
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Re: Tahoe 23 engine/transmission

Post by TomB » Fri Sep 07, 2018 3:56 pm

Ken,

I found a few drawings, a Mercury 350 MAG MPI with a Velvet Drive 72C inline, 5.7L with Hurth 630A 8*, and 5.7L with Hurth 630A 12*. The design sets the shaft at about 12* so the 12* down angle would mean a motor setting level but high. I am thinking about flattening the shaft a little moving the shaft hole forward a little and use the 8* down angle to lower the motor and still bring it in close to level. Makes sense?

Tom

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billy c
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Re: Tahoe 23 engine/transmission

Post by billy c » Fri Sep 07, 2018 4:38 pm

Tom I have the Mercury 350 MAG MPI with a Velvet Drive 72C inline in my Belle Isle no problems and is what Ken drew in your plan (SBC). You may have even a little more room in the Tahoe.
Billy
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kens
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Re: Tahoe 23 engine/transmission

Post by kens » Fri Sep 07, 2018 6:27 pm

Where is this ZF63 series tranny with 12* down angle,
please advise.

The ZF63a series tranny was originally a german Hurth series 630, which in turn was bought out by ZF and renamed to 63a series.
To the best of my knowledge it was, and still is, a 8* tranny.

Please advise of the 12 * option. Inquiring minds want to know. !!
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

TomB
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Re: Tahoe 23 engine/transmission

Post by TomB » Fri Sep 07, 2018 7:19 pm

Billy, Thanks for the info.
To the best of my knowledge it was, and still is, a 8* tranny.
:shock:

Well gosh Ken, I know what I know and it isn't much. This motor/transmission stuff is new to me. This is the schematic info I have but I don't know if its real.
5.7L w Hurth 630A down angle copy.jpg
You've got me digging. I looked at Transmission Marines catalog and they show an 8* HSW 630a/ ZF 63a, no 12*... :roll:


Tom

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Roberta
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Re: Tahoe 23 engine/transmission

Post by Roberta » Sat Sep 08, 2018 5:00 am

I don't think that the drawing implied that there was a 12 deg. down angle transmission. I am not familiar with one of those. ZF and Velvet Drive make 8 deg. down angle transmissions. I think the drawings are showing engine/transmission assembly clearances for given prop shaft angles based in the datum plane for the mounts.

Roberta
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Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

TomB
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Re: Tahoe 23 engine/transmission

Post by TomB » Sat Sep 08, 2018 7:29 am

I did not mean to imply the design suggesting a down angle transmission. The design shows something similar to a 5.7L with an inline transmission. The angle between stringer and prop shaft is 12*, so with an in-line tranny the motor would be tipped back 12*. I cut out a paper doll of the drawing I found of a Mercury 350 MAG w a Velvet Drive 72C and tested it on design drawing (see the first drawing above).

The mistake I made was to not study the schematic engine/transmission closely enough! The drawing gave me a table of dimensions for different prop shaft angles. What I did not recognize was the drawing was showing 8* down angle transmission while varying angles of engine mounting to mate up with potential prop shaft angles. Sorry for sharing my confusion.

So far I’ve learned there are a number of in-line transmissions, a number of 8* down-angle transmissions, and a number of V-drive transmissions. For my Tahoe, I will be using an 8* down-angle transmission. Today, I am going to make a full size boat drawing showing the fixed points: frames 1-4, keel, motor stringer, and the rudder. I made a full size outline drawing of a 5.7L w a 63A 8*down-angle and will lay it on the full size drawing. Since I already have a prop strut and and shaft log, I will lay them on the drawing as well. Then I can play with the engine orientation within the engine bay to get it low in the boat. My objective is to discover the prop shaft angle, confirm the strut location and any mounting angling needs and the prop shaft hole location.

Tom

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billy c
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Re: Tahoe 23 engine/transmission

Post by billy c » Sat Sep 08, 2018 7:43 am

Why make things so hard? You bought plans from a naval architect who has many designs under his belt and think you have to change his engine/transmission recommendations to a down angle.
I don’t get it.
Billy
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kens
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Re: Tahoe 23 engine/transmission

Post by kens » Sat Sep 08, 2018 12:09 pm

billy c wrote:Why make things so hard? You bought plans from a naval architect who has many designs under his belt and think you have to change his engine/transmission recommendations to a down angle.
I don’t get it.
Billy
The VelvetDrive type tranny drawn on the plans dates back to the heyday of Glen-l's career, as well as the heyday of the VelvetDrive itself. The VelvetDrive is all cast iron, possibly bullet proof, and the prop rotation is dependent upon engine rotation. It is over 60years old today and available brand new, but at a high cost. It available as used, rebuilt, and still dependable, but used nonetheless at a fairer price.

The down angle such as ZF 45 series and 63 series are newer designs, lighter aluminum housings, prop rotation is left or right as desired, and priced better when new compared to a new iron VelvetDrive. the ZF's are priced the same, and weigh the same for any gear ratio chosen. Any VelvetDrive with reduction gear is a added on gear package with added cost & weight.

All the Mahogany designs we discuss would use the Velvet 1:1 gear or the ZF 1.2:1 (shallowest gear)
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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Roberta
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Re: Tahoe 23 engine/transmission

Post by Roberta » Sat Sep 08, 2018 12:23 pm

I used a Velvet Drive Liberty A 8 degree down angle with 1:1 ratio in the Torpedo. Runs full speed in forward and reverse for right or left hand rotation.

Roberta
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Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

TomB
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Re: Tahoe 23 engine/transmission

Post by TomB » Sat Sep 08, 2018 2:22 pm

Why make things so hard?
'cause that's the way I'm wired. :D :D :Dand I can't spend this kind of money without lots of info.

But the "why" in selection between in-line and 8* down-angle is best answered by quoting Glen & Ken in Inboard Motor Installation, "The use of a marine transmission with built-in angle will allow the engine to be mounted more-or-less horizontally while still allowing a suitable shaft angle. More space would be required for the same engine, if mounted in line with the shaft angle." (Plate 9, pg 56)

Ok that is the theory. The reality is that the down angle comes off several inches below where an in line would come off, so the space created is mostly below the motor. I can get the space savings above the motor if I slide the motor aft a foot messing up the center of buoyancy. If I flatten the shaft angle I can help things an inch or so, not worth it. All the gymnastic show that in line works just fine. As a bonus I have what I think is an accurate strut location and a target for the shaft hole.

Tom

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billy c
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Re: Tahoe 23 engine/transmission

Post by billy c » Sat Sep 08, 2018 3:39 pm

Tom
...glad you did your homework :D and yes that is a heap of money on the table. :lol:
You are correct in either inline or down-angle would fit in the engine compartment. I think you understand the importance of engine location in the hull and would keep it as designed. That is a lot of weight to overcome if you need to adjust the trim of your boat after the launch.
Have fun I am really enjoying your build.
Billy
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