Topic: 1957 Johnson 10hp and 18hp gears – Antique Outboard Motor Club,Inc

This topic has 20 replies, 9 voices, and was last updated 6 years, 6 months ago by Anonymous.

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July 2, 2018 at 12:48 pm #10446
Anonymous
Questions for the experts: "Would a 1957 Johnson 10hp lower unit as a whole interchange with a 1957 Johnson 18hp whole lower unit? Is the gear ratio the same? The drive shafts are the same part number. The 10hp gears are available for separate sale, but the 18hp gears are only available as a set? Are the 10hp gears straight cut and the 18hp gears spiral cut? Thanks for any info."
July 2, 2018 at 1:52 pm #78886
frankr
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I believe the whole units will bolt up, but the gear ratios are different, meaning the gears are different.
July 2, 2018 at 2:04 pm #78887
fleetwin
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US Member - 2 Years
This is a great thread, have often wondered about it…Tried to look up part numbers on ME.com, but they don’t have breakdowns for these engines…I was under the impression that the gear ratios were the same, OMC just put a smaller pitch prop on the 10hp. Hopefully someone with access to the 1957 parts break downs for these engines can clear this up….
July 2, 2018 at 2:31 pm #78888
chris-p
Participant
The FD11and the QD 18 (18hp and 10hp respectively) from 1957 share the same gear set PN# 377147, share the same gear case shell PN# 379216 and the same drive shaft PN# 308615. It is a direct bolt up, simply change the prop.

This is not the case for ALL 10s and 18s, but for the 1957 lineup it is.
July 2, 2018 at 2:36 pm #78889
chris-p
Participant
The 18hp has a higher pitched prop. 9.25"x11 Pitch
The 10hp has the 9" x 8 Pitch

Using the OMC Parts Reference Guide is the easiest way to navigate swapping questions like this, for me anyways.
July 2, 2018 at 3:02 pm #78891
frankr
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It would appear there is some conflicting information out there somewhere. My statement was based on the 1957 Johnson brochure. .572 vs .578 ratios. Not saying it was correct, though.
July 2, 2018 at 3:34 pm #78893
Mumbles
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From the 1980 parts guide.

Attachments:
July 2, 2018 at 6:51 pm #78906
Anonymous
OK, if the 10 and 18 hp motor in 1957 both use 377147 gear set, my parts list gives separate numbers for the three gears used in a 10hp 1957 motor. Are these then the same for the 1957 18hp motor? Forward 376715, Reverse 304570, Pinion 304569 1957 10hp
July 2, 2018 at 7:23 pm #78908
Mumbles
Participant
They must be if both motors use the same 377147 gear set.

I checked my ’57 FD parts manual and it only gives a P/N for the complete set, not individual gears.
July 3, 2018 at 1:46 am #78926
dan-in-tn
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US Member
My 1972 Common Parts Guide & earlier books shows the gear part numbers in the set as referenced in a recent post for a FD-10 that Bullie posted questions about. Not sure how to reference that? (Little help Mumbles?)

The problem I have XR55 is none of the numbers you are giving show up in my list? Like others I thought the gearcases were the same until the smaller 1958 unit for the 10hp?

Dan in TN
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