1941 Mercury KB-3 Spark Plug Cover Confusion

This topic has 23 replies, 6 voices, and was last updated 1 year, 2 months ago by green-thumbs.

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January 23, 2023 at 5:17 pm #271650
Buccaneer
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The KB-3 project motor I’m working on was missing the spark plug cover,
but the stripped down KB-? (missing tag) had one on it.
The water line and fitting was missing on the motor that had the cover, but
I don’t see how the cover would have worked on it with the fitting and line
in place, nor on the KB-3 motor I want to use it on.

With the 90 deg. fitting screwed into the cylinder, there’s not enough clearance
for the cover. I thought that perhaps my cover was meant for a “twin” cylinder,
but when I looked at my KD-4 twin in storage, it has a cover that’s different,
and perhaps would actually work on the KB-3, having a notch in the area
where the rubber wedge goes.

I “may” be able to notch out the cover to make it work, but am wondering
does anyone have a good photo of a KB-3 with the correct cover in place?
Thanks.

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January 24, 2023 at 10:14 am #271667
The Boat House
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In my files I found this picture of KD-3S
if that will help ya.
Tubs
January 24, 2023 at 12:32 pm #271673
Buccaneer
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Tubs, I see no “tell tale” exiting the back of the cylinder nor
anywhere else on your photo.
That’s how my cover looks like currently though……. not
sure what’s going on!
I do see that one is also missing the rubber wedge (as Louis calls it)
between the plug cover and gas tank.
Thanks.

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January 24, 2023 at 7:34 pm #271682
Boonie
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I have a friend that makes those spark plug covers ( bra cups). Just finished a KD 4 with ones he made for me.
January 24, 2023 at 8:43 pm #271686
green-thumbs
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US Member - 2 Years
I hang my head in shame, I assumed. I checked the New Parts List and could not find sparkplug covers. Normally that is a good source. Then I looked at assembly charts for KD3 and KD4…KD3 singles use Spark Plug cover M-339 KD4 twins use upper M-337 and Lower M-338, So there are 3 Spark Plug Covers involved. KD3 uses a small fitting with a short section of copper tubing that loops around the spark plug and out thru a notch at bottom. The PreWar singles seem to used the same Upper Spark Plug cover as Twins as the all seem to exit Port side same as twins. The Post War KD3 set up is neater and uses lesst tubing. KE3 changes again to a longer tube that runs doown Starbord side of powerhead. due to sheet metal cowling.

I still feel Kiekhaefer would use what they had in a limited production KB3, so my money is on use of Upper Cylinder Spark Plug Cover… I can not prove it.

Louis

T
January 24, 2023 at 10:46 pm #271694
Buccaneer
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Louis, very interesting! So in Tubs photo of a KD-3S the tell – tale may
indeed be in place, inside of the plug cover, and perhaps barely exiting
the hole in the bottom of the cup.

I assumed that the hole in the bottom of the cup was for the spark plug wire?

I’ll look mine over again tomorrow, but I don’t see any reason why I couldn’t
notch out the area where the rubber wedge sits, for the 90 fitting to exit
the cup.
Not that I have a rubber wedge, but if so, would it still fit in the cup with
the plumbing in the way? I never did find anyone reproducing them for sale.

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January 24, 2023 at 10:47 pm #271695
Buccaneer
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Boonie wrote:

I have a friend that makes those spark plug covers ( bra cups). Just finished a KD 4 with ones he made for me.

Boonie, if those cups are “repros”, they look excellent!
Nice looking motor too!

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January 25, 2023 at 5:34 am #271696
billw
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US Member - 2 Years
Sorry I don’t have the exact picture of how it should be; but these three might help. The FIRST thumbnail picture,the one where there is no cover and no tube, that is the fitting location of a KD3 that is in the proper orientation but missing its copper tubing. There’s supposed to be a very short piece, soldered into the brass fitting, that curves around the spark plug, under the bra cover and exits as shown in my THIRD picture, with the cover on. Second picture is a WB2 that never had a cover. I have no idea what I did, to make the wrong picture the giant one. Sorry.

Long live American manufacturing!
- This reply was modified 1 year, 2 months ago by billw. Reason: picture problems
- This reply was modified 1 year, 2 months ago by billw.
- This reply was modified 1 year, 2 months ago by billw.
January 25, 2023 at 10:29 am #271712
Buccaneer
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Thanks for the photos Bill. Heading out to the garage now to take a look and
“think” about the ordeal.

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January 25, 2023 at 4:21 pm #271725
green-thumbs
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US Member - 2 Years
KB-3, KD-3 and KE-3 routed cooling water differently. First year K-1 and K-2 did not have spark plug covers. KE-3 had cowling without spark plug covers.

Spark plug covers have limited space, compact spark plug MA& be required as well as small ignition wire boot.
- This reply was modified 1 year, 2 months ago by green-thumbs.
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