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Pete Twissell
Pete Twissell
Old Buckenham
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Thread Like Summary
Hugh Jörgen, L.A.kevin, Magnetoman, NYBSAGUY
Total Likes: 8
Original Post (Thread Starter)
Gold Star Engine Rebuild: Bottom End #810581 05/28/2020 3:19 AM
by Magnetoman
Magnetoman
Having addressed in detail rebuilding a Gold Star's magneto, carburetor, 6-spring clutch, and gearbox that leaves the engine. So, this is the first of what will be five separate threads covering the entire rebuild of a Gold Star engine (or any pre-unit B-series single) based on my rebuild of a BB34A. A few months from now, when I hope to have finished this sequence, it will have separate threads detailing the step-by-step rebuild of the:

Crankshaft
Bottom End
Cylinder
Head
Rocker Box

Although there are a few detail differences (e.g. breather and rocker boxes), for the purposes of rebuilding an engine the procedure is essentially the same for all Gold Stars from the late ZB with separate rocker box through the DBD. Even with the one-piece head and rocker box the early ZB is essentially the same as well. Further, although my 1956 BB34A "Alloy Clipper" engine has a 'B33' bottom end so is lacking a drive-side bearing retaining plate, otherwise the engine is basically the same as a BB34GS (nb. this plate is shown in the Spares manual for the B32 and B34 so variations exist).

The next three images show, respectively, the bottom ends of a BB34A, BB34GS, and DBD34GS.

[Linked Image]

[Linked Image]

[Linked Image]

Comparing these three images in detail shows the great similarity of all three engines. Because of this, even though my 1949/56 BB34A-based "Alloy Clipper" is in the Projects forum it seems worthwhile to repeat the engine rebuilding information here in expanded form, pointing out where any important differences affecting the rebuild of a Gold Star engine exist (e.g. lipped inner roller bearing on my BB34A whereas Gold Stars have larger, non-lipped bearings).

Since my BB34A came to me in pieces, each thread in this series will be the inverse of usual rebuilds, i.e. they'll end with 'disassemble in reverse order'. Also, as people add to, or correct, what I've written I'll make the appropriate changes in the relevant posts so the information in this thread will be as accurate and self-contained as possible. However, this has to be done within the 5 images/post limitation so I already know that breaks between posts won't always be in ideal locations. Finally, I supplemented the photographs I took while rebuilding my BB34A with additional photographs of parts from the shelf, some of which aren't in great condition, so don't assume all of them are from my engine.

Assembling the Bottom End

If you follow the 17 parts of this section in order it will keep you from having to unbolt something you've already bolted together as you assemble the bottom end.

Supplies needed:
-- Assembly lube
-- Camshaft lube
-- Yamabond 4 or equivalent
-- Permatex Permashield Gasket Dressing and Sealant
-- Loctite 262 (red, high strength)
-- Loctite 680 (green, retaining compound)
-- (2) Sump gaskets (or gasket material to make your own)
-- Timing cover gasket
-- Oil pump gasket
-- (2) ¼-20 UNC socket head cap screws or BSW bolts drilled for safety wire
-- Safety wire
-- Oil seals for cams and crankshaft in timing cover (two for BB and three for later models)
-- Oil seal for magneto pinion
-- Tape or rubber bands to hold studs

1. Inspect all mating surfaces and clean and deburr all tapped holes.

[Linked Image]

2. Rebuild, true, and balance the crankshaft for the piston that will be used.
[this will be the subject of a separate multi-part section in another thread that I haven't written yet]

3. Inspect the following:

-- Condition of tappet faces, and ensure they have minimal runout when rotated. I don't know how much wear is acceptable, but I didn't bother refacing ones for my BB34A that were worn by ~0.002" in the center.

[Linked Image]
Liked Replies
Re: Gold Star Engine Rebuild: Bottom End #810583 May 28th a 03:43 AM
by Kerry W
Kerry W
Fantastic, thanks! Finally, a dissertation that will most likely quantify the 'how much is too much' questions I usually have when looking at 'pre-loved' parts and their wear..

Go to it!
2 members like this
Re: Gold Star Engine Rebuild: Bottom End #810650 May 28th a 08:22 PM
by Rich B
Rich B
Magneto Oil Seal - 20 X 38 X 5

The specific brand in my hand is "Narwhal"
2 members like this
Re: Gold Star Engine Rebuild: Bottom End #810646 May 28th a 07:57 PM
by Magnetoman
Magnetoman
Originally Posted by Peter R
could you please elaborate a bit more on point 8 that said "install the oil seal" ?
Well, I cheated on that point. There isn't an oil seal under the socket because I don't currently have one. However, I installed an oil seal in at least one of my Gold Stars without problem some years ago so it must be a matter of finding one of the correct thickness.

An oil seal is on my list of parts to buy, but since there's no urgency to have anything on that list in hand I'm waiting to see if other items get added to try to avoid paying shipping on two orders (yes, I realize that's futile, but hope springs eternal).

p.s. it's difficult to make an accurate comparison, but nearest to the "concept" of this thread is a 4-part series in Classic and Motorcycle Mechanics magazine 25 years ago in which there are ~19 tiny (~2"x2"), muddy images corresponding to the 30 I have here. A Haynes manual covers assembling the lower end with ~14 photos. Anyway, I'm not aware of anything that already exists in print or on the web that leads someone through the rebuilding process the way this thread does so I'm sure at least a few people will find it useful.
1 member likes this
Re: Gold Star Engine Rebuild: Bottom End #810643 May 28th a 06:37 PM
by Peter R
Peter R
MM, Good writeup, thanks,I enjoyed reading this, but could you please elaborate a bit more on point 8 that said "install the oil seal" ?

I have found that the space between the mag pinion and the crankcase housing is too narrow to fit an oilseal, and I fabricated an alternative solution that is not 100% oil tight.
Not sure if I use the correct seal, Do you have a part nr. or seal dimentions ?
1 member likes this
Re: Gold Star Engine Rebuild: Bottom End #810747 May 29th a 05:12 PM
by Rich B
Rich B
Originally Posted by Magnetoman
Originally Posted by Peter R
I have found that the space between the mag pinion and the crankcase housing is too narrow to fit an oilseal,
Originally Posted by Rich B
Magneto Oil Seal - 20 X 38 X 5
The cavity is 5.7 mm deep so Rich's suggested 5 mm-thick seal wouldn't even protrude from it. The cavity is 1.50" diameter (38.10 mm) so I assume that extra 0.004" is within the ability of the oil seal to accommodate the extra crush.

The seal actually measures 38.10 mm diameter, 4.75 mm thick.

I seem to remember putting something on the outer edge of the seal just be sure, likely one of my usuals of either 3 Bond product or Loctite 518. It didn’t fit loose, took some pressure to instal.
1 member likes this
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