Previous Owners

[RichardL]

Thought Previous Owners should have their very own place on the forum. Someday, a new owner of my bike will probably lambast its previous owner right here.

With crankcase in the frame, time to attack the head. (It's just the lumbering way I approach things.) In the three or four years since I disassembled the bike, I never stopped to look at the fixing of the carb to the head. I'm titling the attached photo "Previous Owner Par Excellence." 5/16-24 allen bolt and 5/16-18 hex head cap screw, both American Standard. Fortunately, I already have a 5/16-18 Whitwrth helicoil kit.

Richard L.

[Black Sheep]

But of course you need a 5/16" x 26 tpi helicoil 

[Butch (cb)]

Back in '79 I had one of those studs pull out on mine - stripped threads. I pushed it back in and then drilled in from the side and pinned it. I guess in my case I kind of am the PO also.

[Greybeard]

I was so lucky with my rebuild that the machine was still pretty much original  There were only two owners before me. The bike was 17 years old when I bought it in 1972. I've added a moderate mileage since then.

[Swarfcut]

    Do those threads hold? If they do, don't waste time on them. They'll do the job, and that's all you need. If things go to plan and from your previous findings of the previous owners' antics, Sods Law means you find that crack in the Head Casting on your first trip out, thus rendering your time and effort wasted. Stick with what you have for now.

    Coarse thread looks to be UNC, the fine thread one UNF and nearest to original CEI thread. Try a known Cycle Thread 26TPI bolt in here, if still the original thread it may hold better than the existing non standard fixing.

    The original carb bolts have a reduced hex head to clear the flare of the carb mounting flange so a cap screw here is a reasonable choice for a fixing. Smaller sizes of your Whitworth set are a working substitute for UNC threads, fixings which will be common Stateside and more useful for repairing coarse threads into Alloy.

 Swarfy. (Joab's Comforter)

 Additional.  Cut down Cycle  Thread bar (eg  rear wheel spindle adjusters) fitted with Gearbox cover nuts having the reduced hex, make a good substitute for the original bolts used on Cast Iron Heads, always assuming the original thread in the casting is good.

[RichardL]

Swarfy,

I think the 18 TPI may be OK, even though a BSW 18 stud didn't thread in easily by hand. The UNF 24 will have to go. The PO obviously ran a UNF 24 tap down the BSW 18 hole. While it could well be OK based on the light torque required at the carb, I'm not comfortable leaving the bodge when it's so easy to fix.

Not having a ball-end allen key, the allen screw was a bit of a pain to remove (but not at cussing level).

This will be remembered as a very minor issue when I get around to fixing the mess made in the alloy at the rear drum.

Richard L.

[Black Sheep]

Am I reading this right? The iron head holes were originally 26 tpi - cycle thread. It's Alloy heads that are tapped BSW.

[RichardL]

I need to look again at the parts book and the parts for sale. I didn't see anything distinguishing between alloy and cast iron heads. The bike is a straight '57 A7 Twin, not A7SS, and I thought the head to be original for that model.

Richard L.

[Joolstacho]

Back in '79 I had one of those studs pull out on mine - stripped threads. I pushed it back in and then drilled in from the side and pinned it. I guess in my case I kind of am the PO also.

BUTCH-er then? 

[RichardL]

I think the 18 TPI may be OK, even though a BSW 18 stud didn't thread in easily by hand. The UNF 24 will have to go. The PO obviously ran a UNF 24 tap down the BSW 18 hole. While it could well be OK based on the light torque required at the carb, I'm not comfortable leaving the bodge when it's so easy to fix.

So, I ran a 5/16-18 UNC tap down both holes and a BSC 5/16-18 stud goes in both pretty nicely. All I can think of is that when the P.O. ran a UNC 24 TPI tap into the left BSC 18 TPI hole (or, maybe, just drove the 24 TPI bolt in the 18 TPI hole), he created a dual-threaded hole where either 18 or 24 TPI works. For now, as Swarfy predicted, seems no need to fix it.

Richard L.

[RichardL]

Am I reading this right? The iron head holes were originally 26 tpi - cycle thread. It's Alloy heads that are tapped BSW.

Thinking of changing the name of this forum topic to "Current Owner."

Unaccustomed to all things cast-iron-head, I've now seen the page with the 26 TPI bolts for carb mounting on cast iron. Anyway, these threads are screwed up in a way I haven't before experienced, because a 26 TPI CEI went easily into the hole that originally held the 18 anythread, so all three (18, 24 and 26) fit there smoothly and appear to be sound, at least when finger tight.

Going back to the top of the story, I guess I'll be going with 18 TPI. (An appropriate response would be, "who cares any more?") Sorrry to be so tedious.

Richard L.

[Black Sheep]

Eek! Going for a non-standard thread. What will future owners think?

[groily]

I don't know what is original for the machine, but is the carb such a tight fit in the space that you couldn't use studs 'n nuts instead of that motley selection Richard?
It's obvs easier to secure a stay-put fastener in a damaged thread than an in-and-out one.
It wouldn't be easy maybe to repair a thread with the head in situ down the line if a gremlin struck  . . .?
Just thinking of your options really (but as Swarfy says, you'll probably be OK with the mish-mash).

See, we do care!

[Rex]

I used studs and nuts on my 53 Star Twin because I knew no different as the fixings were missing. They are BSCy threaded, and although space is tight for carb removal (I'm running an Amal Premier with removable bellmouth) it isn't too much of a faff.

[Greybeard]

I changed to bolts as it makes it much easier to deal with the carb on a Plungie