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After battling the plug to get it out by shaving a drag link and grinding the plug to a size to fit the drag link, and ordering a Whitworth socket set from AB Tools in Stoke (very nice set with unbelievable price including U.S. shipping), and studying the qualities of the hardness of the flywheel bolt with an eye to heat it up since it's possibly red loctited in there since the factory did it that way and you might need new flywheels or EDM (electrical discharge machining) or other means to remove it if you mess it up, and after removing the flywheel bolt with reasonable force with no heat, and attempting to use a 3/8 18 TPI pipe plug to grab the sludge tube only to discover it rotates freely and pulled it out with my pinky, and noting that the sludge was not all choked up and just soft carbon, then I thought clean it all up and get a new plug.

The plug was about 2 threads deep and both of these 2 threads are almost ok, but not quite. So, the right size tapered tap should clean them up nicely. Maybe sellers who have the plug might list the thread size, ya think! ? One seller mentioned CEI thread for the plug .So, started looking up CEI thread sizes and taps. Also, BSC taps since they are the same right? Looked at some you tube videos on pulling the trap hoping one might mention that cleaning up the threads could be done with a certain size tap but struck out on that one. Then I found a vendor who sells the tap for Trumpets: 7/8" 20 TPI. The threaded hole for the plug is about .830 and about right for a 7/8 tap. So, before I go screwing things up after all this, thought I'd ask the BSA Britbike community to confirm.

Also, can CEI thread be cleaned up with SAE taps or dies? I didn't think so. Is the vendor who mentioned CEI thread for the plug off base? Is SAE 7/8" 20 tpi the way to go? CEI thread for this application prior to a certain year and after that SAE?

Also, one youtube guy said only use the OEM style plug since the hex drive ones do not weigh the same and will mess up the left right balance. Made me think does he really think the OEM style mfrs are weighing the plug, and pulled sludge trap on rebuild and all the new stuff weighs the same, but watch out for the plug? LOL

Thanks for your replies and thanks for being nice. I apologize for the long whine but hey it was fun!!!

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https://www.morgo.co.uk/product/morgo-hb6-crankshaft-bung/

Fitment
Triumph sludge plug T110, T120 to 1962 BSA sludge plug A65 & A50 1966 to 73

Details | HB6 | 11.50mm Long | 10.00mm A/F Hex | Thread 7/8″ BSF*20

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Thanks kommando!!!

So, the sludge plug thread is BSF 7/8 20 tpi.
That would be a 55 degree thread angle.

Now if I can find a reasonably priced tap. Carbon steel would be OK since only doing one or two.

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For taps and dies I always use:
a) British Tools and Fasteners in NYS for US source.
b) If BT&F dont have it then Tracy Tools in UK.
HTH

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They say every dog has his day..
Trouble is, nobody tells the dog which day it is !

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Thanks. Doobie.

Aditional sources for tools are always good to know.

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7/8 x 20 is the same thread dia. and pitch
Whether it is called UNEF , BSC or CEI .
( sometimes , randomly , the stars align , enjoy it while it lasts , )
... but try not to read too much into the coincidence

Rather than buying a special tap at an exorbitant cost
you could clean and chase the existing threads with a
hardened grade 7/8 x 20 unef Bolt ( with a couple of slots Dremeled across the threads )
... if you do buy on the american of the pond ,
7/8 x 20 , marked as ( UNEF ) is usually cheaper
Then the same Thread mark in one of the British forms

This thread size and pitch for the A65 sludge plug
started in the 1966
and lasted to the end of bsa production .

the thread interference class should be pretty much a standard thread fit .
But this doesn't mean every aftermarket manufacturer
makes a plug that fits nicely .
If the old plug fits better and is reusable ( usually original fitment )
that old plug would my first pick to re-use

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Wow, one could really screw up on thread sizes!

Tridentman, thanks for the input on a U.S. supplier, British Tools and Fasteners in NY State. They have a very good information breakdown for the uninitiated on Imperial thread sizes like myself. Seems BSF 7/8" 20 TPI is not catalogued there. Also, It seems that thread size is not catalogued anywhere I have looked so far. Found Tracey Tools in the U.K. a day or so ago and thought I hit pay dirt with their BSC 7/8" 20 TPI carbon steel tap for about 12 quid plus ship to U.S. Tracey had no BSF 7/8" 20 TPI taps.

Little D, tried and died on all 3 of the sites looking for BSF 7/8" 20 TPI. U.S. sources are much appreciated So far it seems a tap that size will be hard to find but thanks!

CBS, Complete British Spares, in Lancaster, CA USA had a 7/8" 20 TPI tap for 70 U.S.and described online as fitting the BSA/Triumph 650 and 750 but no thread type described. I emailed CBS inquiring about the thread specification and received a prompt reply that the thread type is UNEF. UNEF 7/8" 20 TPI is a catalogued thread type.

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Hi Bill, glad to hear you're finally meeting with success in finding a tap. (FWIW, it's Classic British Spares.) That's a big boy, so I'm not shocked by the price.

I'm skeptical that the hex socket plug would make a significant difference in crank balance. Are you planning to have the crank balanced? If so, they could use whichever new plug you source. I think the hex socket plug is a good idea *IF* you think you'll ever have to remove it again.


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quentin, yes, I sometimes try my backyard mechanic tricks too; one of my oldest skill sets. The plug that I pulled has threads that are shot. Fortunately, the crank hole threads are fine with the 2 outer threads easily cleaned up with the right tap. This crank has 2 staking dimples and the plug was 2 threads below. Theorize that there was a mismatch in thread size and the plug was softer and gumbyized when I removed it. Learned during this hunt for the right answer that CEI and BSC have alignment and can understand the kissin' cousin aspect of UNEF; all with a 60 degree thread angle. Assigning BSF alignment with its 55 degree thread angle would be a mistake. A 60 thread angle stud with the same pitch as a 55 thread angle hole would have nearly no thread contact since the 60 degree thread would have a shorter tooth giving 5 degrees of empty space. Conversely (55 stud, 60 hole), contact would cause plastic deformation of one or both as its squeezed in with the stud having threads too tall.

So far from where I sit, there is a U.K. mfr, Morgo, with published BSF 7/8" 20 TPI thread type for a sludge trap plug and a U.S. supplier, CBS, with a tap for the same sludge trap plug hole with a thread type UNEF 7/8" 20 TPI.

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Hey, MARK!!! yes, of course it has to be balanced. If not then all that work and it shakes and can't rev. This is all on your 71 A65 FS motor that you sold me. I know you had that Trumpet out by now, hold it down to 90. On the plug affecting balance, nothing a little flywheel cut wouldn't correct, Rather use the oem style with the right size thread. I am guessing that some of the plug removal problems are due to mismatched thread.
Drive safe!
Bill

Last edited by Bustednukel; 03/29/22 1:41 am. Reason: Drive safe
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BSF means British Standard Fine which for 7/8" is 11 TPI. There could be a Parallel Thread of Whitworth Form for 7/8"-20 TPI but it is not a standard just as for Unified threads you can make 20 TPI in any diameter.

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Jaye Strait over in MA made a sludge trap video, while it's nothing groundbreaking for most on here, he had an interesting take on the plugs:

Last edited by DAMadd; 03/29/22 3:18 pm.

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One thing I hate to see on a crank is multiple punch marks from trying to lock the sludge trap plug. One nice thing about the modern hex plugs is you can punch the plug so that it fills the existing punch hole which are often drilled clean.

John Healy did a great article on sludge plugs.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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Did some trig to discover the difference in thread size between BSF 7/8" 20 TPI with its 55 degree thread form, and UNEF 7/8" 20 TPI with its 60 degree thread form. The BSF has a .005" longer nominal thread form from crest to valley. Spent a bit of time trying to discover the tolerance class with more research and study required to establish. Also, since the BSF thread is longer it might be safe to say that the major or minor bolt width dimension of the BSF is also different but this is supposition without a comparison of published resources. There may be no published resource for BSF 7/8" 20 TPI since it appears to be a non-catalogued thread size.

I've ordered a UNEF 7/8" 20 TPI tap to solve my trifling issue since this tap will not enlarge the BSF 7/8" 20 TPI crank hole since the thread is .005 shorter. Found a cheap one. I believe the BSC 7/8" 20 TPI carbon steel tap at Tracey Tools in U.K. would have also solved my issue since it is also comparatively inexpensive; shipping not so much probably.

No other BSF applications should be substituted with UNEF, CEI or BSC if there is a torque value associated with the application IMHO unless you are ok with thread deformation. The converse is also true.

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I am not sure if you need a full size tap, a 3/8 BSF tap is 20 tpi, if you just need to clean up the start threads it would do .


You dont even need a lathe, just a bit of perstince, a bit like an internal thread file.

Last edited by gavin eisler; 03/30/22 3:47 pm. Reason: misspelling persistance.

71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
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Originally Posted by Bustednukel
Hey, MARK!!! yes, of course it has to be balanced. If not then all that work and it shakes and can't rev. This is all on your 71 A65 FS motor that you sold me. I know you had that Trumpet out by now, hold it down to 90. On the plug affecting balance, nothing a little flywheel cut wouldn't correct, Rather use the oem style with the right size thread. I am guessing that some of the plug removal problems are due to mismatched thread.
Drive safe!
Bill

Bill, it sounds like you're suspicious that the hex socket plug will be the correct thread; I see no reason to suspect that, as long as you're buying it from a trusted source, particularly CBS, who's selling you the tap as well. I'm aware you're dealing with the '71 FS engine, and that you realize the importance of balancing. As far as the wrong plug being in there, I have to assume that either the PO or a supplier made an error in sourcing the plug.

The Triumph, no, I'm strictly a "fair weather rider", and I won't venture out on the roads until I'm sure that all the salt is washed away. Also, I had gall bladder surgery just over a month ago, so I'm still taking it slow and easy.


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Mark, hope you get bikin' soon. The roads down here in south central PA have been rained on plenty. It is 33 F here this morning and hopefully they throw no more salt. Yes, I have concern on thread size for the sludge trap plug. Have not ordered one yet, but it seems that some are advertised as NOS on Ebay; some are advertised new with CEI thread and this is what got me hunting for exactly what the correct thread is. Of course, Morgo in U.K has new ones that they make with the hex and since it will be locktited in place, it makes sense. I would blue locktite not red. I'm trusting Morgo to have published the correct thread size. I'm trusting CBS to have informed me of a tap size that will work but $70 is more than I can go.

Thanks all for the help everybody! What a useful group of folks!!!

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I hope the person who loctites a sludge tube plug is the one that has to remove it.

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Originally Posted by John Healy
I hope the person who loctites a sludge tube plug is the one that has to remove it.

Right Bill, I see no reason not to stake the plug. If done right, it can be drilled out without causing damage to the crank. There was a very good discourse a while back on removing and re-staking the plug, with photos - was that yours, John?

As far as sourcing the right plug, I would recommend British Cycle Supply. I've been doing business with them for many years and they have never sent me the wrong stuff. Hope you find a way to clean up those threads; sorry nothing to offer there.


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Quote
was that yours, John?

Yes

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Originally Posted by John Healy
I hope the person who loctites a sludge tube plug is the one that has to remove it.

It's ok if it's a hex, just warm it up. I only ever use a drop of 638 on 'em, no problems.

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Where I come from if a drop is good, more is better. We are a society of the larger hammer. Now in nearly 60 years of doing this I have never seen, or heard, of a sludge tube plug causing a problem using a single punch mark. Being one of those guys who others turn to when they face what they feel is a problem I have seen plenty of plugs that require extra ordinary creative solutions to remove. Using a thread sealant and a single punch mark on the face of the plug into the mark left on the face of the crankshaft cheek will retain the plug safely.

On rare occasions the plug will not seal the cavity. Pump some oil into the end of the crankshaft to check to see if any oil leaks out the plug.

Save your blue loctite for the alternator, and transmission mainshaft nuts. I Belong to a group of mechanics who believe you should have a License to buy Loctite. It’s short comings have been exposed when they changed the formula. To make it work it was required to use a primer on oily, non-reactive metals and coatings (plating). Using Red Loctite on plated hardware and it barely worked. No need to get the nut to 400-450F to get it to release.

We were saved by not reading the technical data. Every one believed the primer was just a cleaner. It contained a missing compound the allowed the Loctite to set-up when used in oily, plated or non-reactive metals. We were lulled into thinking we could work with the stuff. On occasions it would work and you would find out what 400-450F really meant.

With the the new formula you might as well have brazed the nut. No primer required. While in the old days an oily no reactive or plated surface would not let the Loctite to work very well. No such problem with the new Loctite.

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I never went by colour of the gear, only by number and spec. 638 is Green.

Whatever works for you i suppose. It's not governed by law and if you're over 21..............

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In the old days the color green had on the Loctite bottle, “ Replaces brazing.” Still keep that bottle around. There are those jobs that require making a point.

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