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Originally Posted by gavin eisler
The number on the rod is not a part number its a casting number, they are sometimes numerically close to the part number. Generally a con rod part number may include the complete big end and matching crank pin, hence the difference.
Don't suppose this helps

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And you are out by one decimal place.
12 thou is .012" not .0012"
No real drama but it is a little confusing and is people do not read the posts carefully they will be thinking the clearences are too small not too big then giving you the appropriate information to what they saw thus further confusing you.
If it were me I would get a new + 40 piston then take the barrels to the machine shop.
Remind them it is a iron barrel air cooled engine so needs bigger clearences that a water cooled car engine ( they forget and bore them too tight ).
Next take the crank to a workshop ( not a shop front ) that does HD's or Ducattis and ask them to check the bottom end for you.

We all feel for you, it has happened to most of us but if you are going to put the time & money into it then get it done properly.

At a head shop get the valve guides checked.
These are difficult to check at home but the head shops usually have some really cleaver kit to measure them & the valve stems properly.

By the time you have finished, you willbe very knowledgable about B33's and will be offereing advice to others.
Once sorted they will give a very long service life so it is worth the effort to get right the first time.


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Hi Spencer,
Your engine has a high compression piston fitted,(7.5:1?)
the usual LC were flat topped
It has a long rod, easy to spot as the pin is near the bottom ring

The bore is toast, I know they will run with grooves and scores but you are never going to be happy doing a half arsed job
The +040 rings were a bodged attempt to sort it then sell it on mad

Get the engine shop to remove the valves and check the valve and guides as these are more than likely needing attention as well
New valve springs are also advisable

Regarding lapping the head, the inner face is the recess in the head and the top of the lip /spigot on the cylinder
The outer faces are where the head bolt holes are on the cylinder and head

In the video of the bike "running" I can hear a lot of gear noise
This is common on B31/33's when the magneto gear is too tiightly meshed with the idler pinion
This is caused by wear on the mag platform and magneto body
It can be sorted by shimming if not too bad,
The magneto strap tends to pull the gears tighter together eek
Sometimes an alloy strip can be placed between the front strap and magneto body to keep the gears correctly meshed
The mesh is correct when a strip of paper can be passed through the gears without it being cut through by the gear teeth

Of course the "correct" method of reclamation of this probblem involves welding and remachining the cases and restoring the magneto body to original, mucho $$$$$

In the video you posted the engine is eight stroking and misfiring, and reluctant to rev
If this was soley rich mixture there would be clouds of black smoke from the exhaust
Not so!
I suspect a magneto problem ?
I would have the magneto checked out while you have the engine apart.

Sorry to be the bearer of all this "bad news"
I have both a B31 and B33 engines in the workshop at the moment
The B31 was sold to the current owner as "done"
He was "done " allright, !!!!
the engine was totally worn out but still just about able to run, after a very few miles it packed up eek
The B33 bore was totally worn out on max oversize, It has now been resleeved back to std, I had difficulty finding a Std high comp piston

HTH
John








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Originally Posted by BSA_WM20
And you are out by one decimal place.
12 thou is .012" not .0012"
No real drama but it is a little confusing and is people do not read the posts carefully they will be thinking the clearences are too small not too big then giving you the appropriate information to what they saw thus further confusing you.
If it were me I would get a new + 40 piston then take the barrels to the machine shop.
Remind them it is a iron barrel air cooled engine so needs bigger clearences that a water cooled car engine ( they forget and bore them too tight ).
Next take the crank to a workshop ( not a shop front ) that does HD's or Ducattis and ask them to check the bottom end for you.

We all feel for you, it has happened to most of us but if you are going to put the time & money into it then get it done properly.

At a head shop get the valve guides checked.
These are difficult to check at home but the head shops usually have some really cleaver kit to measure them & the valve stems properly.

By the time you have finished, you willbe very knowledgable about B33's and will be offereing advice to others.
Once sorted they will give a very long service life so it is worth the effort to get right the first time.
I was accurate with my decimal place. The only feeler that would get in there needed help and was my smallest one: .0012" or .03mm

Getting it done properly is all I think should be done. I'm interested in this being a regular rider and "just making it work" doesn't fit that end. But now I'm looking at huge costs on a bike I already way over paid for. I mean, I've been seriously bent over a barrel already, and at this point I may as well assume that everything is garbage and rebuild literally the entire bike. Don't get me wrong, I like working on it and I feel confident doing so. Frankly, I expected to be putring in regular work. But the value I paid in purchase will be what it's worth when I'm done, so everything I spend now feels money thrown away, and in spite of my passion for these old singles, that's a hard reality to ignore.

But for the sake of arguement, if I'm looking for a piston and ring set, how do I know what to buy? The engine is stamped HC, which research suggests means high-compression. I don't know if the barrel matches the case though and I also don't know what rod I have, long or short. My spares book is not helpful, so does anyone have a suggestion?*

*The post above came up as soon as I posted this. Thank you for your advice. And as for bad news, so far there hasn't been good news with anything on this bike. So it's just news at this point, haha!

Last edited by SpencerAZ; 01/24/16 9:06 pm.

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I need a little more input regarding the piston. I found this:

http://www.vintage-motorcycle.com/index.php?language=en&site=4&pid=199&id=2988

...and it's listed for my year with a long rod. I cannot find a domed piston like the one I pulled from my motor, but since there was a shim fitted between the head and barrel, I'm going to assume that someone tried using an off-stock piston. I could be wrong though. I've been searching for all kinds of B33 pistons online and the only thing that looks close to the one I pulled is a Hepolite Goldstar piston.

I'm sure that this piston-the flat topped one in the link-would work fine without any ill effects, but not having a frame of reference, I'm open to suggestions. My spares catalogue doesn't list anything but 65-1244, so I'm assuming now that the long vs short rod might be the reason behind the "HC" stamped on my engine case. The piston I currently have is marked inside "B178" which is about as useful as a truckload of dead rats in a tampon factory (is Top Secret not a brilliant film?), so I'm at a loss. Barring any advice to the contrary, I'll probably opt for the piston in the link.

Last edited by SpencerAZ; 01/25/16 2:34 am. Reason: Better example of piston from different web store

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Chaterlea said "It has a long rod, easy to spot as the pin is near the bottom ring",
all of his advice is excellent. +1 on checking the mag.
"
If your skirt clearance is really only 0.0012" then it is too tight, clearance should be around 4-5 thou for a fresh bore.


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Quote
If your skirt clearance is really only 0.0012" then it is too tight, clearance should be around 4-5 thou for a fresh bore.


So you have the possibility to get it bored out 3 to 4 thou only and still stay at +20 thou as long as the rust marks etc clear up. Leave it up to the machinist to decide based on his measurements and if he can bore out that amount.

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Originally Posted by kommando
Quote
If your skirt clearance is really only 0.0012" then it is too tight, clearance should be around 4-5 thou for a fresh bore.


So you have the possibility to get it bored out 3 to 4 thou only and still stay at +20 thou as long as the rust marks etc clear up. Leave it up to the machinist to decide based on his measurements and if he can bore out that amount.
So should I get the machining done and then get a piston, or buy both sizes and return the one I don't use? Zombie recommended that I'll want to bring the piston with me.

The piston is pretty tight. Without the rings, it slips into the barrel easily, but if I put the barrel flat on the table and drop the piston in it, it actually builds up pressure and slows down to a gentle tap when it reaches the bottom.


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Originally Posted by gavin eisler
Chaterlea said "It has a long rod, easy to spot as the pin is near the bottom ring",
all of his advice is excellent. +1 on checking the mag.
"
If your skirt clearance is really only 0.0012" then it is too tight, clearance should be around 4-5 thou for a fresh bore.
He and I posted about the same time, so I didn't see his post until after I hit submit. I'll check the mesh too, but I don't think the mesh is too far off. The pinion slips in and out a lot more easily than I would have imagined, but that might just be proof positive for "the right tool for the job". I'll throw the pinion back in today and try that paper test. I'll put up a photo or two also.


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Take your barrel and current piston to the machinist, a good one, you explain what you have measured but want him to confirm your measurements. If they are right and he can clean up the bore and give you 4 to 5 thou clearance with the current piston leave it all with him.

If he says it will not clean up then he stops at that point and does no more for the time being. You buy a new 40 thou piston and then take this back to him, he can measure the piston and bore to suit again giving you 4 to 5 thou clearance.

Do not allow him to bore without first having a piston, he needs to measure the piston to get the right bore size.

Just because your current piston is stamped +20 do not assume its a BSA B33 +20 thou, as you cannot find an exact copy it may be from a different engine. So measure the bore and check its actually B33 +20 (well minus 3 to 4 thou based on the piston clearance).

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Take your barrel and piston to a place that does re-bores, they will check dimensions, if its as tight as you say they should be able to bore to suit the piston, you are lucky it didnt seize in a big way. Someone au fait with B33s will recommend the correct clearance.


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Hi Again,
Quote
If your skirt clearance is really only 0.0012" then it is too tight, clearance should be around 4-5 thou for a fresh bore.


That wont work!!!
The diffference in size is on the pistons not the bore
There are different types of pistons used on B33's
Split and solid skirt
Splitskirt clearance is 0.001 -0.003
Solid skirt is 0.004- 0.0055

Heres a link to a HC +.040 piston in the USA
http://www.ebay.co.uk/itm/BSA-B34-B33-500-SINGLE-ROBBINS-040-PISTON-PART-M-1230-85MM-PLUS-040-INCH-/311244710832?hash=item4877a163b0:g:efkAAOSwMpZUqhGN

Rings are easily available in USA same as Gold Star

http://www.ebay.co.uk/itm/BSA-040-Piston-Ring-Set-B33-B34-M33-Models-Single-Gold-Star-NOS-/231823741389?hash=item35f9c591cd:g:y28AAOSwo0JWLALI

Go for it!!!
John

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The magneto platform looks a little chewed up; like someone tried to file it even maybe? The base of the magneto itself looks fine though. The pinion was meshed a bit too tight and I think I could get away with shimming the mount. Is there anything special recommended for this? Shims made for this purpose, or something for the whole base, or simply a thin washer around each peg?

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[Linked Image]


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It looks a bit like someone strapped it too tightly, perhaps. The pegs clearly left an impression


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Sorry sir.
That will take much more than "shimming".

That mag was left loose in there at some point, and wore those slots into whatever you could call those shapes.

The only way out that I see is to fill/weld the slots, and have them re-machined.
There is a chance you could build a flat shim to fill the entire mount out of a piece of stainless or other hard metal to hold the alignment but I wouldn't trust that for long.

Let the experts chime in but it looks like more machining to me.

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There is a chance you could build a flat shim to fill the entire mount out of a piece of stainless or other hard metal to hold the alignment but I wouldn't trust that for long.

I have shims on my WM20 made from brass sheet. I took the inlet cam out and left the idler pinion in place then centralised mag armature as best I could looking where the oil seal sits after I had fitted shim and clamped the mag down tight & refitted mag pinion and turned the idler to check mesh for tight spots you could user a thin piece of paper for this between the teeth! Once happy just replace oil seal and put the lot together, bike has done around 9000 miles with no trouble or horrible noises. One you have right shims fitted and you keep the straps tight you shouldnt need to do this again... Dave


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Hi Spencer and All,
On the base of the magneto the machining marks can be seen
This means the magneto base has been skimmed !!
It looks as though the crankcases had some weld applied and "fettled" roughly eek
The mag seems to then have been refitted without shims?
That would mean its spindle was sitting too low
The spindle centre height from the magneto base should be 45mm
Shims can be alloy, brass or stainless
one piece of shim the size of the mag base with holes for the pegs

In my previous posts I covered this issue of cost reclaiming the cases

It really is a piss poor setup mad

John

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Originally Posted by chaterlea25
Hi Spencer and All,
On the base of the magneto the machining marks can be seen
This means the magneto base has been skimmed !!
It looks as though the crankcases had some weld applied and "fettled" roughly eek
The mag seems to then have been refitted without shims?
That would mean its spindle was sitting too low
The spindle centre height from the magneto base should be 45mm
Shims can be alloy, brass or stainless
one piece of shim the size of the mag base with holes for the pegs

In my previous posts I covered this issue of cost reclaiming the cases

It really is a piss poor setup mad

John


It's sounding more and more like this bike had been hacked to pieces and then patched together hastily without any long term use in mind. I don't know what I'm going to do at this point, but I've barely scratched the surface of what this bike needs and for what I've invested already, I could have bought another Royal Enfield. Honestly, I'm hesitant to dig any deeper into this thing for fear I'll find that I'll need to buy a whole bottom end, and it's looking more likely considering the condition of the crankcase. I haven't even dug into the gearbox beyond the outer cover, and given that I found a Permatex kickstarter bumper turned sludge, it's anyone's guess what other bandaids are in there.


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My local magneto guru "Peter Scott Motorcycles " replaes those round pins with real woodruf keys the fill the 1/2 round slots.
These hold the magneto square to the case and are well worth the few $ he charges for them.

However if we do them down here in OZ they must be available elsewhere.


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Slick solution! Square peg in a square hole... Who woulda thunk it?

As he shakes his head, walking off into the sunset, the sound "Dohhh" was heard again, and again.

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Originally Posted by BSA_WM20
replaes those round pins with real woodruf keys the fill the 1/2 round slots. These hold the magneto square to the case...
While that sounds like a good modification, it won't necessarily solve the problem. The keys have to be narrower than the slots to allow for fore/aft movement (with respect to the engine) to get the correct mesh of the gears so the Woodruff keys can't actually hold the magneto square to the case. Some small amount of twisting motion is possible because of the difference in sizes which means only the front or rear edges, rather than than the flat sides, of the Woodruff keys can make contact with the case if it's not properly bolted down. If that happens they'll "eat" into the case just as the round pegs did.

SpencerAZ -- check your PMs.

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Anyone know how to get this clutch sleeve off? I'm trying to get the gearbox out, but hit a dead end. Got the cush drive off easy, but I can't see a solution here.

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See the fine threads on the end of it? There is a puller that screws onto it so you can pull it off the taper on the shaft. Check this link out.
http://www.ebay.co.uk/itm/61-3362-BSA-6-SPRING-CLUTCH-EXTRACTOR-TOOL-B31-M20-A10-ETC-/371463089595?hash=item567cecedbb:g:rC4AAOSw37tV~BPi

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Originally Posted by B31 Ally
See the fine threads on the end of it? There is a puller that screws onto it so you can pull it off the taper on the shaft. Check this link out.
http://www.ebay.co.uk/itm/61-3362-BSA-6-SPRING-CLUTCH-EXTRACTOR-TOOL-B31-M20-A10-ETC-/371463089595?hash=item567cecedbb:g:rC4AAOSw37tV~BPi
Ah! It's always a special tool. Am I going to have a similar issue getting the cush drive on? That spring is impressively strong.


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Mr. Spencer,
You're gonna want to break my fingers but...
What's up with the bronze rod stitching in that case?

I'm positive that the heat generated from that sort of repair attempt has distorted your case.
Actually that is the first time I have seen bronze rod used on aluminium, and the only way it could possibly stay attached is by wicking into the crack, and hanging on by interference rather than a melding of materials.

My vote is for removing that engine from the frame, and... working overtime for a few months to pay for it.

The hit list of must do's is growing.

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