Crankcase alinement

[RichardL]

I think it's safe to say that, even if the numbers match, they are not currently a matched pair. Look for numbers possibly falsified. I'm wondering if a spinning camshaft is enough to trust alignment. Having now personally line-bored a grand total of one timing-side bush, I would want to test the alignment of the drive-side outer race with the timing-side bush. Of course, rebore if needed. After the top and bottom are milled flush and level, I would be working on all the other evidence of misalignment, fairing it out with a Dremel tool, or the like, just for my own satisfaction.

Richard L.

[RDfella]

Whyever not, John? Why should motorcycle engines be any different from other engines? At least the top deck is a flat face (which will be square with the base flange) so you aren't introducing possible errors with multiple parallels to space away from the lower spigot. Never bored a cylinder from the bottom up yet! With the conrod cutaways would be nigh on impossible to centre the boring bar anyway. Remember, my boring bar is portable and so a motorcycle barrel is a bit of a fiddle, needing to be mounted on a plate with the boring bar on the other side.
Pic is of the boring bar in action boring a liner in a Ford diesel. In the 80's I was probably rebuilding one of those motors every ten days.

[tomkilde]

It doesn't look like I have a matched pair of crankcase halves.  In addition to the alignment issues at the barrel & sump faces, someone in the past actually went to the trouble of grinding off the numbers.  That said, the engine spun freely before I disassembled it, and a test with the camshaft just now had it rotating comfortably in its bushings.  Replacement cases with matching numbers are available on eBay for a reasonable price, but I intend to have the faces of my existing cases re-surfaced.

Makes you wonder what kind of event led to the replacement of one half case.  All the internal parts seem to be original, but it's been apart at least twice before.  The crankshaft is on its second grind with -020 bearings, many of the internal threads have been repaired with heli-coils, and the oil seal on the drive side has been re-staked several times.  Is it necessary to do this once again when I install the new oil seal?

Thank you Swarfcut for the tip about the locating dowel.  It is indeed missing, and I had no clue.  There is no mention of it in the Haynes manual, and it's hard to see in the original BSA parts diagram.  I have ordered a new one.

[RichardL]

They probably left out the dowel because it wouldn't fit in the mismatched cases.

Richard L.

[Swarfcut]

  Tom. If the castings are sound then they are worth setting up properly. Another matched set will be cheaper if they are good enough to use with  their existing bushing. If not costs for new bushings, boring etc will be comparable, so the only difference is the machining required to those faces. Also these cases are part of the machines history. In an earlier time what you have here was good enough, and as there is no evidence of major mechanical disaster, it must have been a runner as is.

 The camshaft test is a quick and simple check, sorts out poor cases and banana cams. Saves a lot of frustration when all is assumed correct but the bloody thing locks up solid with the last pull on the spanner. So a good basic starting point.

  Take care with that new dowel. It needs to be a short enough to allow the cases to meet and not hold the joint apart. Common sense really, but as ever the dowel  may be a genuine or pattern part, so never take anything as gospel. The breather cross drilling can be cleaned out while you're there. This often neglected joint must be oiltight, otherwise crankcase compression will tend to vent oil  (rather than oil mist) from the breather outlet.

 Out of interest, does the engine number match the title? Just wondering which half, if any, is the original.

 Swarfy

[Sluggo]

Helloo!!!    I am back checking in, and should probably post up a update during my extended absence,, But thought I would mention, I enjoyed this topic perusing this subject looking up some material for a local guy building a tribute RGS and some others on related topics.
I am ramping up on bike stuff again and will be reconditioning-Blueprinting and Hydroblasting some cases,heads and other extra parts from storage that are excess and selling them.

I hope you dont mind, but I copied & pasted some of the comments and included a link to a rambling-babbling short article I wrote. Anyone reading can see via the link this public forum so, hopefully that was kosher. Good stuff! 

PS, a nice fellow locally is ramping up his hydroblasting business and excited to work with him, plus possibly a video coming soon on "The Mighty Garage" Local Norton club president Mike Tylers Youtube channel.
See: http://vaporhoningpdx.com/
Here is a pix of my neighbor Tonys RGS head just back from this service

[BigJim]

Wellcome back Sluggo, hope all is well. Someone should tell your neighbour that the engine will run better with the valves up the other way but each to their own!
 

[muskrat]

G'day Sluggo.
Good to hear from you again.

Someone should tell your neighbour that the engine will run better with the valves up the other way but each to their own!

And learn left from right  .
Cheers

[chaterlea25]

Hi RD,

Whyever not, John? Why should motorcycle engines be any different from other engines? At least the top deck is a flat face (which will be square with the base flange)

When you bore a car/ marine block the reference is the bottom of the block usually on the centre line of the crank
so boring from the top means you are square to the crank

Old British Motorcycle cylinders cannot be relied on to be square top to bottom is the main reason to use the base flange as the reference, as it is more likely to be parallel to the crank bearings
This may have bee the problem you had with the BSA rebore ??

John

[Swarfcut]

  Back in the day the average street corner rebore shop used the Van Norman portable boring bar, which was designed to bore from the block head face, and on car engines the adjacent bore was used as a location for the machine.

  The same tool was used for motorcycle cylinder barrels, which were mounted on a  dedicated table, but here again from memory the barrel top face was taken as the datum.

 In retrospect, and considering the attitude of the guys in the trade, its remarkable that anything got done with the expected accuracy. We were happy to get the bits back and nail it together again.

 Robert Pursig thought the same, on taking his Honda for service in the good old "Zen and the Art of Motorcycle Maintenance" Came back worse than when it went in. But then it was a Honda....in a US shop.

 Swarfy

[muskrat]

G'day Fellas.
I agree 100% with John. To add further fuel to the fire I also bolt the barrels to a torque plate at the desired value of the base nuts. May be a little overkill but I like it.
Cheers

[Greybeard]

Robert Pursig thought the same, on taking his Honda for service in the good old "Zen and the Art of Motorcycle Maintenance" Came back worse than when it went in. But then it was a Honda....in a US shop.

It's great to see a reference to that book. Although the book gets weird towards the end, (Pursig was having a mental breakdown) he says something that I totally agree with: The gist is, you cannot properly repair something until you understand how it works.

[berger]

I have some barrels at my favourite engineers for re bore so when they are done [which might take some time] I will ask him how he does them just out of interest

[RDfella]

As far as I can see, the argument revolves around whether the base flange is square with the top of the cylinder. Easy enough to check if one is in doubt. The reason I posted a pic of my boring bar was to demonstrate that boring a motorcycle barrel with that requires an interface plate, as Swarfy correctly states. Those adaptors are quite nifty, hinging around a central point so you can seat the barrel then turn it over to mount the boring bar on top. As explained, boring from the bottom would be virtually impossible and certainly not reliably accurate. Point is, if you can't trust the top face then maybe the barrel should be in the bin instead of on a bench. As far as the problem I had when boring my A10, one barrel was fine, the other not perpendicular (with piston marks to verify) so whoever bored it last was the problem.

Add: Just to avoid misunderstanding, I'm not rubbishing referencing from the base flange, only pointing out my boring machine can't do that but had I a static machine where one takes the engine to the machine instead of the boring bar to the engine, of course I'd clamp on the base flange. Logical thing to do. The point regarding motorcycles still remains, though - which of the two faces is most likely to be parallel with the crank? Depends on BSA quality control and what's happened since it left the factory.

[KiwiGF]

Its definitely worth checking the barrel bottom face is flat, both me and a mates barrel were “warped”, mine was found first and resulted in a 1mm or so gap, the engineer made up a plug with one end exactly 90 deg to the bore (and that face bolted to the table to hold the barrel) and the diameter made to fit exactly in one bore to aid in milling around the flange face (a small area needed filing by hand as the milling tool could not reach it).

The cost of making up the plug was not passed onto me which a couple of years later proved a good call as a mate encountered the same issue with his A10 barrel and the tool got re-used.

As far as I can tell getting cranks and barrels lined up perfectly is not easy (and probably too expensive) to do so you end up with a “compromise”.

The fixing of the barrel revealed the (lined) bores on my barrel were slightly tapered, slightly not parallel, and not perpendicular to the top (or bottom) face! On his recommendation I did not try to get all that “fixed” but that did mean he had to make a “judgement” call on which reference to use when machining the bottom face.