Author Topic: Crankcase alinement  (Read 459 times)

Offline Peter in Aus

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Crankcase alinement
« on: 02.11. 2019 00:14 »
I have 3 sets of crankcase’s and was checking them out; as I understand it the timing side face should be square with the barrel mounting face, all 3 are not, about 1 deg. out, as near as I can measure it.
Am I correct in this assumption or is the barrel face just machined parallel with the crankshaft?
Peter.
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Offline duTch

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Re: Crankcase alinement
« Reply #1 on: 02.11. 2019 08:21 »

 Maybe they were all machined friday arvo and no-one checked the mill-rig for square for a while....I'da thought the side faces should be square to the barrel interface, which obviously should be parallel to the crank... *conf2*
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Offline Swarfcut

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Re: Crankcase alinement
« Reply #2 on: 02.11. 2019 08:50 »
 Hi Pete. Needs the production engineer's thoughts, or some idea of how castings were originally machined. In other words which face is the datum from which all other machining is indexed.

 If a camshaft freely turns in a pair of otherwise unknown cases, then for me the alignment is OK and the cases are worth proceeding with as regards further restoration.

 In practice I doubt whether most folks even consider the 1 degree error, and just bolt it all back together, unless you have been searching for the source of some strange wear pattern or seizure in which case congratulations on finding something amiss. Providing the cylinder base face is parallel to the crank axis, all should be fine, the timing face is of no consequence.

Like duTch, I would assume the timing face would be the start, being the largest stable facing to enable the casting to be secured. Time to dig out the old archive films.....there may be this very machining operation featured.

 Reminds me of the story of the Norton Plank, an urban myth which may be familiar to some.

Swarfy.
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Online BSA_54A10

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Re: Crankcase alinement
« Reply #3 on: 02.11. 2019 09:05 »
We are talking about 50's production line technology.
The engine can handle a 1 deg slope, in fact I would be surprised if any were dead true.
Very few barrels are bored dead parallel either.
Now days when we happily spend 200 hours putting an engine together things are different but back then they were making 100 a day so near enough was good enough.
We have the luxury of digital read outs accurate to .0001" and if it is a really good machine 0.00001".

hen I got the M20 relined Master rebores asked me if I wanted the new liner true to the head or the flange as what was in there was true to neither.
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Re: Crankcase alinement
« Reply #4 on: 02.11. 2019 10:38 »
Very true, Trevor.
Being as the vast majority of boring I’ve done (as part of my rebuilding work) has been on automotive or marine engines, I’ve always set up on the cylinder  / head face. Did that with the few motorcycles I’ve bored as well, when really it would be best to bore those from the cylinder / c’case flange. Just habit, I guess – plus it’s easier. Last one I did (my A10) I came across something I’d never seen before. Cyl was + .020” so I bored to + .040”. First cyl was fine, 2nd one ran off to one side to the extent it didn’t clean up. In hundreds of bores over many decades that was the first time I’d seen that. Clearly whoever bored it previously – and maybe the factory before that, though more unlikely – hadn’t set up properly. Naturally I thought it my fault – perhaps I’d allowed some crud to get between the cyl face and the boring plate, but further checking proved not. Regardless, I had to bore both again, this time to + .060”. Damned nuisance, as I had NOS Hepolite pistons ready. Had to get modern rubbish pistons instead - and + .060” were hard to find.

Whilst that was an extreme example, I think sometimes we expect too much from yesterday’s production lines. People tend to think manufacturers make things as well as they possibly can. Wrong, to do so = more expense = less competitive v other manufacturers = going out of business. The aim is to make as cheaply as possible, ie just good enough. Materials chosen are the cheapest capable of doing the job. Tolerances are as wide as possible, as that takes less time and ensures fewer rejects. For example, we like our conrods and crankshafts clean and polished. When I first worked on an American v8 (car engine) in the 60’s I was surprised to find the crank was so rough I had to be careful not to cut my hands on the flash. Yet that engine ran smooth as silk. Take a look at Jaguar XK conrods – a rather spindly and very rough casting yet those engines run smoothly, perform well and I’ve only ever known one rod exit the crankcase – and that was while racing.
I think many people restoring this type of machinery expect too much and go too far. Different if you’re building a race engine, but entirely unnecessary for ‘cooking’ engines that will usually only henceforth do limited, gentle mileage. Unless you’re fitting a billet crank and Carrillo rods, why work to a tenth when building an engine?
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Re: Crankcase alinement
« Reply #5 on: 02.11. 2019 20:04 »
I have 3 sets of crankcase’s and was checking them out; as I understand it the timing side face should be square with the barrel mounting face, all 3 are not, about 1 deg. out, as near as I can measure it.
Am I correct in this assumption or is the barrel face just machined parallel with the crankshaft?
Peter.

From memory my “specialist” machinest worked off the crankcase barrel face, and took a “mid point” on the timing side main bearing housing in the other plane (rather than work off the timing face), the housing was machined bigger as it was oval, a one off oversized main bush made up, with steel outer liner, which can be relived with bronze if ever needed. He used a mill indexed off the drive side main instead of line boring. The cases were mismatched (the resultant sump and barrel faces “step” was fixed), so the cam bearings were bored in line as well. He reckons the mains in the a10s are generally lined up even in mismatched cases, but the further out bearings don’t line up well.

The hardest part of the job was fixing the barrel which I got honed out and the top/head faced off elsewhere by a non bsa specialist. When asked I said do the facing off square to the top face, after that I found the bottom barrel face was warped by over a mm.

 My bsa machinist fixed the barrel by making up a large plug that fitted the bore (it had to tapered slightly to fit accurately!) and then bolted the plug to the mill bed and sliding the barrel over it, then only then was able to machine the Bottom face flat and square to the bore, he had to manually file a small section as the milling tool could not get to it (my thick flange barrel is not so thick anymore!).

Effectively my engine is now mostly “blue printed” but there are many ways of doing the job, and the more accurately you do it, the more it costs!

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Offline Peter in Aus

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Re: Crankcase alinement
« Reply #6 on: 03.11. 2019 00:23 »
Thanks everyone for your input, I think I will not worry about the 1 Deg.
All the cases are mismatched so will have to be alined bored and the camshaft bushes don't line up to good, so that has to be sorted to. I'm building up a A7 SA engine from scratch, having lots of fun. *smile*
Peter
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Offline Tomcat

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Re: Crankcase alinement
« Reply #7 on: 03.11. 2019 05:38 »
We are talking about 50's production line technology.
The engine can handle a 1 deg slope, in fact I would be surprised if any were dead true.
Very few barrels are bored dead parallel either.
Now days when we happily spend 200 hours putting an engine together things are different but back then they were making 100 a day so near enough was good enough.
We have the luxury of digital read outs accurate to .0001" and if it is a really good machine 0.00001".

hen I got the M20 relined Master rebores asked me if I wanted the new liner true to the head or the flange as what was in there was true to neither.


I once read that Peter Brock (#1 race car driver Down Under) got all the perfectly bored 308 blocks, the rest got bigger or smaller pistons to fill the holes and were fitted to the punters cars!
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Offline ironhead

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Re: Crankcase alinement
« Reply #8 on: 03.11. 2019 07:25 »
I have 3 sets of crankcase’s and was checking them out; as I understand it the timing side face should be square with the barrel mounting face, all 3 are not, about 1 deg. out, as near as I can measure it.
Am I correct in this assumption or is the barrel face just machined parallel with the crankshaft?
Peter.

All the above comments plus..If the 1deg. is in the forward / aft plane = no problem. If it is side to side it will need fixing otherwise the barrel will be tilted.  The only datum point worth starting from if machining is required is the mating face of the right side case.  Set this up on a good milling machine then "clock" the timing face to see if it is true or not.
If it is, this can then be used as the Datum. If not then a very light lick can be taken off to make this surface parralell to the inner face. A starting point is now established. Most machining ( if required) needs to be done with the timing side firmly fixed to the milling bed.  Once the left hand case is fitted, use the left hand main bearing as a datum to check if the R/H main is in line. ( The hole will most likely need to be trued up). The barrel & sump faces are next. ( best done on a horizontal milling machine of known good accuracy) The only starting point here is the original R/H barrel mounting flange but a 1 deg. fore/ aft is no problem, the 'tilt' can be rectified though. With mis-matched cases a bit will have to be taken off. Same with the sump surface. Once this is done the cam bush hole will need to be line bored true to the right side.
A fair bit of messing around with mis- matched cases but it can be done & they should be at least as good as they were new.
 PS :  plunger cases are a bit more fun as the gearbox mounting flange will need to be matched up as well. *work* *work*
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Offline BSAmoto

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Re: Crankcase alinement
« Reply #9 on: 26.11. 2019 23:01 »
I have to align Vincent and Norton cases often. I fit a dummy crankshaft in solid bearing substitutes in the cases, rest the shaft on posts on top of the milling machines table and take a flycut over the crankcase mouth - thus getting a perfectly true base for the barrel which will now rest at the correct rectangle  to the crank on the cases. So if the barrel is machined resting on his bottom flange all should be well.

cheers, Harty
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