The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: magicflem on 06.06. 2017 04:54
-
The engineer I am using has line bored/reamed my crank bush and the cam bush, but not aligned them to the idler pinion between (cogs don't mesh, just jam) - I don't know if the magneto cog will mesh either.
In what order should he have bored/reamed?
I would have thought:
1st. line bore crank shaft using roller bearing (drive side) as setup for the brass bush on timing side. This has to be centred, at right angle, parallel etc, and everything else works from this setting.
2nd. fit magneto with cog.
3rd. line bore cam and idler to "mesh with" magneto and crank cogs.
Am I right?
-
This is very odd. Normally I reckon just the timing side bush is line bored without consideration of the timing gears etc, and yes one "reference" is ideally the cylinder base, I'm not sure on the other axis but the journal housing should do, and if used should near enough maintain gear mesh.
On the cam side, I would expect the rhs journal housing to be used as the reference and any misalignment to be compensated for by boring the lhs bush off centre. Again this job is often done without consideration of anything else. This job is tricky for an engineer and there might be a temptation to bore the rhs bush off centre, not lhs?
Are your cases non matched? This can cause an engineer a few issues to resolve if so.......on mine even the barrel bottom face was curved!
Non related possibly, but I bought a new ally mag gear and had quite a bit of fettling to do to make it mesh correctly.
-
You may have needed one of these, if you can find it.
-
How bad is the meshing, is it just "grindy" or is it actually jamming solid?
-
Hi,
The engineer I am using
has made a Boll*x of the job *problem* *angry*
It is unusual to have to renew the cam bushes, they seem to survive all sorts of blow ups and neglect and still be ok
Check the magneto to cam mesh and see if thats ok?
If it is, and the cam spins freely with the cases bolted up,
I would remove the crankcase idler bush and see if its concentric inside to outside or not ?
This is the easiest to remove and check , it may need "adjusting"
The inner timing case idler bush finally must be concentric in its bore with its partner in the crankcase
The original jig worked the cam bushes from the timing side, so I would have followed that method
2 cents worth
John
-
After speaking with one of our knowledgeable members I decided to sort of line bore my new plain bush, locating the reamer accurately from the drive side bearing outer.
By a complete stroke of luck some time ago I was given a brand new adjustable reamer and a large lump of brass which was used to make the bush / reamer guide.
I also made a plug gauge with three progressive diameters to assist in getting the correct size.
Long story short, it seems to have worked; on assembly, the crank turns smoothly, and a light covering of engineers blue on the journal showed up its evenly in the bush. Obviously, proof of success or not, will only show when the engine is run, and as you can imagine, I'm crossing everything I've got! On the crankshaft drive side where the shims locate, I noticed a ridge which was preventing the shims from sitting flush, so I also set the crank up accurately in the lathe, removed the ridge and lightly skimmed the web to provide a good, smooth surface. Preliminary assembly is showing end clearance at 0.0015". Final assembly will start when I get the Wellseal I've just ordered.
-
Congratulations. My only attempt at using an adjustable reamer, a very long time ago, resulted in a total horror. Well 2 horrors in fact - small end bushes.
Perhaps one day I'll have the courage to try again.
-
As mentioned, I was sort of encouraged to give it a go by someone who had done it himself. Prior to biting the bullet, I approached a number of engineering companies that listed line boring as a service, but they all referred me to some-one else who didn't want to do it either, so the die was cast. I knew I was risking an expensive bearing, but I also knew I wasn't going to bugger the cases up, so I took the chance. It remains to be seen if it pays off. When I bought the bike, I expected to be able to use it from day, but it hasn't turned out that way, and one thing leads to another...... my trouble is I can't leave anything alone - hence machining the crank web and clutch centre housing.
It's a disease, I'm afraid. A bit similar to believing that one Moto Guzzi is enough!
It isnt😄
-
On the crankshaft drive side where the shims locate, I noticed a ridge which was preventing the shims from sitting flush, so I also set the crank up accurately in the lathe, removed the ridge and lightly skimmed the web to provide a good, smooth surface. ..............
I really think you should not have done that. .. *bash* *bash*
-
Dutch,
I'm assuming Zander means he just skimmed at the shim landing area, not the whole web.
Zander,
Am I correct?
Richard L.
-
I'm assuming Zander means he just skimmed at the shim landing area, not the whole web.
The way I read it is that zander skimmed the ridge back to flush with the web- maybe I was wrong, and it was just a skim to make it still a raised landing with no run-out *????*
-
Yes- I removed the ridge and skimmed the shim locating surface which cleaned up within a couple of thou. The crank shaft was clocked on both journals and both ran within half a thou at the start of this operation. I was happy with that.
-
If the web is machined I think the main point is not to remove the stress relieving radius between it and the drive shaft and introduce a possible fracture point.
-
Thanks Julian, now I think I understand why radius is important.
-
I stopped short of the radius for the reasons outlined.
-
Ok, not as extreme as I thought- I'm no engineer, but maybe you needed to go further and feather it into the radius to ensure that the bearing inner face isn't mating on just that small corner (?). The bearings (should) have a complementary radius so you may be lucky
-
Bear in mind that the cut I made is only a couple of thou deep, so I've barely touched the web face, and the tool I used was also radiused, so no sharp corners to create a stress point. The original radius machined on the journal is fully intact and untouched, and the rad on the bearing clears both. The crank is currently temporarily fitted in the cases, and when I take it apart, I'm going to treble check everything I've done prior to the rebuild.
-
I hope that the "lump of brass" was in fact the correct grade of bronze.
-
I stopped short of the radius for the reasons outlined.
Good job.
People really don't seem to understand how important that little radius is. When a shaft snaps 99 out of 100 times it's going to be at a shaft size change. That little corner is where all the stress is, the radius spreads the load. If it that corner is left sharp when it is machined, all the stress is concentrated in that one tiny spot.
-
As always, lots of sensible and constructive comments re what I've done to the crank and cases. As mentioned previously, I knew I wouldn't wreck the crank case by boring the bush myself, the worst case scenario would have been another bush and get it done by an engineering company. I have a toolmaking back ground, and everything I've done was considered carefully beforehand.
The reason I very lightly skimmed the shim location area was because the new shims sat on a ridge which locked the crankshaft when, after taking precise measurements I knew that should not be the case. once the ridge had been removed, using the same size shim, the crankshaft ran smoothly. I was aware of the importance of leaving the radius intact.
Regarding the guide I made, fortunately the reamer has an accurately ground long shaft, so the brass bush was machined to fit very snugly into the drive side bearing outer, with the reamer guide hole being accurately bored to size, thus ensuring concentricity between the two locating areas. I did, however allow a couple of thou clearance so that the shank of the reamer would allow me to turn it without the risk of it seizing up in the bush. The bush was made from brass cos that's what I had in stock, in my view, perfectly acceptable as it's just a guide for one off use -nothing is going to "run" in it, so no need for phos. bronze. Just my opinion. If the shank of the reamer had been beaten up through use, I wouldn't have considered doing it, but as it was brand new and unused, everything was on my side. Also, as prev. mentioned, the assembly appears to be fine but I'll only know if it is when I start using the bike. All in all, I'm reasonably content as to the soundness of the work, but if I've buggered it up, it's my own fault.
-
To be honest, my concern was not so much for the radius, but moreso the 'shim/bearing interface'; reason being is the crank I'm running had been butchered before it came to me- which is probably why it came to me *rant*, and I'm tesky about this stuff
The ^^ 'shim/bearing interface' ^^, on my crank was/is not there...in fact worn in the negative to the tune of a few thou *conf*, and the crank spindle where the roller bearing mounts was worn down like it had spun in the bearing...so I had this sleeved (with a 'radius'- not ideal), to accommodate a standard roller bearing. All this was back in the the initial build in late '70's when parts were super scarce (but still unsure if they more scarce then or now)...
I'd forgotten all this until 5-6 years ago, when rebuilding and doing the end-float, the sleeve came loose...by this time, I'd already sussed the fact that the ^^ 'shim/bearing interface' ^^, on my crank was/is not there...but already had the crank re-ground to suit the new Thunder Rods.
So without getting long winded, basically I installed a shim to pack out the 'negative interface', and came to a starting point.
It's been running fine thus far for four years/10K miles, until the Maggy shat itself the other week so have fingers crossed and just need to remember to source a replacement crank. (I do have a couple, but also need 'work' *work*)
I hope yeas get the drift *????* *????*
-
Hi Zander,
Now I fully understand where you are at.
Basically you made a guide bushing for an adjustable reamer and used it to ream a new timing side bushing. That should work great.
The only thing that might have been better than that set up is a Sunnen hone for the bushes. But than that depends on a lot of variables too, like how good are the stones, how clean is the cutting oil, and especially how good is the operator and how well does he know that particular machine.
In my younger days I used one of those quite a bit to ruin otherwise perfectly good parts. There is quite a knack to using one correctly, and being able to hit the size with a desirable finish and not have holes that are shaped like an hour-glass.
-
relax zander, its quite common for screwdriver damage on the the surface above the radius, normally on the drive bearing side . i always use a large adjustable reamer with a thimble to pick up the drive side bearing. no problems other than time consuming as i set the bush clearance by feel with the cases bolted together.
-
I WAS relaxed! The comments from more experienced BSA owners on here have simply caused me to re- examine what I've done to my engine, which is no bad thing.
Yesterday, I checked the radius using an eye glass and am satisfied its ok. One way or another, it's going back in the engine, and I'll have to live with the results! All this for a few thou end play! I wonder how I could replace the plain bush with bearings.......... *smiley4*
SRM mod at £530?