Engine Bush Reaming Setup

[duTch]

 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

[Zander]

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.

[trevinoz]

I hope that the "lump of brass" was in fact the correct grade of bronze.

[coater87]

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.

[Zander]

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.

[duTch]

 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 , 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 , 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'  )

 I hope yeas get the drift 


 

[coater87]

 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.

[edboy]

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.

[Zander]

 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..........
SRM mod at £530?