The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: coater87 on 08.08. 2009 19:54

Title: re-sleeve T/S bushing
Post by: coater87 on 08.08. 2009 19:54
 Guys,

 I was working on turning a new T/S bushing, when the thought hit me about re-using the original metal cage- and just turning the sleeve inside. Now I noticed this is pinned to stop it from rotating.

 My questions are, is re-using the metal cage a do-able idea (or a good idea at all), and if so how do you remove the pin from the cage without doing damage to the outer housing?

 Anyone actually ever do this, or know of someone who did?

 Thank you,
Lee
Title: Re: re-sleeve T/S bushing
Post by: muskrat on 08.08. 2009 20:29
G'day Lee,
              a friend of mine bored the bush out 15thou and coated it with white metal, then reamed it to suit his 2thou under crank. This was 20 years ago and it is still in service.
Cheers.
Title: Re: re-sleeve T/S bushing
Post by: trevinoz on 08.08. 2009 22:26
Lee, the dowel, or pin, will push out and can be reused.
Trev.
Title: Re: re-sleeve T/S bushing
Post by: coater87 on 08.08. 2009 23:30
 Thanks Trev and Muskrat,

 I am going to give this a try and I will let everyone know the out come. Hopefully it works well as it would save a bit on the bronze and quite a bit on the time needed to turn a full bush.

 Lee
Title: Re: re-sleeve T/S bushing
Post by: Josh Cox on 09.08. 2009 04:40
Coater,

I have had exactly that just done, took the old bush ( metal outer copper inner ) to a machinist, he machined out the old centre and replaced it with a shiney new piece of PB, make sure you loctite the new inner inplace. (this guy has done lots of these, he reckons the pinning is not required).

Leave plenty of material there so you can later ream to the crank OD after crank grinding.
Title: Re: re-sleeve T/S bushing
Post by: coater87 on 11.08. 2009 14:10
 Guys,

 That went pretty well. I had a little trouble removing the old bushing, but the pin popped right out- I just had to find it afterward.

 I turned the insert from LB, I made it 1/2 thousandth oversize. I heated the cage, used a little lock tite, and will reuse the pin. Probably over kill, but this is the first time I have done this and want to be sure its OK. I had my reamer resized, it will never ream 1.5 inches again, but it will ream any size T/S bushing comfortably.

 I still have to drill for the oil and pin, but I left .040 for reaming later. Its a lot and will take some time, but I have no idea how square the bushing will go back into the case. Now I just have to make a guide for the drive side, and ream till my arm falls off.

Lee
Title: Re: re-sleeve T/S bushing
Post by: orabanda on 11.08. 2009 14:35
Hey Coater87,
Good work; well done!
Just a suggestion; don't use that reamer on your bush!
The process will not be accurate enough. I am pretty sure that by the time you have reamed it enough for the crankshaft to rotate freely through 360 degrees, there will be too much clearance between the bush and the journal. Also the surface finish will only be average.

I suggest you (literally) drop the bush in the crankcase half (after heating crankcase in mum's oven to 250 C). Then, find a machinist with a borer, and request that he clocks off the machined bore for outer race for the LH (primary side) bearing.

Then he should machine your bush to give 0.0015" clearance on the timing side journal, and it will be hunky-dory!

Make sure:

He doesn't clock off the crankcase half mating face (the crankcase bearings might not have been machined at 90 degrees to this face)
The timing side crankcase journal has been ground  and linished in a crankcase grinder beforehand.
 Regards,
Richard

Title: Re: re-sleeve T/S bushing
Post by: coater87 on 11.08. 2009 15:21
 Hi Richard,

 I would think that turning a guide bush for the drive side (that fits the reamer), bolting the cases together and then reaming would get me to where I need to go. I have found a complete lack of help from local machine shops, most of these guys are high production and seam unwilling to except one small job like this. I live in a foundry area, and I guess that should be expected.

 I have found in the past that I can greatly increase the finish using an expandable reamer. I make quite a mess, but it works well. To remove the harmonics (which cause the chatter), I first pack the cutting end of the reamer in very thick grease, then I wrap the whole mess with wax paper. The finish will be a mirror of the grind, and if done very slow feed/speed, its a very nice finish.

 And if worse came to worst, I can always remove the bushing, rebuild it and send it off. I would like to give this a try though first. A lot of my own enjoyment with this type of project is doing the maximum amount of the work myself and making things and doing the machining are part that too me.

 Heck, I even feel guilty I had to have the crank ground by someone else- but that type of equipment is beyond my budget, and space. Besides, how many cranks would you have to grind to make it worthwhile! *eek*

 Lee
Title: Re: re-sleeve T/S bushing
Post by: A10Boy on 12.08. 2009 21:33
Theres a chap in the UK who will make a LEAD bronze one piece bush for about £38, I got one and had it fitted at T&L Engineering.

I got his number if anyone wants it.

Andy
Title: Re: re-sleeve T/S bushing
Post by: nigeldtr on 23.09. 2009 20:03
Lee,

As I mentioned, I would like to do the same, how did you get on?
Title: Re: re-sleeve T/S bushing
Post by: BSA_54A10 on 24.09. 2009 11:26
It is not a difficult job even for the home machinist to do.
Just be careful which material you use for the new lining.
We had a long and exhaustive discussion a while ago about suitable alternatives.
I very, very , very strongly recommend 85,5,5,5 leadded gunmetal.
Phos bronze is way too hard and I regard it as playing Russian Roulette with your journal.
Let the oil pressure drop and it will be toast.
Ditto for Al bronze.

As for making a complete new one piece bush from LC or LB , not a good idea, as neither have sufficient rigidity or strength,
Phos bronze dose have the ncessary strength but as already stated I consider it too " unforgving" to be a realistic alternative the the leadded bronzes or gunmetals
Title: Re: re-sleeve T/S bushing
Post by: RichardL on 24.09. 2009 13:58
Trevor,

A question. If the oil pressure was to drop to the point of no film on the T/S bush, wouldn't the left-side big end have left the building long since?

Richard L.
Title: Re: re-sleeve T/S bushing
Post by: A10Boy on 24.09. 2009 19:25
Both probably.

Quote
As for making a complete new one piece bush from LC or LB , not a good idea, as neither have sufficient rigidity or strength

Have you any calculations on this or is this just opinion?

I would imagine the forces at say 120mph, which would be around 8,000 rpm, must be huge?

Title: Re: re-sleeve T/S bushing
Post by: nigeldtr on 24.09. 2009 22:20
From what I can remember, it does not take much oil pressure to keep the crankshaft afloat even at high speed and loading. Provided oil gets into the crank, the centrifugal forces while push any oil out to the big ends with a huge pressure so again provided there is oil pressure at the main journal, things will work, perhaps not optimally from a stress and cooling perspective but there will be lubrication. Unless I am mistaken, (please correct me if I am wrong) the killer for white metal is heat and/or direct friction - running dry from cold after standing for 2 weeks etc. I don't have the materials experience but I would tend to a solid one piece Phos/Bronze bush simply because of the above problems. However, I am equally happy to try as recommended. I will probably only ride 2000 miles a year so what every I do should hopefully outlast me *smile*

Nigel
Title: Re: re-sleeve T/S bushing
Post by: A10Boy on 24.09. 2009 23:41
I just don't like the idea of inserts even if they are glued and screwed. You hear horror stories of them turning and cutting the oil supply.
Title: Re: re-sleeve T/S bushing
Post by: coater87 on 25.09. 2009 01:12
Guys,

 Here is my own understanding of the bronze choices. P/B is harder, as tiny bits of metal begin to circulate through the oil system, these will eventually meet the T/S bush. They will become embedded in both leaded, and Phosphorous bronze. The difference comes in how hard the bronze is- these tiny particles will "mush" into the leaded bronze much quicker, minimizing the nasty lapping effect.

 The P/B being harder, these little metal pieces stand proud of the bush surface much longer, increasing wear to the crank.

 As far as I know about white metal (I would call this babbitt), its "mush" effect is even greater- probably the very best available. Its problem is "dry wear", as mentioned this material gives itself up very easily- meaning at start up every day- and with no way to adjust the bearings (like on a model T Ford) to take up the slack, you need to change these much more often. The up-side to this material is longevity to the crank, there would me very minimum lapping effect.


 Very technical term there- "mush factor"! ;) Anyway, that is how I have come to understand this.

 Lee
Title: Re: re-sleeve T/S bushing
Post by: BSA_54A10 on 25.09. 2009 01:22
Quote
A question. If the oil pressure was to drop to the point of no film on the T/S bush, wouldn't the left-side big end have left the building long since?

Nope, the white metal will retain a lot of oil and take a lot longer than you think to run dry.
Once dry a thin film will melt and allow the journal to run for a lot longer than you think.
The big damage to the steel journal occurs once the white metal has been rubbed through and the journal starts hammering ( there will be a lot of space in there by this time) against the steel back of the slipper.
 
Quote
Have you any calculations on this or is this just opinion?

No numbers, more observations than opinions, leaded bronze bushes need either to be fairly thick or supported by a more rigid material such as steel. You need to understand the metallurgy ( or rather crystalography ) of these materials. The lead sits in the grain boundary region of the material as it is the last bit to solidify and forms a continious marix.
Think of the material as a sponge with really big holes. The hole space is where the copper resides and the cellulose bit is the lead. You would have great difficulty in bending a 2" thick rod of even pure lead where as a 1" thick rod will slump under its own weight.

Quote
I just don't like the idea of inserts even if they are glued and screwed. You hear horror stories of them turning and cutting the oil supply
But that is exactly what was in there in the first place and exactly how the steel backed bushes are made.
If the sleeve can come out & rotate then there are a lot more problems than the bush materials and it is usually caused by not enough clearence between the bush & journal which would have killed a solid bush as well.
Do not confuse the sleeve turning which is extreamly rare with the entire bush turning which is quite (unfortuneatly) common
 
Title: Re: re-sleeve T/S bushing
Post by: A10Boy on 25.09. 2009 13:06
As with all these things its a matter of choice. I'm quite happy with my solid bush, it has a nice solid weighty feel to it and I don't believe there's any risk of structural failure.
I will use one on my next bike / rebuild.

(http://i.ebayimg.com/20/!BVdS(g!!Wk~$(KGrHgoH-E!EjlLl0T+JBKSl0v!O-g~~_12.JPG)