The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: coater87 on 20.05. 2009 14:43

Title: Sintered bronze or leaded bronze?
Post by: coater87 on 20.05. 2009 14:43
 Guys,

 I have looked at the specs for the timing side bush and its well within my lathe size limit, so I am able to make my own. Now the problem comes from exactly what type of bronze to use-- there are lots of types but this sintered (oil impregnated) bronze keeps popping up as does leaded bronze (sae 660).

 Can anyone make a recommendation for the sintered bronze, or heard of anyone using this? How about the leaded? Any other type that is better, and available for the home shop machinist in small quantity?

 I know this is off the wall, but the price on a bush (that I can make) is about $50.00, and thats 1 inch long. Or, I can buy a 1 foot bar of the stuff and make my own for about $13.00 (and have extra to screw up during reaming!).

 Also, as I need the crank ground here in the US, could someone give me an idea of cost? Big ends done and timing side skimmed, if its real high, I may be able to weazle my way into a local shop after hours and have a go at it- they wont touch a crank but do have the equipment for it- but that might be dicey.

 Have even looked over a timing side conversion, and have just bought a spare timing side case to play with- I do believe this is outside the size envelope of my small miller though and cannot find a decent "how to" with enough good pics and accurate (not enough info to be comfortable) information.

 Thanks,
Lee
Title: Re: Sintered bronze or leaded bronze?
Post by: MikeN on 20.05. 2009 15:23
Ive made them from solid leaded bronze. I dont fancy sintered bronze .I feel it may extrude under load? maybe thats Just me but it appears to be very low  strength.If you used sintered i would think a steel backing would be needed. You can buy it in bar form or ready made bushes that could be adapted if nessasary.
  Leaded bz is an excellent bearing material and it is useful if the shaft running in it is soft or hard.Phosphor bronze  really likes a hard shaft. dont know how hard a BSA c/shaft is .
  I once pulled apart a C15  that had a knackered sintered main bearing but that could have been a pattern part ,and ceefies arent exactly renowned for their bottom end  longevity.
Mike
Title: Re: Sintered bronze or leaded bronze?
Post by: fido on 20.05. 2009 17:15
Apparently the very early A7s used a white metal bush, I don't know if they were reamed or scraped in some way. Not a suggestion, just a point of interest.
Title: Re: Sintered bronze or leaded bronze?
Post by: beezalex on 20.05. 2009 17:20
I have used SAE 660 (also known as Alloy 932) in this application with good results.  It is a cast bronze with good self-lubricating properties and a high PV and it is easy to machine.  Sintered bronze has a lower PV and generally lower load capacity.  I think this makes it unsuitable in this application.
Title: Re: Sintered bronze or leaded bronze?
Post by: A10Boy on 20.05. 2009 17:41
If you do a search in the forum there are lots of discussion threads on this.

Apparently, one of the types of bronze wears the crank more than the other, but I dont remember which one it is.
Title: Re: Sintered bronze or leaded bronze?
Post by: BSA_54A10 on 21.05. 2009 01:20
In places that speak proper english the material is called "Leaded Gunmetal" and you should be looking at something around the 85/5/5/5  (5% each of tin, lead & zinc ).
My ASTM books are buried in a pile of boxes that I am yet to unpack but I think that 660 will be in the general ball park.
Sintered bronze is not particularly good for high load application and I would not trust that it was a closed sinter and would not leak oil.
Sinters go better in places where they are immersed like gearboxes.

You could also go for a leaded phos bronze which will be a little harder than the 85/5/5/5 but it is a bugger to machine whereas the gunmetal machines beautifully and will take a mirror finish .
Title: Re: Sintered bronze or leaded bronze?
Post by: 69Bonni on 21.05. 2009 14:43
Hi Lee, Guys

Take a look at Beeza bills site..... timing side roller conversion this might give you a greater insight to the conversion simular to Devimeads.

http://www.geocities.com/beezabill/mybsaa10rollerconversion.htm

Very interesting but havnt been brave enough to try it yet, perhaps i'll pick up some spare crankcases for a try!

Kind Regards

Steve