Author Topic: Timing side bush  (Read 875 times)

Offline KeithA

  • A's Good Friend
  • ***
  • Join Date: Oct 2015
  • Posts: 51
  • Karma: 1
Timing side bush
« on: 15.01. 2016 04:39 »
I'm making up a lead bronze timing side bush. If I machine the outside 0.001" interference fit (larger than the boss) and then the internal diameter 0.001" larger than the recommended clearance of 0.0015" - 0.002" Do you think the bush would stay closed up that 1 thou when I shrink it in the freezer, and then drop it into the crankcase boss when the crankcase is warmed up, or is it likely to expand back out to its original dimensions.
Keith

Online KiwiGF

  • Last had an A10 in 1976, in 2011 it was time for my 2nd one. It was the project from HELL (but I learned a lot....)
  • Wise & Enlightened
  • *
  • Join Date: Feb 2011
  • Posts: 1933
  • Karma: 17
Re: Timing side bush
« Reply #1 on: 15.01. 2016 05:49 »
Hi Keith, are you planning to line bore the bush after fitting it in the case? I ask as that is the generally accepted way of getting maximum life out of them, and that would possibly make the answer to your question academic.

However I reckon the amount of inter fence fit on the o.d. Will be how much the I.d. Will be reduced after fitting, I don't think the case will be expanded by the bush in other words
New Zealand

1956 A10 Golden Flash  (1st finished project)
1949 B31 rigid “400cc”  (2nd finished project)
1968 B44 Victor Special (3rd finished project)
2001 GL1800 Goldwing, well, the wife likes it
2009 KTM 990 Adventure, cos it’s 100% nuts

Offline KeithA

  • A's Good Friend
  • ***
  • Join Date: Oct 2015
  • Posts: 51
  • Karma: 1
Re: Timing side bush
« Reply #2 on: 15.01. 2016 07:48 »
Thanks for your reply, Well I have just finished boring out the bush as we speak.
My journal is not out of round, and I have 2 thou clearance on the ID.
I have made my bush half a thou bigger on the OD, than the worn bush I removed, and that was a little bit tight to drift out, so I am interested now to see how much clearance on the ID I will have when I drop it into the boss. I'm hoping my timing side bush will work as it is, but I am aware that it may need line finishing relative to the roller bearing boss on the other side.
From reading on the forum, I need to maintain a minimum of 0.0012" clearance. I only have 0.001" and 0.0015" feeler gauges, so I should succeed I think.
Keith

beezermacc

  • Guest
Re: Timing side bush
« Reply #3 on: 15.01. 2016 09:07 »
Hi Keith. I get my bushes made by Alpha. Their set tolerance on the o/d is about 2 thou over and about 1 thou under on the I/d. what you need to be aware of is that when you shrink the bush in the case it may distort out of round so you need to leave yourself enough spare material to line bore back to round.

Online KiwiGF

  • Last had an A10 in 1976, in 2011 it was time for my 2nd one. It was the project from HELL (but I learned a lot....)
  • Wise & Enlightened
  • *
  • Join Date: Feb 2011
  • Posts: 1933
  • Karma: 17
Re: Timing side bush
« Reply #4 on: 15.01. 2016 23:34 »
I've no direct experience of making a bush , a machinest did the job on mine, but it seems to me it would be best to leave more than 001 under size to allow for line boring? As I understand it one of the reasons for line boring is to cater for cases not having the 2 main bearings axially aligned and 001 would not allow much metal to be removed during line boring, should the cases be more than a few 000 out.

I think you can also take getting it to the next level, as my machinest did, by line boring parallel to the bottom cylinder face as well, but the more "blue printing" one does...... the more $$$$$$ I guess!

My machinest also (line) bored out the plain bush housing in the crank case as it was worn oval, he reckons they nearly all are nowadays, this means of course a standard bush cannot be used and a one off has to be made anyway, he makes them in steel with a suitable bronze liner to keep the cost down at the next rebuild by just replacing the liner (not that he sees many of those he says as if you get the job done right it will outlast the owner!) it also enabled him to get the mains almost perfectly aligned in all directions leaving little left for the line boring to do in the way of achieving perfect alignment. He has a ready made jig for doing the line boring so it's no extra work for him to use it anyway.

As your bush I.d. did not shrink much when fitted I suspect the housing was not round, which I realise is not what you wanted to hear (sorry) but I applaud  *respect* you having a go at this job and if I had the equipment (eg a mill and jigs) and skills I would also give it a go  *bash*

I realise these are just opinions and there are many on this topic and what's best in each case depends on the state of the components ....my cases were not a matched pair so I opted to have the "full monte" job done and I'm lucky as the local machinest guy we all use is incredibly cheap whilst also experienced in this sort of work, particularly on a10's.

New Zealand

1956 A10 Golden Flash  (1st finished project)
1949 B31 rigid “400cc”  (2nd finished project)
1968 B44 Victor Special (3rd finished project)
2001 GL1800 Goldwing, well, the wife likes it
2009 KTM 990 Adventure, cos it’s 100% nuts

Offline The Artful Bodger

  • Moving Up
  • **
  • Join Date: Dec 2013
  • Posts: 31
  • Karma: 3
Re: Timing side bush
« Reply #5 on: 16.01. 2016 10:22 »
I had a problem with a lead bronze bush, not sure if it was down to the bush or the 'ole being oval or over sized. The original bush was a tight press out and the new one seemed a nice fit but...... I line reamed the bush and was happy that it was nicely in line but after around 700 miles I realised that the vibrations just weren't right.
 On stripping the engine the bush came out with the crankshaft, it had been rattling in the crankcase. I did some checking on the internet and found reports that lead bronze while being a good material for bushes did expand a lot if there was enough mass. So did the expansion of the bush open the crankcase? Or was there a problem in the first place with the 'ole itself??
  I was able to bore out the crankcase on my small mill and made an over sized bush with a steel shell, I used phosphor bronze as I had a piece kicking around. I made the bush so the thrust face was bronze and over sized so it went beyond  the damage done to the locating flats in the case made by the rattling bush. The steel shell was just over where it goes inside the crankcase, this prevented any problems with the bronze turning in the steel without having to peg it.
  I had 2 thou on the OD and left 10 thou ID to allow for any slight misalignment when I bored the case out. I used a local engineering company to line bore it in case of any misalignment but apparently it was alright.
  I've only done just over 4000 miles since and all is well so far. My hind sight thinking is, why did BSA go to the extra expense from new of using a steel shell instead of a solid bush here? They must have had expansion problem in mind me thinks? Although I'm sure there's many people running around out there using solid bushes, personally having been bitten once I'll stick to steel shells.
Colin