Author Topic: Timing Side Bush  (Read 483 times)

Offline fido

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Timing Side Bush
« on: 28.03. 2020 10:56 »
I have had my 1948 A7 since 1995 but took the engine apart for the first time a couple of weeks ago. When I split the cases I was expecting the crankshaft to remain in the timing side case as I had not yet removed the timing pinion. What actually happened was the crank came out of the timing case half, leaving the pinion and bush on the crankshaft. There are some witness marks to suggest that the whole bearing has been turning in the cases. It is the 2 piece type bush but it is the steel part that looks to have turned, I have read in other threads here that sometimes the bronze part gets detached from the steel outer shell. I might be mistaken, it could be something like chatter rather than rotation. At the moment I don't have a way of posting photos. I used to use Photobucket but just tried to log in and they say I have exceeded my allowed storage capacity.
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beezermacc

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Re: Timing Side Bush
« Reply #1 on: 28.03. 2020 13:24 »
Presumably your 1948 A7 is a longstroke. If the bush has actually turned in the crankcase half it may be necessary to have a special, solid, bush made which is a few thou bigger than standard. Hopefully your crankcases won't be damaged but this would need checking out very carefully before getting a bush made. The two-piece type do often separate and cut off the oil supply but you say yours has turned as a whole. I'm not sufficiently familiar with longstrokes but can state that the later A7 and A10 crankcases have cast flats and flats on the bushes to prevent this happening. You may be better off getting hold of some second hand crankcases. Even though they are quite rare they don't usually command a very high price. A further suggestion would be to put a post-1950 engine in it which would be superior to the longstroke but obviously the bike would lose its originality.
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Offline Swarfcut

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Re: Timing Side Bush
« Reply #2 on: 28.03. 2020 13:41 »
fido  If your engine number is higher than XA7 600 you should have a conventional type of crank with steel rods having detachable end caps.   Bearing, bush and journal sizes are the same as later shortstroke engines.

   Timing side bush has the same dimensions for all engines. Early types were a steel carrier with cast in bearing material. This bearing surface sometimes suffers fatigue cracking where the engine has been subject to heavy, sustained loading, typically a slow slog with a laden sidecar. A true 2 piece bush as you describe will not be original, and the bearing material, a thin copper/bronze coloured material should be pegged to the carrier to prevent rotation and consequent blockage of the oil holes.

  An original or replacement bush has a top hat flange with two flats which locate it in the timing side case. How you proceed depends on what has happened. If the bush is a later two piece  bush  with the bearing material seized to the crank, but free in the carrier and the steel carrier is still in place then you are lucky. Otherwise if the whole thing has turned with the crank then there must be damage to the case, or it is a non standard cylindrical bush with no locating flats.

 To rectify, in a case of damage, the cases need to be line bored to clean up the bush location, and then a custom bush made to fit. A standard bush will not fit tightly enough in the cases, if you have evidence of damage. Any gap between the bush outer and the cases will allow pressurised oil to escape, rather than being forced to the big ends. The cases  require to be warmed, bush cooled, to give a good interference fit on rebuild. Then the bush line bored  to give a running clearance to the crank journal. Here the crank can be ground just enough to clean up, you don't need to stick to a set size as a custom bush takes care of that. If the cases are OK, a well undersize one piece bronze bush can be installed and line bored to fit the cleaned up crank. This all depends on the final dimensions of the crank and how much material you have to play with.
 
 The inner wall of the case may need work to restore the bush flange locating positions. Look on the forum, all this and the attention to the crank sludge trap has been dealt with in great detail, just a matter of searching.

 Drive side main bearing was originally a deep groove ball race. This eliminates crank end float. Someone may have fitted a non standard unflanged bush to get the bike back on the road in the time when official spares were unobtainable.

 How easy was it to get that race off the crank?

 beezermac has already posted, while I was typing, so this post repeats some of his notes.

 

 Swarfy
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Online RichardL

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Re: Timing Side Bush
« Reply #3 on: 28.03. 2020 14:06 »
Fido,

With the bearing explanations well covered, let me say "welcome back."  *welcome* *spider* Until yesterday, four years since you last posted. Have you heard about the pandemic? *eek*
 ;) (Attempted humor aside, hope you and yours are well.)

Richard L.
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Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020. This year it's a solo or pillion ride in dapper attire. Watch website at https://www.gentlemansride.com for details.


Offline fido

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Re: Timing Side Bush
« Reply #4 on: 28.03. 2020 15:30 »
Fido,

With the bearing explanations well covered, let me say "welcome back."  *welcome* *spider* Until yesterday, four years since you last posted. Have you heard about the pandemic? *eek*
 ;) (Attempted humor aside, hope you and yours are well.)

Richard L.

Yes but 10 years since I used the bike on the road. This is due to me having a bad back and the bike having no rear suspension. The plan is to get it running well and looking OK so that I can sell it. I would like to get another classic bike but I  probably won't be able to afford it as prices seem to have gone silly. I need to update my profile here as I now live in Croatia. When I lived in Hungary I did start the bike now and again and ride it on my own land but did not have it on the road. I will be sad to let it go as it has been a good, reliable bike but circumstances change.
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Offline fido

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Re: Timing Side Bush
« Reply #5 on: 28.03. 2020 15:55 »
I am now wondering if the outside of the bush was somehow ground or polished to save reaming the bearing surface. I took off the pinion and bush from the crankshaft and put the bush into the crankcase. It did not drop in but did not take much force to put it in. Another theory is that the witness marks could be from chatter rather than rotation. The bush does have the flange with flats and there is no evidence of the flange having scraped against the inside surface of the crankcase. In any case, it would need a huge amount of end float for the flange to come out of the slot. Having said that, I don't know how end float is controlled, is it purely shimmed from the drive side? The pins holding the steel to the bronze look OK. I think if the oil supply had been compromised there would be damage evident elsewhere in the engine. Everything seems fine apart from one slightly stiff little end. I'm hoping I can rectify that with a reamer and a bit of wet & dry to polish off any scuff marks to the piston skirt. On my '59 Shooting Star I found quite a lot of wear to the cam lobes and cam followers but the ones on this look fine.
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Offline Swarfcut

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Re: Timing Side Bush
« Reply #6 on: 28.03. 2020 17:52 »
fido. Your last post added more detail, and I think I got some of my previous thoughts a bit awry.

 This is what I think you mean....

 Crank is not seized to the bush. Bush supports the crank as normal, but outside of the bush is loose in the case. 

 As I mentioned earlier, the timing bush should be a tight physical and oil tight fit in the crankcase. Replacing the bush requires heating of the case to open up the hole, bush is then tightly gripped as the case cools down.

 The service sheet is confusing, as it was written at a time when the later Hopwood design for the A10 had been introduced, but the A7 references refer to the Perkins Longstroke, not the later A10 Hopwood clone.

 Crank endfloat on the Longstroke is eliminated by tightening up the cush drive assembly, this sandwiches the inner race of the drive side ball bearing against the crank web.

    The service sheet gives a figure of allowable float before tightening, which means the crank must be able to move freely through the bore of the race (in my opinion). Also if it was tight, stripping the motor without force and heat would be well nigh impossible.  This initial float is controlled in the usual way, circular shims between inner race and crank web, and this float ensures that on final assembly the crank has some room for expansion towards the timing bush.
   The later design uses a single lipped roller bearing, allowing the drive side case to come away easily, and the float is effectively the difference between the inner face of the timing bush and the inner lip of the roller bearing compared to the dimension of the crank web face, timing side, to outer face of the bearing rollers. Much more awkward to set up, more expensive bearing, but BSA had their reasons for the change.


  Looks like you have had a lucky escape from damage, but the motor will  probably need the case reworking and a custom bush with bigger O/D. In the end it depends how things measure up.

 Don't forget that sludge trap!

 Swarfy
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Online JulianS

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Re: Timing Side Bush
« Reply #7 on: 28.03. 2020 18:45 »
Have you considered using one of the specialised Loctite products to secure the bush? Loctite 638?

https://www.henkel-adhesives.com/us/en/product/retaining-compounds/loctite_638.html

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Offline fido

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Re: Timing Side Bush
« Reply #8 on: 29.03. 2020 07:15 »
I suppose the danger with Loctite is that it could get into the oil passages. One idea I had thought about and was later suggested on a Facebook BSA group is to electroplate the outside of the bush to make it a tighter fit. As the bike was running OK and I'm selling it anyway I am not keen on costly, complicated engineering solutions. If I still lived in UK I would no doubt find people who could help with this but here in Croatia things are quite different. Talking of Loctite though, am I right in thinking that some people these days use it instead of tab washers? Pretty much every tab washer in this engine was broken before I got it so they can't be re-used.  I think you can buy a set of tab washers for the shortstroke but I don't know if they are all the same ones on the longstroke. I can get a gasket set from Draganfly and they also sell the piston circlips. When using Loctite, what do people use to degrease the threads?
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Online JulianS

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Re: Timing Side Bush
« Reply #9 on: 29.03. 2020 09:14 »
I dont use any lock washers in my A10, just loctite. Also use it on the sludge trap plugs rather than hit my crankshaft with a punch and hammer.

I degrease threads with a simple spray carburetter cleaner.
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Online berger

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Re: Timing Side Bush
« Reply #10 on: 29.03. 2020 11:08 »
if your steel bush housing is still a push fit and not loose I would carefully use Loctite and when it is set test the oil ways. as you say you are selling it and haven't got easy engineering access . ps this is not a practice I would do even if I was selling it. I would centre punch the bloody thing and ram it in  *eek* *pull hair out* joke
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Online TT John

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Re: Timing Side Bush
« Reply #11 on: 02.09. 2020 22:32 »
Have you considered using one of the specialised Loctite products to secure the bush? Loctite 638?

https://www.henkel-adhesives.com/us/en/product/retaining-compounds/loctite_638.html

Thanks for that Julian, I was about to suggest this method and there is very little chance of obstructing the oil passageways.

TTJohn
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