A10 Timing side main bush/bearing

[terryk]

Hi all, I've heard it mentioned on this site that the bronze timing side main bush wears the crankshaft main journal and the lead bronze two part ones are the ones to get. What does everyone think? Where can you get the NOS ones. Thanks in advance for comments.

[RichardL]

If I recall correctly, I asked this same question of SRM and was told that the solid bushes were the only ones they sold. I took this to mean they had great faith in them.  Do give them a call to ask confirm this point.

Richard

[RichardL]

Adding to my previous post, I note that the point regarding solid phosher bronze wearing the crank, versus 2-piece lead branze was made by a member of this Forum who's opinions I greatly respect. So, I redouble my suggestion to check this out for yourself with SRM, read the posts at http://www.a7a10.net/forum/index.php?topic=485.0 (which, I think, you already did), and contact the member directly who gave the advice (G/F Dave).

Richard

[G/F DAVE]

Re; Timing side bush I have had problems in the past using PB1 phoshur bronze bush.The ones I had fitted came from SRM within 15000mls I had the familiar rumblings thru footrests. The crank was worn oval so had to be ground from -020 to -040. Another 12000 mls  then the rumblings were back. Needless to say -040 is the last grind so time for another crank. I was lucky to find a big bearing super rocket crank on STD which I had ground to -010 timing side & big end journals, the guy who did the work had new old stock alpha lead/bronze bushes & glacier big end shells.These were fitted 23000 mls ago and the engine is still smooth and nearly vibe free.The lead bronze bush is the type fitted from the BSA  factory, but be aware there are cheap nasty pattern ones about that are not pegged but glued and may turn inside steel housing shutting off oil supply to big ends. If you can find original BSA or ALPHA you are going to be very lucky but I have seen them on EBAY site from time to time. These are my experiances with PB1 bushes yours may be different . I do give my goldflash some stick as with all my old bikes also regular oil changes & more important a inline oil filter are essential. G/F DAVE....

[trevinoz]

I made an insert for the original bush from LG1, which is leaded gunmetal. It is in my '55 Flash and so far so good, only a few thousand miles so far. I previously had a bush made from Aluminium Bronze fitted to my RGS and it wore the journal badly as noted above with PB1.
                                 Trev.

[Brian]

Ive been watching this subject for some time now with interest. My plunger A10 is still running on the original BSA bush and has done who knows how many miles, thousands. I have recently rebuilt my 61' A10 and after discussion with SRM fitted a solid bush, I will know in the next twelve months or so if this is good or bad. One thing we all say on the forum is that how important it is to have a replacement bush line reamed or bored to the opposing case to be absolutely sure it is in line. The original BSA workshop didnt do this, they had a reaming plate that fixed to the outer timing side and acted as a guide to ream the bush. I have added a scan from the original manual showing this. Apparently they trusted the accuracy of their maching of the cases, interesting.       Brian.

[groily]

'tis very interesting Brian. Wonder how they machined the the case to get such accuracy (if they did indeed). Or maybe they were just happy to get the timing side bush reamed square with the case? Or  - maybe they had a mandrel attachment to the reamer which was supported in the drive side inner race . . . ?(which is what I'd have expected seeing the trouble they went to to make the guide plate in the first place!)
When at some point I have to do my A10's bottom end, which I'm sure is only a matter of time, I'll come back to this!

[Brian]

I found this interesting too when I came across this picture and part in the manual. They dont mention any sort of guide or mandrel but it is hard to imagine not using one. I guess that when this was written it was all new stuff so maybe they thought their machining was good enough. The plate also has a hole in it to ream the camshaft and idler pinion bushes and thay would be difficult to put any sort of guide behind. Who know's ? I have some video footage taken in the BSA factory I think in 1962 or early 63' and it shows them assembling a A10 engine but unfortunately doesnt show that part of the operation. It does show them doing some things like drilling and tapping holes in crankcases for barrel studs etc and they just rely on the accuracy of their machines to get everything square. I always line ream the main bush and would not recommend otherwise but just thought this was interesting.

[GuyboA10]

G'day Brian & co. In regards to this matter i came across a photo and description of a reaming tool that entered the left side case and protruded through to the timing side for acurate reaming of the T-side bush. The cases were bolted together and the tool was guided by the drive side bearing. This to me seems like the only way it should be done. As a novice brit bike builder, who has learned alot, i cant see any other way that would be as accurate. maybe on a very expensive machine, but for the average brit bike builder on a limited budget, the reaming tool seems to be the most effective solution.
i will try and find the photo. Also i think it was demonstrated on an A65, but i'm sure it would work on an A7/10. I think the guys name was Mark Parker, an Aussie Nsw? don't quote me on that. ( apologies to M Parker if i am mistaken)
cheers Guy.

[terryk]

There must be someone who can make lead bronze timing bushes like the Alpha ones to put our minds at ease. Has anyone used the SRM bronze ones for a long time with success also making sure it's line bored properly and pulled the engine apart for some other reason and seen that there is not a lot of wear on the crank from them?  If so we have nothing to worry about but I don't like the idea of wearing the crank out in a hurry they are getting too had to find and too expensive. Beside I dont want to be pulling the engine apart because of unreliable parts demaging had to find good parts. I want to put lots of miles on my bike not lots of hours working on it and looking for other cranks. Terry in Australia

[octane]

G'day Brian & co. In regards to this matter i came across a photo and description of a reaming tool that entered the left side case and protruded through to the timing side for acurate reaming of the T-side bush. The cases were bolted together and the tool was guided by the drive side bearing. This to me seems like the only way it should be done. As a novice brit bike builder, who has learned alot, i cant see any other way that would be as accurate. maybe on a very expensive machine, but for the average brit bike builder on a limited budget, the reaming tool seems to be the most effective solution.
i will try and find the photo. Also i think it was demonstrated on an A65, but i'm sure it would work on an A7/10. I think the guys name was Mark Parker, an Aussie Nsw? don't quote me on that. ( apologies to M Parker if i am mistaken)
cheers Guy.

Hi Guy

It's here: CLICK

...scroll down a bit.

[RichardL]

Gents,

I couldn't resist borrowing this post from the BritBikeForum. I don't believe there are any copyright issues to be concerned with, however, as always, I rely on our administrator to make the determination.

Richard





Ok here are some pictures of the ream;

The piece with the cone screws onto the handle of the ream and the cone slides up and down and the ream turns inside it. This ream is 1.5" and bigger but seems to adj down a little from that. A smaller ream would have a smaller cone and need perhaps something made to fit into the D/Side case. As it is this larger cone fits tightly into the old oil seal, for those who think that may be too imprecise something could be made, however the seal seems to work fine and that end of the ream stays well held.

The ream adjusts by the two collars that can be turned to move the blades along the slots in the shaft that are tapered.

The ream makes for a very square hole, and the process would be made much simpler with inside and outside mics, so you could slowly approach correct size. You can guess clearence probably quite good if you remove the oil pump studs and test the crank from the outside and slowly creep it up. The ream can be removed and re-inserted without unbolting the cases. Once the crank drops in, and is only in the bush, the amount it rocks will indicate clearance. The one I did some years ago hardly rocked, but when in the motor, in both bearings, it would spin very freely, indicating good alignment.

[RichardL]

... I don't like the idea of wearing the crank out in a hurry they are getting too had to find and too expensive.

Until just recently, I always considered crank grinds in 0.010"increments because of the available sizes of rod bearings. Then, I woke up to the fact that the timing-side bushes do not need to follow the same logic. One need only take off as much from the crank as necessary to clean up, then ream the new bushing accordingly (or vice-versa, perhaps). This could afford more main journal grinds if one does not need to do the rod journals or if there are more steps left in the rod journal life.

Of course, this is old news to some, but may be helpful to others with my brand of sleeping sickness.

Richard

[Brian]

That was the very reason I went for a solid bush, thinking that when it wore I would get the crank ground just enough to clean it up and then make a new bush to suit. By what I understand from this thread the solid bush seems to cause the crank to wear so that being the case the bronze used must be too hard. So I wonder is it possible to get a softer bronze. I do know that bronze varies in hardness, I have been buying bronze bar for years to make bushes etc out of and have learnt that you can get some idea of how hard it is by its colour. The lighter [or whiter] it is, the harder and the yellower it is the softer. I have queried this with my supplier but they only know it is bronze bar and have no idea about its properties. Do we have a metalurgist amongst us ?

[GuyboA10]

hi, yep , thats the one! cheers to octane & manosound. i thought i'd seen it on britbike.com.
Has anyone here used that tool? on their a7/10's?
cheers, Guybo.