Author Topic: SRM preground timing side bushes  (Read 322 times)

Offline roadrocket

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SRM preground timing side bushes
« on: 10.05. 2020 21:14 »
Hello, distinguished folks

I have a case of timing side knock, but am not keen to just send everything out to be done in town. I had the whole bottom end done by the best available guys in 2013, and am a bit miffed that after less than 10.000 miles the timing side is worn out. Anyhow, I see that SRM sell buhses ground to size. Are these supposed to be installed and be ready for service without any reaming? I think the shop  that did my crank have just cleaned up the timing side race regardless of size, and reamed the new bush to size. How about I order the first size bush from SRM that isn't too big, and then ream that once in the case? I have thought of a way to ream true, as I don't have the setup for proper line boring. I imagined just to buy an adjustable reamer in the right range.

Cheers, Otto
Otto in Denmark

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Re: SRM preground timing side bushes
« Reply #1 on: 10.05. 2020 22:18 »
the bush you are on about doesn't knock and any different bush put in a case needs it's own attention regarding a shaft or crank journal running in it. big ends knock, and little ends have a distinctive knock under load like excessive piston slap, as for do it yourself line reaming there is more to it than just reaming , you need a pilot in the drive side, so I think you should be listening to the engine with a wooden handled screw driver and try to pinpoint the knock before ordering ground to size? bushes. apart from that even if you buy the smallest id bush something like -40thou your crank may have only been ground -10   and getting one reamer to expand to what your crank journal is may prove difficult, I don't know ive never used one that big and think they are expensive

Offline roadrocket

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Re: SRM preground timing side bushes
« Reply #2 on: 11.05. 2020 07:33 »
Well, knock is maybe not the correct description of the sound, a rising and falling rumble that can be heard at low to medium revs is probably more correct. The thing about the SRM bushes is that they can be ordered at 10 thou intervals, so less than 10 thou will need to be removed in any case.
Otto in Denmark

beezermacc

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Re: SRM preground timing side bushes
« Reply #3 on: 11.05. 2020 08:38 »
I have done a lot of timing side bushes, over the last twenty years, myself, using an expanding reamer made by 'Dormer'. I have had great success in that all the bushes I have done (apart from one) have proved to be absolutely fine and are still in use, untouched. The one that failed, actually it didn't fail but seemed to show more wear than expected, was a victim of something which got the big ends too - I suspect vapour/grit blasting residue, and not my bike! I always get the crankshaft ground to 'round' regardless of size then use the closest fit solid phosphur bush and ream to fit with about half a thou clearance. I find it a more difficult job getting the end-float right afterwards, but that's another story!

Offline roadrocket

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Re: SRM preground timing side bushes
« Reply #4 on: 11.05. 2020 08:47 »
Thanks Andrew! I'll carry on. I have successfully shimmed the crank earlier, it just takes some trial and error. The crank was reground not many miles ago, so not expected to be out of round. Will measure of course.

Cheers, Otto
Otto in Denmark

beezermacc

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Re: SRM preground timing side bushes
« Reply #5 on: 11.05. 2020 09:13 »
One thing to be wary of is the lip which occurs on the end of the timing side journal. If you don't get the journal reground you need to 'dress off' the outside 1mm of the journal or it will prevent you from passing the journal into the bush. Even if the lip is only a fraction of a thou it must be removed.

Offline Swarfcut

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Re: SRM preground timing side bushes
« Reply #6 on: 11.05. 2020 09:45 »
Good point there BM. Often overlooked, the extreme end of the journal protrudes through the bush, and will be unworn. Stating the obvious the difference in shaft diameter here, if any, gives a quick visual indication of  wear to that journal which has taken place since the crank was last ground. It's another clue in finding the reason for the knock. If the crank has no visible lift in the bush, I would consider the running clearance  to be adequate for normal leisure riding, and would be prepared to put up with less than perfect considering the type and amount of use the machine gets.

 A high performance, more stressed engine needs a more accurate assessment, and probably a lot more expense for true perfection.



 Swarfy.

Offline roadrocket

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Re: SRM preground timing side bushes
« Reply #7 on: 11.05. 2020 09:51 »
It's a small journal crank anyway, so I don't flog it. I have a large journal crank waiting, but that was supposed to be at a later date when other projects had been taken care of, so a shedmade solution is on the cards for now.
Otto in Denmark

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Re: SRM preground timing side bushes
« Reply #8 on: 11.05. 2020 12:53 »
If I were doing it with a reamer, I'd turn up a bush to fit on the reamer shank to locate in the drive side crankcase, otherwise there's a very good chance of reaming the bush out of line. Don't like expanding reamers anyway, and only use them as a last resort. They have a habit, because of equal blade numbers, of chattering - and sometimes cutting oversize for no obvious reason. If no facility for line boring available (or access to a mill) I'd probably be looking for a lathe with a chuck with known little run-out. I'd then bore the bush to size, allowing half the interference fit of bush to case extra to allow for the bush closing up when fitted to the case.
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Online Bsareg

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Re: SRM preground timing side bushes
« Reply #9 on: 11.05. 2020 13:43 »
Blueing and hand scraping is another way to go. Just need a ground out drive side bearing and a bit of patiences. Over the years I've done many this way with no problems.
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