Author Topic: timing side bush failure  (Read 2594 times)

Offline MG

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Re: timing side bush failure
« Reply #15 on: 26.06. 2010 19:06 »
Generally speaking, the higher alloyed the steel, the harder the surface will come out after nitriding, while the depth of the diffusion zone will decrease.

Considering the mileage Brian's engine has covered with the (presumably) very first bush, I'd say the needle roller conversion is not really necessary, especially as it is a rather costly operation. The most important thing is correct and accurate machining of the bush, then it should last at least until the next rebore and pistons, assumed that oil is kept clean and changed regularly. I think the setup is not as bad as it's reputation.
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

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Offline bonny

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Re: timing side bush failure
« Reply #16 on: 26.06. 2010 21:52 »
another thing about the bush which i'd like to know is the endfloat issue , what are the symptoms of the clearance being too much and too little ? knocking and banging i presume ?

Offline olev

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Re: timing side bush failure
« Reply #17 on: 27.06. 2010 02:10 »
I've just got the A7s bottom end back from the machine shop.
They turned up a new main bush from the small end of a large perkins or isuzu diesel.
The cam and crank bushes have been aligned and reamed so hopefully all will be good.

Like Brians this will get a ball bearing. I wanted to use a NTN TMB206C3 or TAB206C3 with seals but have not been able to obtain one.
These bearings have special heat treatment (nitrided balls??) and are designed for transmissions.
The husaberg boys retro fit TMB206C3's to their scramblers.

If anyone knows where I can get one of these bearings (with a seal) please let me know. The local agents just go glassy eyed.

Does anyone know if the distance between the crank and the timing bush matters if the crank is fixed?
Will it effect oil pressure if the gap is large ?
cheers

Online muskrat

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Re: timing side bush failure
« Reply #18 on: 27.06. 2010 07:45 »
G'day Olev,
                   just did a google on that bearing and got nothing, I found the size 30,62,16.
Even with a ball I'd get the end float as close as possible, say 2-4 thou. Less stress on the bearing and wont affect the oil pressure.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline Brian

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Re: timing side bush failure
« Reply #19 on: 27.06. 2010 08:06 »
The bearing is a 6206, metric. 62mm OD, 30mm ID, 16mm wide. I used a SKF explorer bearing in the one I put the ball bearing in and left the outer seal in place. If you have 53' or later cases they will have a seal so you can remove both seals from the bearing. The roller bearing is a NF206.

We could probably discuss for years the pro's and con's of a ball or roller bearing so I wont go into that except to say just about all modern motorcycles run on ball bearing mains, not rollers. The reason I chose to try a engine with a ball was to eliminate end float, the thing is no matter what you set up the end float to it changes with heat. I had the primary cover off my 61' when the motor was hot a few months ago and hot it had about .010'' end float (only a estimate as I didnt measure it accurately) as the motor cooled down the end float dissapeared back to the zero I had put it together with. Just how much end float affects the wear etc I dont know but it cant help having the crank being able to float around.

All this started because it wouldnt go up a big hill as easily as the A7 !!!!!!!

Offline BSA_54A10

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Re: timing side bush failure
« Reply #20 on: 27.06. 2010 09:38 »
Quote
For the reason you mentioned I always use the nitriding process and not carbo-nitriding. Why you mentioned the ammonia furnace treatment in that context is not clear to me. Where would the carbon come from in ammonia atmosphere (=NH3)?
Compared to the nitriding process, carbo-nitriding is not true to size, so can not be done without subsequent grinding. The nitrided journals will only need a bit of polishing and are ready to fit.
Comes from not checking my post properly before I send then and changing my train of thought on the fly ( somthing about playing on the net when I should really be in bed )

I am nearing the limit of my Ferrous metallurgical knowledge as I was principally in tertiary metallurgy and non ferrous foundry to boot so did not do much with steel after I left uni.

As for the formation of nitrides & complex nitrogen phases at the surface , this is something that I was totally unaware of and would have thought both the concentrations of nitrogen and temperatures were too low for the formation of such phases in sufficient quantaties to alter the bulk properties if at all.
I no longer have access to TTT curves so could not verify how near the tempering temperatures nitriding would be done and what affect if any this heating would have on the microstructure of the particular alloy. I was always led to believe that gas nitriding was done very close to the tempering temperature to reduce the heating time ( & costs )
A couple more things that I have learned for which I thank you.

The principal object of the post was to distinguish between the two processes which just sound like different names for the same thing and as we have established are totally different and clarify which you were talking about.

As stated I always recommend nitriding and have had a couple of locals looking to shed my blood after they Carbo ritrided their cranks which failed very quickly.
 
Bike Beesa
Trevor

Offline MG

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Re: timing side bush failure
« Reply #21 on: 27.06. 2010 11:35 »
I've been co-working on a university research project on that stuff (tribological behaviour and wear properties of nitrided surfaces), so gained a little knowledge about it, but in fact I'm a mechanical engineer and no metallurgist, so mainly have to believe what these tell me.  *smile*

Since plasma nitriding has become common, the process temperatures could be reduced significantly, compared to gas and salt bath nitriding. I was told that if necessary they could go down to 350°C (with an increase in nitriding time though).

Thank you however for the clarification of the process names. It is not easy to keep things apart, especially with all those creative trade names around.

Cheers, Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Offline olev

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Re: timing side bush failure
« Reply #22 on: 27.06. 2010 13:07 »
Muskrat,

Here is a couple of links that headed me in this direction.

http://www.ntnamerica.com/pdf/Other/tmbspec.pdf

http://www.husaberg.org/forum/viewtopic.php?f=5&t=6195&start=270

The second link gets into it about half way down. They talk about SKF TMB bearings but the SKF distributers don't know anything about it and its not on their web site. I'm pretty sure its an NTN.

NSK make an interesting variation called TM206 sealed clean where they fit seals that lets the oil in but keeps the lumps out.

My engine is a 52 so like Brian says it would be good to have a seal on the drive side.
cheers

Offline Brian

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Re: timing side bush failure
« Reply #23 on: 05.07. 2010 12:41 »
Engine rebuilt and all back together and running again. Now, what else can I pull apart............................