Sprocket interchangeability

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SeanG
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Sprocket interchangeability

Postby SeanG » Wed May 15, 2019 12:34 am

Hi all,

I am preparing to reassemble the bottom end of my R60/7. Basically, I’m up for ordering a new camshaft, chain, cam sprocket & oil pump rotors.

It seems ‘77 - ‘78 had some transitions, namely duplex to simplex chains. I gather the crankshaft remained the same.

Mine previously had the duplex chain. But I have since removed the mechanical tachometer cable, and I plan on installing a cam-mounted timing advance.

So my question is, would it be possible to use the later style single chain & sprockets? The parts seem to be cheaper, so there is that advantage. But if it were possible, I am guessing it would be the better (newer) system?
My bike is a 1977 R60/7.

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Rob Frankhamr
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Re: Sprocket interchangeability

Postby Rob Frankhamr » Wed May 15, 2019 10:00 am

A simple answer... No.

The camshafts aren't the same and the timing chest covers are quite different. The ignition triggering arrangements are also completely different and dependant on the nose of the camshaft. Even if you replaced the timing chest, and all of the associated parts, you would still have to replace the front main bearing support and I don't think the later support would work with the early crankcase. To put it another way, you'd end up having to replace most of the engine (or carry out major engineering modifications to the parts). Really, you're much better of sticking with the original arrangement...

Rob
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Mike D
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Re: Sprocket interchangeability

Postby Mike D » Wed May 15, 2019 12:38 pm

All what Rob has said, plus the duplex chain lasts a lot longer than the simplex one.

Mike

Neil Robertson
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Re: Sprocket interchangeability

Postby Neil Robertson » Wed May 15, 2019 5:38 pm

Just in case anyone may be interested ,when a catastrophic lubrication failure destroyed the crank and bearings of my R80/7 I bought a slightly later (simplex timing chain and points in bean can ignition)R100RT engine from an autojumble.I swapped the crankshaft (which was identical) along with its bearings and front carrier.
The carrier fitted straight into the crankcase but required some trimming at the front to clear the duplex chain and it's tensioner, the amount of metal that needs removed is quite small and within the capabilitys of a file and dremill.

SeanG
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Re: Sprocket interchangeability

Postby SeanG » Wed May 15, 2019 9:09 pm

Thanks Rob,

I knew there would be a catch. Had to ask though...
My bike is a 1977 R60/7.

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Rob Frankhamr
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Re: Sprocket interchangeability

Postby Rob Frankhamr » Wed May 15, 2019 9:15 pm

Just in case anyone may be interested ,when a catastrophic lubrication failure destroyed the crank and bearings of my R80/7 I bought a slightly later (simplex timing chain and points in bean can ignition)R100RT engine from an autojumble.I swapped the crankshaft (which was identical) along with its bearings and front carrier.
The carrier fitted straight into the crankcase but required some trimming at the front to clear the duplex chain and it's tensioner, the amount of metal that needs removed is quite small and within the capabilitys of a file and dremill.
That's interesting to know... Did the oilways match up?

Rob
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Neil Robertson
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Re: Sprocket interchangeability

Postby Neil Robertson » Wed May 15, 2019 9:59 pm

Yes,I'm glad to say,it was quite a while ago but I remember comparing the two parts and apart from the extra metal both parts were the same.you could actually see where the mould had been altered to make the newer part.

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Re: Sprocket interchangeability

Postby SeanG » Sat May 25, 2019 12:07 pm

Sorry to not let this die...

But, I’ve been doin some digging into online parts fiche and as far as I can see the difference between the camshafts, is one has the nose to accept tacho drive and timing advance. The other has blunt end to it. But they both have the exact same bearing holder. So that leaves the oil pump inner rotor, which I need anyway so I can get the compatible one in either case. The only major issue I can see is the camshaft seal opening to the timing cover - small vs large. But if I was going with a cam mounted timing advance, it would just be a matter of plugging the seal opening to prevent oil spilling out.

Am I missing something?
My bike is a 1977 R60/7.

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Rob Frankhamr
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Re: Sprocket interchangeability

Postby Rob Frankhamr » Sat May 25, 2019 5:15 pm

I'm not quite sure what you mean by a 'Cam mounted timing advance'. On the face of it, all of the systems used on this type engine by BMW are 'Camshaft mounted' or 'Camshaft driven' so I'm guessing you have something else in mind.

The other issue is the camchain tensioner. I don't know whether the original tensioner will work with a simplex chain but I suspect the later type tensioner with it's back run support, which was designed for such a chain and which has an oil damped motion is a much better tensioner. You can't fit the later tensioner to the front crankcase bearing support casting, I suppose if you were to replace the casting with the later version, it might work... but then you're gambling on it not fouling the older type timing chest cover.

I wish you luck if you do decide to go ahead with this... but I do think it's an awful lot of work and risk to no practical advantage.

Rob
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SeanG
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Re: Sprocket interchangeability

Postby SeanG » Sat May 25, 2019 5:36 pm

Thanks rob,

It’s a long story as to why I’m pursuing this, but just wanted to explore all my options. I meant to say ‘crank’-mounted timing - sorry about the confusion.
My bike is a 1977 R60/7.

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Rob Frankhamr
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Re: Sprocket interchangeability

Postby Rob Frankhamr » Sat May 25, 2019 10:25 pm

OK, although I must say I'm intrigued...

Rob
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SeanG
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Re: Sprocket interchangeability

Postby SeanG » Thu May 30, 2019 9:23 pm

To anyone following along...

I came across this bulletin from BMW, via http://bmwmotorcycletech.info/engine%20 ... s-2031.pdf

Page 2, paragraph 3 seems to suggest it is possible.

I have ordered a used later model bearing cover to compare.
My bike is a 1977 R60/7.


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