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Old 04-24-2011, 07:57 PM   #61
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i dont know about how unusual it is, but anton staked mine in pretty damn good, as its known well enough to cook engines, just like yours did. Its like: Only got to do that job usually once in a bike's life.
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Old 04-24-2011, 08:15 PM   #62
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Thanks for the WP50 manual, btw, Solo.

Might just throw this front end on the DR650 in the mean time because it'll likely be a few years before the GSPD's ready to roll again reborn in HPN-esque guise.


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Old 04-24-2011, 08:32 PM   #63
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Originally Posted by ontic View Post
My bike aint matching numbers, so I don't think there is much point being too puritanical.
Someone correct me if I'm wrong, but I don't think ANY later airheads have matching frame and engine numbers.
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Old 04-24-2011, 09:16 PM   #64
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Someone correct me if I'm wrong, but I don't think ANY later airheads have matching frame and engine numbers.
Really???
very interested in this. I was assuming mine (an 1981 btw) has had an engine swap in its past.
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Old 04-24-2011, 09:51 PM   #65
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Hey Solo,
just wondering if you could do a few measurements or post up any links you have found for the stock KTM triples for the WP 50mm forks.

As we are discussing in PM's I am trying to find compatible triples from other bikes (primarily ducati at present) that could be used/adapted that have a similar-to-stock bmw offset.
Main dimension I am looking for at the moment is the distance between the centres of the fork tubes.

Cheers,
Hans.

Edit- just adding in a diagram of Ducati MTS triples with some measurements for an example and possible template to start comparing different triples. Note: with these two fork tube clamps ranging from 53-7mm these would obviously require sleeving to downsize to the 50mm tube. Just trying to work with some ideas and get some baselines.
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Old 04-25-2011, 07:54 AM   #66
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that's a handly little diagram. Thanks for putting that together.
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Old 04-25-2011, 09:04 AM   #67
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Putting it together? Me? no such luck but thanks.
I found that diagram as I was researching Ducati triple clamp dimensions. I have found it surprising how hard it is to find these sort of measurements, so I was pretty happy with that one.

And, re-reading this thread and then Rdubbs again I think I found the answer to my previous question- right in front of my eyes (sorry Solo)- the dimension between the centers on the stock KTM triple = 190mm.

in looking for triples with similar bmw offset that could be made to work, I am wondering if there might be another issue. Please excuse if this is a dumb question.
I've just read that some triples (for lack of a better explanation) are non-parallel- that the upper and lower triple clamps can have differing offsets. Apparently common to some 70's trials bikes...
(I suppose this would have required slightly non-perpendicular hole(s) for either the stem or the forks??)
Now I don't know how common this is beyond a particular sort and/or era of bike, but after reading this it struck a note. Previously, through looking at many pictures of different triples I had seen a few that had the definite appearance of different offsets for the upper and lower clamps. I had assumed this was just an illusion inherent to photography, computers, and my eye.

I note Rdubb's triples have the same offset for upper and lower. It is hard to note much about the Boxxer Supplies or Gletter triples because I can find no dimensions.
I am assuming this is probably a non-concern... but because I don't particularly understand it, I might as well put it out there
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Old 04-25-2011, 09:34 AM   #68
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Rake and "offset" basically combine to create a specific trail dimension.

Trail would be the same for a given front end regardless of how long the forks were - provided the chassis maintained a constant attitude and the same front wheel was employed. ie: as long as the rear of the bike was raised or lowered along with the front.

Trail is the most critical of motorcycle geometry dimensions. It has a dramatic influence on dynamic stability.

Rake, as far as most have been able to determine, primarily effects suspension action.

The above is a gross over-simplification but helpful as an overview.

Reading anything by Tony Foale is helpful in understanding motorcycle geometry and chassis dynamics. Interestingly, the actual physics of motorcycle dynamics are still argued at the highest levels.

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Old 04-25-2011, 09:36 AM   #69
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its MAgic
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Old 04-25-2011, 09:41 AM   #70
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Quote:
Originally Posted by ontic View Post
Really???
very interested in this. I was assuming mine (an 1981 btw) has had an engine swap in its past.
snobum says:


"NOTE!! BMW has used at times a quite different frame identification system for NON-U.S. motorcycles. There may be a serial number followed by one extra number, and then the TYPE of motorcycle. The first digits are the serial number, and you can enter them into any serial number search. This means that if you have 8 digits at the beginning, 7 are used for the serial number. I do NOT know what the 8th digit means. The following article applies to the North American shipments, and will also apply to wherever the 17 character VIN is in use, as far as I know.

In the OLD days, BMW simply used a serial number. Simple. Find the number on the engine, find the frame number. They may even have been the same number....usually were, actually....except a very long time ago. For more information on the really old models, see Duane Ausherman's website.

In 1980, the VIN system was begun. This was, and remains, a 17 character Vehicle Identification Number (VIN), which is a combination of letters and numbers. At first, BMW matched the serial numbers of frame and engine. 1980 was the transition year, and some anomalies for 1980-1981 production are around, so if you have a 1980-1981, do not be upset if things seem strange. At the end of 1983, with the introduction of the 1984 model year bikes, BMW decided not to match up these numbers. They said so officially, so if YOUR numbers DO match, don't blame me! Not only that, but BMW phased in something new....they were NO LONGER stamping the engine serial numbers next to the dipstick. You can see that on 1984 and later.

Frame numbers were stamped at the steering head to 1982, then on the frame below the right cylinder. Early bikes will usually have a frame number on a tag in the steering head area. Engine numbers up to and well into 1983 were generally next to the dipstick. After the 1983 model year, and this was phased in, they MIGHT have moved to a milled engine pad, where any engine number MIGHT not be even the same system, IF THERE, as previously. Confused? Well, BMW put some weird stuff on that milled area. On that engine pad, sometimes the pad was missing!...were lots more characters identifying more things, some not revealed to me nor anyone outside the factory. All that being said, some bikes don't conform to the published standards, limited as they are, for that engine pad....so, read on...

BMW has also not held itself strictly to its bulletins (Service Information, or SI) on these matters, so one may well see some combinations or variances.

On models with a VIN, that number is probably; but may not be, all there, or is on the steering head, or partially there, on some 1980-1982 calendar models. Where they are fully there, you will find all 17 characters (ALWAYS 17), on your lower right side frame tubing, roughly in line with the right side carburetor. Again, the transition period was mostly ending by 1982, after which the frame fully complied, always (AFAIK!)...and you may find yours on the steering head area plate/tag. You may also find it on a metalized tag on top of the driveshaft housing...which may not agree in ONE letter ID (year); and, you may have funny other things going on. In general, the VIN on the metalized tag on the driveshaft housing will agree with the VIN on the steering head or lower right frame. In a FEW cases, there may be a single LETTER difference. That letter is the YEAR identification letter. An example might be a late 1983-built RT. The UNofficial information ... is that BMW did not submit this end of production 1983, early enough for California smog testing. So BMW cleverly put a letter (E) in the VIN number on that driveshaft label showing it as a 1984, so it passes the smog requirements, yet the FRAME number, the number that is "official" for registration, has the letter (D) showing a 1983 model. The actual facts on this discrepancy are not known for sure by me. But, it does lend itself to folks possibly registering/titling a bike for either year. The actual month and year of production are easy to find out from the last 7 digits on these models. In fact, the last 8 characters will identify any vehicle for date of manufacture...and often, as in our Airheads, one needs only the last 7 digits."


Read more here: http://bmwmotorcycletech.info/IDnumbrs.htm
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Old 04-25-2011, 09:49 AM   #71
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Originally Posted by Lornce View Post
the actual physics of motorcycle dynamics are still argued at the highest levels.

Excellent, well I shouldn't have a problem in promptly mastering it then
Thanks for the brief explanation. I've been trying to read up on this stuff a bit lately. I sort of seem to understand it, at times, but it hasn't stuck yet. What really confused the matter for me was the possibility of having forks that, due to different offsets in upper and lower triples, were not parallel to the stem/headstock. I understand that regardless of all this, with the steering pointed straight ahead, the rake and trail would be whatever they are for the given set up- however when turning the forks it would seem to add in a whole nother level of complexity to the equation. How irrelevant this all is open to question.
Sorry for stupiding up your thread Solo
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Old 04-25-2011, 10:07 AM   #72
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Originally Posted by Airhead Wrangler View Post
snobum says:
Clear as mud eh?
my 1981 R80G/S has these numbers.

Metal tag riveted to the headstock (TYP 247E):
6252171

Just below this stamped into the frame is, again (* is a round mark with bmw symbol):
*6252171*R80G/S*

on the engine, just above the dipstick is:
6251767

On the rear of the frame on that funny triangle bit where the right pillion peg is there is another riveted metal tag:
BMW(SCHEIZ)AG
CH 607231
the 6072 is printed, and the 31 is stamped...

who knows?

Having previously believed that the engine must have been a transplant due to non-matching numbers, I was struck by the fact that the numbers were so similar. Good luck? MAgic?
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Old 04-25-2011, 10:28 AM   #73
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Excellent, well I shouldn't have a problem in promptly mastering it then
Thanks for the brief explanation. I've been trying to read up on this stuff a bit lately. I sort of seem to understand it, at times, but it hasn't stuck yet. What really confused the matter for me was the possibility of having forks that, due to different offsets in upper and lower triples, were not parallel to the stem/headstock. I understand that regardless of all this, with the steering pointed straight ahead, the rake and trail would be whatever they are for the given set up- however when turning the forks it would seem to add in a whole nother level of complexity to the equation. How irrelevant this all is open to question.
Sorry for stupiding up your thread Solo
Not at all. HD's been using non parallel triples for decades on their big touring rigs. They were an Erik Buell innovation from the early '80's. In that instance, I believe it was used to create a generous trail dimension while maintaining a specific and desired aesthetic. Might have been chosen to enhance suspension action, too. Don't quote me on either point.

Trail's much easier to explain with a diagram. Once you get the idea behind the grocery cart trolley wheel in your head it's pretty straight forward.

1. Imagine a line defined by the centre point of both steering head bearings being extended to meet the surface of the road in front of the bike.

2. Imagine the centre of your tire's contact patch, or a perpendicular line passing through the centre of your bike's front axle and meeting the road surface.

Are you with me so far?

3. At the surface of the road measure back from the first line's point of intersection to the second line's point of intersection. That is your trail dimension.

The longer that is the more stable your bike will be in a straight line. The shorter it is, the less dynamically stable - but it'll steer quicker. Within reason. 4" or 100mm of trail is pretty common for street bikes.

On a big dual sport intended for use in lots of varying terrain we should probably be shooting for closer to 5 inches of trail.

imho, fwiw, ymmv,
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Old 04-25-2011, 11:46 AM   #74
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Good explanations Lornce!
This is one of my favorite topics!
I however was explaining trail to my nephew, and used the shopping cart analogy, and he stopped me right there. "now I know your full if s#!t old man, shopping carts wobble all over the place" I could not really explain why shopping carts suck, but I swear this makes a 200mph Superbike stable as a Aircraft carrier!

I've got a great old book by Foale, and another fellow. They build several special bikes, to experiment with. They build bikes with zero rake, and find, the less rake, the less trail is required, with no stability loss, if fact it increased at lower speeds, and no offset is used at all.

I'm personally of the belief that offset is the worst thing you can put into the front end of a motorcycle, and that the minimum possible should always be used.

BTW, experimenting with some of the race cars I build, we ran as little as 1/2 degree of castor (rake) with very good stability.
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Old 04-25-2011, 12:07 PM   #75
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Good explanations Lornce!
This is one of my favorite topics!
I however was explaining trail to my nephew, and used the shopping cart analogy, and he stopped me right there. "now I know your full if s#!t old man, shopping carts wobble all over the place" I could not really explain why shopping carts suck, but I swear this makes a 200mph Superbike stable as a Aircraft carrier!

bearings are usually trashed on those carts.
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