R65LS front end tweaks and aftermarket forkbraces.
Posted: Sat Mar 14, 2015 1:25 am
An interesting read.
AFTERMARKET FORKBRACES AND FRONT END TWEEKS
http://www.advrider.com/forums/showthre ... 726&page=5
JohnJen from ADVrider as editor note:
This tome was originally written by Michael Beresford in 1998 and was never ‘finished’ in that life took us both in different directions, so it lacks some details and wasn’t fully ‘fleshed out’ so to speak.
However for those with enough understanding, between this write up and what I remember, there should be enough to put together a means of utilizing these ‘techniques’.
In one of those ongoing 'threads' there was a question about aftermarket fork-braces and front ends. I thought I'd see what the responses to the questions were and then summarize my findings. I've seen a few postings that were close to what my experience has taught me, so at the request of some of those I have shared this experience/knowledge with, (“shared with” as in me incorporating this knowledge into the machines I've re-built for them), I decided to add my 2¢ worth here.
FIRST A LITTLE HISTORY.
I bought my first BMW after riding an friends R100 RS. At that time I had a shop in the Northwest and specialized in fuel delivery systems of all types (carbs and fuel injection), from stock to full race, and factory spec. restorations of all kinds. I also restored European cars at the shop.
At one point this one bikes owner complained that the stock carbs were not for him and came in asking about Mikuni square slides. We settled on some round slide Mikunis I had in the shop. I changed the jetting and installed them so they look stock and test rode it when I was finished.
A month or so later I bought a 1976 - R90/6. And as a matter of course I started fixing it up. I early on, (shortly after I started fixing it up) decided to write this M/C off on my business as a test platform/experimental test subject. I went to the local dealer looking for any and all information I could get ahold of and got the cold shoulder treatment. Needless to say, I didn’t feel like returning for any of their mechanical advise or help.
I have always had a knack at being able to make any engine produce more horsepower than an un-modified vehicle could safely handle, no matter what state/condition it is in when it first comes into the shop. When I was younger I used to build 'fire-breathing' stuff that needed to be torn down again and again. I then turned to maximizing stock stuff. Now my aim is to maximize long term durability, usable horsepower and torque, from basically stock components.
Today I choose oilhead beemers in the m/c class, Volvo's and Bimmers in the car division. My philosophical and mechanical intent is to do the work right the first time which allows me to guarantee the finished product, parts and labor, for one year.
The clients I choose to work with usually want to purchase a machine and make it drivable for another 100,000 miles with only regular maintenance as described in the owners manual. This is basically how my current partner got involved. While there are those who already own some sort of vintage machine that needs to be restored, they also want to ride/drive a vintage machine long term.
Owning my own shop allows me to play with/research many of the different aspects of being able to build and then ride BMWs fast, while having the m/c remain 'stable' under all operational conditions. By 'stable' I mean that I can use more of the available h.p. and torque without increasing the recommended maintenance requirements. Indeed, I have found that I could significantly reduce the wear and tear, thus greatly increasing the bikes useful life (an obvious advantage on a vintage machine). Or needlessly putting myself or a client in danger by building machinery that would behave badly when pushed to it's limits.
THAT WAS THEN, THIS IS NOW, WHAT’S THIS BRACE THING?
One of the first things I heard was, “put a fork brace on.” Two were available at the time. The one from C.C. Products was a round tube bent over the front fender unit and the other one was a four piece bolted together flat unit from Telefix. I bought a Telefix first and found that it helped. At this point I had not taken my front end apart, but it did seem to help.
I had also heard that Progressive springs were the way to go, so I bought front springs and rear shocks. I took the front end apart and cleaned it up, noticing the wear patterns, and took notes. I put everything back together using all the local tricks (plate glass etc.) for checking the tubes for alignment, new rings on valving, new seals everywhere, and 7.5 weight BMW oil from the local BMW dealer. Boy, what a difference, or so I thought at the time. Yes, the m/c handled much better at first with the new springs and shocks and fresh parts. I rode this set-up for about a year. "Harsh" is the best way to describe the way the ride became, though it did seem to handle well in the corners at first.
One thing became apparent to me from day one, the m/c sat much higher off the ground, although I didn't think too much about it at the time. When I took the front end apart at the end of a year to change the oil etc., I noticed the wear had accelerated and changed locations in the sliders and on the tubes. As a result of the changed wear patterns - out came the progressive springs.
The progressive springs which were purchased at the local BMW dealer kept the front end fully extended even loaded with the weight of the driver and passenger. By “extended” I mean that the stiffer springs did not allow the tubes to sit down in the specially machined areas inside the sliders far enough for the ends of the tubes to not want to dig into the sliders as the suspension tried to do it's job. This is the wear pattern that I saw and have seen numerous other times since on other front ends I’ve worked on.
If you take a slider off a BMW and clean the inside of all oil and dirt you will be able to see that there are two distinct surfaces machined into the cast slider along its inner length. The upper load bearing portion of the machined surface is only about two inches in length. Then next there is a relieved cast area that is not machined, then another longer load bearing machined surface below. If one takes a ruler and measures inside the slider where this lower surface begins and then transfers that measurement to the outside of the slider and thinks about how far the tube extends down inside, it may clear up some questions. My conclusion is that using stiffer springs, the tubes rarely ever reach far enough down into the lower machined load bearing surface which constitutes the second guide surface as was intended by BMW engineers.
Another way to understand what is happening is to strip down and clean a tube and slider, and remove the upper seal.
Being careful not to scratch the slider, measure from the top of the slider to the top of the lower machined surface.
Carefully (this procedure is usually done best, clamped in a vise) insert a clean dry tube the same measured distance into the slider adding at least one more inch. While holding the tube and slider so they can not slide in or out, push either the tube or the slider back and forth and notice the maximum amount of side to side play between them. Next insert the tube two more inches into the slider, for a total of three inches now inserted beyond where the lower machining surface begins and check for of side to side play again. Most people can feel the difference.
With the tube inserted one inch more than the initial measurement to the lower machined surface, is approximately where the m/c rests with the Progressive springs installed.
Now, with the tube inserted one inch more than the initial measurement, slowly slide the tube into the slider about four or five inches while pulling and pushing the slider side ways against the tube. This side force represents normal loading of the front end because the forks extend forward. I have noticed a great deal of difference as the two pieces slide deeper into each other, the deeper tube is inserted the smoother the sliding action. Also the deeper the tube (up to the limits specified by BMW), the less 'rattling' I get while pulling or pushing the slider side ways while sliding the tube up and down a couple of inches.
There simply isn't enough surface contact to keep the tube aligned with the slider as the m/c is rolling over bumps and moving up and down when it's “oversprung.”
I'm going to change the subject slightly and say something that some people may take offense at. I still can’t understand why BMW of N.A. doesn’t mandate certain basic tools be in each dealers repair area. The most basic tool is a granite surface plate and a real measuring table-grade Vernier height gauge with a rudimentary dial indicator set up to measure everything from piston retaining ring thickness to the accuracy of brake shoes seating on the shoe spreader. One of my all time favorite responses from a local dealer was "We (BMW dealers) don’t have the money to buy this equipment.” My problem with this claim is that anyone can buy an 18”x 24” surface plate that is guaranteed to be flat within .000015 of an inch, and vernier height gauge with a dial indicator accurate to .0005” for $250 or less. This isn’t the highest quality equipment available, but it is more than adequate to measure damn near everything on a BMW, tubes, fork-braces, etc.
Another thing I have noticed is that for all the slamming I hear and read about Harley’s, they (dealers) usually are set up to measure and straighten front ends. Almost all of the factory repair manuals for H.D. show all the tools required to do this type of job. Harley front tubes are the only tubes I’ve seen that have a material (wall) thickness comparable to that of BMW’s. Although I personally haven’t owned a H.D. since I was a teen, I do restore and build them for the long term for those who have the money. Yes it is possible to do this in spite of all the rumors to the contrary.
In the factory repair manual, BMW gives all the specs for all the twins from 1970 thru the mid 1980’s. Front fork tubes are allowed no greater deflection than .003937", which is slightly under four thousandths of an inch. BMW says the clearance between the tube and the slider is the same thirty-nine-+ hundredths of an inch. The manual also states there is approx. 4.29" of upward/unloading travel, and 3.82" downward/compressible travel. Simply putting an identical-length yet stiffer spring in the front suspension doesn't allow the front suspension to take advantage of BMWs design. If you look carefully at the length of the valveing rod inside the tube you will get a rough idea of the total travel up and down as designed by BMW.
To cut to the chase here, for this suspension to work as designed, you need to see about 10 inches of the length of the tube below the upper slider seal (m/c off all stands with rider on seat) in order to work best under all driving conditions. Stiffer -SHORTER- springs, which allow the tubes to be inserted 10" past the upper seal with m/c fully loaded and off all stands ---- might actually work. However, there are other aspects to consider if one were to doing something like this which I won't go into here.
AFTERMARKET FORKBRACES AND FRONT END TWEEKS
http://www.advrider.com/forums/showthre ... 726&page=5
JohnJen from ADVrider as editor note:
This tome was originally written by Michael Beresford in 1998 and was never ‘finished’ in that life took us both in different directions, so it lacks some details and wasn’t fully ‘fleshed out’ so to speak.
However for those with enough understanding, between this write up and what I remember, there should be enough to put together a means of utilizing these ‘techniques’.
In one of those ongoing 'threads' there was a question about aftermarket fork-braces and front ends. I thought I'd see what the responses to the questions were and then summarize my findings. I've seen a few postings that were close to what my experience has taught me, so at the request of some of those I have shared this experience/knowledge with, (“shared with” as in me incorporating this knowledge into the machines I've re-built for them), I decided to add my 2¢ worth here.
FIRST A LITTLE HISTORY.
I bought my first BMW after riding an friends R100 RS. At that time I had a shop in the Northwest and specialized in fuel delivery systems of all types (carbs and fuel injection), from stock to full race, and factory spec. restorations of all kinds. I also restored European cars at the shop.
At one point this one bikes owner complained that the stock carbs were not for him and came in asking about Mikuni square slides. We settled on some round slide Mikunis I had in the shop. I changed the jetting and installed them so they look stock and test rode it when I was finished.
A month or so later I bought a 1976 - R90/6. And as a matter of course I started fixing it up. I early on, (shortly after I started fixing it up) decided to write this M/C off on my business as a test platform/experimental test subject. I went to the local dealer looking for any and all information I could get ahold of and got the cold shoulder treatment. Needless to say, I didn’t feel like returning for any of their mechanical advise or help.
I have always had a knack at being able to make any engine produce more horsepower than an un-modified vehicle could safely handle, no matter what state/condition it is in when it first comes into the shop. When I was younger I used to build 'fire-breathing' stuff that needed to be torn down again and again. I then turned to maximizing stock stuff. Now my aim is to maximize long term durability, usable horsepower and torque, from basically stock components.
Today I choose oilhead beemers in the m/c class, Volvo's and Bimmers in the car division. My philosophical and mechanical intent is to do the work right the first time which allows me to guarantee the finished product, parts and labor, for one year.
The clients I choose to work with usually want to purchase a machine and make it drivable for another 100,000 miles with only regular maintenance as described in the owners manual. This is basically how my current partner got involved. While there are those who already own some sort of vintage machine that needs to be restored, they also want to ride/drive a vintage machine long term.
Owning my own shop allows me to play with/research many of the different aspects of being able to build and then ride BMWs fast, while having the m/c remain 'stable' under all operational conditions. By 'stable' I mean that I can use more of the available h.p. and torque without increasing the recommended maintenance requirements. Indeed, I have found that I could significantly reduce the wear and tear, thus greatly increasing the bikes useful life (an obvious advantage on a vintage machine). Or needlessly putting myself or a client in danger by building machinery that would behave badly when pushed to it's limits.
THAT WAS THEN, THIS IS NOW, WHAT’S THIS BRACE THING?
One of the first things I heard was, “put a fork brace on.” Two were available at the time. The one from C.C. Products was a round tube bent over the front fender unit and the other one was a four piece bolted together flat unit from Telefix. I bought a Telefix first and found that it helped. At this point I had not taken my front end apart, but it did seem to help.
I had also heard that Progressive springs were the way to go, so I bought front springs and rear shocks. I took the front end apart and cleaned it up, noticing the wear patterns, and took notes. I put everything back together using all the local tricks (plate glass etc.) for checking the tubes for alignment, new rings on valving, new seals everywhere, and 7.5 weight BMW oil from the local BMW dealer. Boy, what a difference, or so I thought at the time. Yes, the m/c handled much better at first with the new springs and shocks and fresh parts. I rode this set-up for about a year. "Harsh" is the best way to describe the way the ride became, though it did seem to handle well in the corners at first.
One thing became apparent to me from day one, the m/c sat much higher off the ground, although I didn't think too much about it at the time. When I took the front end apart at the end of a year to change the oil etc., I noticed the wear had accelerated and changed locations in the sliders and on the tubes. As a result of the changed wear patterns - out came the progressive springs.
The progressive springs which were purchased at the local BMW dealer kept the front end fully extended even loaded with the weight of the driver and passenger. By “extended” I mean that the stiffer springs did not allow the tubes to sit down in the specially machined areas inside the sliders far enough for the ends of the tubes to not want to dig into the sliders as the suspension tried to do it's job. This is the wear pattern that I saw and have seen numerous other times since on other front ends I’ve worked on.
If you take a slider off a BMW and clean the inside of all oil and dirt you will be able to see that there are two distinct surfaces machined into the cast slider along its inner length. The upper load bearing portion of the machined surface is only about two inches in length. Then next there is a relieved cast area that is not machined, then another longer load bearing machined surface below. If one takes a ruler and measures inside the slider where this lower surface begins and then transfers that measurement to the outside of the slider and thinks about how far the tube extends down inside, it may clear up some questions. My conclusion is that using stiffer springs, the tubes rarely ever reach far enough down into the lower machined load bearing surface which constitutes the second guide surface as was intended by BMW engineers.
Another way to understand what is happening is to strip down and clean a tube and slider, and remove the upper seal.
Being careful not to scratch the slider, measure from the top of the slider to the top of the lower machined surface.
Carefully (this procedure is usually done best, clamped in a vise) insert a clean dry tube the same measured distance into the slider adding at least one more inch. While holding the tube and slider so they can not slide in or out, push either the tube or the slider back and forth and notice the maximum amount of side to side play between them. Next insert the tube two more inches into the slider, for a total of three inches now inserted beyond where the lower machining surface begins and check for of side to side play again. Most people can feel the difference.
With the tube inserted one inch more than the initial measurement to the lower machined surface, is approximately where the m/c rests with the Progressive springs installed.
Now, with the tube inserted one inch more than the initial measurement, slowly slide the tube into the slider about four or five inches while pulling and pushing the slider side ways against the tube. This side force represents normal loading of the front end because the forks extend forward. I have noticed a great deal of difference as the two pieces slide deeper into each other, the deeper tube is inserted the smoother the sliding action. Also the deeper the tube (up to the limits specified by BMW), the less 'rattling' I get while pulling or pushing the slider side ways while sliding the tube up and down a couple of inches.
There simply isn't enough surface contact to keep the tube aligned with the slider as the m/c is rolling over bumps and moving up and down when it's “oversprung.”
I'm going to change the subject slightly and say something that some people may take offense at. I still can’t understand why BMW of N.A. doesn’t mandate certain basic tools be in each dealers repair area. The most basic tool is a granite surface plate and a real measuring table-grade Vernier height gauge with a rudimentary dial indicator set up to measure everything from piston retaining ring thickness to the accuracy of brake shoes seating on the shoe spreader. One of my all time favorite responses from a local dealer was "We (BMW dealers) don’t have the money to buy this equipment.” My problem with this claim is that anyone can buy an 18”x 24” surface plate that is guaranteed to be flat within .000015 of an inch, and vernier height gauge with a dial indicator accurate to .0005” for $250 or less. This isn’t the highest quality equipment available, but it is more than adequate to measure damn near everything on a BMW, tubes, fork-braces, etc.
Another thing I have noticed is that for all the slamming I hear and read about Harley’s, they (dealers) usually are set up to measure and straighten front ends. Almost all of the factory repair manuals for H.D. show all the tools required to do this type of job. Harley front tubes are the only tubes I’ve seen that have a material (wall) thickness comparable to that of BMW’s. Although I personally haven’t owned a H.D. since I was a teen, I do restore and build them for the long term for those who have the money. Yes it is possible to do this in spite of all the rumors to the contrary.
In the factory repair manual, BMW gives all the specs for all the twins from 1970 thru the mid 1980’s. Front fork tubes are allowed no greater deflection than .003937", which is slightly under four thousandths of an inch. BMW says the clearance between the tube and the slider is the same thirty-nine-+ hundredths of an inch. The manual also states there is approx. 4.29" of upward/unloading travel, and 3.82" downward/compressible travel. Simply putting an identical-length yet stiffer spring in the front suspension doesn't allow the front suspension to take advantage of BMWs design. If you look carefully at the length of the valveing rod inside the tube you will get a rough idea of the total travel up and down as designed by BMW.
To cut to the chase here, for this suspension to work as designed, you need to see about 10 inches of the length of the tube below the upper slider seal (m/c off all stands with rider on seat) in order to work best under all driving conditions. Stiffer -SHORTER- springs, which allow the tubes to be inserted 10" past the upper seal with m/c fully loaded and off all stands ---- might actually work. However, there are other aspects to consider if one were to doing something like this which I won't go into here.
