covenant kit?
- Thread starter pelican
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Sorry for the late arrival in this thread 
I'm in the process of ordering a fork rebuild kit, and I'm considering the RGM longer bushes and the alloy damper mod.
I notice they also list a cast Iron top cap "061347CI CAST IRON DAMPER BODY TOP CAPS FOR USE WITH ALLOY DAMPER ROD"
A couple of questions for those familiar with these:
Are the alloy dampers significantly different from the stock items, or are they just another way of relocating the bleed holes; and are the cast iron caps essential?
It seems the dampers and caps are listed individually, and not as pairs. Still not shockingly (ahem) expensive though.
I'm in the process of ordering a fork rebuild kit, and I'm considering the RGM longer bushes and the alloy damper mod.
I notice they also list a cast Iron top cap "061347CI CAST IRON DAMPER BODY TOP CAPS FOR USE WITH ALLOY DAMPER ROD"
A couple of questions for those familiar with these:
Are the alloy dampers significantly different from the stock items, or are they just another way of relocating the bleed holes; and are the cast iron caps essential?
It seems the dampers and caps are listed individually, and not as pairs. Still not shockingly (ahem
) expensive though.
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B+Bogus,
The alloy damper tube looks very similar to the standard steel unit but the bleed holes are smaller and lower. If you do buy a pair get a matching pair of bolts, mine were BSF and should have been UNF for a Mk3. I used the alloy caps but the iron version should have a longer service life. I'm not so sure the alloy rods would be a good idea on a road bike, they may wear quickly. And I also use Progressive springs.
I had access to the Norton damper drawings and interestingly there were at least four differently bored caps available.
Cash
The alloy damper tube looks very similar to the standard steel unit but the bleed holes are smaller and lower. If you do buy a pair get a matching pair of bolts, mine were BSF and should have been UNF for a Mk3. I used the alloy caps but the iron version should have a longer service life. I'm not so sure the alloy rods would be a good idea on a road bike, they may wear quickly. And I also use Progressive springs.
I had access to the Norton damper drawings and interestingly there were at least four differently bored caps available.
Cash
L.A.B.
The article by P. Crespin is old. Thats coz it is the original study.
I studied the article a great deal before modifying my own forks.
As an practicing design engineer with a degree in mechanical engineering I felt I was equipped to do so.
I agree with the original aricle and its principles.
In my opinion RGM have copied his ideas but failed to understand a very important concept.
If you want to allow the sleeve to float on your forks, I don't have a problem with that.
But you won't convince me it is right and I will argue against you convincing others that is is right.
I think I have said all I can on this thread.....lets agree to disagree
Stu
The article by P. Crespin is old. Thats coz it is the original study.
I studied the article a great deal before modifying my own forks.
As an practicing design engineer with a degree in mechanical engineering I felt I was equipped to do so.
I agree with the original aricle and its principles.
In my opinion RGM have copied his ideas but failed to understand a very important concept.
If you want to allow the sleeve to float on your forks, I don't have a problem with that.
But you won't convince me it is right and I will argue against you convincing others that is is right.
I think I have said all I can on this thread.....lets agree to disagree
Stu
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bigstu said:
bigstu said:
I certainly respect and value your (and others') opinion on this subject, which has stimulated a certain amount of debate, and it wasn't my intention to try to convince anyone that this is some sort of definitive argument for allowing the sleeves to float (as I'm sure others are capable of reaching their own decisions) but only to give an alternative viewpoint that I did fit the RGM kit to my Commando's forks in accordance with the instructions supplied, which has been in use now certainly for several years, and has resulted in no adverse affects whatsoever during that time. Maybe it is because I'm a lowly and (reasonably) uneducated construction worker that I'm not bound by engineering principals of what should or shouldn't work 'on paper', and can only rely on the actual experiences I've had with the RGM kit in this particular instance, so yes....let's agree to differ. :wink:
Cash — I hope you don't mind me asking you a few questions, because I am thinking of doing what you have done. What material did you make your new top bushes from? Was it sintered bronze? And if so, did you buy Oilite bushes that were oversize on OD and ID and finish them to size? What clearance did you use between fork bush and stanchion? Finally, did you make the new bushes 1.5" longer or did you determine the length by some other means? As an aside, Maxton Suspension told me that they make replacement Roadholder bushes from oil-impregnated nylon. I wonder if it is easy to source and how it machines. This material should help reduce fork stiction and further improve the ride.
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Daveh,
Man it was a while ago, and at times I can't remember what I did yesterday.
Now this won't sound too clever, but that's how I do things from time to time.
I used Oilite and there are many grades. By chance the piece I scrounged looked much the same as the standard bush material. (My own risk)
I took no records of any dimensions at all. I just measured up and copied a new bush as I went. The extra length was simply the length of a Covenant sleeve, which I'm sure is as long as the length of the bush under the collar. I machined the longer bushes to as near to the donor bush as possible, no more than 0'001" smaller in the bore. The idea was to machine to fit, I'm sure I got lucky cos I don't remember having a problem. The extra length bore was relieved by I think 0.010". After machining the bushes were carefully washed with petrol, dried and then left to soak for 48 hours in 20wt oil.
Oilite machines Ok, I prefer small rad tool tip but used a larger rad in the bore, at speed the oil flings out and it doesn't like standard reamers cos the pores block.
Oylon and I suppose the rest of the impregnated plastics again machine easily and often cut better with zero rake. The problem is that some are hydroscopic (I think that's the word) they absorb water and swell. The manufacturer will or should help you resolve this.
Be carefull what ever material you choose to use, however, I've got a long length of plastic self lubrcated bush material. I would need to dig out it's trade name and properties, if it was suitable you'd be welcome to a bit.
Cash
Man it was a while ago, and at times I can't remember what I did yesterday.
Now this won't sound too clever, but that's how I do things from time to time.
I used Oilite and there are many grades. By chance the piece I scrounged looked much the same as the standard bush material. (My own risk)
I took no records of any dimensions at all. I just measured up and copied a new bush as I went. The extra length was simply the length of a Covenant sleeve, which I'm sure is as long as the length of the bush under the collar. I machined the longer bushes to as near to the donor bush as possible, no more than 0'001" smaller in the bore. The idea was to machine to fit, I'm sure I got lucky cos I don't remember having a problem. The extra length bore was relieved by I think 0.010". After machining the bushes were carefully washed with petrol, dried and then left to soak for 48 hours in 20wt oil.
Oilite machines Ok, I prefer small rad tool tip but used a larger rad in the bore, at speed the oil flings out and it doesn't like standard reamers cos the pores block.
Oylon and I suppose the rest of the impregnated plastics again machine easily and often cut better with zero rake. The problem is that some are hydroscopic (I think that's the word) they absorb water and swell. The manufacturer will or should help you resolve this.
Be carefull what ever material you choose to use, however, I've got a long length of plastic self lubrcated bush material. I would need to dig out it's trade name and properties, if it was suitable you'd be welcome to a bit.
Cash
Cash — thanks very much for going into detail on materials, lathe tool shapes and tool rake — that's exactly the info I needed. From what you have said, I should be cautious about using Oylon or other such materials, unless the properties and machinability are well researched. I made a few enquiries a few months back, but no-one I asked was forthcoming. Maybe the best bet is to machine the longer bushes from a well-known material like Oilite and see how it goes. Thanks also for the offer of the material — much appreciated! I will talk to the Oilite stockist in Dublin and see if they have anything suitable and I may come back to you if I have no joy with them! 
Dave
Dave
Just to stick my oar in here, I made my top bushes from DTD197A (CA104) over 10,000 miles ago & they are still going strong. I figured that a rolled bronze would last longer than a sintered bronze. Can't remember if I made them longer, got a feeling I did.
A sintered bronze, such as oilite, could offer less sticion. I haven't thought about this until now.
The proper way to put the oil back into the oilite, is to boil it in oil.
Managed to bottom my forks out again this morning, might be worth looking into some changes in the winter time.
Bye the way, what thickness of oil do most owmers use?
A sintered bronze, such as oilite, could offer less sticion. I haven't thought about this until now.
The proper way to put the oil back into the oilite, is to boil it in oil.
Managed to bottom my forks out again this morning, might be worth looking into some changes in the winter time.
Bye the way, what thickness of oil do most owmers use?
Flo — I use 50:50 mix of 20 wt and 30 wt fork oil, together with Progressive springs, new RGM alloy damper tubes (with claimed improved damping), new steel damper rods and new alloy top caps. I moved up from 20 wt, which wasn't quite thick enough for me. The forks give quite a compliant ride but they still can't really deal very well with hard braking and also 'top out'.
Interesting that you used rolled bronze for yours. What is your fork action like? Also, I wonder are the original bushes made of sintered bronze?
I think that unless you go for a sophisticated and expensive solution, such as modern cartridge dampers, there is only so much you can do and you have to ride within the limits of the forks and the rest of the chassis.
Interesting that you used rolled bronze for yours. What is your fork action like? Also, I wonder are the original bushes made of sintered bronze?
I think that unless you go for a sophisticated and expensive solution, such as modern cartridge dampers, there is only so much you can do and you have to ride within the limits of the forks and the rest of the chassis.
I see you all are using forl oil. I was looking at the "Rider's Manual" for recommended lubricants. Two things struck me, 1) specifying multi-viscosity motor oil and 2) the naming of "Filtrate A.T. Fluid 'F'". I have never heard of using motor oil in the forks. Is the Filtrate reference specifying automatic transmission fluid type F?
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Rob94010 said:
'Hydraulically damped telescopic forks' were around long before "fork" oils became commonly available, so early forks (as fitted to BSA,Triumph, Norton and many other makes) normally used SAE20 & SAE30 motor oil as the damping fluid.
Rob94010 said:
Yes, apparently Filtrate type F was ATF.
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Redundant now....total adjustable control is available..pelican said:
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yes....motor oil was used,,,and mags..and monoblocks...and 6v ...and 5in drums....and.......L.A.B. said:
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Evolution....can anyone crack this problem ?daveh said:
Hi John — I am very impressed by your fork damper kit and want it!! I wrote those comments before your kit came on the scene. Fork stiction is a problem I have observed not just with Roadholders but with many old designs. I wanted to experiment with a particular nylon compound that seems to be a suitable replacement for the bronze top bushes. However, having thought about it some more, I wonder if the stiction is due to wear in the middle of the fork leg, which allows the stanchion to be cocked very slightly and encourages excessive friction between the bottom steel bush and the bore of the leg? Any thoughts on the above? Have you noticed stiction in Roadholders that have your damper kit fitted? If one could reduce stiction together with your kit, it would make the fork action even better.
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