G/S project... sort of

G/S project... sort of
Sorry if this is a bit long but I'd best do a quick intro first since I'm new to the airheads forum.

I was on this site a few years ago, mainly in the G650X forum when I owned an X-challenge which, after 46k miles and several modifications, I eventually sold to buy a road bike and lighter dirt bike. After that I rode an ex-Dakar finishing XR650R for a few years - sort of similar to the X-challenge but a bit lighter and racier. I brought this bike with me when we moved to Cyprus in 2015 and despite not being quite as civilised as the X-Ch I managed to ride it 1000 miles through Turkey to Greece, complete the Serres Rally and then return 1000 miles back in a day. I really like the 650 class bikes but it was eventually sold as in Cyprus my riding was increasingly over very technical terrain. I swapped to a 2 stroke dirt bike but wasn't really gelling with it but then had a slight mishap - I went head on with a crew-cab who was on the wrong side off the road.

So that brings me to my airhead - I would call it a G/S but it is actually a bitsa bike with an ST frame, G/S engine, GS forks and wheels which I brought out here in Novemeber. I don't need to explain the charms of an airhead here but after riding with a mate who had a well sorted airhead bike many years ago they have always been on my list of bikes to own when the time was right. After 4 sets of surgery I am able to ride but not strong enough to head up the side of the nearest mountain but I felt bereft without a bike in the shed. What better time to undertake a project... So along came a bike which, since it was already for from standard, I could modify and hopefully improve without feeling guilty.

I have already done a few wee jobs on the bike - sorting sticking chokes and helicoils in the drive shaft fill and drain bolts - and am planning the next steps. What I want to do is update suspension at both ends then see where it takes me. A baja style rear fender and lighter silencer are possible, as is a capacity increase eventually but probably not unless the current engine parts wear out. Since I am on a budget this will be done over a period of time.

So to the suspension and a few questions.

I know the GS forks are an improvement over the original G/S front end but I still find them jarring my wrists over speed bumps in a way that my more recent bikes never have. I have tried lighter oil but they still don't match the compliance of modern forks. I know there are options available for cartridge type inserts but, from what I have read it seems they cost more and are not as effective as a straight swap for a modern front end. Add to that the fact that I have a spare Excel front wheel and the brake system from my crashed GasGas and it seems a sensible option. It seems a common option is to fit DRZ forks which fit the stem with a change of bearings. I don't have the cash for the custom yokes available over on AdvRider so plan to use a set of DRZ yokes. The GasGas brake calliper is the same as the DRZ, the wheel will fit the DRZ axle with a change of bearings and a 320mm SM disc is available which should be enough to cope with the weight of the G/S.

At the rear I definitely want a new shock as the existing one is from an ST and short compared to the forks. I will probably stick with standard length mono lever but haven't yet ruled out an extension. When cash allows I may also have the rear wheel rebuilt by Haan with an 18" rim rather than the current 17" GS wheel which has limited tyre choice in the narrow widths.

Questions then.

Am I on the right track or is there a better option? Please don't suggest I sell the bike for a modern dirt bike though.

Is there likely to be much demand for the GS front end currently fitted to the bike? My hope is that this will fund the purchase of the DRZ front end making it a free upgrade - I swapped the forks on my X-ch this way.

I am undecided on the shock - emulsion, remote reservoir or a half-way house like the Hyperpro 3D or Nitron which have a separating piston between the oil and nitrogen? l have read that greater travel can be obtained from a standard mono-lever with a custom shock and even steps such as strategically denting the cross member to allow greater clearance. I need a new shock anyway so having a custom shock built is feasible but I don't want to stress the U/J. Also some shocks have a different diameter which can impact on wheel clearance. Any thoughts, particularly those based on experience, would be appreciated.

Is there likely to be a value for the parts I remove?

GS front wheel, forks, yokes brake calliper
Rear rim and spokes. Unfortunately I can't exchange the complete GS rear wheel as the hub was modified to fit the 4 bolt bevel drive.
(the wheels have both been recently rebuilt with black powder coated rims and stainless spokes)
Original ST shock
Eventually a Keihan GS exhaust

I can post them back to UK via BFPO at UK rates, although a courier would be quicker.

Sorry for the rambling post.

Have a look at threads started by Mikeyboy in this Airheads section.

At least you'll see how he does his builds.

Hi Rossi,
Welcome to the airhead section.
The big problem with DRZ forks is two fold,
Firstly,they don’t have a lot of yoke offset,so the stancions will hit the tank limiting the amount of lock,
You could dent the tank in to get around this but will then find that the stepped lower drz yoke will hit the frame,again resulting in poor lock

Thanks for the reply. I am aware of the yoke off-set and reduced steering lock but was thinking of the right way up forks would be less affected than USD forks as the diameter at the top is smaller. So would a set of 4354 WP forks have greater clearance to the frame if dents were added to the tank? I liked the 4354's on my X-ch and they are both cheaper and less prone to stiction than the later 48mm forks.

Alternatively is it better to improve the GS forks?
What can be achieved with different weight fork oil / springs / gold valves. That should fall within the budget but I don't want to spend too much on them as the stanchions are starting to pit between the yokes.
I have seen cartridge inserts on an Italian site for €500 but have not found any reviews of how effective they are.

I'm not sure how seriously you'll take this off road, but I found the Hyperpro kit for my g/s made a huge difference to the forks.

rossi said:

Thanks for the reply. I am aware of the yoke off-set and reduced steering lock but was thinking of the right way up forks would be less affected than USD forks as the diameter at the top is smaller. So would a set of 4354 WP forks have greater clearance to the frame if dents were added to the tank? I liked the 4354's on my X-ch and they are both cheaper and less prone to stiction than the later 48mm forks.

Click to expand...

I’m currently fitting a set of wp forks to an st,
Bespoke yokes are essential

mikeyboy said:

I’m currently fitting a set of wp forks to an st,
Bespoke yokes are essential

Click to expand...

Is that because of the reduced offset causing clearance issues or the stem on the mainly KTM yokes having no compatible bearing with the BMW frame?

One of the reasons I chose the WP 4354's for the X-ch was that they fitted into the X-ch yokes. Some people chose to fit the 48mm forks with KTM yokes but had to use a custom stem or have the KTM stem turned to the a smaller diameter as there is no taper bearing that matches the diameter of the KTM stem and the BMW frame.

I was hoping to avoid custom yokes as they all seem to cost £££

tuftywhite said:

I'm not sure how seriously you'll take this off road, but I found the Hyperpro kit for my g/s made a huge difference to the forks.

Click to expand...

With the metalwork I am now carrying my rallying days are probably over but there are lots of gravel roads here in Cyprus, some of them quite rough. I have also spotted some interesting routes over the mountains in southern Turkey on Wikiloc so I do want something that will handle some off-road use.

Hi Rossi,

Did you see Phreaky Phil's thread back on that other site? That covers off exactly what you were looking at. He used a set of RM250 triples with 24mm of offset, but sleeved them down to fit the DRZ forks. He still had to add some clearance on the tank though. He also used a mono final drive & GS rear wheel.



Or any number of other fork conversion thread under the 'unholy union' banner. I've done a YZ250F 48mm fork conversion on a GS & now a G/S (2005 triples have 26 mm off set). I note Moorespeed & Paul Rooney both do a 46mm fork conversion using the earlier KYB USD forks.

I've also done a WP4860 conversion on a GS using HPM triples.

Pretty much anything is possible, but you need to think through utility, triples, fork offset, what that will do to trail, axle size, what wheel (& wheel size), & what brakes you are going to use. And the image that you want for the bike at the end of the project, i.e. do you want it to look like a stockish G/S or something else?

rossi said:

Is that because of the reduced offset causing clearance issues or the stem on the mainly KTM yokes having no compatible bearing with the BMW frame?

One of the reasons I chose the WP 4354's for the X-ch was that they fitted into the X-ch yokes. Some people chose to fit the 48mm forks with KTM yokes but had to use a custom stem or have the KTM stem turned to the a smaller diameter as there is no taper bearing that matches the diameter of the KTM stem and the BMW frame.

I was hoping to avoid custom yokes as they all seem to cost £££

Click to expand...

Mostly down to a lack of offset on the yokes,the shape of the yoke ar the rear dosnt help much either.
A custom stem is no big problem.
You could move the tank back slightly to get some clearance back. But I think once you get hold of some forks and try a “dry fit” you will start to see the issues you will have to face.

Box’a’bits said:

Hi Rossi,

Did you see Phreaky Phil's thread back on that other site? That covers off exactly what you were looking at. He used a set of RM250 triples with 24mm of offset, but sleeved them down to fit the DRZ forks. He still had to add some clearance on the tank though. He also used a mono final drive & GS rear wheel.

Or any number of other fork conversion thread under the 'unholy union' banner. I've done a YZ250F 48mm fork conversion on a GS & now a G/S (2005 triples have 26 mm off set). I note Moorespeed & Paul Rooney both do a 46mm fork conversion using the earlier KYB USD forks.

I've also done a WP4860 conversion on a GS using HPM triples.

Pretty much anything is possible, but you need to think through utility, triples, fork offset, what that will do to trail, axle size, what wheel (& wheel size), & what brakes you are going to use. And the image that you want for the bike at the end of the project, i.e. do you want it to look like a stockish G/S or something else?

Click to expand...

Purposeful. That's what that bike looks. Very nice. Sorry! Carry on!

scotboxer said:

Purposeful. That's what that bike looks. Very nice. Sorry! Carry on!

Click to expand...

Much more fit for purpose than the overexpensive, overweight and overcomplicated wassrhead GS's (or luxury tourers as I know them) being pumped out these days....IMHO. But what do I know....

Purposeful - a good description.

Thanks for all the replies.

I have read though the unholy union threads but perhaps need to do so in more detail as I had missed that RM yokes have greater offset than DRZ.

It's fine to say buy a set of forks and then you will see the problem, but what I am trying to do is avoid running in to too many problems in the first place, particularly when others have been there before and found solutions. So, short of investing in custom yokes, is there a definitive answer for the least problematic set of forks to look for before I go shopping?

Regarding the final look, something approaching the above would be great although I have the stock G/S tank and wasn't planning to have a rack behind the seat.

mikeyboy said:

Mostly down to a lack of offset on the yokes,the shape of the yoke ar the rear dosnt help much either.
A custom stem is no big problem.
You could move the tank back slightly to get some clearance back. But I think once you get hold of some forks and try a “dry fit” you will start to see the issues you will have to face.

Click to expand...

I’m not suggesting you buy forks ,but you seem set ,that you are not going to invest in bespoke yokes.
The bike pictured above does not look to have much clearance between tank and forks,if the 26mm offset quoted is correct it would certainly be better than stock drz yokes,with the added advantage of not having the stepped drz lower yoke.it would seem though that modification are still necessary to shoehorn them in.
The bike will still have a limited lock when compared to standard forks,which is a right pain in the arse when it comes to using the bike day to day and on tracks and trails where frequent u turns are encountered.
If you read ADV rider you will see offsets of over 30mm quoted to get adequate lock.
Without bespoke yokes the bike will just end up being a poor compromise and any advantage gained through better suspension will be lost through being unpractical ( unless of course you ride on straight roads and never miss a turn or entrance to a lane)

I have done this a few times
The easiest conversions are the bikes that have had different tanks fitted.
The standard tank comes further forward and causes the most hassle.
The g/s with ktm WP forks will prob end up with 35mm offset

mikeyboy said:

I have done this a few times
The easiest conversions are the bikes that have had different tanks fitted.
The standard tank comes further forward and causes the most hassle.
The g/s with ktm WP forks will prob end up with 35mm offset

Click to expand...

You keep yourself busy and I am really impressed by your skills.

It sounds like there isn't a low budget way of doing this. So the next question is how much does a set of custom yokes cost, or perhaps is there a way to get hold of a set for a sensible price? I have seen some advertised but all for serious money. I suppose that to make a set from scratch I would need some serious kit. I have access to lathes and a milling machine but I think it is all manual control rather than CAD-CAM.

I’ll keep you updated with the progress on the yokes being made now,
If you choose to go with the same dia forks maybe 2 sets could be made whilst the machines are set up.

mikeyboy said:

I’ll keep you updated with the progress on the yokes being made now,
If you choose to go with the same dia forks maybe 2 sets could be made whilst the machines are set up.

Click to expand...

Thanks!

Fit a Ohlins on the rear with a 400 lb spring and springs in the forks which give around 10% more rider sag than the rear, with around 25 mm preload.
They will be big figures , around 65/60 mm but they will work fine for the sort of work you envisage.


Then find someone who can set up and fine tune the suspension - you will need access to these skills no matter what you decide to do, and if you don't have access to them there is no point in even considering any other course of action anyway1