Suspension Part 2

Decided to rebuild the Fox shocks that I had on the Husqvarna 360 as they looked like they were pretty tired and the measurements showed a lot of sag. I didn’t have a service kit for them so it was a bit of a rough and ready job. For the longer term, I’ll make a spring compressor, but for this job it was out with the rachet straps and slip off the bottom collet. There is a preload adjuster on these Fox (non-air) shocks and noticed I could have tried them with increased compression.

 

Fox shocks on rear

Fox Shocks had a bit too much sag, so there would be very little suspension travel on the rear of the bike. 

They are relatively easy to strip and a relatively straight forward design. The only challenge is getting out the lower circlip which is about 40mm down inside the bottom tube and ideally need some long nose internal circlip pliers. There was oil left in the shock but not a lot (<50ml) and expect 60-70ml in the shock. Didn’t change any seals but ideally would want to this going forward.  There is an air top for the shocks, where you’d normally put some form of inert gas, lets say 50 psi as air will heat up with work on the track. However, can probably get away with this for now.

 

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The oil looked a bit original and maybe missing some volume

Shock back together with some fiddling, again with the lower circlip and the compressing the spring. It didn’t seem quite right when back together but the proof will be the using.  Doing a proper service with seals etc might be the better plan. But given they were £50 shocks (from Telford) and period items, I’m happy to experiment with them  Did some other work on the bike to get ready for the North Devon meeting coming up, but have worked out the starting technique for the bike, which has a Mikuni carb.  All of the Huskies flood easily and then can be buggers to start (you need to take the plug out and given them dry) and the Automatic isn’t an exception.

I’m also becoming more of a fan of the looks of the 360 Automatic despite it having a large enduro tank (which has its uses if I ever do another Gentle One). The 1976 models are lower than the 1975 models it seems and the frame and shock length different.

Bike after cleaning

 

Classic MX Suspension Setup ?

Spent 30 minutes or so at lunch today looking at the suspension on 3 of the Husqvarna’s. Like a lot of riders, probably spend more time tuning engines, fuel and ignition than we do suspension and even then spent 80% of that time looking at the rear suspension. The front suspension on the 360 Automatic was looking a bit wrong at Abbeycwmhir on the weekend, but decided to do some more research, before doing an overhaul.

Most conversation about suspension is whether it is within the regulations

The measurements are as follows, all in mm.  Rear suspension travel was calculated using the ECMO online calculator, and front was measurement/estimate on the front forks.

[table width="500px"]
Bike, Suspension, Travel, Free,Load, Sag
Husqvarna CR250 1970,Rear,108,435,405,30(27%)
,Front,200,775,738,37(15%)
Husqvarna 250 Bolt-up 1966,Rear,115,440,403,37(30%)
,Front,200,750,720,30(27%)
Husqvarna Automatic 1976,Rear,140,420,380,40(26%)
,Front,250,820,775,45(18%)
[/table]

 

Looking at a modern MX suspension set up example, it says that rider sag should be 33% of the total suspension travel, but this is of course for modern bikes that might have 300mm+ suspension travel, where of course pre74 classic bikes are limited to 130mm in Europe and 120mm in the UK. Therefore, for your classic scrambler, rider sag of 35-40mm would be about the maximum using this formula.

One thing you also notice, well I did with the Automatic, is the impact of having an imbalance between the front and the rear if one set of suspension is either too hard or too soft.  On the 360 Automatic, I’d picked up some very used Fox rear shocks at Telford, but with them on the bike it’s clear they are worn out and too soft. On the other hand the front was a bit too stiff and so this made the rear work in a different way. They need to be in balance to work effectively and getting the rear wrong impacts on the handling of the front.

Based on the measurements above,  the front was too stiff and sticking so decided to strip it down.

The fork oil had been contaminated with something, probably water and needed a complete strip to clean
The fork oil had been contaminated with something, probably water and needed a complete strip to clean

One of the fork stanchions was also bent, as usual just below the bottom yoke and the took a bit of cleaning out. The springs seemed okay and put in 250ml of oil into each leg. One of the advantages of having an Automatic is that you have plenty of HVI26 oil, which is primarily for hydraulic applications, and same spec as Ohlins fork/shock oil.  Works out cheaper than fork oil and is around 10 weight, it seems.

 

The fork tube isn't quite straight
The fork tube isn’t quite straight

 

Some further adjustment needed as once back on the bike, they still seemed to be too stiff but this might be because of the rear being too soft and that is where all the give is in the suspension.

 

 

 

A quick rebuild

The Husqvarna 360 Automatic was complete but looking a bit tatty in particular the rusty frame and swingarm. Never a better way to go through the bike than with a complete strip down.

Ready to strip

The plastics have obviously been in the sun and though had lost some sheen they are in good condition and very much race useable. One of the rubber mounts to the airbox was perished and broke off. Exhaust was in good shape, but a bit heavy, probably due to the US requirement spark arrestor.

Not the best bolt

Drained the oil before removing the engine, but kept the oil in a clean jug as hadn’t quire decided what oil I’d need. (more on this later). One really knackered bolt holding the sprocket cover but wih subtle use of the impact driver managed to get it out.

Spent the last 90 minutes of work on day 1 doing the messy job of prepping the frame and parts for painting. Shot blasting takes time and I’ve a cabinet for the small pieces, but usually get good results on a frame with a small thumb sander. It takes a while and cleaning off the rust and marks doesn’t usually take too long. Then rub down the frame with some meths to remove any grease.

Progress

Brake plates and shoes were fairly worn but cleaned up okay. The tyres looked period from the 70’s (Baumn MX tyres) and were perished but given the way the inner tubes disintegrated on site, amazing they still held air. Didn’t have to get the angle grinder to them, but changing them to some new rubber (Michelin S12 130/90 18 on the rear and Metzeler on the front) was the longest part of the job. Cold mornings don’t help as ,means stiff tyres and need to get the heater on them.

Not the biggest engine

Paul had spayed a frame with Silver Wheel paint and though the original frame is a more bronze / silver in colour I went for something effective and cheap. Not powder coated a frame since the SWM Jumbo restoration many moons ago, as always concerned about the way it chips. If I was doing a restoration for the front room on something then might consider it. The recent 1970 Husky acquisition has been powder coated and its true it does provide a professional looking depth to the paint, so maybe something to consider for the future.

Broken rear axle adjuster bolt

Paint when on during the morning whilst working I could nip out and spend 10-15 minutes applying a coat of paint and in the end put 4 layers on the frame, swingarm and other components.

Sunny lunchtime spraying

I’d acquired some Fox rear shocks for £80 at Telford and look nice and period, even though they won’t be as good as modern ones, like the YSS items, but expedience over expense on this project. They look good on the bike, who’s age is right at the start of the extremely laid down shock period.

Rebuild break to cut the lawn

Used the glue gun on the carb to aribox rubber for now, but it ideally needs a replacement which I’ll seek out from Jef Bens, along with some new break pads. I changed the bars to a spare set of Desert Bend Renthals that I’d save from another bike I’d sold somewhere.

Slightly knackered tube

The electronic ignition was functioning and I limited myself to checking the cables. I do need to rig up the kill switch as this wasn’t working. Given you cannot stall the bike in gear something to stop the engine running will be pretty handy.

Fox shocks

It has a loose sounding piston and isn’t far away from a rebore and next size piston I would think, but again expedience pays and there is compression and it runs and starts. So for now will stay as it is, though may take the head off and measure the cylinder bore and piston to see where we are in the evolutionary cycle of the engine.

Helicoil fit

Need some grips and a better throttle and she’ll be ready to go. Currently targeting the Narberth Hare and Hounds on 4/April, as the bike has an enduro tank will be excellent if it is wet and muddy.

Day 3 evening

Garage of dreams

Replacement parts list:
– carb inlet rubber
– grips
– brake shoes, front and rear 25mm pads
– fork seals
– front sprocket, 11 tooth, serviceable but replacement not far away.
– clutch cable; is okay but the adjuster on the bar lever is broken
– new tyres (Michelin S12 130/90 18 rear, Metzeler 90/90 21 front

Twist and go !

Though the Husky collection has continued to grow, this is something a bit different. Picked it up in the car park at Telford from Richard, who along with his son James run RJP Motorcycles in Oxfordshire. Like the other importers they have some good stock, but based on the pictures seen and bike purchased it tends to be of good quality. Had a choice of 2 360 Autos and plumped for this one as although the frame was rusty it hadn’t been buggered around with as the other, which had a rear brake lever placed on the bars. Husqvarna made Automatics from 1976 through to 1982 having responded to a request from the Swedish army to develop a bike that could be ridden by a new recruit within a week.

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They use a centrifugal clutch with 4 speeds selected automatically, so it is really twist and go. Not intending to strip the bike straight away so details on its operation will (hopefully) remain obscure for a while. Operation is relatively straightforward, with a centre-of-the-bars mounted clutch lever being engaged for kickstarting and when the engine is warmed up, it can released. Forward motion is obtain by simply twisting the throttle, with drive disengaged when the throttle is shut off. This means there is no engine braking, which might mean that you will be a little hot into the corners on some occasions.

The bike fired up 3rd kick, which was bit unfortunate as this was in the hall at Telford as we were clearing up on the Sunday. A significant shock was obtained from kill switch and it was stopped by removing the plug lead. Fired up back in Wales and it started easily again (it has a Mikuni carb conversion, probably a period modification) and a couple of minutes, I let the clutch out and twisted the throttle to be pleasantly surprised by solid forward motion. A quick test up the lane proved that the higher gears were engaged and that I could look forward to a more solid test in a field somewhere. A bit of a top end rattle, so the bore is probably a bit worn, but still good enough for a race or two I would think. The only problem with the bike is that it looks a bit tatty so a strip down to paint the frame before racing would be worthwhile.

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Looking forward to getting this out for a spin and the Gentle One Enduro run by the Narberth Club on the 4th April might be a good place to try it out.