Fork oil change
OK, I've only just done my 10,000 km service, but the suspense is killing me. I'm very confident with meeting the service requirements for my LC but at 30,000 km I'm due to change the fork oil and the BMW manual specifies a complex tool to compress the fork springs.
Anyone willing to share the technique specified in the Haynes manual for disassembly/re-assembly of each fork leg? The books aren't yet available here (to my knowledge) and OS freight is prohibitive.
EDIT: In the fullness of time, I changed the oil. My experience is documented later in this thread,
here, and a list of steps
here.
At just over 120,000km, I also replaced the front fork bushings and (consequently) seals and oil, the oil being due for a change anyway.
The seals were the originals and had occasional weeps that had responded to cleaning. Some years ago, after a couple of episodes, I'd bought a set of All Balls Racing seals, ready for when I needed to replace them. The bushings needed replacing before the seals, but the latter need to be changed after full disassembly anyway. The All Balls seal and scraper sets for 2015 Roadster ESA suspension are catalogue items 55-156 and 57-170, also fitting BMW HP4 2013-14, R Nine T 2013-19, R1200R LC 2017-18, R1250R 2019, S1000R 2014-20, S1000RR 2010-18, S1000XR 2015-19 and Moto Guzzi California 1400 2013. SKF also do a quality product at a fraction of the BMW part price, with claimed longer life and lower stiction – cross-check part fitment with these models.
When checking the front end at the last service I could feel a tiny amount of slack in the forks – I initially assumed it would be the bearings, but they were fine and have never needed attention. I was also able to detect a slight click from the front end when first applying the front brakes. Two bushing kits are required, each comprising an upper and lower Teflon coated bushing (plain bearing) and two plastic sleeves – the latter seemingly superfluous as they're not a wear item. Two kits are required - for ESA, part number 31 42 8 550 169.
The old bushings still had their inner Teflon coating but it didn't have the surface texture of the new ones, so were clearly worn. Being the only contact points for the fork tube (not counting the seals) it would seem that there should be virtually no metal wear on the fork internals other than, perhaps, scuffing of the front surface of the tubes from captured dust and grit under the scraper.
Test riding after repair shows the issue is solved and handling is even more sure-footed, although it was delightful before and the new oil probably made the most difference, along with a tad more friction/stiction from the new seals. I've reported some months ago that BMW Motorrad no longer sells their brand-specific fork oil in Australia (I haven't checked if this has changed). But no matter – Maxima 10W has a virtually identical cSt rating and suits the suspension perfectly. It’s OEM recommended by several manufacturers so has become my go-to for future changes.
A few fitment points:
- The scraper and seals take a fair bit of force to prise out. I trimmed the top surface off the scraper with a craft knife so that I had the remaining top rubber of the scraper as a hard surface to lever against. For prising out the seal, I placed a scrap of aluminium across the top edge of the fork outer tube.
- The bushings are a press-in fit split ring, the deeper one fitted adjacent to the seals while the other is part way up the outer tube. They need to be tapped out from the opposite end of the fork outer tube. I used a length of larger diameter plastic electrical conduit rather than metal to avoid any potential scratching, tapping alternate sides around the bushing. For the deeper mounted bushing in particular, try to keep the bushing perpendicular to the tube to avoid jamming.
- To tap each new bushing in, after applying a little fork oil I used a poly pipe blind cap suited to a 32mm ID pipe as a drift. The diameter closely matches the bushing, being just a little smaller, so it keeps the bushing square as you tap it in using a longer piece of tubing (the aforementioned conduit). You can also hear the change in tone once it is fully seated, although I had measured the depth to the old bushing as a reference.
- The dust scraper, circlip then oil seal need to be fitted to the chrome tube before insertion into the outer tube, followed by driving the oils seal in, fitting the circlip, then driving in the scraper. The BMW manual suggests first putting a plastic bag over the end of the chrome tube to protect from sharp edges, but I found this unnecessary (meaning I forgot ...). The edges on mine aren't sharp and I found that tilting the scraper/seal and pressing the tube into it created enough slack to easily slip the oiled scraper/seal over the top without catching the edge.
- I purchased a 46-48mm seal driver off the internet, finding it easy enough to then press the oil seal down into place after lubricating with fork oil. Don't forget the washer that sits between the bushing and the seal before inserting the chrome tube into the outer tube. Also, handle the assembled tubes carefully as they easily slide apart when the seal and scraper have yet to be fitted.
- I didn't follow the Dave Moss method of applying grease under the seal/scraper - to me it would be a dust trap, even if it does reduce stiction, and I don't service forks as frequently as he recommends.
- For fitting each seal and scraper, I found it best to rest the outer tube on a block of wood to give a solid surface, rather than the flexible plastic folding table I was using as a temporary work bench. For the left fork, this meant two blocks to give room for the electrical lead and central rod, which doesn't easily retract.
- While the seals pressed in fairly readily, I found the the scraper a very tight fit and the seal driver could not fit over the high lip of the scraper. I took one of the old bushings, stretched it out to a larger diameter, bent it open, then fitted it over the chrome tube above the scraper and closed it back. This formed a drift and I found I could use the alloy part of the fork as a slide hammer to seat the scraper. The solid blocks of wood were again very useful.
- Once the seals and scrapers were in place, normal oil filling and reassembly procedures apply.
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