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Front fork problem

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Front fork problem

Posted by mark_woodward at March 01. 2017

Hi chaps, the fork drain screws on my 850 Mk.2a are both seized up and so chewed up that I cannot remove them. I need to remove the lower fork legs to get a fix done but was wondering whether I need to remove the entire assembly (yokes etc.) just to remove the lower fork legs. Looking at the (genuine) workshop manual it looks like I could do it but do any of you know better?

Cheers.

Re: Front fork problem

Posted by john_holmes at March 01. 2017

The yokes can stay in position, you can leave the stanchions in position if you can get the seal holders unscrewed but they are steel screwed into alloy and can be stuck, if stuck then the stanchions will need to be slide downwards out of the yokes leaving the yokes on the bike.

Re: Front fork problem

Posted by david_evans at March 01. 2017

Hi Mark, provided you can loosen the collars at the top of the slider that retain the seal and top bush, you can then undo the screw in the bottom of the fork leg that retains the damper tube. the whole slider will then pull down leaving the collar, seal, top bush in place, the damper tube will remain inside the stanchion. Make sure if you go down this route that you locate and re-fit the fibre washer on the botton of the damper tube or see if it is in the bottom of the slider.

Before you commit to this, you may consider carefully centre punching the centre of the drain screw head and drilling the head off. Once the head is gone there is nothing exerting pressure on the threaded section of the screw, also being as that part of the screw is above the sealing washer, it should be oily and give up without a fight. If you use a left handed drill bit, about 3/16", the screw will probably come out during the drilling process. Let us know how you get on.

Re: Front fork problem

Posted by david_evans at March 01. 2017

LH spiral drill bits on eBay.

Re: Front fork problem

Posted by mark_woodward at March 01. 2017

Hi all, thanks for the replies. David - good thinking - I have ordered the drill bit from eBay and I'll let you know how things proceed.

Re: Front fork problem

Posted by Barry Carson. at March 01. 2017

or you could try dot punching the drain screws around. give the dot punch little short taps with it placed in the screw driver slot as near the outer edge as you can. then tap it in the direction you would normally undo them  .

Barry.

Re: Front fork problem

Posted by christopher_winsby at March 01. 2017

Previously mark_woodward wrote:

Hi all, thanks for the replies. David - good thinking - I have ordered the drill bit from eBay and I'll let you know how things proceed.

Dave Idea is good but what I would do is having started with a dot punch and then checked it is central before centre punching. I would then drill a small hole through probably about 1/16 inch. Now if the screw does not come out when you take the head off you have then got a centred hole in which to fit a tapered extractor. If you heated the fork leg with a good heat gun on full about 640 deg c the steel screw would probably release from the expanding Aluminum leg. You do need patience while you let it heat up and its best to wear gloves. If it fails to come out if you have drilled central you can open up to tapping size, pick out the top thread and then run a tap through it.

Extractors I make normally from old screw drivers grinding a square taper on the end and tempering to blue. Drill max a third of screw thread size and if possible step drill to give two biting levels.

Re: Front fork problem

Posted by Martyn Watson at March 01. 2017

IMHO 640 degrees Fahrenheit is probably safer.

Re: Front fork problem

Posted by mark_woodward at March 02. 2017

Thanks for all the ideas chaps - much appreciated - I'll let you know ... .

Re: Front fork problem

Posted by christopher_winsby at March 02. 2017

Previously Martyn Watson wrote:

IMHO 640 degrees Fahrenheit is probably safer.

That's what I set the heat gun to. The fork leg will not get to that temperature and the hot air is already dropping in temperature as it leaves the electric heat gun. It is not like a blow lamp. You are trying to get enough heat in the fork leg to expand the Aluminium so that the screw becomes loose. The with two fingered force you can undo the screw.

I have used this method numerous times on screws from 0-80 UNF instrument screws to 1 inch. Steel screw in Aluminium relatively easy due to the different rates of expansion.

Biggest mistake is to drill too large a hole and use :-easy outs. They have a tendency to expand the screw if too much force applied.

 

 

 

 

Re: Front fork problem

Posted by Martyn Watson at March 02. 2017

i miss-understood, 660 degrees c being the melting point of aluminium, i thought 640 was getting a little close.

I know it may not be a piece of kit everyone has in the garage but a tig welder is a great tool. to remove broken off bolts/studs or anything really its great, the localised heat is very precise. even if the stud is broken off flush or even slightly below the surface, build up a little peek with weld deposit on the bit you can see until high enough to slip a nut over, weld the nut on and undo. its never failed. usually the stud has  loosened up so much with the heat it'll come out without the nut welded on, but thats just showing off.

even if the bolt hasnt broken, the arc it so precise you can heat the tiniest stuck screws without damaging anything.

Re: Front fork problem

Posted by christopher_winsby at March 02. 2017

Previously Martyn Watson wrote:

i miss-understood, 660 degrees c being the melting point of aluminium, i thought 640 was getting a little close.

I know it may not be a piece of kit everyone has in the garage but a tig welder is a great tool. to remove broken off bolts/studs or anything really its great, the localised heat is very precise. even if the stud is broken off flush or even slightly below the surface, build up a little peek with weld deposit on the bit you can see until high enough to slip a nut over, weld the nut on and undo. its never failed. usually the stud has  loosened up so much with the heat it'll come out without the nut welded on, but thats just showing off.

even if the bolt hasnt broken, the arc it so precise you can heat the tiniest stuck screws without damaging anything.

The other way of heating it is in the electric oven on full, like getting the main bearings out. But make sure the misses has gone out and you have time to clean up any oil.

Re: Front fork problem

Posted by Martyn Watson at March 02. 2017

The kitchen oven, a fantastic piece of kit. Use oven roasting bags though, keeps the smell in.

Re: Front fork problem

Posted by alan_blackhurst at March 02. 2017

Those ultra sonic baths for jewellery cleaning are also good for small motorcycle parts. Again make sure her who must be obeyed is out 😀

Re: Front fork problem

Posted by mark_woodward at March 12. 2017

Well chaps - I failed (on the first fork leg at least - no doubt the other leg will be a b*gger as well) - even with plenty of gas heat and careful use of stud extractors the remains of the screw head broke off and came clear but the alloy fork leg thread is damaged - helicoil time I'm afraid. I intend to fit the RGM allen headed drain screws instead of the standard cheese headed originals. I cannot seem to find out what size the original screws are - I gather they changed a few times. What's really annoying is that there was plenty of oil in fork - still it shows the seals are OK if nothing else - ho-hum...

Re: Front fork problem

Posted by K Glassborow at March 13. 2017

Suggested impact driver then read the original text mentioning chewed heads!

Re: Front fork problem

Posted by Andrew Heathwood at March 13. 2017

Mark

I had a look for info on thread sizes. Part No. 06.0354.

Andover list as UNC for 850 Mk2.

This list has 1/4 x 20 UNC

http://stainlessbits.com/link12a.html

RGM has BSW for the Allen screws.

I guess you just need to match the helocoil or thread insert to whatever screw size you settle on.

Andy

Re: Front fork problem

Posted by david_evans at March 13. 2017

I'm inclined to go with 1/4" BSW though both that and 1/4"UNC have 20 tpi, the thread angle is 55 degrees on the Whit and 60 on the Unified. Probably not an issue over the length you are talking about here. You may need to grind through the helicoil to get the length you need in view of the short length of thread. The important thing is to recover the tang when you break it off. Difficult if you haven't fully dismantled the forks

Re: Front fork problem

Posted by mark_woodward at March 14. 2017

Thanks for the comments, I have ordered the BSW Allen Head screws and helicoil kit, I gather this is a common(ish) problem judging by the fact RGM put the helicoil repair kit in the same catalogue page as the fork legs etc. As David suggests, I'm resigned to stripping the fork legs to ensure that I retrieve the helicoil tangs. I did think about getting reverse thread inserts such that the tang was on the 'outside' when screwed in and thus more easily recovered - would this work I wonder?

Re: Front fork problem

Posted by George Phillips at March 14. 2017
Your reverse thread idea would work whilst you're the owner, Mark. But when you're not around or the bike is sold on, the next owner/s would have a nightmare trying to remove the screws. I think it's dangerous to do anything as radical and perverse as changing a thread direction. It's not something that would occur to a new owner. George
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