Author Topic: Forks bottoming out  (Read 1585 times)

Offline nigeldtr

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Forks bottoming out
« on: 29.05. 2011 14:38 »
What is the best way to stop the forks on my plunger A10  bottoming out when I go over a rough road, they make a terrible clunk, same one my SA A10 ? does the Dow type damper help?
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

Online bsa-bill

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Re: Forks bottoming out
« Reply #1 on: 29.05. 2011 15:03 »
Yes
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline muskrat

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Re: Forks bottoming out
« Reply #2 on: 29.05. 2011 20:48 »
Loose weight!!! *smile* ride slower  ;)
Best thing I've done in fitting those double dampers.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline nigeldtr

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Re: Forks bottoming out
« Reply #3 on: 29.05. 2011 21:06 »
Thanks guys - found the drawing from JOR earlier and will set about making some up!
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

Online chaterlea25

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Re: Forks bottoming out
« Reply #4 on: 29.05. 2011 22:03 »
Jeez!!!!
I wish I could claim royalties  ;) ;)

John O R
1961 Super Rocket
1963 RGS (ongoing)

Online trevinoz

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Re: Forks bottoming out
« Reply #5 on: 29.05. 2011 22:49 »
John,
             I thought that you Irish were dead set against Royalty!

   Trev.

Online Jules

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Re: Forks bottoming out
« Reply #6 on: 30.05. 2011 07:23 »
ok now you have my attention  *eek*..... I posted a thread regarding the loss of the tapered "protrusion" in the bottom of one of my fork legs, wrt how this may or may not give me a problem. Having read this I'm thinking that bottoming out happens regularly - is that so? If it is then perhaps I should look into these "double dampers" ?? what are they and how do they work please? oh and do they rely on the tapered protrusion in the bottom of the leg  (of course  ;) ?? cheers

Offline MG

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Re: Forks bottoming out
« Reply #7 on: 30.05. 2011 07:44 »
Hmm, I never had the forks bottoming out with SAE 30 monograde (in the forks that is  *smile*).

Might be worth a try until you got the Dow dampers (which are a great mod!). With those fitted, I have to use much thinner oil (SAE 10 or 15 fork oil iirc). YOu will have to try what suits your personal taste best anyway.

Cheers, Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Online bsa-bill

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Re: Forks bottoming out
« Reply #8 on: 30.05. 2011 08:53 »
No pot holes around your way then Markus   *smile*

Jules the protrusion (tapered) is a form of damper, wont stop the forks bottoming but should stop the Clunk, as Markus has mentioned the thickness of oil has a lot to do with this.
However getting an oil thick enough to stop the clunk could well mean the forks are too stiff for the rest of the travel, depends on your local roads, strength of the springs and probably other factors.

The Dow type dampers provided the same effect as the bottom protrusion but for the the whole travel of the fork not just the last inch, I use 10 or 15 (sorry memory) fork oil and they seem about right for Northumberland's rural autobahns.
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline MG

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Re: Forks bottoming out
« Reply #9 on: 30.05. 2011 09:32 »
Quote
No pot holes around your way then Markus   

none deep enough to hide an A10 in it at least  *smile*
Our roads are basically quite good, and probably much better than those in the 50s/60s our bikes were designed for. I found that the thicker oil improved the handling a lot, but that is personal taste of course.
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Online chaterlea25

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Re: Forks bottoming out
« Reply #10 on: 30.05. 2011 23:19 »
Hi All,
Jules,
the taper plug in the fork leg prevents bottoming out, the taper closes the hole in the bottom nut gradually to prevent
mechanical bottoming, (it becomes a hydraulic lock) the noises most people hear is topping out after hitting a pothole or whatever on the rebound.
I think the taper plugs are very necessary
The later stanchions with bleed holes help to prevent topping out, again by hydraulic lock,

2 way damper drawing
http://www.a7a10.net/forum/index.php/topic,2895.0.html


Trev,
Didnt You see the welcome the Queen got in Cork City on Her recent visit to Ireland??
It was the only place that She went walking among the people!!
I can only thank the UK and their Universities who have given my Son David the opportunity to earn  a PHD
in Physics at Cambridge  *smile* *smile*

Cheers
John O R
1961 Super Rocket
1963 RGS (ongoing)

Online Jules

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Re: Forks bottoming out
« Reply #11 on: 31.05. 2011 10:31 »
thanks John, I think I'll have a go at making the dampers up so that the reliance on the bottom taper is further reduced. I noticed that the dimensions are quite "generic" ie they dont seem very fine wrt tolerancing, and presume that +/- something like 10 thou. is not an issue on diameters, plus the debate on overall length suggests that longer is better than shorter. Any thoughts? cheers

Offline muskrat

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Re: Forks bottoming out
« Reply #12 on: 31.05. 2011 11:04 »
Stick to the dimensions Jules. The OD is 0.950" which gives a .025" gap all round when in the fork. This governs the oil flow in one direction. If it was 0.010" larger or smaller it would affect the flow a fair bit. As for length it should just be under the oil level.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online Jules

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Re: Forks bottoming out
« Reply #13 on: 31.05. 2011 11:06 »
thanks Muskrat.........