2013-'15 A - Broken fork Compression Valve

[wheatonFJR]

With this piece being inside the fork and constantly bathed in fork oil I don't think corrosion will be much of an issue. My machinist coworker suggested stainless steel being an option.

I was thinking dissimilar metals chemical reaction... but yeah, stainless usually minimizes that effect.

[raYzerman]

As Chuck says, totally bathed in oil, so not worried. Going with steel, I think tool steel is appropriate. My preliminary drawing isn't quite right nor complete, as it doesn't show the correct depth of thread to the 3mm hole. but I think the main contributor/cause for failure is drilling and tapping the lower bolt threads half way up into the 3mm hole where the oil enters from the compression adjuster.... resulting in a stress point and thinner wall... likely about 2mm of aluminum. IF you don't have the cartridge seated when tightening the bolt, you stretch the aluminum right through the middle of the 3mm hole. One individual noticed this when he stretched his but hadn't quite broken it. The suspension guys (KYB/Showa) in my opinion should have not drilled/tapped so deep and kept the threads in the thicker part below the groove/3mm hole.... in other words use a 20mm M10 bolt rather than a 25mm. That I think would make it much better.

However, too complicated to 'splain right now, but that 8.8mm fluid chamber bore above the bolt also didn't have to be that big. They drilled it 8.8mm for convenience I think, so they could do it all in one operation and coincidentally tap the M10 threads... note, it tapers down at the top to a 2.5mm dia. orifice to go up into the damping shim pack... could have had more wall thickness had they made that say a 7mm chamber... I have seen other damping designs with a much smaller bore, e.g., 2.5-3mm all the way up into the shim stack... duh. However, I have to now counterbore and thread the main body, so going with a 1/2" -20 thread and steel will be stronger with a thinner wall. I don't trust using any aluminum for this "retrofit" regardless of grade, the original grade does seem premium but not going there.

OK, I've been studying damping and noodling, hang in there for the final drawing... You'll "get it" then...

[BkerChuck]

Ray, what you're saying is very much in line with my coworker. That tapped hole for the retaining bolt comes too close to the cross drilled 3mm passage. He suggested a shorter retention bolt and not drilling/tapping that hole as deep. Unsure how many threads of engagement are really needed.

[raYzerman]

After much consideration of various things, and going with steel..... since it's much stronger, I can keep the original thread depth and M10-25mm bolt with copper washer.... used 1/2" -20 threads into the aluminum valve body, and the steel insert threads right in and seals on a small shoulder.... now to get some quotes this week.
Note, these steel inserts can be used on all FJR's if you broke yours, but you keep your original broken valve (preserves your original damping) and drill/tap it for 1/2"-20. The drawing should be self-explanatory, but if not, just ask.

@dan - will quote small quantity, say half dozen.... no idea at this point.. Owner not planning to use the RT Gold Valves, if anyone is interested for their Gen3A, I'll sell it off at some discount (U$200 is MSRP). That one's on me for not digging deeper into what the kit actually contained.. although RT did not respond to me.....

I don't think any further tweaks are needed to the drawing, and if anyone wants it, I can provide DXF or DWG or .pdf versions. Here you get a screen shot, lol....

[Mudslide Miller]

Maybe ES versions aren't so bad after all.

Until you have to disassemble half your bike for a rear shock rebuild; just ask someone who knows!

[raYzerman]

Reposted drawing above with minor revisions to comments..... steel choice TBD, may go with carbon steel.

[CollingsBob]

Reposted drawing above with minor revisions to comments..... steel choice TBD, may go with carbon steel.

Carbon steel might be too brittle. That piece is under compression…I’d choose something just a tad tougher than mild steel.

[Festus]

Unless things have changed (which they may have), the golden rule was always 2 1/2 threads is all you need to get the strength of the bolt.

Something like 4140 would be pretty darn tough, if you needed it to be.

[raYzerman]

I'm not an expert on grades of steel.... will have to do some more consulting. There should be no issue with stress, spring preload keeps everything compressed together, and as long as the 18mm length is correct at the bottom, shouldn't be any "pull" stress either... we just want it stronger than aluminum due to the thin wall thickness in the groove/3mm hole.

[wheatonFJR]

Unless things have changed (which they may have), the golden rule was always 2 1/2 threads is all you need to get the strength of the bolt.

Something like 4140 would be pretty darn tough, if you needed it to be.

Not on building construction, I can tell you that. The full depth of the nut is required.

Obviously, different fineness and pitch of threads, so I defer to those that know better. I certainly wouldn't bet a building's stability on 2 1/2 threads. I certainly would want the bolt and nut standards Institute reference. Not doubting it, I just don't personally know if that is the case for mechanical fasteners.

However, in any event, it is up to whoever uses it (the end user) to be comfortable with it.

[Festus]

That was the standard for building machinery, not buildings, so I'm sure they are far different loads involved on structural steels/etc.

[Festus]

In all the documentation I can find, 2 1/2 threads is more than enough to hold the average screw, in steel.

[raYzerman]

In this case, that would be minimum, however since it's a service item one might do multiple times, and somebody will overtorque with the original 26 ft. lbs. spec....... I"d say somebody would strip that if only ~3 threads. And because you got the room, more is better. My calculation, with a 20mm bolt instead of 25, we have ~6-7mm of full thread.... or about 5 full threads. With the original 25mm bolt, we got about 9 threads. Being the new part is steel, more than adequate. Sticking with the original 25mm bolt. Tapped into steel even up to the 3mm hole, no worries, so staying with that design also.

[raYzerman]

Update, so we had three quotes, settled on a machine shop not too far away. Original valve will be prepped and making 6 of the steel inserts. Keeping 2 to fix this bike and a spare for just in case I break the one on my old '14. There will be more who have a problem, and this will save them all the research, etc. for a fix.

[Panman]

Old machinist tool maker here, we always went by the rule Minimum thread length equaled the diameter of the bolt. If I wanted something tough I'd go with 4340. I always order my 4340 round stock in heat treated to 35-38 RC so what ever we made was pretty damm tough.

[raYzerman]

Got the broken valve back with machining to remove the broken part flush, then drilled and tapped 1/2-20 to accept the new steel insert. Insert ready, and tapped to accept M10-1.25 drain bolt... first re-assemble all the valve shim pack back on the valve. Then some red loctite on the threads and install into cartridge tube. then some red loctite on the steel insert and install into the valve body...... cartridge assembled.... then re-assemble right fork, fill with oil, blah blah blah..... success!!

I will keep a spare steel insert in my stash for emergency..... a couple extras coming should somebody need one someday, but they'll cost ya 'cuz machine shops don't work fer nuthin'..... FYI, insert should work for any Gen but you have to get your broken valve fixed up and threaded to accept it....