that could be the best solution...the only reservation is taking "meat" out of the supporting tabs holding the shaft.

I wouldnt disagree with this, but I would like to ask; at what cost?
You dont need the "factory" tool to have the ears bored. Any machinist worth his salt could do the job on a horizontal boring mill, in deep jawed chuck on a lathe, or a verticle mill, no sweat.
Of course I am talking a real machinst...Not some "on button" jocky they call machinists these daze.:rolleyes:

IIRC, it was $100 for the shaft and $55 for the guide tube (2005 pricing). We did it while doing the clutch and a few other items so labor cost is harder to figure.

The nice thing about the factory tool is it doesn't require a trip to a machinist.

called LA place Chromal - very close maybe more to get chrome hard plating compared to San Jose. Most of the cost is in the machine work.
I got some very good info. from Ray there - hard chome on 660 bronze cast bushing should work very well - they do this all the time.
If RMG will guarantee no tab breakage - this could be a way to go.

Dan from RMG is a forum member (syncroid). I don't know if they can or will guarantee "no tab breakage" but having done it, it is really a matter of keeping it properly lubricated/cooled during the process - it's a two man job.

I should have been more clear, not worried about breaking tabs during machining, I guess it could happen, worried about during normal operation. It happens. Having a sticking fork shaft would make the forces higher, but not sure that is the primary root cause.

Henry-
Sounds like you have your options open, now its just a matter of selecting one process & fix over another. Please keep up posted on your choice, and the outcome.
Cheers!

to those following along - here is an update
I got the one sample type of Igus plasitc bushing. I thought the press fit was going to be too tight but they pressed in with about 100 pounds force. The clearance on the shaft is about 0.003". They feel is pretty slippery compared to the 660 cast bronze. The Igus website mentions that it is fine to run on a mild steel shaft so maybe no need to chrome harden. I have another model of Igus coming, thinner flange and for higher temperatures but shorter 15mm instead of 20mm.

I want to consider "inventing" a seal to keep brake dust out of the bushings (at least one side), all bright ideas welcome. Included are a few pictures to explain. The seal material could be a number of things e.g. : brass, galv. metal washer, leather, felt, lip seal with a way to attach or ? other ideas. It looks like the only way to attach is using something like JB Weld.

closeup where seal invention would go - 2 places

Thanks for any ideas.http://forums.pelicanparts.com/uploa...1267897110.jpg


diagram of seal invention location


http://forums.pelicanparts.com/uploa...1267897183.jpg

shows Igus bushings installed

http://forums.pelicanparts.com/uploa...1267897300.jpg

The fork in the 993 clutch came with plastic bushings in them. I bought a used clutch fork and had to take out the plastic to put in the bronze. This seems to be a better solution than the bronze bushing.

I'm thinking that one day the washer you've JB welded to the fork could come loose and then you'd have it rattling around in there. Maybe a thin bead of RTV would provide just enough of a barrier, and adhere to the shaft. I don't think contaminants would be much of an issue...

JB

an update - pictures coming later

1-I got the shaft hard chromed and ground to size - seemed to come out fine - $200 - fits with about 0.001" clearance in the trans.

2-I pressed the high temp. plastic bushings into the fork and a very fine crack showed up, very likley from too much press fit interference - I was pushing it by 0.002". I have more bushings - the OD can be sanded down, I'll do that and try again. Hopefully the ID will not open up too much. I feel this is an issue with plasitc bushings - the tolerance planning before and after press in can be a bit tricky. Also it is not recommended to machine the ID of the bushing. Given that and the shaft needs to match the trans and you don't really want to machine the fork, this provides something of a design corner you end up in. The IGUS catalog info. doesn't provide good detail on this in my opinion. I feel they should have very clear algorithms you could use to estimate the final ID. Also, since the parts are plastic the final as made dimensions have a rather wide tolerance going by the book.

3-ordered and recieved shaft seals 22x16 that should press in - this will seal the shaft to the fork on the side that sees the clutch dust - I haven't seen these yet, a buddy picked them up.

That's about it for now.

Henry,
I had the same thought as JB earlier in your post when I was reviewing your thoughts on some protective measures to keep the harsh dust out of your bushing bores. At the time I couldn't come up with a solution to make the RTV stick to the parent material around the bushings, while allowing the shaft movement. But now I'm thinking maybe wrapping a single layer of celophane around the shaft while the RTV cures, would do the trick.
BTW, was it cost that brought you to use plastic v bronze bushings? I know the plastic would be more difficult the control the bore sizing.
Please keep us posted on the net results. :cool:

Cost was/is not a consideration.

I was thinking this "new" technology should be given a chance. The plastic bushings are supposed to be designed for no lubrication and operation in dirty environments as replacements for cast bronze.

The goal is long term durability with no negative issues e.g. friction or clutch chatter.

I don't think the net result will be a solid recommendation to use the plastic bushings, at least not any time soon. Better engineering and testing would be needed. If after say 5 years I need to pull the engine out again, I will know more at that point because the wear can be inspected.

Likely the safest thing is to get the shaft hard chromed and use sealing to keep the clutch debris out of the bearing surface areas and at the same time use the cast bronze bushings available because they look to be the correct dimensions. If one can get some sort of sealing setup then high temp. grease should be able to be used without attracting debris.

While the "replacement or upgraded" shaft and bushing had wear... the needed function was still working, therefore one might say the off the shelf available kit is not that bad.

I dont know if I can buy into this statement...If so, what was the point of the entire post? Looking at those initial photos of the shaft after 5 yrs and 25k miles. I view the released product design as immature; unless of course the primary function of the design was "return" business. http://forums.pelicanparts.com/suppo...oilet_claw.gif

When I showed all this to my mechanic, who has seen these after they have been in cars, he said, yeah we see this and haven't seen a failure to the point where it had to be addressed as the primary repair needed. To give the benefit of the doubt to the designer of the kit, I said "one" might say..... I agree the design doesn't appear to be very good, I would not say it is a disaster however. I think you and I are in agreement. Likely a much better design is possible without too much effort. I'm giving the plastic bushing approach a try in an attempt to move the knowledge forward on various fixes as replacement for the original design.

Thanks for all you've done for the community, Henry. I know I may eventually have to address the same issue with my 87.
Cheers!

update-
I got the seals and tried them out... they seem to be exactly what I was hoping.
seals are 22x16x3 - probably any bearing house can get these.

Note: if the cast bronze bushing that comes in the kit was just a bit shorter, I think these seals would fit right in. This would cut the amount of debris getting in the bushing considerably. Providing a hardened shaft, slightly shorter bushing and seals would improve the kit for not too much added cost. It might add $30 to the kit depending on how many shafts are ordered at one time.

Here are a few and maybe last pictures of:

repaired and hard chromed shaft ground to 0.6286"
high temp plastic bushings from Igus GFM-1622-12
shims from McMaster to shim out to close to trans ears
seals



http://forums.pelicanparts.com/uploa...1269296115.jpg

seal installed - note backwards because of shaft insertion direction


http://forums.pelicanparts.com/uploa...1269296161.jpg

seal by itself

http://forums.pelicanparts.com/uploa...1269296190.jpg

Henry,
Sweet! I'd have the bronze bushings machined/faced, in order to accomodate the seals.
Great job on the intelligent upgrading of an inadequate "upgrade" released to the Porsche public.
You're right...Mass production should significantly reduce some of the cost incurred.
Even at $50 more, I'd be willing to bet your upgrade is a fix once, and forget it.

Update - got the car back on the road finally. So far clutch feels very free and no odd judder, or at least not more than previous. Hopefully this is the last anyone ever has to fix this again.

That last Ignus bushing looks very much like Delrin.
Delrin is a hard machinable "plastic" that is available from several sources.
We use it a lot in the movie industry to make bearing and movable surfaces.
The nice thing about it...cheap.
A piece of round bar stock and about 20 minutes on a lathe would give you the exact size of bushing you need.
Also...if correctly machined..it could have its own seal included...(very thin extension that would curl into the shaft at the inner end).
Just a thought.
Bob