Leon Speed

Right is looking pretty good. almost all coating there, although thin. Just a few shiny spots.








Left is looking worse. Almost half the gear has shiny teeth.









Still, not bad for 22 year old gears I think.

So, can these be recoated?

danglerb

Might be interesting to compare the diameter of the gears, tooth top to tooth top, and valley to valley.

RFJ

Ask Colin J aka Lizard931,I believe he is very knowledgeable.

heinrich

Throw the left one away or use it to test on. The right one can be re-coated IMHO, but what will you coat it with and how will you strip existing coating?

Dave928S

Pics can be deceptive when judging these sort of things (although the right one doesn't look too good) ... I'd be doing some comparative measurements too.

blown 87

IMHO they are toast.

Randy V

Someone recently posted a pic of some newly-coated cam gears?

Can anyone find that?

AO

I would recoat them...

Mike Frye

I think it was Andrew that posted his from when they were recoated, although they were newly coated like 5 years ago. He said he's going to take them out to check them this winter and post results.

Colin (Lizard) has had some done also.

IMO the answer is the shape of the teeth, not necessarily the shiny appearance. If you can put a straightedge across all of the teeth and have no light getting through then they haven't lost any material.

Then I'd check each one with the back of a fingernail to see if I can feel any 'burr' on the edge of it.


Here's a thought I just came up with, let me know if you think it would work:

Maybe mark the teeth with an ink pad and roll them on a piece of paper and see if you can see a complete mark from the whole top of each tooth. That would indicate that there's no appreciable wear and that the shape is uniform.

If the tracks are wider in the middle or the ink doesn't transfer in the middle of any of them then they're dished and can't be used.

I think I'll have to try this on my spare set (removed 5 years ago but kept for just this reason).

I'll post the results...

EDIT: my gears are noticeably worn and very shiny but I need to know if anyone thinks blasting the gears is necessary before determining if they're usable.

What say you all? Is there a way to blast the original coating then replace it with something new or should they be coated over the original coating or whatever's left of it?

Hilton

If you look at the wear patterns, then even with coating still intact, most will be "dished", where the belt wears through the coating towards the middle of each tooth.

Putting a straight edge to them to check, or rolling, would have to be done once the gears were blasted to remove the original coating. Then, if the alloy teeth were intact, applying a new coating to a similar thickness as the factory coating would be the sensible approach.

Does anyone know whether bead blasting is good enough to remove the factory coating off the gears? Or would something more abrasive like alu. oxide be needed?

AO

Here is the thread that had the before and after pics... but sadly it appears the 928OC has killed where the files were hosted.

https://rennlist.com/forums/928-foru...t-replace.html

hacker-pschorr

Same here.

But I do a lot of crazy things, like having water pumps rebuilt.......

AO

But if you want to know how it's done... watch this.

Mike Frye

I don't think anyone who has re-coated them has stripped off the previous coating, unless I missed the memo. Maybe someone can enlighten me.

I see your point and it makes sense that the shiny spots would naturally be lower but I don't think the previous coating can be removed, I think they're just cleaning them up and adding a new layer of something that will hopefully resist wear.

AO

I know when MrLexse recoated them he media blasted them first to remove the factor coating. Not sure what media he used.

We tried to get them dipped, but the acid didn't react well to the magnesium in the gears.

This is what happened..



By the way... you can see the condition of the gears we started with in this pic.