Struggling with Stuart D10 Crankshaft

R

RPerez

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Hello all,
So I have just finished my 3rd Stuart D10 crankshaft. Thy have all been built using the single center shaft, pinned and then cut the extra between the webs. The fit has been almost press fit(I could push the webs on the center shaft by hand firmly.) I used Loctite 603 with thorough cleaning with acetone before assembly. I let it fully cure between drilling, pinning and cutting between the webs.

The last two crankshafts have run true, but the Loctite on all of them has failed. I thought the 3rd one would finally work, as I was extra careful with gluing, but two of the joints are now loose!

I am feeling frustrated, and not sure what I am doing wrong. Should I use taper pins or a different Loctite?

Thanks in advance,
Rafael
 
Have you tried using the primer/activator?
 
Every time I used loctite retaining compound it failed.

I have had better luck with knurling or an interference fit using heat to expand one part and cold to contract the other. Acetone and dry ice slurry can freeze to - 108F. With a 300 deg oven you should get movement of 2 to 3 thousandths per inch . You do need to be quick when putting parts together with no second chance. I usually have a press of some type on hand in case a part gets stuck near the end of pressing together.

A .5" steel dowel pin pressed into a 1" steel plate will generate 45kN axial force ( weight of a 1 ton truck) if the pin is .0002 over and the hole .0005 under.

That type of precision may be difficult to attain, quality reamers and accurate measurement needed here.

I suspect that will hold better than retaining compound.
 
markba633csi said:
I would use epoxy not loctite
-Mark
Click to expand...
Epoxies need a certain amount of clearance between parts: an interference fit will squeeze out all the epoxy
and starve the joint, thus negating the value of the epoxy.
 
Uh, well it could be tried. But if the manufacturers advise against it, why bother?

I recently epoxied an assembly of two aluminum parts and used an epoxy called Araldite,
which is similar to JB Weld. The product literature advised a gap between the parts of
.002 to .004" was optimum. I also have some experience with boat builders epoxies, and
their product literature also advises not to over clamp the joint, since starving it can cause
failure.
 
I was wondering about joint starvation as well, but reading the tech sheet for Loctite 603 it acknowledges shrink fit or press fit so that kind of shot my theory out the window. I was thinking about scarifying the joint surfaces a bit though, not as much as knurling, but just something to take the smoothness off a bit.

-frank
 
Pacifica-
Unfortunately I don't have access to dry ice for the hot/cold interference fit. Also I don't think I can get .0002 accuracy. I can get .001 with no problem, I can be get .0005, but probably not consistently.

I wonder if the drilling of the holes for the dowel pins created enough heat for the loctite to fail?

Is there any advantage to using taper pins to straight pins?

pacifica said:
Every time I used loctite retaining compound it failed.

I have had better luck with knurling or an interference fit using heat to expand one part and cold to contract the other. Acetone and dry ice slurry can freeze to - 108F. With a 300 deg oven you should get movement of 2 to 3 thousandths per inch . You do need to be quick when putting parts together with no second chance. I usually have a press of some type on hand in case a part gets stuck near the end of pressing together.

A .5" steel dowel pin pressed into a 1" steel plate will generate 45kN axial force ( weight of a 1 ton truck) if the pin is .0002 over and the hole .0005 under.

That type of precision may be difficult to attain, quality reamers and accurate measurement needed here.

I suspect that will hold better than retaining compound.
Click to expand...
 
What loctite are you using? For permanent joints, you should use bearing retaining compound like Loctite No. 641.

I would not trust Loctite threadlocker to do the job. Why not wait for the loctite to cure then cross drill the joint and pin in place?

EDIT I see now... I thought 603 would work well...
 
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