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Crack in crankshaft 2006 fe 650

S

stromfo

Joined Mar 2016
16 Posts | 1+
Trondheim, Norway
Hi

I'm rebuilding my engine, and have found what seems to be a crack in the crankshaft:eek: It seems like it has started from the woodruff keyway where it seems to be missing a little piece.
I'm wondering if anybody else on the forum has seen something like this? For all I know, it could have been like this for some time and maybe it can hold until the next rebuild. Seems to be trickier than I thought to get my hands on a used crank.
It is one for sale in Norway now, but that's the old one with the smaller rod pin..

Would love to hear your thoughts about this:)
 

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I've seen metal missing before but never the crack. I can get it repaired for 200gbp. I wouldn't worry about it. it only happened because a previous owner had left the crank nut a little loose. with a tight nut and a repair it won't happen again.

Taffy
 
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Nice Taffy, that's exactly what's happened with one of the previous owners. The nut has come loose and the gear has fallen off.

How much do you want for the repair + change the rod and rod bearing? It's ok if you want to take it as PM instead :)

Thanks for the answer :)
 
well a pin and bearing are 76gbp to a Norwegian! the crank pressed together is 45gbp.

the repair is about 125gbp. postage each way is 30 in the UK and 20gbp back to Norway. my man does a very good job and he can either just do the repair or leave it to me to fit the above.

Taffy
 
Ok, I thought you use to change the rod as well when you split the crank?

I'm wondering how you are thinking to repair it? I thought about cut out a little where the crack is and weld it, then machine it down again, but I don't know how far in the crack is, and I think it will be difficult to see it when you start to grind (if you don't have x-ray inspection equipment).


Regards
Steinar
 
I'm guessing but I think the damaged metal would br machined out and then built up again.

we go by what we see when we talk about rods being changed. however, niormally, if a rod is inspected before failure it is good enough to try again!

the problem is the 'true-ness' of the crank. if it has been a few 0.01mm out it wears away the outside 1/3rds of the rod leaving only the middle 1/3rd.

we often change the little end as well. I should have mentioned that.

Taffy
 
Ok. I will get back to you when I have spoken to the local engine workshop. Thanks for the quick answers :)

Regards
Steinar
 
Hi again Taffy

Spoke to the local workshop yesterday, and they recommended me to leave the crank be, because if they started welding on it, they would take the hardening out of it etc. And they meant it's probable it will hold as is, since the crack probably came because a previous owner had driven it with a loose nut, and with the nut tight and some loctite on the gear, it would be so tight that the crack won't have the space to grow any further.
They also could change the big end pin and bearing and inspect the rod for me, so I don't have to ship it to the UK.

But I do need some parts from you, so you'll hear from me again :)

Regards
Steinar
 
thats fine, nobody is 100% sure here. but thanks for letting me know.

Taffy
 
That's true. Will be on the lookout for a used crank so I have one in spare just in case.

Regards
Steinar
 
usually, if the crank and gear taper are not compromised, it is the taper that primarily holds it, and the key is a locator.
 
No, there's no taper. But if I use loctite when I assemble it, I hope that's gonna help take the load off the key. Gonna do some calculations to see how much torque the loctite will hold according to it's specs, but that will be later, now I'm gonna get drunk :) Happy new year :)

Regards
Steinar
 
Hi again

According to my calculations, the Loctite 638 will hold about 135 Nm torque in these conditions. I don't know the numbers the engine put out, but it should be much lower than that.

Taffy; I've ordered a big end pin and bearing from you now, they said the rod looked good and it wasn't any noticeable play in the little end, so it should be enough to replace the big end.
 
in don't think you can just leave it like that? the woodruff key can fall over creating a tremendous torque and it will try and open the gear and break it right at its weakest point. the gear isd weak where the woodruff key slot is and more specifically: in the corners.

if nothing else, some way of supporting the key must be found. added to that, if the key can fall over even slightly: it will retard your cam timing significantly and you can't afford that.

I'm not saying, start at the beginning, I'm saying that you have to do 'something' in the slot for the woodruff key to support the back of it.

regards

Taffy
 
I don't think it will be a problem, it's not as bad as it looks. Maybe I'll fill it with jb weld where the little piece is missing, I'm afraid of welding there, since that will take the hardening around the weld.
Also, with loctite, the key shouldn't be taking any of the load. And it's beens like this all the time I've had it, and it haven't broken yet.

Regards
Steinar
 
I can't believe what I just read. you have w-w-w-w-a-a-a-a-y-y-y-y more faith in glues, resins and that '****' than I do.

Taffy
 
Well, I believe that the Loctite will hold as much as my calculations show. I used the formulas from their web pages and was very conservative when determining the correction factors used in the calculations.
Regarding the JB Weld, that's not meant to glue the crank together or something, that's just to fill where it's missing a very little piece from the key slot. Honestly, I believe it's unnecessary to do that, since the key will have no place to go when the nut is in it's place.

I have used the bike as it was for almost a year, and then all the load was on the key. Now, with Loctite, the stress distribution will be uniformly spread around the surface, not a very high stress just where the key is...
 
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