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Old 11-02-2010, 09:23 PM   #91
dirty_sanchez
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Quote:
Originally Posted by Tseta
Some pictures to recap the situation:


It is thought that this type of fretting corrosion is caused by too loose fits. Vibration then causes microscopic relative motion between the contact surfaces, which in this case are not intended to move against each other....

I've also been contemplating about increasing the strength of the interference fit with anaerobic adhesives or retaining compounds. This includes a potential problem as the heat required to assemble the bearing inner rings onto crankshaft may affect the retaining properties of such a compound. Disassembly (doG forbid it would ever again be required... MUST get crankshaft shims right the first time!) could also be negatively affected.
Tseta- you are exactly right about the fretting shown in the piston pin bearing which is caused by micro-movement.

Just like sandpaper moved back and forth across a surface removes material, an inner or outer race in service can also remove material. The photo you posted proves out this theory. This assembly started life as an interference fit, but due to the miniscule airgap present between the outer race and connecting rod coupled with the non-smooth jagged surface, oxidation occurs, and micro-movement takes place. The peaks on the bearing races wear down and before you know it, the bearing race spins when it normally shouldn't.

You're right, a retaining compound is the thing to use to fill in the surface roughness which fills the air gap, and makes for a much stronger fit that will not spin.

As for the heat fit since it's an interference fit, I'll call tech support tomorrow to explain the situation and get a suggestion on a retaining compound that won't start to cure when exposed to a heated interference fit.

Good thread!

We're all learning about the gizzards of this mill.

Dirty
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Old 11-02-2010, 10:30 PM   #92
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Quote:
Originally Posted by dirty_sanchez
...
Thanks for taking the time to respond and confirm my suspicions about the failure cause, Dirty.

So, fretting corrosion it is. Since the cause of fretting corrosion is generally accepted to be too loose fits, it would mean that the crankshaft and the bearing race have basically been too loose to begin with.

It makes me wonder that why doesn't the other side's crank bearing show any similar wear...

I have a container of Loctite 648 retaining compound. I was reading it's data sheet and it seems that it is best suited for assemblies that have some clearance.

The instructions, however, talk about using the compound even with a shrink fit:

Quote:
5. For Shrink Fitted Assemblies the adhesive should be coated onto the pin, the collar should then be heated to create sufficient clearance for free assembly.
I am concerned about the crankshaft shimming and the possible disassembly required with that. If I would somehow mess up the crankshaft shimming, the bearing races would have to removed to alter the shims. Now if there is a retaining compound holding the race onto the crankshaft, removing the race may become challenging. The official Loctite instructions for disassembling say to heat the area to 250C. That's a problem because it would heat up the whole assembly, maintaining the interference fit. KTM's method of removing the bearing race involves quickly bringing localized heat (only) onto the bearing race with a slip-ring type heater/puller.

Of course the simple solution is to not mess up the crankshaft shimming and get it right the first time.


----

I see the thread has rolled onto another new page. There is still another big unanswered question, which is detailed in the last few posts of the previous page, concerning the piston to cylinder clearance. Does anyone have any insight they would be willing to share about that issue?

Cheers,

Tseta
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Old 11-02-2010, 10:53 PM   #93
clintnz
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Quote:
Originally Posted by Tseta
The official Loctite instructions for disassembling say to heat the area to 250C. That's a problem because it would heat up the whole assembly, maintaining the interference fit. KTM's method of removing the bearing race involves quickly bringing localized heat (only) onto the bearing race with a slip-ring type heater/puller.
I'm sure Mr Sanchez will correct me if I am wrong, but my understanding is that heat of over 250C will permanently break down the loctite. So you would just need to heat up the whole thing, let it cool & then use the heater puller.

Interested to hear if there is a suitable retaining compound available I'm right into the belt & braces approach when it comes to critical parts deep in the engine.

Cheers
Clint
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Old 11-03-2010, 09:23 AM   #94
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Tseta,
Have you tried contacting Pro-X directly to see what their advice is?
I bet they know something.

It might sound crazy but you could try heating the old piston in an oven and measuring it...then do the same with the Pro-X.
Or ask Pro-x what they know.

Is the concern that the pistons grow 'larger' when heated?

Are you using KTM rings on the Pro-X piston.

Pro-X engineers must have had these questions before this.

bill
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Old 11-03-2010, 10:51 PM   #95
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the second size piston is used when material is taken off the cylinder
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Old 11-04-2010, 12:21 AM   #96
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Quote:
Originally Posted by wrk2surf
the second size piston is used when material is taken off the cylinder
According to my dealer's catalogue, Pro-X basically has three pistons for the 640 LC4: "A", "B" and "C", which correspond to sizes 100.94mm, 100.95mm, and 100.96mm, respectively. Only the "B" piston was available at the time, though.

The sizes differences are thus very minute, and any of those pistons would make the assembly clearance be within specification, if it was assumed that the pistons are actually forged and that the larger assembly clearance can be used.

If the pistons are cast, not even the largest piston results in small enough assembly clearance, while the cylinder's measurements suggest that it is still within specifications.

I'm probably making this somehow too complicated, aren't I?

-T
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Old 11-04-2010, 04:08 AM   #97
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Well well, I've just received reply from Pro-X directly, and they say that:

Quote:
Part# 01.6604.B is a forged piston.

Clearance: 0.06mm
This is good news, I think. By these numbers, I'm just slightly over the Pro-X recommendation at 0.07mm, but still well within the KTM specified max. clearance of 0.12mm. Considering that the "C" piston is still not available from the distributor here in Finland, I think I will be installing this piston, hoping for the best.

-T
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Old 11-12-2010, 01:00 PM   #98
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Word of the day is frustration.

I installed the new crankshaft. It does not spin freely when the cases are bolted together.

Let's back up for a minute. I removed the old crank bearings from the cases and installed new ones. I measured the case depth up to the bearing inner rings. I measured the crankshaft width at the bearing seats. I did the necessary calculations and came up with the required shims. I then did the measurements and calculations again to check. Then, somebody with more experience did all the measurements and calculations. Every time, the measurements were done very carefully and every time, the same results were arrived at...

So, in light of these measurements, the crank bearing inner races were installed with the correct amount of shims. The transmission, kickstarter and other components were installed into the case and the crank was lifted in. Then the right side cover was bolted on, and now the crank does not spin at all.



I'm sure there's a lesson here somewhere to be learned. At the moment it feels like it might be: "Let a pro shim your LC4 crank!"

-T
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Old 11-12-2010, 01:13 PM   #99
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It's very easy to over shim and get it too tight....The last time I did it I tried to measure with the depth guage to straightedge to bearing race and it came up too tight for me also... I then switched to grinding a metal pin to the right length and miked it with the caliper before I got it right....

Measure the shims you took out from the original crank... It is very likely that the shims required for the new crank will very close if not the same as the original...
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Old 11-12-2010, 01:21 PM   #100
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Quote:
Measure the shims you took out from the original crank... It is very likely that the shims required for the new crank will very close if not the same as the original...
I did not forget this good advice you had already told me earlier. I measured the old shims.

However, the new crankshaft I received is the updated version of the LC4 crankshaft, very different all around. For example, the old crank had full circle profile "lobes" while the new one looks a little bit like the one LucasM posted a few pages back.

Most importantly, the new crankshaft was a little bit narrower than the old crankshaft, and as such, the old shimming data is not really applicable.

I am just feeling very very frustrated at the moment. Don't get me wrong, though, I really appreciate all the help and advice.
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Old 11-12-2010, 01:37 PM   #101
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I can understand your frustration as it is a pain to get the races back off as well as not destroying the center case gasket....

I will be doing the shimming on my case very soon as well...
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Old 11-12-2010, 06:09 PM   #102
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yup, you over shimmed it. dont ask me how i know......

these engine can be an exercise in patience. just find your Zen and keep going. it will all be Ok.

the good thing is if you have a race remover and the correct shims it should be any easy fix. if not, it will definitely be a pain in the ass. we built several versions of a race remover and i was never able to get it to work. i finally sent mine off with the correct shims to someone you had the proper tools. i wasnt going to pay another $80 for a "special" ktm tool that i would only use once. i thought i was being VERY precise when i measured my cases, the problem was i took an average of all my measurements. instead i should have went with the tightest to ensure i didnt over do it. the crank turned like a charm until the final torque was put on the case bolts, then it became tight. i guess there is only one way to learn though.....

laramie
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Old 11-13-2010, 09:44 AM   #103
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So, how did it all come to this? Let's go back and look at a few photos...



The old crank bearings were removed from the cases.



This is most of the new parts that came from KTM.



Then the new bearings were installed into the cases and the case depth was measured up to the bearing inner ring with the help of a engineer's straightedge and a depth micrometer.





A new crankshaft seal was installed. Other shaft seals on the engine cases were changed as well.



Unfortunately (and perhaps understandably) there are no pictures of the bearing inner race installation onto the crankshaft. Next step was to install the kickstarter and the transmission into the left case half.







All good so far...



Then the crankshaft goes into the case. When the left side was bolted on with the gasket, the crankshaft would completely lock up.

My local KTM was friendly enough to let me borrow the bearing remover tools. The crank bearings were easy enough to pop out with them. All the measurements were done again but still the same results were arrived at. It would seem that there is some type of systematic error in either my measurements or the KTM method of determining the clearance. I went ahead and removed about 0.20mm of shims from the crank and tried again. After installing the inner rings (again) onto the crankshaft, I noticed that there was a small gap between one of the rings and the edge of the crank. For some reason, the bearing had not gone in far enough on the shaft. Much apprehension and frustration was caused here again. However, with a little bit of heat and a few "determined" mallet blows, the gap was closed.

Gunnerbuck's thread here has some very good pictures and explanations of the crank bearing removal process. The installation process is quite similar: I chilled the crank in the freezer and heated the bearing inner rings with a hot air gun. For removing the bearing inner rings, the official KTM tools were really useful. They are expensive, but thankfully my dealer was kind enough to loan them to me. I'm thinking that I might try making the bearing tools myself, like Gunner's homemade pipe version. Much thanks, Gunner, for the inspiration, helpful pictures and explanations!

So then today, the crank was lifted into the engine again. Now the engine spins freely even when the case bolts are tightened.



I used this type of setup, with a dial indicator, to measure the crankshaft axial clearance. It is now just a touch over the max. specification of 0.12mm. However, I think it will be just fine once the paper gasket compresses a little bit. I will torque the case bolts again tomorrow and see how much the play is then.

Like Laramie said, this engine has really been a exercise in patience. Hopefully things will be easier from now on.

Cheers,

Tseta
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Old 11-13-2010, 10:10 AM   #104
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I would of made a copy of the official KTM race puller if I had the tools to bore the race sized holes in plate steel... I think a copy of this tool would be the best because it has more mass to hold the heat than my pipe puller contraption...

Your work area looks like a surgical ward...
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Old 11-13-2010, 11:20 AM   #105
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Quote:
Originally Posted by gunnerbuck
Your work area looks like a surgical ward...


Some other random observations about this rebuild so far:

The new crankshaft did not have the stop disks on the conrod big end. The axial clearance there was withing specification, still. I suspect that this is somehow related to the updated crank version.

The German E-bay deal for the kickstarter ratchet gears went sour. The parts never arrived, but fortunately I was able to get the money back. Thankfully I found a local source for the parts. It was expensive, but still much cheaper than going through KTM. Interestingly enough, the guy I bought the replacement parts from had a few of these gears. Unfortunately all of them showed varying degrees of similar wear as with this engine I'm rebuilding. I'm guessing that it must be a common fault with the LC4. So, I was forced to buy the "best" gear combination that the guy had available. It is not 100% perfect, some teeth are still chipped, but it is much better than the one that was taken out.

The crankshaft axial clearance is quite difficult to measure, as the crank is still quite stiff to move in the case (axially). I guess this is understandable, as the crank is a quite heavy lump of metal.

Part of the difficulty with removing the crankshaft bearing inner rings came from the fact that I used Loctite 648 retaining compound on the shaft before installing the bearings. The idea here was that the retaining compound should increase the strength of the shrink fit and prevent the bearing races from spinning in the future. According to some measurements I had done, the actual interference between the bearing inner ring and the crankshaft is just on the minimum limit of what SKF (the bearing manufacturer) recommends for this type of fit.

So, once the loctite had hardened, it took some effort and multiple tries to remove the bearings from the shaft. The heat helped here though, to soften the loctite. Retaining compound was also applied this second time that the bearings were installed.

-T
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