Can anyone tell me what would break a locating pin/lug on the timming/flywheel side main bearing? seems that mine has been damaged, broken and as such killed a bearing and scorred the crank cases, Ive looked at the workshop pic and looked at the parts diagram, but can see how it would have broken., surley once in and tightened up the lugs have done there job its now down to the cases being together and holding it all in place?

I pulled this from the installation of a crank so you can read for your self, I can understand why it would break.

"Pre-fit the crank to align the seals and bearings. You will notice the seal on the flywheel side has lugs to help locate it in the cases, and the clutch side has a lip around its' entire edge, and neither actually sit flush to the bearings. The bearings have locating pins to help prevent them spinning in the cases and align correctly. Pre-fitting the crank will ensure that it can be fitted with minimum time and fuss once the new sealer has been applied to the cases."

Any techies out there give it your best shot! very intrested to know HOW a lug can break off ????

Could a previous spun ring break and sieze have caused it?

my be that the bearings nipped up a bit let me know how you sortout your cases as i have a set in the shed with the same problem mate


Last edited by fenton on Sat Aug 12, 2006 8:20 pm; edited 1 time in total

Ive seen crank cases where the crank has been fitted wrong and has done crankcase damage.

Like you said, once the bearing is in place and the cases bolted up that bearing isnt going far. I would doubt even a seized bearing would shear its pin. I guess the crank has been incorectley fitted.

Do the cases show any signs of hammering (looks like black marks) where the bearing has been loose in the case? If thats the case then all the load will of been taken on the pin.
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If I have to take the carbs off once more...

dosent look like hammering, more of a score mark, the bearing sounded a little rough, not megga, but still spun smooth, its now been replaced and the lug replaced too!, the case has been repaired, but ill have to find out how that was done. as its been repaired since i saw it last. could cases be incorrectly fitted? With a shagged bearing and broken lug, could the bits fall in crank side? and get draged into the piston/chamber? the diagram looks sealed? but i can never figure out these things somtimes, someone who has had them apart a few times might be able to answer that?

Can you get pictures?
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james
Its not how fast you go...Its how you go fast.
MC21 Rothmans
RS250
RC31
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not now no! its back together waiting to get dyno'd and set up! ill have the bits in a few days, but as i say the case's are now repaired and back together!

If the bearing still span freely then the bearing must of been broken on assembly as if it span freely there is very little load at all on the pin.

If the bearing broke up or the pin (somehow) managed to get from out side of the bearing to the inside then yes it could make its way into the crank case and then up into the cylinder. I Cant see how that could ever happen though.
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If I have to take the carbs off once more...

its back together waiting to get dyno'd and set up!

I thought all that had already been done before it died.
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If I have to take the carbs off once more...

Yup, its been dyno'd any everything and she was 63bhp on 95 unleaded, but im guessing since its had new rings, and piston and the barrel rehoned (thank FOOK that didnt go again) it needs checking again!. And yes the Lug did make its way up! all the way to the top!

The bearing was in my hand when i played with it, so no idea what that is all i know is it felt worse than the one going in.

ah all these questions!!! So could a locating pin/lug once broken, make its way up to the top of a piston and sieze it SOLID? would it look like a spun ring damage? (LOTS OF KNOCKS OUT THE CROWN) i have to ask as im compltely in the dark here, looking at diagrams etc something isnt right with my motor, (well its been completly rebuilt now, so fingers crossed) and id like to try and work out whats caused it, the crank is fairly new, 3000kms on it now and cant understand a bearing going, its never run lean but has spun a ring in the past. MMMM something fishy is afoot and its not the local ho's down the street! senario's are this.

1. the pin/lug has gone because of bearing failer/ damage from past siezeure, Fallen into crank, sucked up into crown and siezed my enine.

2. bearing has gone pin snapped etc But piston has been damaged from a bit of old ring left in the crank case? not the lug / pin

3. Pin/Lug has broken, bearing failed as case/crank not correctly installed?

Lots of possabiltys, i have my own idea whats happened but ill save that for later, as if im right ill be getting outa 2 strokes all together and i dont wana be right...

only things certain here is Bearing has gone, Pin has snapped, and damge to the pistong crown? how is what id like to find out, ill have some pics of the parts but dont think itll help much.

Dose anyone have a picture of a pin/lug, at least i can tell from that if damage to the crown looks like it was a ring or bit of pin/lug.

Cheers all your help has been great, look forward to more of your thoughts on this one

doesnt look like hammering, more of a score mark, the bearing sounded a little rough, not megga, but still spun smooth, its now been replaced and the lug replaced too

How do you replace the lug ? Its an integral part of the bearing .

As the lug/locating pin is located in a hole in the crankcase, there should be a groove in the case, leading into the case, if the pin wandered in there.

I guess the pin could snap, if the case was worn. so only the lug kept the bearing from rotating. This could in the long run snap the pin when accelerating and deccelerating, but at the same time, I think that the locating hole should be elongated as the lug is much harder than the alu case.

It is possible to mount the bearing with the lug outside the hole. The lug will then dig into the alu but I can't figure out what the consequences would be. It doesn't look like the lug could be pressed through the bearing. Maybe it'l make the seal fail prematurely as the crank isn't aligned exactly in the case.
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Poul
"If Life Gets Boring, Risk It!"
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The only way the locating pin from the main bearing can get into the crank case its self is as pbekkerh says by hammering a grove right around almost 90degs of the case.

If you look at the picture, you can see the locating slot for the pin (bottom arrow) The only way that pin can get to the crack case is if it goes though the oil hole (top arrow) and then drops though there and out into the case. This woudl mean though that teh cases have a huuuge score in them and the bearing was so loose that the cases must be totaled.

The other option is someone has built it wrong and has put the locating pin for the bearing not in its slot but on the oil drain hole (top arrow) and its fallen out. If thats the cases you shoudl see damage aroudn that oil drain hole where the pin has hammered back and forth.


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If I have to take the carbs off once more...

Is that the case before you got it fixed? What is that other pin onthe other side of the case in the hole?
_________________
james
Its not how fast you go...Its how you go fast.
MC21 Rothmans
RS250
RC31
CRF250X
748R
Porsche (many)
http://members.rennlist.com/j911brick/rennlist3_002.htm

Hey?

No this is just a set of cases that was kicking around in the workshop, Ive never had a set of cases repaired. That other pin isnt a pin, its another oil drilling hole.
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If I have to take the carbs off once more...

j911brick wrote:Is that the case before you got it fixed? What is that other pin onthe other side of the case in the hole?

No these are Stephens, I cant get a pic of mine.

Stephen Thanks Very much, i can see clearly now the hole's, very intresting.

when i get the old bits back this week ill copare damage with my last piston, Im not convinced that the pin/lug caused the sieze on the engine this time. it looks way to difficult for a pin or lug to get through there with out (as you said) mass distruction of the cases. Ho Hum!! anybody want a 2 stroke LOL full engine rebuild LOL