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View Full Version : How do I remove gudgeon pin? It won't move.



nudedaytona
28th April 2008, 10:10
(I've started a new thread on this. The bike is a 1996 aprilia rs250)

It looks like the piston in the right cylinder is broken. I've removed the cylinder and you can clearly see that on side underneath the head there is a whole chunk missing.

I've had huge problems removing this piston though. I removed one circlip, no problems. But I could not remove the circlip on the other side because the gap in the circlip is right where the hole is to put your screwdriver in, meaning I could not push it out using a screwdriver.

This shouldn't matter because I thought I'd just push out the gudgeon pin through the side where I have removed a circlip. But it won't budge. I've tried using a screwdriver and hammering with a mallet on the screwdriver handle, and that moved it a little bit, but not any more. Plus I'm worried that I might move the piston out of alignment if I keep at it like that.

I've tried using a clamp but that doesn't work either. Can anyone tell me the best way to remove the gudgeon pin. Is there a tool that would make it easier?

(There's no danger of bits dropping into crankcase because the piston is hanging downwards out of the engine).

Subike
28th April 2008, 10:20
this will be interesting to see what is posted
I take it the conrod is still attached to the crank
heating the piston around the wrist pin bosses will expand the alloy to allow for the wrist pin to be withdrawn.
Using a screwdriver to remove the retaining clips is not wise, but I guess cost is a factor here,
I am not aware of the type of wrist pin, floating - semi floating.
A press is needed if semi floating
Others will have more info than me
Dont try and force it out using a hammer, a bend conrod will be the result, not noticed till you assemble the engine, thenwonder why it dies sooner than you expect from ring failure. ! .005 thou bent conrod is not needed.

Ixion
28th April 2008, 10:21
Heat the piston up. GENTLY (NB , gently) play a gas torch on the crown. Lacking that, use a hot air gun, your wife's hair dryer (DON'T LET HER CATCH YOU! DAMHIK) , or even just a one bar heater . You want it too hot to comfortably touch, no hotter. (Actullay, probably doesn't really matter in this case since the piston is stuffed anyway, but good practice is always good practice)

You should be able to move the circlip around in its groove by pushing it radially with a screwdriver blade. But, as you note, it's not really necessary because you can push the pin out from the free side . BTW be sure you are pushing on the gudgeon pin, not the still-in-place circlip

Ixion
28th April 2008, 10:25
this will be interesting to see what is posted
I take it the conrod is still attached to the crank
heating the piston around the wrist pin bosses will expand the alloy to allow for the wrist pin to be withdrawn.
Using a screwdriver to remove the retaining clips is not wise, but I guess cost is a factor here,
I am not aware of the type of wrist pin, floating - semi floating.
A press is needed if semi floating
Others will have more info than me
Dont try and force it out using a hammer, a bend conrod will be the result, not noticed till you assemble the engine, thenwonder why it dies sooner than you expect from ring failure. ! .005 thou bent conrod is not needed.

Unfortunately, it'll be wire circlips, no real option but a screwdriver (you can file a wee notch in the end to prevent nasty slippages)

It'll be a needle roller little end, the pin is just held in the bosses. The piston bosses may have distorted as a result of whatever (presumably detonation) took the piston out. Those pins can be jolly tight.

If heating the piston doesn't allow you to push the pin out using the palm of your hand (support the other side of the piston with your other hand), then make a little extractor using a bit of tube and a long bolt.I find tube spanners very useful for the requisite bit of tube. And coach bolts come in long lengths and cost cents.

moT
28th April 2008, 10:48
Use the following tools....Hack saw, grinder, hammer, crowbar

zxcvbnm
28th April 2008, 11:46
Your rod is probably bent if have been hitting it:buggerd: Here's a picture of the puller Ixion's mentioned.

nudedaytona
28th April 2008, 13:19
Thanks for all the advice. Fingers crossed I haven't bent the conrod. It still looks pretty straight to me, moves up and down without any obvious sideways movement.

I'll heat it up and try again, using Ixion's contraption.

Ixion
28th April 2008, 13:34
Takes more than one might think to bend a two stroke conrod. Certainly can be done, but you have to hit pretty hard. Thing is if the pin is tight even hard hitting may not move it.

If you do want to hammer a gudgeon pin out, grasp the hammer immediately under the head (or, use what I do, a hammer head with no handle). And rata-tat-tat it out, series of short sharps taps, not hard wallops. Keep your free hand behind the piston, let the pin slide out between your fingers (which also makes it easy to catch if the last bit comes out fast! Before it goes down into the crankcase!)

kevfromcoro
28th April 2008, 16:08
Normally a bit of heat is enough to get it out..Alloy expands pretty quick.
I have done it by dunking the piston in boiling water.but have to take the rod off the crank to do that.
Wouldnt go near the thing with a hamer.
As stated .005 thou is sod all.if bent.

westie
28th April 2008, 16:25
If the piston is broken I'd go with toms advice and smash it:crazy:

MaxB
28th April 2008, 18:04
Heat and patience is what needed. IMO.

The other thing is that did you get a chance to look at any causes of failure? Any bits, scorch marks etc? Last thing you want is to slap it back together and to fail straight away.

At least the motor is RGV based so you can still get parts, if required.

munterk6
28th April 2008, 23:13
Have you thought about where the missing alloy from the piston has gone?
Ya better split the cases and thoroughly clean out the crankcase, not worth NOT doing it, ya know how shit happens eh.
Also, you will need to establish the actual cause of piston failure/breakage.
Most likely detonation caused by lean mixture/poor fuel(low octane)

nudedaytona
29th April 2008, 12:50
Some alloy has rubbed off on to the cylinder. How do I get it off? I think that would account for most of it. I'd say it's a about a thumb full of alloy, no more than two thumb fulls at the most that has broken off from the piston.

Apart from the alloy on the inside of the cylinder it looks pretty clean. No scorch marks on the cylinder or inside the crankcase. The base gasket is looking a bit shitty so I'll get a new one of those, and a new head gasket too I suppose.

I appreciate your input about taking the crankcase apart but it just seems a bit of overkill. I've had a look inside - it looked pretty clean, just a few rust speckles - not bad for a 12yr old engine IMO. And the conrod moves around, the crank turns, no problems there. I guess I could rub around in there with a white cloth and see what it picks up. Or maybe use a magnetised screwdriver - Does that pick up alloy? If there was something in there wouldn't I have heard it when I turned the crank? So far I haven't heard anything.

As to what caused it? Seems to me to be the old in pieces air filter as the most likely cause. Everyone on this website seems to have their own opinion as to what caused it, so I'm going to go for the obvious and simple one. Nothing wrong with the fuel - I've emptied the tank and put the fuel in my cage it didn't cause any problems there. It was 98 octane too. I'm picking up a new air filter on the weekend. And I'll clean out the carbeurettors as well.

nudedaytona
29th April 2008, 13:03
Thanks to Ixion who suggested bolt pulley system for removing the gudgeon pin. It worked like a charm! At first I tried dipping piston in container of just boiled water, (remember it's hanging down) and having another few taps at it, but that didn't work.

Then I had the idea of using the exhaust mounting bolt - it was just the right size and length to go inside gudgeon pin. I combined that with a cylinder head nut, and some sockets, and pulled the gudgeon pin right out. I had to keep adding sockets, and then some wrenches so I could get more clearance, but eventually got there. So thanks :banana:

After removing piston, I spent about 10 min eyeballing conrod and turning crank. It looked straight to me, but I gave it a few whacks back the other way just to be sure. It still looked straight, and it lines up with an etching at the bottom of the crankcase, so hopefully that's a case of no harm no foul there.

zxcvbnm
29th April 2008, 14:41
There's an acid that eats the aluminum off without harming the barrels plating, can't remember what it is but I can find out.

Your crank might be poked from the melted aluminum from the piston going through the big end/main bearings if it was ridden for long like that.

Does it look like this.

nudedaytona
29th April 2008, 15:50
No the missing part is at the bottom (crankcase side) of the piston. Basically there's two parts where the piston extends over the conrod towards the crank, and the piston is missing a portion of one of these. I can take a photo. I'll take photos of crankcase, piston and cylinder and post on here.

FROSTY
29th April 2008, 16:05
Geeze All I do is squeeze em out nice n easy like with a modified g clamp.
G clamp goes round piston and just turn the handle -no bashing thumping or distorting going down

FROSTY
29th April 2008, 16:10
After removing piston, I spent about 10 min eyeballing conrod and turning crank. It looked straight to me, but I gave it a few whacks back the other way just to be sure. It still looked straight, and it lines up with an etching at the bottom of the crankcase, so hopefully that's a case of no harm no foul there.
SHUDDERING --Im sorry dude but the idea of giving a conroad a "few whacks" with a hammer gives me the heebee jeebees.

nudedaytona
29th April 2008, 16:41
I tried with the g clamp. I had one g clamp that was too small and one that was too big. If I had known that a clamp pulley system would work I would have done that first, but I wasn't born in a workshop.

Tapping it out seemed the best way to go, and they don't tell you how to do it in the manual.

The conrod looks like a sturdy wrench, the kind you'd use to bash someone over the head with or to undo a really big nut, so it's hard to see how I could have bent it. I guess we'll see once I get new piston

Subike
29th April 2008, 16:51
After removing piston, I spent about 10 min eyeballing conrod and turning crank. It looked straight to me, but I gave it a few whacks back the other way just to be sure. It still looked straight, and it lines up with an etching at the bottom of the crankcase, so hopefully that's a case of no harm no foul there.

OMG!!
you really dont know do you?
I think more than one rider in here has seen the wong end of a fractured conrod hanging out the sump of bike.......not a pretty sight,
I wish you luck when its running again, that it hangs in there

nudedaytona
29th April 2008, 17:19
Yeah I didn't know no need to piss your pants. I'm not a mechanic by any means, but I think that one of the good things about doing you own work is that you don't need to explain yourself to everyone who has an opinion.

it's hard to see how a few whacks with a rubber mallet (not a heavy post hammer ) could have hurt it, and it looked straight to me.

Subike
29th April 2008, 17:29
Yeah I didn't know no need to piss your pants. I'm not a mechanic by any means, but I think that one of the good things about doing you own work is that you don't need to explain yourself to everyone who has an opinion.

it's hard to see how a few whacks with a rubber mallet (not a heavy post hammer ) could have hurt it, and it looked straight to me.

Fair enough bud... sorry to assume the worst senario on you.
I hope you learn heaps with this experiance, good experiance is hard earnt.
Art least your asking the right people for advice, even if we do rib you a bit.
Hope the reassembly goes without any more big hassels.
Make sure you clean everything twice, including your hands whilst assembling.

zxcvbnm
29th April 2008, 18:22
Muriatic acid is the stuff to get the aluminum of the nikasil, just remember the rest of the barrel is aluminum to.

speedpro
29th April 2008, 20:37
Caustic soda to clean the alloy from the piston off the bore. Been there, done that, it's other use is as a drain cleaner. I use "Wipe out" crystals mixed with water to make a real strong brew and then dab it on using a cotton bud or similar. It'll make the alloy fizz but doesn't affect iron liners or nicasil/chrome. It can take a while - be patient.

speedpro
29th April 2008, 20:40
Back in the old days we used to clean out 2-stroke pipes, H1s and H2s etc, with it as well. Jam a spud in one end, mix up a brew and pour it in. Leave as long as you dare then rinse out real well. It softens the carbon and what doesn't just wash out will blow out the first time you give it the gas.

FROSTY
30th April 2008, 08:27
Back in the old days we used to clean out 2-stroke pipes, H1s and H2s etc, with it as well. Jam a spud in one end, mix up a brew and pour it in. Leave as long as you dare then rinse out real well. It softens the carbon and what doesn't just wash out will blow out the first time you give it the gas.
A good trick for two stroke race bikes -everyone behind you has a coating of black glugg all over their visors :whistle:

speedpro
30th April 2008, 20:19
Except that the mixture dissolves all the oily deposits leaving just a dry dust once it's poured out and drys

speedpro
30th April 2008, 20:25
By the way - standard conrods are tough as hell, they will not just fracture. Check out my avatar. That is a standard rod with a 90deg twist and a 90deg bend. The piston was shrapnell, the little end cage was in the pipe, and the gudgeon pin was just sitting in the cases. The rod is bent and twisted but there is no sign that it is going to part.

nudedaytona
1st May 2008, 11:05
Sorry forgot about photos. Will do that after work and post tomorrow.

quallman1234
2nd May 2008, 12:12
Before buying a standard sized pistion, you might wanna get the cylinder measured up to decide if you have to go to an Oversized pistion etc.

The max tolernce between the cylinder and the pistion for my RG150 is 0.120 (MASSIVE!) you probabaly don't really wanna have anything greater than 0.6-0.8 over as your get some pistion rattle/ scoring on the barrel.

A simple vernier will kinda do the trick but what you want is a barrel measurey thingy!

Not sure how much new pistions are for RS250's but a RG150 one including guegon pin and circlips is 210$ per pistion so that give's you an idea. Don't buy geniune as it will probabaly be stuipdly priced!

Good luck, also note there's a technique of putting the pistion back in (etc lining up the clips) so ask on here first before you get too far ahead of yourself and snap a ring!