pulling piston pin

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#1
What is the best way to remove the piston pin without a piston pin puller that the manual suggests you need? Also the manual says to grease the new piston and put oil on the piston surface I'am not sure what the difference between the piston and piston surface is. How do you prep the new piston? Thanks in advance for the much needed advice.
 

KDX1

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#2
The best thing to use to pull the piston pin is a small flat blade screwdriver or pick. As far as the piston goes, I would use grease on the bearings and then coat the entire piston with 2 stroke oil before putting it back on the connecting rod. I hope this helps.:D



00 KDX 200
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Strick

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#3
As per MX tuner I have used Marvel Mystery Oil during assembly of the last 3 top ends. It works great. I use it liberally.

Removing the wrist pin: I support the connecting rod with a piece of wood (2X4). I take a 10or 11mm deep socket (whichever fits), and knock the pin through after lubricating both sides of the pin and the socket. I have only had one pin (out of the last three) stuck that bad though.
 
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#4
I generally use a ball ended allen key of the correct diameter. Make sure the piston is supported before you tap on it or you may bend the conrod which will ruin your day. If it is a little tight you can gently heat the piston by wrapping it with a rag dipped in hot water & wrung out.

When you put the piston back in make sure the sharp edge at the circlip hole is de-chamfered a bit to stop the next one snagging on the way out. While you are at it you could take some time to remove sharp edges over the rest of the piston. This removes any stress raiser points. Maybe a bit pedantic I know…

Don’t re use circlips!

I would be careful of using anything too sticky in needle roller bearings as you don’t want them to skid at any stage or they will wear flats on the rollers. I just use 2 stroke. That’s what they will be fed the rest of their life, it’s not like they are cams being started up dry on plain bearings. A good finger full in the bearings & a light smear on the piston esp near the ex port. As soon as it starts it will be fed new oil.

New parts, what a great feeling. Enjoy.
 

Mac

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#5
I would not use a heavy grease on any of the top end parts, I use a light oil like WD-40 or a small amount of 2stroke oil. You do not need gobs of grease or oil to do the job.

You can make a pin puller with a long threaded bolt or threaded rod, a long socket with a larger opening than the diameter of the pin, a few washers and a nut. Put the threaded rod through the socket and piston pin with the socket opening tight against the piston. Then add the washers and nuts. Tighten the nuts until the pin is pulled into the socket.
 
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#6
and dont forget to put a rag or two around the crank case opening
wrap it around the connecting rod and cover up the hole
just incase the circlip decides to pop out
id rather it fall on a rag ,,,,,,,,, instead of in the crankcase
hey its just a thought!! good luck
 
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#7
I must be HE-man

I have always pushed them out with a deep well socket.

I hold the piston in my left hand allowing the pin to come out between my two fingers , and push.

If its hard at first I tap the socket with the plastic end of a screwdriver, once it moves I push.

I use Yamalube to assemble
 
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#8
Ouch!!

re: 'support' of a con-rod with a block of wood? How does that NOT just become a fulcrum? Force will still be exerted on the bottom bearing if you're banging on the top!

Sure...it probably works most of the time...but why tempt fate?


Use a c-clamp. Use a larger socket on the 'out' side..a smaller one to push with. That way there is NO pressure on the lower bearing. Everything goes smoothly...much less likely to have things 'sproinging' someplace.

This is all assuming there is SOME force required..that the pin does NOT push out with your fingers.


Putting rags over the crankcase opening is a MUST! The one time you don't is the one time you'll drop some junk into it.

As far as 'wet' and 'dry' assembly...there's a good deal of difference of opinion as to which is best on a plated cylinder. 'Wet' (using 2-stroke oil) seems better to me. No 'facts' to back that up. Well, except that the svc manual SAYS so.

Circlips commonly have a radiused edge and a flat edge. If yours do, put the FLAT edge to the outside.

You'd do better with spirolocks. They are NEVER going to fall out! Besides, they are SO much fun to get OUT!
 
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#9
thanks for the advice

This time, my first top end replace on my first dirt bike, the pin practically fell out. Thanks for all the input. I will print it out in the event I need it next time around.