cant get wrist pin in piston

[amamet]

im reinstalling the top end on my 78 g5, I'm ready to put it all back together and cant get the wrist pin into the piston with out it get stuck about 1/4" in.  it fits the con rod easily.  i remember it was tough to remove. i am trying with the piston already in the cylinder as i slide it altogether onto the bolts.  do i try to just put the piston on the rod and install the cylinder afterwards?  does putting the wrist pins in the freezer work?  i have both a propane torch and heat gun for the pistons if that were to help
thx
allen

[guzzisteve]

I freeze the pin w/assembly lube on it, and use the MG piston pin tool.

[amamet]

A- i don't have that tool
B- i don't even see it their tool section

anything else i can do?

[pressureangle]

Heat the piston. You can use a hairdryer if you have nothing else; heat gun is preferred. Have some gloves handy, it may go fast or you may have to get it uncomfortably warm. The pin should slide right in.

[LaMojo]

C-clamp and a socket a tad smaller in diameter than the wrist pin.  Use wood blocking on the opposite side of the clamp and piston.

[dxhall]

Aluminum (the piston) has a much greater coefficient of expansion than steel (the pin).  You get more bang for the buck by heating the piston than freezing the pin.  I've always used a heat gun on the piston, pin at room temperature.

[guzzisteve]

Not MG cycle, Guzzi pn #GU26907800

[chuck peterson]

i believe that is an interference fit...my machinist does it for me, as well as checking all the radiuii's everywhere, wear marks, plus straightness, twist, elongation and what nots with the rod...not so simple..he also put on the rings and inserted the piston into the cylinder...then all i had to do was drop it back in as a unit with gasket, torque the new rod bolts badabing

[Sasquatch Jim]

  For Italian pistons use bigga hamma.

[PeteS]

Heat the piston. You can use a hairdryer if you have nothing else; heat gun is preferred. Have some gloves handy, it may go fast or you may have to get it uncomfortably warm. The pin should slide right in.

Agreed except for the hair dryer part. I just use a propane torch and wear thick work gloves. No other tools needed. It should just slide in when hot enough.

Pete

[Rough Edge racing]

I assume this engine has full floating pins,  ... If so the proper fit should be a little less than .001 inch and a slightly snug finger press fit . If you're using a press tool or hammers and blocks of wood on a full floating pin you might as well rebuild the engine in a sand box. .... Heat the piston with a hair dryer and push it in by hand using oil or a light assembly lube  .If it is an interference fit in the rod then the general procedure is to heat the rod small end and press in the pin using proper procedures...Bangin g on pin while the crank is still in the engine is not proper technique for a high performance engine...

[Antietam Classic Cycle]

Aluminum (the piston) has a much greater coefficient of expansion than steel (the pin).  You get more bang for the buck by heating the piston than freezing the pin.  I've always used a heat gun on the piston, pin at room temperature.

Heat the piston. You can use a hairdryer if you have nothing else; heat gun is preferred. Have some gloves handy, it may go fast or you may have to get it uncomfortably warm. The pin should slide right in.

This ^^^

The pin is not "full floating" on original Guzzi pistons (but is on Gilardonis).

[rodekyll]

I have a little kiln for that, but you can pop the piston in the toaster oven for a few minutes and heat it enough to slip the pin in.  Yes, they should slip into the rod, but should not float in the piston.

[Rough Edge racing]

This ^^^

The pin is not "full floating" on original Guzzi pistons (but is on Gilardonis).

 Cast auto pistons were like that for many years...The pin is an interference fit into the piston at room temperature and heating the piston to about 200 degrees ,the pin can be pressed in by hand with a bit of effort....When the engine is running ,typical piston temperature around the pin boss area is about 300 F degrees and the pin frees up and floats....Is this similar to what's being discussed here?

[Antietam Classic Cycle]

Cast auto pistons were like that for many years...The pin is an interference fit into the piston at room temperature and heating the piston to about 200 degrees ,the pin can be pressed in by hand with a bit of effort....When the engine is running ,typical piston temperature around the pin boss area is about 300 F degrees and the pin frees up and floats....Is this similar to what's being discussed here?

I guess when you put it that way, it is considered "free floating" then.

[Muzz]

I use (but have not done it on a Guzzi) a small top cook oven to heat the piston. Gives an even heat distribution. Also throw the pin in the freezer. If it was still tight I have resorted to making a wooden jig shaped to the piston and a G clamp, pushing the pin through with a socket just a bit smaller than the pin.

[Testarossa]

Heat the piston -- and use this:
https://www.amazon.com/SPI-09-610-Piston-Puller-Made/dp/B0093PFTRW/ref=sr_1_1?ie=UTF8&qid=1467754228&sr=8-1&keywords=piston+pin

[acogoff]

     You gots an oven in your kitchen? That is what I use.  250F  for 1/2 hour soak and it is best if the wife is not home!!!!

[amamet]

thx for all the advice,  heated the piston, froze the pin and used a c-clamp with a little block of wood and a small socket.  was still tight, but got it

[Tom]

 

[n3303j]

I always trial fit wrist pins on the work bench. Nothing to sharpen up the act like a dress rehearsal. Master heat gun and gloves and the pin should slide in/out. Very often I find the smallest of burrs raised by removing the retaining rings will bind the pin. I deal with any burr at the trial fit. Then the actual installation goes a lot smoother.

[Phang]

when I replaced the stock pistons and cylinders with Gilardoni, both stock pin and the gilardoni pin are very tight fitted. Both pins wouldn't move in room temperature with finger power.

I used a heat gun, the pin went in with no effort and a 'ting' sound when it hits the circlip on the other side 

[canuck750]

when I replaced the stock pistons and cylinders with Gilardoni, both stock pin and the gilardoni pin are very tight fitted. Both pins wouldn't move in room temperature with finger power.

I used a heat gun, the pin went in with no effort and a 'ting' sound when it hits the circlip on the other side 

 

Yep a heat gun works great

[Muzz]

     You gots an oven in your kitchen? That is what I use.  250F  for 1/2 hour soak and it is best if the wife is not home!!!!

We had not been married long when my darling opened our oven to find a Matchless crankcase being cooked in it. ensued. After negotiation I ended up with a gas welder.

[Rough Edge racing]

I guess when you put it that way, it is considered "free floating" then.

 Yes it does float at normal operating temperature... And forcing the pin by not following proper assembly techniques can gall the aluminum piston pin bore...

[Tom]

I do the cooking.  Ends the argument from the "Boss".  Having a toaster oven and small air oven works too also have a heat gun that Phang has in Singapore.  Doesn't hurt to have options.