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Username Post: SBC sticky wrist pins.        (Topic#357708)
65 GMC 930 
Poster
Posts: 30

Reg: 09-08-07
08-18-19 12:57 PM - Post#2773494    

I recently acquired a low mileage 350 crate motor (mexico) that precious owner attempted to install hotter cam and heads on. Clearly the cam break in did not go so well. He was so disgusted that he pulled it and it sat wrapped up in the corner for several years. After I got my hands on it, I disassembled and cleaned it all up. Plans are to replace all bearings, and install a mild cam in it, and just make a good runner for my work truck.
Question is, most of the wrist pins are very tight. I've used heat gun and penetrating oil, dipped in hot motor oil, and then tried ATF to free up. They become slack after 15-30 seconds in hot oil, but once cooled they are stiff again. Is there a magic bullet to fix this, or am I SOL and spending more money on machine shop? Money is tight, any insight is appreciated.



 


Algoma56 
Contributor
Posts: 713

Loc: Sault Ste. Marie, ON, Can...
Reg: 03-14-05
08-19-19 05:36 AM - Post#2773537    
    In response to 65 GMC 930

A friend of mine had same issue with a 350 in his coupe. Only one piston was tight. He pressed it off, lightly honed the piston pin bore, and reassembled. Okay after that.



 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17390
grumpyvette
Age: 71
Loc: FLORIDA USA
Reg: 03-16-01
08-19-19 06:12 AM - Post#2773539    
    In response to Algoma56

I've got too ask...are the wrist pins designed to be free floating or are they using stock pistons?
stock pressed wrist pins are locked in the small end of the connecting rod, and only rotate in the piston
wrist pin bore.

most crate motors use pressed in piston pins,
not free floating piston wrist pins
free floating piston wrist pins rotate in the connecting rod small end and in the piston pin bores
pressed wrist pins are designed to be firmly locked in the connecting rod small end and only rotate in the piston pin bore's

most stock engines use pressed wrist pins, it requires pistons designed to use free floating wrist pins to use free float or bushed wrist pins.

if the wrist pins are designed to move in the rods small end the piston will be designed to keep the wrist pin centered in the piston,
pistons without a design to retain the wrist pin use pressed in wrist pins,
that should not be free to move in the connecting rod small end.

read these links, (below) and Id certainly pull a rod and piston,
and determine exactly what type of piston and wrist pin combo your dealing with for sure.

https://www.youtube.com/watch?v=dSWNPMYUE1s


http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.com/index.php?thr...


IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


Edited by grumpyvette on 08-19-19 06:53 AM. Reason for edit: No reason given.

 
65 GMC 930 
Poster
Posts: 30

Reg: 09-08-07
08-19-19 10:32 AM - Post#2773565    
    In response to grumpyvette

Pressed in wrist pins. Factory rods and pistons.
It sounds like I'm not getting out of spending money to have pressed out, light hone, a d reassemble.
Thanks for the input fella's.



 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17390
grumpyvette
Age: 71
Loc: FLORIDA USA
Reg: 03-16-01
08-19-19 03:59 PM - Post#2773593    
    In response to 65 GMC 930

your not getting/ grasping the concept,
I can,t help but assume you did not carefully read the supplied links and watch the linked sub videos,
pressed pin pistons will cause the engine to self destruct if you hone the small end of the connecting rods to allow the piston pin to slide freely in the small end of the rod, free-floating piston pins are almost always used with bronze pin bushing support, and REQUIRE pistons designed to retain the piston wrist pin centered in the piston,this is quite different from the existing pressed pin piston design.







IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


 
65 GMC 930 
Poster
Posts: 30

Reg: 09-08-07
08-19-19 05:18 PM - Post#2773602    
    In response to grumpyvette

Yes, I understood the first time. The pin portion is held to the small end of rod by friction fit. The pin rotates in pin bores of piston. The pin is not moving freely in the piston pin bores now. Stock 290hp 350 do not come with any other style of wrist pin.
Thanks for your concern though.



 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17390
grumpyvette
Age: 71
Loc: FLORIDA USA
Reg: 03-16-01
08-19-19 05:39 PM - Post#2773605    
    In response to 65 GMC 930

ok,as long as you understand that pressed pins only rotate in the piston pin bore and not the small connecting rod end, I just did not want you, or anyone else reading the thread later, to assemble an engine incorrectly in a way that would almost certainly over time develop major problems that would eventually cause the engine to fail.

IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


 
Algoma56 
Contributor
Posts: 713

Loc: Sault Ste. Marie, ON, Can...
Reg: 03-14-05
08-21-19 07:04 PM - Post#2773787    
    In response to grumpyvette

I hope my post wasn't too vague. We honed the bore of the piston's pin bore just enough so that pin would rotate in it. The assembly was then pressed back together on the connecting rod. The fit was still tight on the rod.



 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17390
grumpyvette
Age: 71
Loc: FLORIDA USA
Reg: 03-16-01
08-21-19 07:07 PM - Post#2773788    
    In response to Algoma56

the piston pins used on pressed pin pistons are NOT supposed to rotate in the connecting rods

IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


Edited by grumpyvette on 08-21-19 07:09 PM. Reason for edit: No reason given.

 
Algoma56 
Contributor
Posts: 713

Loc: Sault Ste. Marie, ON, Can...
Reg: 03-14-05
08-21-19 08:02 PM - Post#2773792    
    In response to grumpyvette

Yes, grumpy, that's why we honed the pin bore of the piston.



Edited by Algoma56 on 08-21-19 08:03 PM. Reason for edit: No reason given.

 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17390
grumpyvette
Age: 71
Loc: FLORIDA USA
Reg: 03-16-01
08-22-19 04:45 AM - Post#2773801    
    In response to Algoma56

ok,that should be whats required,
I hope it works out well with no further issues

IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


 


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