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MC91B1 rod, piston, wrist pin assembly
#1
I just tore down an engine to freshen it up for Avon and discovered, to my dismay, that the rod cap was cracked. Why it didn't fly apart the last time it was run is a mystery, just lucky I guess. So I have to change the rod. Problem is it's something I've never done, I always had the machine shop change the piston when I had a block bored.

I know it's a press fit between the rod and pin, but what's the procedure? The pin bearings are open on one end and closed on the other. Do you push from the open side and drive the closed bearing out with the pin? What is the proper way to support the piston?

Help!  BP
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#2
well sir ., id say it be really really tuff with out a mcculloch wrist pin puller ..
you could make one ..
then ya have to heat up piston and rod snake the wrist pin out threw the rod ..
seems like I seen a vid that scott K. posted ..or maybe you tube ..
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#3
Bill,

Below is the link to Scott Kneisel's rebuild tutorial that Steve mentioned. It should answer some of your questions; I hope it helps...


http://www.briansantee.com/vintage/www.v...orum_id=55
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#4
bill call me i'll sell or lend you a pin puller.
Cool
Dave L.
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#5
OK, this is getting too complicated. So I put that engine aside and will deal with it later. After all I have two more in the basement. So I start taking one apart and find that it's extensively modified (port work, full circle crank, cuts in the piston skirt, etc.), the very definition of "Stock appearing". Now I remember buying it but never running it. Put that one aside. Maybe if we do another Thompson style test day I'll get it going and see if it'll run. OK, last chance. Took that one apart and everything looks good so far (ran out of time, dinner with the in-laws).

Anyway guys, thanks for the input. I'll find someone to change the rod for me, that's assuming I can find a usable one in my pile of junk. Got to find a crank too. The rod journal on this one is pretty badly rust pitted (that may explain the cracked cap). Is it possible to polish out the pits and fit larger needles?
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#6
(06-23-2017, 05:11 PM)Bill Peck Wrote: OK, this is getting too complicated. So I put that engine aside and will deal with it later. After all I have two more in the basement. So I start taking one apart and find that it's extensively modified (port work, full circle crank, cuts in the piston skirt, etc.), the very definition of "Stock appearing". Now I remember buying it but never running it. Put that one aside. Maybe if we do another Thompson style test day I'll get it going and see if it'll run. OK, last chance. Took that one apart and everything looks good so far (ran out of time, dinner with the in-laws).

Anyway guys, thanks for the input. I'll find someone to change the rod for me, that's assuming I can find a usable one in my pile of junk. Got to find a crank too. The rod journal on this one is pretty badly rust pitted (that may explain the cracked cap). Is it possible to polish out the pits and fit larger needles?

Bill, back in the day there was supposedly a bearing kit you could get to replace bearing on a reground crank.
we've never actually had anyone disclose details on the forums .
just rumors about them.
i can supply you with a new con rod i have a few spares i suppose. the crank will be harder as i never seem to have enough.
you're welcome to come visit and buy stuff directly if you ever get the urge to see my stash.
Cool
Dave L.
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#7
Bill,

I have NOS cranks and rods listed on ebay right now.
Any other 91 series parts you need are available as well.
I discount for package deals.
Contact me if you decide to replace the worn out or damaged parts.
Steve O'Hara
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#8
Dave & Steve - thanks, but for the time being I have everything I need to get the other engine going, at least so far. I just finished cleaning it up this afternoon but haven't looked at it in detail yet. But I will keep you in mind when I get around to dealing with the rod & crank. Let's get past Avon first.
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#9
(06-24-2017, 11:59 AM)David Luciani Wrote:
(06-23-2017, 05:11 PM)Bill Peck Wrote: OK, this is getting too complicated. So I put that engine aside and will deal with it later. After all I have two more in the basement. So I start taking one apart and find that it's extensively modified (port work, full circle crank, cuts in the piston skirt, etc.), the very definition of "Stock appearing". Now I remember buying it but never running it. Put that one aside. Maybe if we do another Thompson style test day I'll get it going and see if it'll run. OK, last chance. Took that one apart and everything looks good so far (ran out of time, dinner with the in-laws).

Anyway guys, thanks for the input. I'll find someone to change the rod for me, that's assuming I can find a usable one in my pile of junk. Got to find a crank too. The rod journal on this one is pretty badly rust pitted (that may explain the cracked cap). Is it possible to polish out the pits and fit larger needles?

Bill, back in the day there was supposedly a bearing kit you could get to replace bearing on a reground crank.
we've never actually had anyone disclose details on the forums .
just rumors about them.
i can supply you with a new con rod i have a few spares i suppose. the crank will be harder as i never seem to have enough.
you're welcome to come visit and buy stuff directly if you ever get the urge to see my stash.
Cool
 Dave, 

I have some questions pertaining to wrist pin and bearing removal/installation? Using the search function, I found this post.  I'm new to forum etiquette, so should I ask my questions in this older post, or should I create a new one? 

v/r
Ryan Courts
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#10
Ask away here or start a new thread more specific to what you want.
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