how to rebuild bottom end robins

[justlakinit]

Just picked up a cheap cart...87 Marathon.
Motor is locked up.
Turns out piston was froze....OK easy fix.. but after I got that apart, the connecting rod is also not moving freely.
Not sure how to go about rebuilding the bottom end...can't find any youtube videos....any help would be much appreciated.

[Heliarc]

I just checked my youtube channel, I could have sworn I did a video on it but I only got the top end.

Anyhow, the bottom end is tricky business. Everything excluding a few bolts in the case halves, are pressed together. The main bearings are pressed onto the crank and into the case. If the bottom bearing on your connecting rod is shot you're going to buy an entire crankshaft assembly or you'll need the services or a very talented welder and machinist since the bearing does not come apart normally.

I managed to get mine together with wooden block and a mallet but I imagine a small amount of luck was involved. Also the fact that I've changed many front wheel drive wheel bearings helped out.

If you know a guy with a hydraulic press and he's good with it though I'd go that route. I did it once with the mallet but I wouldn't suggest it. For me it was a case of the only people with presses are monkeys and they won't let me use it even if I paid. That's why I end up doing so many wheel bearings as well.

[justlakinit]

I guess at this point...my main concern is getting the halves apart. Still looking for some good directions on this.

[Heliarc]

Like I said, a guy with a press who really knows how to use it. The bearings are pressed into the case halves as well as being pressed onto the crank. You're not getting it apart without a press or a lot of luck and a mallet.

[justlakinit]

Got it apart without a press. Actually it was pretty easy....used some ratchet straps to pull it apart.
Now if I can get it back together without a press....HMMMM...I'll see what I can come up with for this.

[Heliarc]

I really should have done a video when I did mine. If you paid attention as to how it came apart though and keep in mind to only put pressure on the outer races of the bearings you'd probably be ok. Mine went together with only wooden blocks touching anything metal be it bearings or the case. It should pretty well go together with moderate tapping, not hard whacks. At least mine did. if I'd have had to pound on anything my workbench would have rattles everything onto the floor. If something starts requiring a lot of effort, stop and check that something isn't cocked in there. Everything is a press fit but it shouldn't be a "tight" press fit. You won't slip it together with your fingers but you should be able to make progress with a wooden mallet/blocks and claw hammer. You shouldn't even need one of those little hand sledge hammers.

[oachs83]

Put crank bearings and crankshaft in the freezer for about 2 hours. Find a socket that is about the same size of the bearings outside cage. Do not hit where the bearings are or the inner race just the outside metal portion of the bearing. Now take one bearing out of the freezer. Take a handheld propane torch only. Do not use a acetylene torch as you will wreck everything. Heat up the walls of the crank case where the bearing will seat then once heated drive the frozen bearing in with your appropriate size socket. I have had times they fall in but drive till you hear a thud knowing your seated. Let cool and then put your crank seal in unless it's already in. Now heat up the inner race of that bearing be very careful not to burn your seal as it does not take much heat. Once heated,drive in frozen crank shaft. Put case and crank shaft back in freezer to refreeze your crankshaft and repeat steps for the other side. I have done this method countless times working great. The contraction and shrinking of the metals gives it just enough clearance to work. Once everything cools the metals go back to original state.

[justlakinit]

Ended up dropping off the motor at the machine shop hoping they can press it back together. It was not going together for me....so thought this was my best option....only hoping they can do it...LOL

[Heliarc]

That's the best way if you can afford it. When I did mine I spent my wad on just the parts so I had no choice. I have a fair degree of skill when dealing with things mechanical but I was also kinda lucky.

[justlakinit]

Well things are on hold...dropped it off at the machine shop last Friday and after many calls to them, I finally got a response....
They have not had time to look at it yet...have never done one before and will not have time to look at it until next week.
In the mean time I called a golf cart shop and they said they could do it in about a half hour to one hour labor at $75 hr. I am betting on the one hour charge...LOL
Hate to spend that much more money on it...just to press it back together.
Might go get it and tinker with it some more...if I can't get it, then take it to the golf cart shop. I just don't want to crack the case trying to get it back together.