crankshaft conundrum

Jason Luther /

okay, so heres my situation. the needle bearing on the big-end of the connecting rod are pretty bad. i can see that they are just flopping around in there. but..... it spins freely, there is no up and down movement in the rod, and there is little side to side movement. if you were me (god help you) and you had a limited moped budget, and assuming i can even get a new crankshaft, would you replace it? the crank bearings are bad, and im going to replace those, for thats whats keeping my motor from turning freely.-jason

Re: crankshaft conundrum

Is this the same crank of which you said: " next…. the needle bearings in the small end of the connecting arm are missing, broken, halfway hanging out etc.," ?

Sideplay specs (go get a feeler guage set if you dont have one.. auto-parts store, $5 )

Big end sideplay should be near .006 to .01.

More than .03 and it may not be salvagable.

As far as up/down play, you have to measure this correctly. I forget the proceedure but it's not as simple as tugging on the rod and trying to feel a bump.

However, in my experience, if the thing feels like zero movement up/down, it's probably OK.

im just wondering if we are talking the same motor..

Re: crankshaft conundrum

Sometimes it's just better to throw out the old engine(repair it THEN at YOUR leisure) and find a bolt-in replacement that's in good shape. don-ohio

Re: crankshaft conundrum

i bet he'd snatch an available replacement engine in a heartbeat.. where would you look for a monkey-wards riverside engine?

Re: crankshaft conundrum

First.....you always call Ike and Mopedwarehouse. Then there's a lot OF Puchs out there. I see them quite often on e-bay. Also, KJRIND ,Kevin R., of Dayton comes to mind, and Zippy,of course. Puchs are plentiful, but apparently have some bearing problems.

If I owned one, I'd be running synthetic at 32:1 to help protect those bearings and upper rod bearing. don-ohio

Re: crankshaft conundrum

Jason Luther /

yes joe, its the same engine. the crank is $125. i paid $100 for the ped. but like i said i can see the needle bearings arent in the best shape, but it still spins free. but i know eventually theyll go and drop everything right into the piston. as far as getting a new engine, i can only imagine there are 10 in the whole world that still work. heh.-jason

Re: crankshaft conundrum

heh.. actually, i knew it was the _same freakin' engine!_

hmm.. heres the thing about your description of those needles. You can actually see the needles? How? There is only like a couple thousandths of an inch on either side. If you are loooking through the oil cutouts in the connecting rod end, you can see maybe the end of one or two needles. The needle bearing cage might not even extend to the ends so you may never see that although it is intact.

If you know what they are supposed to look like and they look different, then don't bother describing it.. I'll take your word for it that they are toasted.

Anyway, you actually found a crank? amazing. Well, i usually put about a $1000 into my average little basket case $75 moped.. but it's worth it because it keeps me off the streets..

Re: crankshaft conundrum

Puchs use the Montgomery Ward / Benelli engine?

Re: crankshaft conundrum

Jason Luther /

no, i think the arch-enemy of my monkey is the puch allstate. sold at sears. the cage seems to be disintigrated and the needles are just floating in there. but $125. come on! ill buy it, put it in, then ill find something else thats wrong. wheres tom hanks, this thing is a money pit. but its sweat looking.-jason

Re: crankshaft conundrum

Jason Luther /

oh yeah, there is an 1/8 inch slit in the 'big end' where i can see the bearing quite clearly. like i said, they spin free, and there is no up and down movement. if there is a 50/50 chance that there wont be a catastrophic failure, ill take it. after all ill ride 6 miles to work with a 50/50 chance of rain. (i almost never win though)-jason

Re: crankshaft conundrum

Not _all_ needle bearings are caged. If there was a cage and now it's gone, there is going to be obvious evidence of the cage's destruction. Needles "flopping around" may mean nothing.

If you have room to see, take a real close look with a magnifier under good light and examine what you can see of the needles' surfaces and the crank journal surface. Look for signs of overheating, or scratches or wear of some kind. And check the clearances.

If everything looks like smooth, bright steel it's probably OK and won't need rebuilding.

Re: crankshaft conundrum

Jason Luther /

i did that today, if i spin it around and look carefully, i can see that part of the cage is missing. dont tell my wife, but i need a new crank :( -jason

Re: crankshaft conundrum

Jason Luther /

i thought about it. im not giving into 'the man', ill fix this old crank. somehow....-jason

Re: crankshaft conundrum

did i mention i once tried to disassemble a crank myself? I went as far as welding up a suitable jig and used a 10 ton hydraulic press. No luck. The crankpin didn't budge. And I'm sure i tweaked it a bit so the crank was trash anyway.

But forget the problems involved in just taking it apart.. the real problems come when the crank has to be reassembled perfectly lined up...

Re: crankshaft conundrum

Jason Luther /

there is no way this thing is coming apart. looks like im putting someones kid through school at cosmo motors. granted it will only buy one text book, maybe.-jason

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