Unique, hard to understand problems, and too many variables.

Frankenstein

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Jun 24, 2016
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5,078
Well, first time posting on this forum (or any motorized bicycle forums, for that matter,) so I'll give the back story of my bike(s). Around the same time last year, I picked up a cheapo 150 or so dollar happy "go lucky or broke" time engine from that Gasbike site, worked beautifully as a single speed set up. Then later on, I got my shift kit, from sbp, put that and the original engine into a mongoose terrex. Well as time went by, I broke my crankshaft, twice, picked up a ported cylinder and piston to match, and a Reed valve, even made custom turn signals and headlamp, rear light and waterproofish box to hold the whole thing to run it.

Now recently, after my crank was damaged a second time (bevel gear was loose, ended up shearing the key, and turned it into a grinding paste, destroying the taper and preventing a gear from being pressed on tightly, all my fault because I figured "it'll be OK till I get around to it" not!) Anywho, damaged crank, decided to rebuild, put it together, reused my main bearings, figured they were OK, and after a month of in-between repairs, the bearing seized in under 24 hours, on the second time I rode it. Now, spent a week or 2 re-repairing, and new bearings, brand new! They are already failing, making lots of bad evil sound and sticking, making the engine stall on idle, with the idle screw full on tight. And stopping it in general. Here's the interesting part. My crankcase is 2 different engines. Left side is from my original, right side is a different engine, one that blew up on the top end, the crankshaft was in that engine, but good condition otherwise. Also I find that pressing the bearings onto the crank was a little harder than I remember last time, and getting the engine cases together required quite a bit of tapping with a 16 oz hammer, then torqueing the case bolts down to finish the press. So, are the bearings supposed to be a tight fit on the crankshaft arms. And after pressing the crankcase together should turning the crank over be resistive. And finally, could having 2 different halves, being that they probably came from opposite sides of China, be a bad thing, making for misalignment, and resulting in early bearing failure, the bearings I originally had in the original engine were perfect considering they had nearly 8 months on them, and practically no air filter. Also worth noting, the engine case with the crankcase that make up 2/3rds of the trio when opened to check things out, had a failed main bearing, same side that it failed on recently, and probably the same failing yet again (I have not opened it yet, it's still installed on my bike, and only began failing yesterday.) Oh and since I'm mentioning things, right before the bearing failed the first time, the engine started making a whirring sorta sound, got louder, then failed, this one did the same exact thing, but I also installed a new (old beat up) large 2 and a half gallon motorcycle engine, from a vintage suzuki ts125 or ts185, it has a very small leak and drips gas right on the hot engine head, shouldn't be the source of the problem though. The reason I mention it is I can't tell if the tank makes more sound as it gets empty, as in as the gas is used, creating more empty space and exposed metal to vibrate and make that sound louder as it gets even more empty, get it?

Anyways, sorry for the way too long novel, but I tend to write in novels rather than paragraphs. Thanks for input when it comes.
 


jaguar

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Nov 25, 2010
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3,453
yes you shouldn't mix and match crank halves. No the crank shouldn't resist turning. Did you not put a spacer between the crank wheels to keep from misaligning them when you put it all back together? Put your fingernail on the crank wheel while stabilizing your finger position by pressing it onto the crankcase and turn the crank over to feel for out-of-roundness.
Also use a digital caliper to measure the space between the halves close to the conrod pin and ot the opposite side.
Let me know the results.
 

Frankenstein

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Jun 24, 2016
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5,078
yes you shouldn't mix and match crank halves. No the crank shouldn't resist turning. Did you not put a spacer between the crank wheels to keep from misaligning them when you put it all back together? Put your fingernail on the crank wheel while stabilizing your finger position by pressing it onto the crankcase and turn the crank over to feel for out-of-roundness.
Also use a digital caliper to measure the space between the halves close to the conrod pin and ot the opposite side.
Let me know the results.
Figured as much, never actually expected the 2 halves to be a good match, I'm planing on going back to the original halves, besides, the side that replaced the original stripped out on a bolt hole, has a big black bolt sticking out its neck driven past the threads and digging into the crankcase surface, I was hoping to stick wires or something to that bolt.

What is this spacer you speak of? What I meant is that the bearings are very difficult to get onto the crank arms, bearings for the most part fall into the halves of the case, with gental (whoa auto correct just tried to fix this word badly) pushing of course. Then getting the crank to meet nicely in the middle is difficult.

Originally the crankcase had a checker board box smartly cut to a crankcase gasket, that seal never failed, and came apart twice and reinstalled no problems. New one is a stock gasket, and red rtv, messy.

That could give it some budge room...
Got it sitting on a pane of glass soaking in oil, original damaged, this cardboard is litteraly the other half of the checkerboard box, had to find the innards a new place to live... How poetic. I had all intentions to use it, I left it at home when I needed it most. Sacrifices... How very poetic. Damn bike.

Not sure if I understand the finger nail trick, I was planing to put the crankshaft on a glass sheet and check it for a wobble, like them being misaligned. Chances are if the case is off a tiny bit, then the bearings are off, and so is the crankshaft spinning like a 7 pound top at 3000 times a minute, that subtle unbalance goes from perfect motorbike day to wrecking ball to the censored words here.

I own and use a caliper.

I'm not planing on measuring the crankcase, I just could feel it was wrong, I'm going back to the original lower end setup, with new crankshaft, looked over on a sheet of glass for completion sake, since otherwise my bike will be parked on its side with shoe print design, right behind my ford, which is also broke. Good thing I have to go to the dmv tomorrow.

Conrod pin? I'd Google it if I wasn't lazy, I'm guessing the joint (no jokes please) between the 2 round halves?

You're saying the entire crankshaft assembly can be bent inward towards itself?

I should have used more wd40 the lube things up like I did the first time, that reminds me....

I'll post more later, as time goes, I'm mostly trying to confirm some suspicions. Trying to figure out where the water leak in my gremlin cage is comming from. You basically answered it well out in full, by giving enough info to backtrack through the problems. Thank you.







Damn bike.
 

jaguar

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Nov 25, 2010
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3,453
yes the joint connecting the halves.
use anything of metal the right distance to keep the halves spaced apart correctly when putting everything together, unless the crankshaft wants to just slide into the bearings. when it doesn't then that resistance tries to force the two halves closer together which makes the assembly wobbly
 

jaguar

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Nov 25, 2010
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3,453
sometimes you can find a socket from a socket wrench set that is the right length.
spin the crank and see if it has high spots that touch your fingernail.
 

Frankenstein

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Jun 24, 2016
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5,078
sometimes you can find a socket from a socket wrench set that is the right length.
spin the crank and see if it has high spots that touch your fingernail.
Can't really spin it, it's a turn by wrench only type of thing now, can it be checked outside the case? Also what exactly am I checking for, like it being twisted along its conrod pin?
 

Frankenstein

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Jun 24, 2016
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5,078
Again I'm replacing the crank completely, 3 times its been used it had main bearings fail, all within a few days of initial operation.
 

jaguar

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Nov 25, 2010
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3,453
you can check it in or out of the crankcases.
does the crank wheels wobble side to side?
are they out of round with high spots when you rotate it?
 

crassius

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Jul 23, 2012
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4,575
folks that treat these motors as disposable smile more than folks that try to fix them
 
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