Broken crank bolt/nut - Page 3 - Pocket Bike Forum - Mini Bikes
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post #41 of 81 (permalink) Old 2 Weeks Ago Thread Starter
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Re: Broken crank bolt/nut

Ok after some effort there was a startling pop and out she came.

I’m still curious about your opinion about the welder and any advise...

Also from your experience does welding these broken mount ever hold? What’s the best thing to do?

Am I better off replacing that flywheel cover? Am I ever going to find a replacement flywheel cover?

And finally now that I have this thing open and can see the pin on the flywheel side is fixed on Is pretty long. On the opposite side the crank side the pin had came loose and is quite a bit smaller as you can see in my hand. Is that the original size or is that just remnants of what it use to be? What can I do about this pin are they replaceable?

Sorry about being such a noob man

Thank you!
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post #42 of 81 (permalink) Old 2 Weeks Ago
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Both woodruff keys come out of the slot in the crankshaft the one on the starter side that is half there is because what's all that was holding it for a little bit after it let go your going to defentley need to replace it you can tap the other one out with a small punch and probably get one at a lownmower shop ( I just grind them out of a peace of what ever steal I have )

I haven't had success welding aluminum with wire feed or those aluminum sticks for stick welders I suppose it whould work for welding thick stuff but China cast aluminum no way... The onley thing that has worked for me is that aluminum brazing rod and map gass. Another option is see if you can make a Fab shop feal sorry for you and see if they will do it for 10$ 20$ with a tig.

Or just get this and be done with it https://www.amazon.com/Engine-crankc.../dp/B01MZ282YK

Faster then a speeding E Revo

Last edited by MrKitty; 2 Weeks Ago at 09:31 PM.
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Ok after some effort there was a startling pop and out she came.

I’m still curious about your opinion about the welder and any advise...

Also from your experience does welding these broken mount ever hold? What’s the best thing to do?

Am I better off replacing that flywheel cover? Am I ever going to find a replacement flywheel cover?

And finally now that I have this thing open and can see the pin on the flywheel side is fixed on Is pretty long. On the opposite side the crank side the pin had came loose and is quite a bit smaller as you can see in my hand. Is that the original size or is that just remnants of what it use to be? What can I do about this pin are they replaceable?

Sorry about being such a noob man <img src="https://www.pocketbikeplanet.com/images/smilies/frown.gif" border="0" alt="" title="Frown" class="inlineimg" />

Thank you!
Sorry I have been crazy busy. You are doing a great job. I wouldn't even try to weld that aluminum. Welding aluminum is difficult enough without trying on Chinese pot metal. If it was mine I would get a new case, remember if you get a new case you have to get crank seals and crank bearings as well. Amazon or Ebay are usually the best sources
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post #44 of 81 (permalink) Old 2 Weeks Ago
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I re-use crank seals and bearings all the time as long as they look and feal good there is no real reason to replace that stuff he will have a lot more power after doing the generator delete and if he bumps the compershon by doing the base gasket delete

Faster then a speeding E Revo
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Re: Broken crank bolt/nut

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Sorry I have been crazy busy. You are doing a great job. I wouldn't even try to weld that aluminum. Welding aluminum is difficult enough without trying on Chinese pot metal. If it was mine I would get a new case, remember if you get a new case you have to get crank seals and crank bearings as well. Amazon or Ebay are usually the best sources
Thanks for the encouraging words and advice. Man I donít know where I would be without you guys. Iím really trying to research most of these questions but There are so many variations that itís hard to find the answers. Plus you guys have so much trial & error experience, so valuable. Thanks man!
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Re: Broken crank bolt/nut

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I re-use crank seals and bearings all the time as long as they look and feal good there is no real reason to replace that stuff he will have a lot more power after doing the generator delete and if he bumps the compershon by doing the base gasket delete
Thanks Mr Kitty! I’m on it. I really appreciate that link to replacement crankcase. I would have never been able to find that. I Really appreciate your mentorship. I hope to one day be able to help others like you have done for me. Thank you again!

Have a good night

Last edited by salzamani; 2 Weeks Ago at 12:57 AM.
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Re: Broken crank bolt/nut

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I re-use crank seals and bearings all the time as long as they look and feal good there is no real reason to replace that stuff he will have a lot more power after doing the generator delete and if he bumps the compershon by doing the base gasket delete
Good morning Mr. kitty

Ok so youíre saying eliminate this gasket for more compression and power right? Would that cause more leaking? If did do I have to make any other changes to compensate?
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You can't have any leaks at all! If your going to delete the gasket you need to use gasket sealant instead...

Faster then a speeding E Revo
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I re-use crank seals and bearings all the time as long as they look and feal good there is no real reason to replace that stuff he will have a lot more power after doing the generator delete and if he bumps the compershon by doing the base gasket delete
Good morning Mr. kitty <img src="https://www.pocketbikeplanet.com/images/smilies/smile.gif" border="0" alt="" title="Smile" class="inlineimg" />

Ok so you’re saying eliminate this gasket for more compression and power right? Would that cause more leaking? If did do I have to make any other changes to compensate?
Gasket sealant, yes. But check your squish. With and without the gasket. Dont ever reuse your crank seals. Bearings you can get away with. Swaping seals from the old case to the new one can easily damage them. Plus they might have been bad before you take them out of the old engine. You do all that work and then it won't fire up because the seals are bad. It's just good practice to put in fresh seals and gaskets. They are not expensive
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Re: Broken crank bolt/nut

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You can't have any leaks at all! If your going to delete the gasket you need to use gasket sealant instead...
Ok so here is what I was able to get done today.

I decided to just cut a new gasket for that cylinder head.

I JB welded those mounts that had broken off and if they end up failing then I’ll just get the new crankcase that you send me the link for.

I decided to skip purchasing a or making a woodruff key for the crankshaft on the starter side. Instead I found a m6-1.00 x70mm long bolt at Home Depot that I threw on 36 washers under the claw pawl and one larger one over the claw pawl and JB welded the last washer and the larger washer to the claw pawl.

Just waiting for the drying time for the JB weld and I’m keeping my finger crossed it all holds up. Time will tell.
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Last edited by salzamani; 1 Week Ago at 10:00 AM.
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You can't have any leaks at all! If your going to delete the gasket you need to use gasket sealant instead...
Ok so here is what I was able to get done today.

I decided to just cut a new gasket for that cylinder head.

I JB welded those mounts that had broken off and if they end up failing then I’ll just get the new crankcase that you send me the link for.

I decided to skip purchasing a or making a woodruff key for the crankshaft on the starter side. Instead I found a 6m-1.0 x70mm long bolt at Home Depot that I threw on 36 washers under the claw pawl and one larger one over the claw pawl and JB welded the last washer and the larger washer to the claw pawl.

Just waiting for the drying time for the JB weld and I’m keeping my finger crossed it all holds up. Time will tell.
You know what, I probably would have done the same thing. Just to get it up and running. Can't hurt it anymore then it already is. &#x1f602;
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Re: Broken crank bolt/nut

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You know what, I probably would have done the same thing. Just to get it up and running. Can't hurt it anymore then it already is. &#x1f602;
Yeah I figured I have nothing to lose. Anything that doesn’t hold up will then be replaced instead of bandaged. I’ll gain the the experiences. I just hope I got the right clearance for head of that m6 bold and the inside of that pull start right( right amount of washers).

So what do you guys do when an engine like this eventually needs to be replaced? Pop the same engine in there or upgrade? Does upgrading require a lot of modifications? do they pretty much have the same mounting points?

Last edited by salzamani; 1 Week Ago at 10:17 AM.
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Most people just soup up the stock 49cc engine. You can get 4 to 4.5 hp just by deleteing the base gasket, rocket key, porting, starter delete, boost bottle and skf crank bearings

I never run base gaskets I will get brand new engines and delete the gasket before even starting it 100% free .3 HP boost...
IMG_20200508_161240478_1590163166338.jpg
The hardest part of the mod is going to the Honda dealership for hondabond crank case gasket maker without buying anything. I try not to even look around lol!!!

If your going to swap it make sure the engine is not to heavy and it spins the correct way ( harbor freight engines are to heavy and spin the wrong way )

Anything you can get for free is the way to go for swapping you don't want spend more then what you can get a used better bike for...

Faster then a speeding E Revo

Last edited by MrKitty; 1 Week Ago at 11:07 AM.
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Re: Broken crank bolt/nut

So the JB weld was dry and ready today and I started to mount the motor today and just as I was screwing in the mount screws I heard a snap. I could hear Mr. Kitty giggling in my mind. Like he know all along that JB weld wouldnít be strong enough for the motor mounts screws. I bet you knew all along and a you were right. the weight of the motor alone snapped them right off. So back to my modified mounting point. The right side is just fine but that left Iím gonna have to come up with something good. So I figured why not just fire her up and make sure I didnít F anything up while I had the whole motor apart and so I tightened 3 out of the 4 mounting points up the best I could and gave it a go. She fired right up on the 4th pull and idled better than ever! That was such a rush. Took her for a quick spin which truly restored my faith in her.

I just gotta figure out a couple of things. I think I will try the Honda bond I already have some from back when I did a valve cover on my Integra and the 4 mount Iím gonna need to figure out how Iím Iím going to fabricate a bracket to bolt it on on another spot.

By the way Mr. Kitty when I had the motor out with one of the bolts off on the crankcase I lost a bit of oil (very little probably not enough to cause problem)from the case where the sprocket housing is. I guess that is the crankcase right? should I drain a refill it? and what type of oil does that take?

incidentally the JB weld is holding just fine on that washer/bolt that is securing the pawl claw.
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Thang thing there is the transmission.

Drain the Chinese cooking oil out!

Then put gasoline inside of it and give it a spin and shake for about 5 minutes then drain the gas out ( repeat if necessary)

Put that thing in a warm place for 24 hours obviously nowhere near an open flame make sure all the gasoline is evaporated out before you refill it with a 100 mL ( aprox 3.5 ounces )of ATF transmission fluid. (I believe that thing says 100ml somewhere on it you should check that)

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When you do the base gasket delete mod use a very thin layer of silicone on the cylinder part you don't want to put too much because you don't want it to ooz out inside of the engine

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Re: Broken crank bolt/nut

Man whatís disappointing day. I made a nice little bracket to mount that last motor mount and this thing is nice and solid now. Did a few touch up preparations. Bondo the body kit and got her all set up and fired her up and mind you she ran great yesterday, but not today. She started up just fine and held a idle beautifully but when I tried to accelerate there was nothing there it just bogged down. Iím going to blame it on that carburetor because today it started leaking like crazy. I canít imagine it could be anything else.
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Defentley the carburetor when those typs (pumper) leak that means when it's running it's sucking air... When you gass it and it goes supper lean then wants to backfire bog shutdown and die!

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Re: Broken crank bolt/nut

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Defentley the carburetor when those typs (pumper) leak that means when it's running it's sucking air... When you gass it and it goes supper lean then wants to backfire bog shutdown and die!
Yeah thatís what it did alright. That carburetor was only a month old too what a shame. I also have that Walbro Wt-603 that I can get a rebuild kit for. What do you think should I rebuild the Walbro or just get another cheap Chinese pumper carb? What do you recommend? Do you have a link to a good seller that you have had good luck with?
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Defentley the carburetor when those typs (pumper) leak that means when it's running it's sucking air... When you gass it and it goes supper lean then wants to backfire bog shutdown and die!
Yeah that’s what it did alright. That carburetor was only a month old too what a shame. I also have that Walbro Wt-603 that I can get a rebuild kit for. What do you think should I rebuild the Walbro or just get another cheap Chinese pumper carb? What do you recommend? Do you have a link to a good seller that you have had good luck with?
2 walbro is better for many reasons but I like to keep a couple Chinese pumper carbs on the Shelf just in case I need them. Although I've never had one crap out on me in one month
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