Engine rebuild

[Lit Hawk]

Originally Posted by Megadan

At this point I would have them send me new bearings for everything as well. Those metal fragments get in everything.

As far as cleaning it. Diesel or kerosene works. A parts washing detergent works. It really just depends on what you are after.

So I guess they’re not sending me the bearings I requested or the bottom engine gaskets. Does anyone know where I can get bottom engine gastkets. And also if I can buy the bearings from a bearing distributer or do I need to get specific dirtbike bearings. Do you think the engine would be ok with not replacing bearings?

[Megadan]

Originally Posted by Lit Hawk

So I guess they’re not sending me the bearings I requested or the bottom engine gaskets. Does anyone know where I can get bottom engine gastkets. And also if I can buy the bearings from a bearing distributer or do I need to get specific dirtbike bearings. Do you think the engine would be ok with not replacing bearings?

I wouldn't personally re-use the bearings if I didn't have to as there is no way to ensure you get every fragment out that may be trapped. There is also always the risk of damaging the race when removing a bearing if you find yourself having to do so. The crank should come with new ones, but as far as the others go, you can easily source new bearings by using the bearing codes on the bearings themselves. Just make sure to match the style (seals, no seals, one side seal, etc). Any bearing distributor can easily help you match up what you need, and doing it this way you can also ensure that you get really good quality bearings.

As far as case gaskets, you can get whole kits off of ebay. Here is one from a US Distributor. https://www.ebay.com/itm/67mm-250cc-...4383.l4275.c10

I would look into having new shifter shaft and kick start seals as well, and don't forget the exhaust gasket. They might be fine now, but the lips can get damaged when removing or re-installing, so it never hurts to be prepared. Lastly, as I am sure you are well away but I want to state it anyway for posterity, make sure to clean the crap out of those cases.

[Lit Hawk]

Awesome as always! Thanks megadan, just the info I was looking for! I wanna throw this engine together as soon as possible but wanna do it the right way the first time. I guess next step is removing bearings and seals and replacing. Also thanks for the link for gasket I searched and really couldn’t come up with anything that I knew was a for sure fit. I’ll probably pull all bearings and seals out in the next couple of days and post them for reference but don’t seem like y’all need them like I do. Thanks againe

[Megadan]

I would love it if you posted any bearing and seal information. The more info we have, the better. Your misfortune could probably help the next guy.

[_skid87]

Originally Posted by Megadan

I would love it if you posted any bearing and seal information. The more info we have, the better. Your misfortune could probably help the next guy.

Tangent.. What is the recommended oil change interval on these motors Megadan?

[2LZ]

Definitely seems like you're needing the new gearing on the rear.....and an oil cooler. Man...that's grenaded and twice. I've beat the snot out of my CG motors without mishap. Maybe extended super-high RPM's on really hot days is the proper combination for "BOOM!" on these little motors? With TXP's reputation, I'm really happy to hear that Manny at least coughed up some free parts for you.

[Wild Dog]

If you blew two pistons in 8000 miles there is something wrong with the engine.
You can't really over rev these engines, because the stock CDI has a cut-off and it is set quite low for a CG, so you are always on the safe side. At worst you are going to waste fuel.
North of my country is as hot if not more than Texas and the CG live a long life, in fact on these chinese motorcycle, they first lose the plastic, then the exhaust start to rust, then they lose the speedo, then the owners gets bored and get a new motorcycle and sells the old one still running.

What kind of oil are you using???

[Megadan]

Originally Posted by _skid87

Tangent.. What is the recommended oil change interval on these motors Megadan?

Depends on where/how you ride and what oil you are using. Generally between 500 to 1000 miles. I stick to about 500 mile intervals using regular dino oil like Rotella T4. Being air/oil cooled, pulling double duty as engine and trans oil, and with such a small capacity, the oil doesn't have a very long life before it starts to break down. A good synthetic oil will last a bit longer because it generally resists thermal breakdown a bit better.

Originally Posted by Wild Dog

If you blew two pistons in 8000 miles there is something wrong with the engine.
You can't really over rev these engines, because the stock CDI has a cut-off and it is set quite low for a CG, so you are always on the safe side. At worst you are going to waste fuel.
North of my country is as hot if not more than Texas and the CG live a long life, in fact on these chinese motorcycle, they first lose the plastic, then the exhaust start to rust, then they lose the speedo, then the owners gets bored and get a new motorcycle and sells the old one still running.

What kind of oil are you using???

There are too many variables at play to try and speculate what went wrong. On air cooled engines the most common cause for piston destruction is an overheated piston/cylinder. If it soft seizes enough at high RPM the force can be enough to break the wrist pin gussets and result in similar damage. That is the reason many others, myself included, tend to run the main jet fueling on the fat side. I will literally go up in main size until I start to get bogging issues and then back off one or half a size.

[timcosby]

didnt see what jet you were using but running lean for that long could of done it.

[Wild Dog]

Originally Posted by Megadan

There are too many variables at play to try and speculate what went wrong. On air cooled engines the most common cause for piston destruction is an overheated piston/cylinder. If it soft seizes enough at high RPM the force can be enough to break the wrist pin gussets and result in similar damage. That is the reason many others, myself included, tend to run the main jet fueling on the fat side. I will literally go up in main size until I start to get bogging issues and then back off one or half a size.

If that bike was mine, the first thing i would do is try and speculate why i broke two cylinders and pistons in less than 8000 miles.
Thousands and thousands of those engine run with the original carb without any mod without issues and they run more miles than 8000.

I think that before he assemble the engine, he should find a service manual and check that every part is in good working order. Hell it could the oil pump that is not doing a good job and it's starving the engine of oil that plus the high temps is a good receipt for a busted engine.

[Lit Hawk]

I was using synthetic rotella. Before the engine blew I did install the amazon exhaust everyone recommends I had that on for a couple of weeks and was playing around with carb and jets but it seems like I had it good. I also adjusted the valves about a week before. This second engine was about 8 months brand new not rebuilt. I’ve never had to crack the case on this one till now the first I did have transmission gear problems that I did have to open case and fix. Anyways I got all the bearings and seals out of the engine

Except one small I’m having trouble getting out. Any help on how to pull out. I’ve heated it up like crazy and still not coming out.

[2LZ]

Sure seems like you have a mean lean condition. Have you checked the rubber part of the intake manifold to see if it's cracked? It's happened on two of my CG's.

[tomrom]

Originally Posted by Sochin

They should send you a whole new engine.

If your engine is under warranty your vendor should be able to stick up for you.

When this happened to me last summer Don from apscusa.com insisted his supplier, Goldenvale inc issue a new engine. I was involved in the process and spoke direct to the decision maker at Goldenvale Inc. with some testimony. It was thought there was a vacuum leak.

I don't think it was an easy process for him but Don stood up for me and got me the engine. It took about 3 months which is a crazy long time.The bike has tons more power now also.

[Megadan]

Originally Posted by Lit Hawk

Except one small I’m having trouble getting out. Any help on how to pull out. I’ve heated it up like crazy and still not coming out.

That little needle bearing will be tricky. A personal favorite of mine is to use hydraulic pressure to push the bearing out. Find a rod that is just small enough to fit past that bearing, then fill the hole behind the bearing with grease or even bar soap shavings, put rod in the hole, and tap on the rod to create force to push the bearing out.

One word of caution though, if the engine case is thin on the back side of that hole there is the risk of it possibly busting out the case behind it, so be careful if you decide to try this method.

The proper way to remove that bearing, and the one I would recommend, will be to use a blind hole bearing puller with a slide hammer. If you don't have one Northern Tool or Harbor Freight both sell decent kits. Just watch your thumb with that slide hammer or you will get the imfamous blood blister lol. This is a good tool to have on hand for multiple jobs, so it is worth picking one up.

Or, when in doubt, take that case half to a local garage or machine shop and just have them pull it for you. Probably won't cost much and will take a few minutes for them to do.

[Megadan]

Originally Posted by tomrom

When this happened to me last summer

Holy moly! That is some serious meltdown!