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1992 kdx 250 Rebuild Project

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I was out riding yesterday and blew the bottom end (connecting rod bearings semi seized to crank) Having a hard time finding a bottom end kit (crank and rod) still have to pull motor from bike and split case to make sure no other damage occurred, top end is all good head and cylinder has no damage hone it and a new piston kit and good. This is the first dirtbike Rebuild for me have rebuilt boat motors, snowmobiles, atv's chainsaws but never a bike. Any pointers I'm all ears  

 

Also looking into some performance modifications to go with the build. So far I have opening the air box for better airflow, a thinner head gasket, aftermarket reeds and complete exhaust I have found a fmf fatty pipe with a turbine core silence also boysen reeds can't locate any v-force reeds for this model. 

 

 

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I also have a 92....rebuilt it less than a yr ago...you'll have to get all the parts seperate rod, bearings yada yada....i ebay'd everything.....as far as mods....its a great engine....needs jetting cleaned, new exhaust....other than that...with what u have listed. I found a 96 kx250 complete roller and put the engine in that....its really fun bike now....lighter, handles way better, decent suspension. 

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thanks for the reply @argclh6670 I have jetted the carb to the best tuning I can without changing the stock slide and needle. Have been keeping an eye out for a kx frame to swap for the the for weight and handling. Hard to come by in Central Oregon. 

Got this bike for a couple hundred bucks so have been wanting to throw some good $ into it to make it great. A blown lower end will help with the cleaning process  😁 

 

Got the engine out and as disassembled as I can get it at my house. I can't find my flywheel puller so will have to wait until tomorrow when I'm at the shop to finish splitting the case. The crank is not looking good so far (from what I can see with it still in and rod attached) the needle bearings are completely flattened and looks like they weleded themselves to the bearing case. Probably going to have to get a new crank or possibly have this one repaired. 

 

My my next question is will a kx250 crank work? I am having a hard time finding a 1991-1994 kdx250 crank (I have the 92) 

 

Another question: do any other motors fit my 1992 kdx 250 frame like a standard kx250? is the kx250 liquid cooled also? 

 

Thanks for theread and replies all are greatly appreciated. 

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After looking online the p/n for the crankshaft assembly is p/n 13031-1302 and it fits 91-94 KDX 250 also 90 KX 250 if anybody is looking.  Hard to find new have found a handful on eBay used. 

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Are the crankshaft halves damaged? If not, then several places can sepaprate them, install a new connecting rod kit and bearings / washers / pin.

 

If they are damaged, you will have to buy a used crank and either chance it or have it rebuilt.

 

You mentioned honing. The cylinder was plated in stock form. Honing is a big no no on plated cylinders. Inspect and determine if some later owner sleeved it or if it is still plated. If it is still plated and the plating is worn out, it can be replated by Millenium, Power Seal and others. Plating is going to be your best option.

 

Good luck on the rebuild.

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@KDXGarage the crank appears damaged, very miscolored and I can see flattened needle bearings in the rod. Going assume crank will need to be reworked before it is good again. I found a used crank for $100 and the owner claims they tested it for out of round and end play and it is good. Still going to test it before using it, going to keep the crank and have it sent out repaired and save it for a very very rainy day.  

Also the top end and cylinder walls were all undamaged. It is still the stock plated cylinder no one has messed with it so going to get a new top end kit and  be done with the top end. 

Thank you for your input  learned something new today.

@SS109 thank you for the information, I actually placed a parts order this morning for the top end kit a fmf fatty pipe and boysen reeds due to not finding the vforce reeds and needing to place the order to get the parts here before birthday ride(Sunday)   If possible.    Thank you for your knowledge will be keeping it in mind, have never ran boysen reeds and will replace them if unhappy, might even get the vforce reeds now and see what I'm happier with they are only $30-$45 

 

Also cannot find a silencer besides a stock one that they want $300 for. My stock one is bent up the internal packing area is caved in. It's pretty much toasted, wondering what I can get that might be close enough to modify the mounts for to make it work. Have looked at the "universal 2 stroke silencer" but universal means it fits nothing right. 

 

Have the bike down to the frame and air box and thinking about tearing the rest down and painting the frame, willing to have someone do it at a shop but everyone is weeks out and I'm an impatient type of guy. I will tear it down again this winter to paint it properly if needed. My question is will a rattle can paint job work out well?  Has anyone  tried it out with happy results. 

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Rattle can won't last real long unless it is HIGH dollar rattle can like colorrite.com 

Great for touch up, though.

 

Good luck on the build.

 

SS109, thanks for the info!

 

This Kawasaki 12021-1070 VALVE-ASSY-REED is used on these models and components:

 

1988 KX500-D1 KX500 CYLINDER HEAD-CYLINDER

1989 KX500-E1 KX500 CYLINDER HEAD-CYLINDER

1990 KX500-E2 KX500 CYLINDER HEAD-CYLINDER

1991 KDX250-D1 KDX250 CYLINDER HEAD-CYLINDER

1991 KX500-E3 KX500 CYLINDER HEAD-CYLINDER

1992 KDX250-D2 KDX250 CYLINDER HEAD-CYLINDER

1992 KX500-E4 KX500 CYLINDER HEAD-CYLINDER

1993 KDX250-D3 KDX250 CYLINDER HEAD-CYLINDER

1993 KX500-E5 KX500 CYLINDER HEAD-CYLINDER

1994 KDX250-D4 KDX250 CYLINDER HEAD-CYLINDER

1994 KX500-E6 KX500 CYLINDER HEAD-CYLINDER

1995 KX500-E7 KX500 CYLINDER HEAD-CYLINDER

1996 KX500-E8 KX500 CYLINDER HEAD-CYLINDER

1997 KX500-E9 KX500 CYLINDER HEAD-CYLINDER

1998 KX500-E10 KX500 CYLINDER HEAD-CYLINDER

1999 KX500-E11 KX500 CYLINDER HEAD-CYLINDER

2000 KX500-E12 KX500 CYLINDER HEAD-CYLINDER

2001 KX500-E13 KX500 CYLINDER HEAD-CYLINDER

2002 KX500-E14 KX500 CYLINDER HEAD-CYLINDER

2003 KX500-E15 KX500 CYLINDER HEAD-CYLINDER

2004 KX500-E16 KX500 CYLINDER HEAD-CYLINDER

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@KDXGarage Thank you for more of your knowledge I didn't have high hopes on the rattle can job. Will probably touch up the area where your feet and legs where the frame down just to keep it from bare frame. 

The build is on track, Got in the top end kit, fmf fatty pipe, also the reeds with some new carb boots. The crankshaft should be here thursday and the complete gasket set should be here friday, hopefully get the engine all back together friday evening.

 Thanks to all have put in their time to read and give their input. Will post some pictures online soon.

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If you do touch up the paint, you might want to put a cler sticker over that area. Look at some of the KDX200 later model diagrams. It will show the part on there. I am not saying to buy an OEM clear sticker, just copy what they did.

 

Good luck on it.

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Pro Circuit still lists a silencer (regular 304) in stock for the '94 model (which fits the 91-93 models too).  I did run one of these on my KDX250 from '92-'93, in conjunction with a stock '91 KX250 expansion chamber.

You can fit a stock 90-91 KX250 silencer on the KDX250 with a little work.  It has been a long long time since I have done it, but I do remember doing it in a pinch just to see if I could do it (and my younger brother wasn't home to see me take the silencer off his KX).

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1 hour ago, eastreich said:

Pro Circuit still lists a silencer (regular 304) in stock for the '94 model (which fits the 91-93 models too).  I did run one of these on my KDX250 from '92-'93, in conjunction with a stock '91 KX250 expansion chamber.

You can fit a stock 90-91 KX250 silencer on the KDX250 with a little work.  It has been a long long time since I have done it, but I do remember doing it in a pinch just to see if I could do it (and my younger brother wasn't home to see me take the silencer off his KX).

In that case then DG exhaust makes a silencer for the KX still but no expansion chamber. Dyno port may if you call them.

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i have got my new crank seals and bearing all installed, now i am having the hardest of time getting the crankshaft and bearings into the cases. i tried to freeze the crankshaft for 4 hours and that gave me no improvement. i don't feel comfortable heating the cases because the seals will get damaged. any tips are greatly appreciated, is a tool required? i was looking online and thats all i could see was how tos using a special tool. i know that there is a way to do it without the tool. thank you for any help.

i will get back to everyone soon in the middle of working on this trying to get running for sunday and its fighting me hard. 

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Heat the cases at 250 degrees in the oven for at least 15 minutes. It will not hurt the seals. Freeze bearings and crank. Drop frozen bearings in to heated case halves and let cool. Install transmission in to right case half and the heat it up both halves in the oven again. Remove trans half and slide in crank and quickly cover all case sealing surfaces with Yamabond case sealer. Don't burn yourself! Remove other half from oven and immediately install. Everything should slide together with ease. If you don't get it together quick enough you can use a crank puller to pull the crank in the rest of the way.

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