250r bottomend rebuild and upgrade

[80'427]

Well I guess this is just how it goes. I was doing some last min repairs on the 85 250r before going to the sand on tuesday and thought I would do a little more digging. Pulled the reed cage and everything looked good, stock but good. So I was looking at the piston and it had a big scuff on the side. No big deal I ordered a .25 piston 2 years ago just get it bored we will still be set for tuesday. Pull the jug yep time to rebuild the top end. So I was looking the rod and crank and what is this? A crack in the crank? Oh heck! Now I think I will rebuild the bottomend when I get back. The plan is a hot rods crank/rod and some port work and the new piston. Better reeds/cage and a 38mm carb(cr 250r right?). So now for the question part of the post. I see there is a stroker crank but it is listed for newer trx 250rs, I am guessing this is something to do with the short rod long rod thing. Can I use this crank if I get the right piston? What special machining is required? Worth the work and money? I was looking at the duncan porting but can't decided between the NATIONAL Cross Country (low end) and the NATIONAL Midrange (midrange). Has anyone used eather of these? I do a lot of hill climbing and woods and trail riding but do ride in the sand 1-2 times a year. I think the low end would fit the best but don't want to be still behind the 700 raptors out of the hole after the build up. Reed suggestions? Still going to use my fmf pipe and silencer for now. I can't imagine how it run even with a rebuild cause I thought it ran good wore out!

Thanks Guys

[Billy Golightly]

The old cylinder that came off of my flat tracker had the Duncan midrange national porting, and it ran like a freakin raped ape. It had barely any port work on the inside of it (and what was done, looked very questionable to me) but the thing ran like a bat out of aboslute hell. It had good lowend and the midrange and upper RPM power was almost comparable to my stock cylindered cr500 motor (I kid you not). I would still be running that cylinder but its on last bore :( I think you would definitely be happy with their porting.

As for the crank, you can run the 4mil stroker with the longer rod in your engine, but you'll have to get the newer windowed (87+) style piston to fit it because the wristpin location is different from the older ones to compensate for the longer rod. If you run the newer style piston though you'll also need a newer style 87+ cylinder that has the bridges in the intake, otherwise there is a small chance the skirt on the newer style pistons could catch on the open intake of the earlier year cylinders on the down stroke, and that would not be a pretty thing on a new build.

[deathman53]

instead of a hot-rod crank, use a oem 88/89 trx250r crank. Hot-rod cranks are hit or miss. I've had good luck with them, but others haven't.

[80'427]

So to save myself trouble I should just do a stock stroke bottomend and have the cylinder ported. Anyone else have hot rods trouble?

[Billy Golightly]

I'm running one of their long rod drop in cranks, but have very little time on it. There was a post here just a day or two ago about the hot rods connecting rod kits and how a few guys have only have them for a year or two and they are already sloppy and ready to replaced. The aftermarket hotrods are for the most part made in China and are of pretty inferior quality of the OEM Japanese parts. A whole new stock crank shaft is very spendy...but you can have your stock one rebuilt for probably $250 tops with an OEM parts and you'll be just about good as new.

[deathman53]

I have 3 friends that haven't had good luck with them. I have one of their motors, ~30 hours on the bottom end and the crank was out of spec. All have changed to oem cranks. I had that motor rebuilt for a oem 88/89 crank. I got 2 years out of a hot-rod long rod crank, I locked up the tranny on my motor, tore everything apart and when I took off the cylinder, the crank was out of spec. From what it appears, they don't like high compression top ends, on a normal compression top end, they last have better life. I had a nearly stock compression top end on my old trx motor, 3 top ends, I then put on a high compression top end(my other motor was being rebuilt then), the counterbalancer blew up(not the top ends fault), took the cases out with it. However the crank was still in spec. My friends didn't have such luck with them. That is why I posted that they are hit and miss. Sometimes good and sometimes bad, I would rather stay with at stock crank, they are ~$40(from service honda), but have better consistancy.

13300-HB9-770 CRANKSHAFT 392.89 259.35

the first price is the list and second is your cost.

[edog]

Good thread!!!!!!!!!!!!!

[Jason Hall]

I think you might want to check again on availability of the stock honda crank. I though my buddy In parts told me about a year ago they were Discontinued. There might be a few left someplace, but I would check. I have a hot rod crank In my 310, but have not ran It hardly at all since TF06. I know CT put stock honda cranks In all their motors, there must have been a reason why. I know honda cranks are tough.

[80'427]

I will check tomarrow at my local honda dealer. I am a bit afraid after what I spent on kick starter gears. I found a hot rod crank for 185 on evil bay and a stock take out 87 crank for 315. I don't think they can rebuild my crank one of the counter weights is cracked thought the rod pin hole. I will call duncan tomarrow and see what they recommend.

[80'427]

Well Hot Rods it is. The 85 crank has been discontinued and the locator turned up none. I may send mine off for a rebuild after swapping. I plan on still running on 91 pump gas for the reason that I have had problems getting race gas when going on those inprompto sunday rides. So this will keep the compression low and help prevent excessive pressure. I may run race gas in the sand to prevent detonation. I forgot to say the stock piston had a big divote in the top from detonation. I don't think I did it but who knows. Will be going with honda main bearings and what ever other parts I will need.

[ceaserthethird]

Any Up-date's ?

[deathman53]

that crank I posted the info for is a 88/89 crank. 85/86 cranks have been discontinued for about 2 years now. 88/89 cranks are availble.

[80'427]

I ordered a stock replacment hot rods crank found it for 169 on evilbay. Sending my jug and head off to duncan to get national midrange ported and bored for my new piston (+.25mm). Also getting a 36 pj carb to split the difference between low speed and midrange. Staying with my fmf pipe and silencer for now. Bought a new swing arm to lengthen 4". Spent the last week in the sand in waynoka and missed my r. The 400ex I rode was OK but still missed that 2 stroke buzz. Since I ride mostly trails and climb hills I am building it to work best there with a bit of concession to being better in the sand. Does anyone have a link to a good how to swing arm extending link or post. I saw a great one here about a year ago after coming back from the sand but can't find it now.

You guys ever seen these graphics?

http://www.verdepowersports.com/Graphics/ATC250R.html

[SYKO]

how much are those graphic kits?

edit: never mind duh why dont I look better!

[80'427]

My wife thinks I should pimp it out. I kinda like stock looking and fast but may be loosing the gold wheels. she bought me some new wheels and tires for the rear.

[edog]

I see those for sale on E Gay.