questions about rebuilding new 250r engine

[Jimmyt420]

hey guys i got a few questions im wanting to rebuild my engine and make it bad ass how much do you guys think it would cost to rebuild my 84 250r engine and bore it over and make it really nice looking and just completely fill it with new stuff becides the gears and what not i wanna have a beautiful engine in it if you guys know of any links that would help me out it would be appreciate thanks for the help

[DirtDevil]

The best thing to do is find yourself a couple of old, small engine blocks for free. You can usually find some at the landfill. practice boring the cylinders yourself. It's not as hard as you would think, mostly stone controll and hatch pattern stuff. You can find lots of videos on Youtube to show you the basics. All you need is a drill, good quality stones, lube, and a good quality cylinder bore guage. After that, it's just a lot of spittin polishin, rubbin, and paintin. And, it's a lot of fun and much cheaper than having a machine shop bore you out.

[beets442]

84' is the last year of the air cooled and to me, rarest year to find parts. Depending on what your going to do and who's going to do it, factors in the price.my guess is $500-1000, but haven't done it in over 10 years so prices have changed. If you don't need to bore it, I wouldn't. Boring it doesn't make it that much faster and saves jug for future bores. I'd work on the crank and seals first so the bottonend handle a newer top end, then brakes and suspension and LEAVE the motor close to stock, Its fast as Hal anyways and easier to tune. I've used partsunlimited.com,and evilbay to find parts. You have a nice machine, if you want to unload it some day, contact me I'll make a fair offer. I sold mine and miss it alot....Good luck and have fun...Beets

[Dirtcrasher]

"BORING a cylinder is not hard??" HUH?? The dimensions are critical and must be spot on for the full length. Honing a cylinder is not hard but I wouldn't wanna watch the wrong video, I'd watch a MMI video before I tried honing and the ball hones work best on 2 strokes.

If you have an air cooled R, boring is CRITICAL. .003-.004 ain't gonna cut it with a Wiseco piston, it will most likely seize. More like .005-.006 and 2 holes drilled in the exhaust bridge to help lubricate and cool it..........

How many guys blow up an 81 or 82R, quite a few with fresh rebuilds and thats the builders fault. A machinist just does what he's told........... and some of them suk!

[dksix]

I wouldn't advise boring a cylinder yourself. I'm sure there are guys who can do it themselves but, no offence intended, they wouldn't have to ask the questions you have. Honing is much less of a process and honing is necessary to get the rings to seat (maybe not in a Nikasil liner but definitely a must in steel liners). If you try to bore a cylinder by hand it's not likely it would be a cylinder but rather a cone, oval or hour glass shape. I just had a 4 stroke top end done which included a valve job and valve seals, the machine shop bill was only $50. I know guys here like to do it themselves but some jobs are better left to the pros with the proper experience and equipment. If you take it to an engine shop, with the pistons and rings you'll be using) you have the piece of mind that comes with knowing something is done right. If you aren't a well skilled engine builder, with the right equipment and are going to be the one who has to tow that thing back to the truck: spend the money. Doing a top end on an aired cooled 2 stroke is about as basic as it gets but splitting the cases is something everyone should have help with the first time. I know many have done it and I also know many more have gotten it wrong than right the first time out. If you do attempt to go into the bottom end, have the manual and a clean place to work and a bench where the parts can be contained when they fall out (and there is things that will fall out in there) don't forget that there's a tranny in there too.

[DirtDevil]

OK, I guess I skimmed the post too fast. I meant HONE. I have never taken enough meat out of a cylinder to need oversized pistons. Way out of my experience level. I just use the ball-type flex-hones to knock off the glaze and to hatch the cylinder to seat stock rings. I've had good luck so far, but I have never messed with a machine that required .005 either. My dad use to lathe cylinders with torque plates and all that fancy stuff, but it always intimidated me. Maybe one day. I've only done one 2-stroke, and that had to be completed by my mechanic friend who said he needed to "treat the ports". I have no clue what he was talking about, but the bike ran great after we were done.

Guess I'll keep my advice to myself until I learn how to give it.