67mm risky bore??

[HaggLE]

You can get a sleeve from any other bike/trike (4 stroke that is) as long as the outer measurement of the skirt is about 73-74mm and the inner size (bore size) is smaller than 70mm. 4 cylinder bikes are the best to search for.
All you need to do now is machine out the old sleeve out and press in the new sleeve (done at a machine shop) and bore and hone to suit 70mm.

For the head gasket run a standard Honda TLR250 head gasket. It will fit straight in and is designed for a 70mm piston.

The piston to use is a TLR250 piston because as i previously said the bore size is 70mm. The only problem with the TLR250 piston is that it will sit lower down in the bore. To fix this you will have to have the bottom of the cylinder machined off to suit. Measure this with verniers after you have had the sleeve put in and sit it together without rings and with the head off and using a new base gasket. Make it sit down the bore about .030" to ensure that the compression isnt too high. You will need to run a new cam chain to compensate for the shorter cylinder.

The next step is you will have to machine out the hole that the skirt goes into in the cases. The bigger sleeve skirt wont fit in. A machine shop can do this also. Trim the base gasket to suit the bigger sleeve.

An alternative to changing the sleeve is to buy a complete TLR250 cylinder new from Honda and adjusting the length to suit. The bore will already be done and you will be machining the cylinder length either way.

Let me know if you have any further questions and ill try and get a picture for you.

[hondagrant]

Thats interesting i've heard people talking about taking them out to 70mm but i didnt know how it was done.Im runing a 67mm piston in my 200x but when it comes time for a rebuild I might consider that conversion...

[short4stuff]

hey .. what year is that tlr250 ? .. whats years were they made...
also is 70mm the max bore for that piston .. or can you get oversized? .. will the bottom end accept a larger piston than that..
you know incase it blows or .. yeah you need to bore ..

[Bigmikeyall]

I put a 66mm 12:1 skirted piston in the original stroker motor that came with my trike (it was an old race bike). I ported and polished the head and installed heavy duty valves and springs. I broke the bike in for about a month because I stuck so much money in it. Then one day later I was really on it going down my road the whole engine blew. When I say blew the crank case split in three areas and the jug cracked all the way up to the head. I stripped the engine down and couldn't even find something that resembled a piston. My advise to you is keep it simple. Don't go over anymore than you need to clean the cylinder. Be very worried........I like to think I built my motor the right way and it still took a crap.

[short4stuff]

HaggLE - do you know how much lower the tlr piston sits down compared to the stock piston?

Bigmikeyall = break it in the way your gonna drive it

[leevarnado]

really old thread ,but has anyone done this.

[factoryX]

wait, so boring out a 250r to a 310 is a waste? am I missing something? or is this a 4 stroke only type deal?

[oscarmayer]

ok jsut for the record, you don't have to run race fuel with 12:1. if you proeprly tune it then 93 pump will run just fine. tuning is the key just like any other thing. I've seen well tuned stocker bikes out run tweaked bikes cause the knuckle head could not tune to save his life. learn to tune or find someone who can tune it. it'll not only make you more power, but also help it last way longer!

[leevarnado]

would like to if anyone has put the trl 250 head on a honda atc 200 engine .