do I need to overbore?

[destey]

I was removing the main drive gear, had the washer jammed in the counterbalancer gear but it fell out just as I hit the impact turning the crank and forcing the piston skirt against where the cylinder mounts. There's a little gouge, should I get a new piston and overbore, or can I just take some sandpaper and file off the burr?

Second question, the connecting rod looks a little rusty, like the motor's been sitting for a while (I just bought it). should I take the crank to someone and have new connecting rod bearings put in?

[Honda 250r 001]

we have to see pics of the bore, but i would bore it just to be safe.

And the connecting rod doesnt matter unless there is rust in the bearing.

[destey]

i'll try and get pics this evening.

I was thinking the rust on the rod means the bearings probably are bad or soon to be bad as well. Everything inside the stator cover was extremely rusty, like water had been pooled up inside.

Out of curiousity, how does a shop disassemble a crankshaft?

[KP250R]

at a minimum it sounds like you need a new piston of the same bore....if you fix the dink in the piston, it will be a weak area of the skirt and the probability that it will crack, break off and fall down inside your cases increases.

If I understood correctly you had the jug off, piston and rod unprotected while about to impact the main drive nut...correct?

Why would you need to bore the jug?

Does your bottom end turn over freely with no abnormal noises while turning?

A little rusty discoloration on the rod is normal for a bottom end that has been sitting...you sure don't want any rust on the crank bearings though.

Pics would be helpful....but not necessary if you can accurately describe everything.

Post them pics up, or tell us more.


Here are some video's that show how to go through a 2 stroke:
(its not specific to a Honda 250R, but the 2 stroke engine is similar across manufacturers)

1 of 3 - http://www.youtube.com/watch?v=kYX-bOG9vR4
2 of 3 - http://www.youtube.com/watch?v=vVKeT8Mh2dQ&feature=related
3 of 3 - http://www.youtube.com/watch?v=ti_UkR3XjyE&feature=related

[wilkin250r]

Rust in the stator area isn't uncommon. It's not desireable, certainly, but it's usually not a big problem unless things stop working. I'd hit the area with WD-40 to stop it from rusting worse, put a new gasket on (maybe a little silicone where the stator wires exit the cover to stop any possible leaks there) and wouldn't worry too much more about it.

Use the connecting rod to cycle the crank several times, you would probably be able to feel any grit or rust in the connecting rod bearing.

Crank work is very precise, (regular automotive machine shops can't do it). As a result, it's rather expensive, probably a couple hundred. I'm thinking it wouldn't be that much more to just get a brand new crank.

[destey]

http://img232.imageshack.us/img232/1091/1000855.jpg

http://img217.imageshack.us/img217/2691/1000856z.jpg

not sure how well the color comes through in the picture

I was thinking the overbore would be in order as i was taught the honing is done to make the piston and cylinder walls to form to each other and its not good to throw a new piston in a cylinder without overboring at least .010

I can take more pictures if anyone wants to see something up close

[KP250R]

That little dink on the lower left reed side of the piston? I see it.....

I do not know about that...I bet it could be fixed though.....Banshee guys run skirtless pistons.

If there is cross-hatch in the bore, I'd just oil up a piston and new rings and go for it....boring is for going beyond the damage in a sleeve....honing is for cleaning up the "bore" machining so rings can seat into it....like I said if there is still cross-hatch "hone" marks its still useable....usually.

I was on the understanding your cases were still together and you witnessed rust on the rod....your crank looks ok from what I can see...how does the rod move on there?, clean rotation?....spec is 1mm side-side....0.00 up and down on the Crank Pin....and your gonna use NEW MAIN BEARINGS right?

there's my worthless .02

[Honda 250r 001]

you know, i think you could make it work, but unless thats a new piston or somehthing, dont chance it.

[destey]

So its pretty standard to throw a new piston in a honed but not overbored cylinder? So something like this is my option layout (wild guesses for $ cost)

hone ($30?) + new piston ($130)

hone ($30) + same piston

overbore+hone ($60) + new piston ($130)

Is it agreeable that there's not much performance gain from going +.020 or .030?

So really I have to decide if I want to chance it with removing that ding and go with the old one or throw in a new. I'll give a little background. The guy who I bought it from said the piston was brand new. He said it wasn't overbored (i always thought it needed to be as earlier discussed). But I was going to just run it and see what happened. So I did the engine breakin as describe on the sticky, and at the point where I was putting around slowly on the trails varying speed, winter was getting close and I had another quad so I put this one away.

Trying to fix the hard starting over the winter, I pulled off the stator cover and tried switching to the cr250 ignition, but I couldn't get the flywheel off. Being not so bright, with the puller on I tapped the flywheel trying to break it free(more like something harder than a tap, but not quite a hit). After I did that I noticed slop that wasn't there before and went "oh ****" Since I had another bike I decided it was time to rip it down and replace the main bearings. And now here we are.

But a bigger question is, do I replace the crank because of the rust? There's also quite a bit of side to side freeplay, not sure what the tolerance is supposed to be but it feels excessive. I'll check my clymers as to what the limits are. Thoughts?

[Honda 250r 001]

ooooh man i re-read the thread, and i thought you had the cylinder bolted on and it ruined the bore. NO you do not need to bore, but i would file that off the piston and throw it in and go.

[All250R]

If the rod is rusting, you will want to consider replacing it. Cracks in the rod from normal stress will likely start from the outside surface. Rust will compromise the integrity of the rod. Make sure it's corrosion and not just the natural color of the rod. if it's rust, you probably have a lower lifeaspan, high stress part.

[wilkin250r]

I don't like it. Look at the second picture, the closeup. You can see the machine marks on the piston, but those machine marks disappear at the edge of the piston skirt, right at the ding.

There's a REASON the machine marks on gone in that area. That's where the piston is riding, that's the area that's in contact with the sleeve.

You can give it a shot, you might be okay, but I don't like it. If that's the area th piston is riding on, I wouldn't be too keen on messing with it.

[destey]

Originally posted by wilkin250r
I don't like it. Look at the second picture, the closeup. You can see the machine marks on the piston, but those machine marks disappear at the edge of the piston skirt, right at the ding.

There's a REASON the machine marks on gone in that area. That's where the piston is riding, that's the area that's in contact with the sleeve.

You can give it a shot, you might be okay, but I don't like it. If that's the area th piston is riding on, I wouldn't be too keen on messing with it.

I see what you mean by the machining marks worn off near the bottom.

I think you've convinced me to get a new piston. you probably saved me a rebuild down the road :cool:

any reason to overbore? i'll call up on some prices, maybe the question is, any reason not to overbore..

what're your thoughts on the crank? the rod kit is about 62

[Honda 250r 001]

if there is no rust in the bearing, and your not going big bore. I think it would be fine as long as thats not really rust. I think all the rods are just sort of that color from ageing. Buff it down with a buffer wheel and go.

[wilkin250r]

Originally posted by destey
any reason to overbore? i'll call up on some prices, maybe the question is, any reason not to overbore..

What bore is it on now? What do you know about the history on it, any idea on the number of hours?

[destey]

Originally posted by wilkin250r
What bore is it on now? What do you know about the history on it, any idea on the number of hours?

no clue about the cylinder. He did say the bottom end had never been touched. From my understanding it used to be raced

[destey]

Originally posted by Honda 250r 001
if there is no rust in the bearing, and your not going big bore. I think it would be fine as long as thats not really rust. I think all the rods are just sort of that color from ageing. Buff it down with a buffer wheel and go.


Should there be a lot of freeplay side to side on the connecting rod? Mine goes back and forth like a 1/2"

[86 Quad R]

how are you measuring the slack? it should be measured at the crank and shouldnt be no more than the service limit, which is .040".

[Aceman]

Originally posted by destey
Should there be a lot of freeplay side to side on the connecting rod? Mine goes back and forth like a 1/2"


Originally posted by 86 Quad R
how are you measuring the slack? it should be measured at the crank and shouldnt be no more than the service limit, which is .040".

A half inch of freeplay sounds like a whole lot more than .040 of clearance. I'd get it checked by someone who can measure it properly. It's definitely not good practice taking chances with cranks.

[destey]

Originally posted by Aceman
A half inch of freeplay sounds like a whole lot more than .040 of clearance. I'd get it checked by someone who can measure it properly. It's definitely not good practice taking chances with cranks.

I've got height gauges, measuring plates etc here at work but I can see its a lot more than .040.

Local shop says they can rebuild it for $85 and I'll have to supply the parts. Sounds like a new one is the way to go here. Its an 1986, so I'll need the 86 crank I assume.

They quoted me a price of $53 to overbore/hone, so it sounds like i'll be doing that.

time to do a little investigating about the 86 vs 87-89 crank/rod/piston setups

[regg187]

1/2" wow! thats a lotta play. those shop prices seem pretty cheap 85 to split the cases and and do rod bearings seems like a deal and 53 to bore and hone seems like a great price too. but with the economy taken into consideration, maybe there just needin work.