1982 YZ250 project

[JustInMass]

the bug has bitten eh?
I strongly remember the giddiness I had on my first trail ride.
It was on an 85 SP250 that Deeto gave me and boy oh boy what a different life mx is compared to roadracing.
Glad you guys had a good time. Hopefully you can get your jets, motor and clutch sorted out without a problem.

[BMFR6]

yeah, i think i'm going to pull the top end tonight. rings will be done first, as there probably isn't much use dialing in the jetting for an engine that is lacking compression to begin with. from there i'll probably head back out to oxford for a couple hours. i need to make a couple oil changes as whatever did get into this case is still a factor. think i'm just going to pick up a 5 quart of cheap stuff and change the oil until its draining clean. then we'll tackle the jetting and getting the carb dialed in. 20 days! i feel like i'm getting ready for a race season, never enough time!

[McBiggity]

Southwick is going to hurt

[JustInMass]

if you need a compression tester and are in the area (Bolton), let me know

[Daytona440]

if you need a compression tester and are in the area (Bolton), let me know

I forgot you were that close to me.

Mark if you need stuff from Justin I can grab it...

[Paul_E_D]

Southwick is going to hurt

At least the ground will be soft

[breakdirt916]

the yz ran "ok", not where i would like it to be, but it could have been much worse. ...i guess the best way i could describe it, "lazy and a little weak", perhaps a 250 with a hangover would be a good explanation

break-in time + tuning will come with time

how lazy of a bike are we talking? does lazy = XR80R + 6'0 140lb rider slow? if so, then maybe I'll join you guys sometime

but glad to see that it "works"! the worst part about such a project is if it didn't at all...

[BMFR6]

if you need a compression tester and are in the area (Bolton), let me know

i may take you up on that in the future. is it just a simple gauge that screws into the spark plug hole? probably do it when we get out to ride if so. i just pulled the top end tonight, compression may not be an issue. post on that to follow.

break-in time + tuning will come with time
how lazy of a bike are we talking? does lazy = XR80R + 6'0 140lb rider slow? if so, then maybe I'll join you guys sometime

i wouldn't say its that lazy, maybe like a clapped out 125 four stroke. but if you are talking lazy as in how we ride, come on out. if there is a pee-wee beer league for dirtbikes, thats me and mike. an xr would keep up fine and we can always use more company.

[BMFR6]

so i pulled the top end tonight. the cylinder is in good shape, the piston is good as well. i think the top may have been done recently, this isn't an oem piston and if it is, Yamaha was way ahead of their time in 83. the head is a little pitted. if the bike was a 2009 i would be concerned, but for this vintage i think its as good as i'll get. i am still going to do new rings and gaskets just to be safe. i have two concerns with the cylinder however.

1. You have the cylinder and then the actual cylinder sleeve. well its typical for the sleeve to hang below the cylinder at two points and actually fits into the crankcase. now typically, the actual cylinder hangs down at these points as well to protect the sleeve. on one side, the actual cylinder portion that hangs down for protection is broken off so the sleeve itself is all that is there. i don't think this is a huge issue for what i am doing with the bike. anyone disagree?

2. the yamaha "power valve" is fubar. the power valve is on the exhaust side of the cylinder. picture a wooden dowel with a half moon cut out of it lengthwise. now my assumption, at low rpm's, the valve is rotated reducing the size of the exhaust outlet. as rpm's increase, the valve rotates, exposing the half moon, thus increasing the size of the exhaust outlet. like i say, mine is fubar and i am not sure how much it impacts performance. from my understanding, 2 strokes rely on back pressure, creating too much or too little would be an issue then right? follow these pics and their explanations.

now as you go through the pics, keep in mind the valve is composed of two pieces that fit together. each piece is slipped in from the corresponding side of the engine, held from twisting on each other by two pins and a bolt in the center.

this is how the valve should look. this is from the 82 engine this valve is assembled, bolted tight so you can see what it should look like. swapping is not an option as the 82 is longer than the 83. already tried.
Attachment 15267

this is how the 83 valve looks. (the 83 engine is the one in the bike). as you can see, this does not bolt together at all. the holes on the end which receive the two pins and bolt are stretched into ovals. i can twist them about a quarter inch worth of play...... when they are actually installed.
Attachment 15268

these are just end shots of the valve. you can see the two pin holes as well as the bolt hole in the center.
Attachment 15269
Attachment 15270

replacing the valve with a new one isn't an option, that would put me over budget and i'll never get my money back on this bike. i am literally thinking of jb welding them together once they are installed. it would function correctly, but they'll never come out again.
thoughts?

[Doyle670]

yeah, you could actually drop the 490 engine into the frame if you really wanted to, it's all fairly inter-changeable.

can you do me a favor and take a look at the right side of your headstock and tell me how many digits are in your VIN?

Are you going to try and register yours?

Sorry I haven't gotten a chance to check yet. Haven't been on here in a few days. I'll check tonight.

I was thinking about registering mine just so that I have proof that I own it. That way if ever down the road I want to sell it, i'll have a registration.

[gregp]

The power valves duty is not so much to change the size of the exhaust port as it is to alter the height, or position of the top of the port. The piece that you have pictured rotates to allow the upper edge of the port to allow exhaust gasses to begin to exit the combustion chamber sooner. At lower RPM's, the valve is "closed" and it effectively lowers the top of the exhaust port, holding the combustion in the chamber longer, for a stronger low end pull.
Can you press in a couple of custom made, slightly over sized pins? JB weld will probably not sustain the heat that piece will be subject to.
JMO.

[breakdirt916]

...but if you are talking lazy as in how we ride, come on out. if there is a pee-wee beer league for dirtbikes, thats me and mike. an xr would keep up fine and we can always use more company.

I'm ordering brake pads tonight and will pick up a functional rear brake lever tomorrow

do I need to get registered to ride at hodges?

and can you run a used valve? I'll check with sky used cycle salvage tomorrow when I'm getting parts for the XR

[Paul_E_D]

THat's you lazy bike problem right there. When the powervalves aren't rotating you get an extremely weak bike.

Can you swap the valves from the other motor?

[SSearchVT]

I'm not sure if it applies to this bike or not... Aftermarket expansion chambers on a lot of the bikes in the 80's removed the exhaust power valves completely from the bike - 84 CR125 for example.

Another option is to have someone drop an endmil into the existing ovaled holes to increase the size to accept a larger pin.

[breakdirt916]

no luck at sky used in fitchburg...he said used valves that don't have ovals are tough to come by, so he said to try your luck on ebay with a used cylinder that's still in good shape

the other thing he recommended was taking it to a machine shop with mechanics that have ridden dirt bikes who have fixes like the one SSearchVT recommended with enlarging the oval holes

[BMFR6]

thanks for checking, that's pretty awesome of you!

[JustInMass]

I have nothing constructive to add to this conversation, but is that a new husky or something?? He looks like he's gonna grow into a BIG boy
Sorry the ordeal continues...

[BMFR6]

I have nothing constructive to add to this conversation, but is that a new husky or something?? He looks like he's gonna grow into a BIG boy
Sorry the ordeal continues...

haha. yeah that's Kaiya, our husky. she's still just a pup, only about two weeks old now. we'll be picking her up from the breeder at the end of july. they should only get to 60 lbs or so, but her brother lives down the street from us and was 60 lbs at 6 months, lol.


so in any event, what are you up to Sunday morning? if all goes according to plan, me and timmy will probably be at hodges for a couple hours. timmy is getting his feet wet on mike's bike and i'm still shaking things out so it wouldn't be anything wicked, but we'll be there.

[breakdirt916]

I got some brake shoes for the XR80 and will try to bend the brake lever to make it useful tonight

I might come, pending how much school work I actually get done...pm sent

[JustInMass]

haha. yeah that's Kaiya, our husky. she's still just a pup, only about two weeks old now. we'll be picking her up from the breeder at the end of july. they should only get to 60 lbs or so, but her brother lives down the street from us and was 60 lbs at 6 months, lol.


so in any event, what are you up to Sunday morning? if all goes according to plan, me and timmy will probably be at hodges for a couple hours. timmy is getting his feet wet on mike's bike and i'm still shaking things out so it wouldn't be anything wicked, but we'll be there.

He's gonna be gorgeous.
Sorry can't make Sunday - I'm hitting Crow Hill for my 2nd ride of the season. I'm so out of shape right now and have to ride hard for the next 2 weeks. As hard as I can with my little guy and wife waiting for me every minute.

[breakdirt916]

mark: I left you a message to say that I'm in!

unless I hear otherwise, I'll be at the updated address by 9am

look for the minivan, red XR80R, and indian guy wearing all his street gear and a dirt bike helmet

[BMFR6]

see you then. look for a tan silverado (me) or a silver trailblazer (tim). worst case scenario, look for the oldest bikes out there.

[Paul_E_D]

There was some vintage iron out at Crow Hill yesterday...

[BMFR6]

There was some vintage iron out at Crow Hill yesterday...

if things go well today, i'm going to plan a trip out there soon.

[typeone]

There was some vintage iron out at Crow Hill yesterday...

wish i had scoped that bike up close, i think Chris did and said it was a CR500 (?). thing looked mint!