Vintage Project - Yamaha DS7 - 250

[extrememarine]

It's plenty rich right now, too much so...

More tinkering this afternoon. It is pumping a pretty steady stream of oil out the right side exhaust pipe; I'm pretty sure that will point to it needing seals and other internal parts. I have to do a little reading, but based on what I have right now, I'm pretty sure there's no sense in going any further without pulling the motor and freshening up the internals.

I think we gotta engineer a richer oil mixture so we can keep the mosquitoes down at tech day........

[Red]

More tinkering this afternoon. It is pumping a pretty steady stream of oil out the right side exhaust pipe; I'm pretty sure that will point to it needing seals and other internal parts. I have to do a little reading, but based on what I have right now, I'm pretty sure there's no sense in going any further without pulling the motor and freshening up the internals.

Extrememarine,

Before you do, check that the oil feed from the pump to the dry side is not plugged or blocked in some way. That problem would put too much oil into the other side.
.

[extrememarine]

Oil pump is not in play yet. I have the rebuilt pump installed, but no oil feed to it. I am running pre-mixed fuel; my intent was to see if it would run, then add in the oil pump and go back to straight gas with the oil tank / pump once confirming it was operational.

I'm getting plenty of stroke oil smoke out the exhaust as well, a sign it is running plenty rich (wanted to make sure not the seize the motor). The oil that it is pumping out of the exhaust looks to be out of the crankcase, like the there is excessive blow-by around the piston.

With as long as the bike sat (40+ years), I expected the motor to need to be split open.

Wayne

More tinkering this afternoon. It is pumping a pretty steady stream of oil out the right side exhaust pipe; I'm pretty sure that will point to it needing seals and other internal parts. I have to do a little reading, but based on what I have right now, I'm pretty sure there's no sense in going any further without pulling the motor and freshening up the internals.

Extrememarine,

Before you do, check that the oil feed from the pump to the dry side is not plugged or blocked in some way. That problem would put too much oil into the other side.
.

[HotRodZilla]

Dude...See if you can get a Lectron Carb for it. They're pretty badass. My buddy has one on his KTM 2-stroke.

[bungie4]

The oil that it is pumping out of the exhaust looks to be out of the crankcase, like the there is excessive blow-by around the piston.

It would pretty much have to be from the crankcase, if it was gearcase oil, man, that thing would be in a world of hurt.

I'd take a good hard look at the reed valve on that side before deciding to deep dive.

[Hppants]

There has to be at least one seal that separates each holes' crankcase. If he's pre-mixing and those are leaking, then I would think that hole would not make compression or make low compression. Maybe it is sealing enough to fire some of the fuel, but some of it is spitting out of the pipe?

But there also has to be at least one seal that separates the input shaft on the transmission (via the clutch) from the crankshaft. If that one is leaking, and the tranny oil is getting into the closest crankcase, I would think that the motor would try to burn the oil and not spew it out of the exhaust. Unless of course that hole is not firing.

Could it be a shitpot of water/condensation mixed with years of oily residue that was stuck in the pipe(s) over years disguising itself as something else?

I'm not doubting you, Wayne. I'm just baffled and intrigued at how straight oil can get thrown out of the pipes. I get that you are going to tear it down and replace all soft parts, which is exactly what I would (attempt) to do as well. Up to this point, you just wanted to verify that you didn't have a locked up motor, or some serious and obvious hard part failure that would preclude a waste of your time and money.

This whole thread is taking me way back to simpler and very fun times. When I was a kid, this dude in the neighborhood had an RD400 and that bike was so stupid fast, no one (and I mean NO ONE) could touch him. As a younger adult, I bought a Yamaha Banshee 4-wheeler and while not much of a trails bike, for just playing around, that thing was more fun than I should have been allowed to have.

[extrememarine]

Reed valves - I need to do some more research; from what I see in limited searches, reed valves go right down stream from the carb, in the intake track. ON this RD250, when the carbs are off, there's a rubber boot and you can see the piston right there, inside the cylinder.

Both sides are firing, I confirmed by pulling one plug wire at a time. I'm sure there is still a good bit of sludge inside the motor.

But the point of this exercise was to determine if there was life in this bike; there is, in my opinion, enough there to move forward. I am certain the two crankcase seals are bad - like much of the rubber bits on the bike - due to age. I'd also assume there's a good chance the cylindar walls are scored and / or the piston (sides) and rings as well are in poor shape from sitting 40 years.

To be trusted at any level on the road - which is what I want out of this bike - I'm of the mindset now that the motor needs to come apart, soft parts replaced, the rest cleaned, inspected, and refreshed as needed.

So that's the direction now - pull the motor, assess and build a solid runner.

[El Toro Joe]

So, are we gonna see it at tech day?

[raYzerman]

Joe, I think we'll bring a couple of baskets.... then when we take it all apart we can send Wayne home with the baskets.....

[bungie4]

Wayne, the reed valves are in the intact tract, they exist to stop the 'flow back' of air/fuel on the downstroke of the piston (remember, 2 bangers actually charge the crankcase with fuel/air/oil), this increases power 'n stuff. If one or both are bad you'll see those mixture symptoms you witnessed.

Of course, the same is true for crank seals because you'll have one side affecting the other.

2 smoke edumacation over. Of course, if your 2moker doesn't have reed valves, all bets are off

[extrememarine]

When I had the carbs off, there was nothing between the round intake boot and the piston. Just the rubber boot, round at the carb side, square at the cylinder head side. Parts sources list reed valves for other RD models, but not this specific 250. Must have come later as the models progressed to the 350 and then RD400.

Pretty sure that bad crankcase seals would be allowing gear case oil to be sucked into the crankshaft/ combustion chamber and be pumped out the exhaust.

So, new crankcase seals and clean out the insides and see what else needs attention in there.

Wayne, the reed valves are in the intact tract, they exist to stop the 'flow back' of air/fuel on the downstroke of the piston (remember, 2 bangers actually charge the crankcase with fuel/air/oil), this increases power 'n stuff. If one or both are bad you'll see those mixture symptoms you witnessed.

Of course, the same is true for crank seals because you'll have one side affecting the other.

2 smoke edumacation over. Of course, if your 2moker doesn't have reed valves, all bets are off

[extrememarine]

Only if I trailer it over; I don't think I'll have it road-worth inside the next 6 weeks. And I have two other bikes to get annual maintenance work done on - Need to show them some love so they are ready to go in March.

So, are we gonna see it at tech day?

[Hppants]

I'm not totally familiar with the motorcycle 2-stroke design. My oil burner engine experience is with outboard engines. There, the reed valves are placed on the flow that goes into the crankcase side of the piston, not the top of the piston. Of course, the reed valve is just a check valve the prohibits the gas from spitting back out of the motor when the crankcase is pressurized by the downward motion of the piston. If not a reed valve, there has to be something that does this function?

Again, on a boat motor, that crankcase gas lubricates the crank and rod bearings and is then pushed to the top of the motor where it is burned. There must be a seal of some kind that separates the clutch/gearcase from the closest crankcase (the piston crankcase that is closest to the clutch) - this is supposed to keep the tranny/clutch oil from getting into the motor. But if oil is leaking into that crankcase, it should be pushed with the gas mixture to the top of the piston and then burned (or at least attempted to be burned).

IIRC, that bike has dual exhaust - is the pipe that is spitting the oil out the one that is for the hole closest to the clutch? Did that spark plug look oil fouled?

Are the parts for that bike hard to find?

[raYzerman]

Only if I trailer it over; I don't think I'll have it road-worth inside the next 6 weeks. And I have two other bikes to get annual maintenance work done on - Need to show them some love so they are ready to go in March.

So, are we gonna see it at tech day?

Make sure the trailer has enough room for the baskets of parts we're gonna send you home with!

[extrememarine]

Parts seem to be fairly well available. There is a left and right crankcase seal, and I believe those are the culprits allowing crankcase oil to be pumped into the cylinder(s) and out the exhaust.

Plugs are not fouled, but show that the bike is running rich, which it should be based on the fact I'm running 32:1 premix fuel in it with the oilpump not plumbed.

IIRC, that bike has dual exhaust - is the pipe that is spitting the oil out the one that is for the hole closest to the clutch? Did that spark plug look oil fouled?

Are the parts for that bike hard to find?

[NBB]

Is the crankcase oil a multiweght or an gear oil. If a gear oil you would definitely smell that through the exhaust.

I have a '56 Jawa that needs the cases split due to a seal or gasket leak, it runs fine for a few minutes with great power until it warms up and then the seal/gasket opens, and then with the added oil there is the power level as well. Lets say it turns into a fogger...This is a fun old bike to ride.

[Bust]

Could a center crankcase seal failure cause this.

[extrememarine]

Could a center crankcase seal failure cause this.

That is another potential contributor, the labryth seal that sits on the crankshaft between the 2 cylinders. I'm going to start with the outer seals and see what it looks like inside.

Sent from my SM-G930P using Tapatalk

[extrememarine]

Update - October 2018.

The leaves are turning, it's raining with temps in the 40's this evening - time to get moving on this project...

I've decided to pull the motor in order to replace the seals on the crankshaft; that should cure the crankcase oil being pumped out the exhaust. It didn't take much to get the motor out - 4-5 bolts after all the wiring, drive chain and cables were disconnected. The frame isn't in bad shape - some surface rust across the majority of it.

I've decided that I am going to continue stripping down the bike to a bare frame. Then I'm going to have it bead blasted along with the swing arm and center stand / side stands. From there, I'll primer it and put down a few layers of flat black on it. I know powder coat could be more durable, but I need to be mindful of the budget. My thought is that a flat black frame will go with any color direction I decide on for the tank and tins; I may leave the tank and side panels the original orange color and just clean up the surface rust and seal them with a mat clear coat.

[raYzerman]

We coulda had that all apart for ya at tech day!!