RM-Z250 Oil starved cam journal? How bad?

Mihylo33

Mihylo33

JoniX:
Most likely, yes. As long as it holds together and nothing else breaks.
Yeah I'll maybe do it, but right now it's money I can't spend on this hobby. I just use it to ride in the woods with my friends, nothing extreme, not really pushing the bike at all. Just getting from point A to B and enjoying the ride.
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I would do it right the 1st time so I didn't get stuck on the trail. Doing it right the 1st time won't cost as much as having to do it twice just to save a couple of euro the 1st time.
 
O

ossagp

JoniX:
Thank you for the tip!

Excellent information, good to know! So basically as long as I pre-lube everything, I should be OK starting the bike and leaving it on for a short period of time, even if oil does not flow or lacking oil pressure.

I had a look and changing the oil pump seems to be do-able for me but will take me some time, and I suppose the oil pump won't be cheap either.
I'll try blowing compressed air from the head then. I've got no ideas how the oil channels run on the engine, but blowing it back will send it to the filter I assume?

There's a ball bearing on the cams at end with the gears, and basically nothing at all (from what I can tell) on the other end. Just the cam on the surface of the head, with a layer of oil between. Is that what a plain bearing is? I'm unsure on translating some technical terms between Swedish and English.

To be honest, I do not know what a machine shop would be called in Swedish, nor where to find one :( But what can be done to recover my parts? I can't see how any bearing can be fitted on the cam as one of the lobes are in the way.
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The term "machine shop" refers to a place that does advanced metal work on parts for machinery. they vary in capability, but most have presses, lathes, metal milling machines (simply called a mill), welding capabilities etc. they really vary in what they can do. on this side some can build or cast all of the components we are talking about, though none that i know of could do that cheaper than the company built your engine. repairing heads and the cam bearing portion has been fairly popular over here in the past. the honda xr's for instance almost made an industry possible.
 
JoniX

JoniX

I'll see if I can find a new pump then. Do any of you know if there's a repair-kit avalible with all the parts necessary? I can't find one. What parts do you replace, just the two "wheel-in-a-wheel" things?

ossagp:
Maybe Kawasaki did put a one way valve beyond the oil filter. The other things I have worked on from single cyls engines to 16 cylinder ones put the back flow preventer as close to the pump as possible when one is deemed necessary.

Anyway it is easy to check. I haven't bought a kawasaki oil pump other than for some kz 900/1000's. But other makers sell them reasonably.
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How would I check if it has a one-way valve? Or maybe it's obvious once I take it apart. I've been busy working and moving during the last weeks so I have still not dug any further into the bike.

Mihylo33:
I would do it right the 1st time so I didn't get stuck on the trail. Doing it right the 1st time won't cost as much as having to do it twice just to save a couple of euro the 1st time.
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Yeah I know it's the best option, but I'm still not sure if I want to pour $900 on this old bike.

ossagp:
The term "machine shop" refers to a place that does advanced metal work on parts for machinery. they vary in capability, but most have presses, lathes, metal milling machines (simply called a mill), welding capabilities etc. they really vary in what they can do. on this side some can build or cast all of the components we are talking about, though none that i know of could do that cheaper than the company built your engine. repairing heads and the cam bearing portion has been fairly popular over here in the past. the honda xr's for instance almost made an industry possible.
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Thank you for the explanation! I'm still not sure of where to find one here in Sweden although, but I'll try to ask around.
 
JoniX

JoniX

And a thought.. if I measure the clearance and it's still within specs (although not likely), and I put it all back together as it is, what would be the worst case scenario? Cam seizes, chain snap, valves get bent.. so basically a new head?
 
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ossagp

When the valves hit the piston at speed it gets unpredictable. The rod bends and brakes about half the time I have seen it. Then that takes the cases.

The one way valve won't matter if you are trying to determine whether the oil passage is open. If your filter isn't in place the passage will just blow back to that cavity. The oils had to be getting past the filter or you would have had other damage too. I doubt you will find one anywhere in your rig.
 
M

MADMATEMATT

ossagp:
When the valves hit the piston at speed it gets unpredictable. The rod bends and brakes about half the time I have seen it. Then that takes the cases.

The one way valve won't matter if you are trying to determine whether the oil passage is open. If your filter isn't in place the passage will just blow back to that cavity. The oils had to be getting past the filter or you would have had other damage too. I doubt you will find one anywhere in your rig.
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the valve between the oil filter and the pick up is more a "non-return" valve than a one way valve. it is more than likely located right at the oil pump and stops oil draining back down into the sump when the bike stops. this is to ensure there is oil to the head as quickly as possible. as far as i know all late model engines have them. you also have two oil filters in your sump on your model which will need to be checked. if they have blocked up then the oil wont be getting picked up and flow rate will diminish.
 
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ossagp

MADMATEMATT:
the valve between the oil filter and the pick up is more a "non-return" valve than a one way valve. it is more than likely located right at the oil pump and stops oil draining back down into the sump when the bike stops. this is to ensure there is oil to the head as quickly as possible. as far as i know all late model engines have them. you also have two oil filters in your sump on your model which will need to be checked. if they have blocked up then the oil wont be getting picked up and flow rate will diminish.
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Exactly. (As stated before.) Most bleed backs etc are on the pump or very near it rather than upstream, therefore makes it quite simple to trace or clear a line simply by removing the filter if there is one. Some filters contain a valve of sorts known as a bypass and that can keep oil from bleeding back down too. Having it remain up in the lines is a two edged sword: If it stays up in the head where it gets hot, and in the case of early honda xr's even in the supply tube which runs up a stud on the cylinder it ends up baking when the motor is shutoff hot.
anyway, Joni it isn't something to stress about. right now honda crf's are the only bikes i know that have a "one way valve". that one is again, not used for the purpose of holding the oil up stream (the outbound flow) of the pump. it rests in the bottom of the case, consists of a screen and a "reed" that keeps the oil that is scavenged (the downward force from the piston pushes the oil out) from the crank case in the tiny reservoir from drifting back to the crank cases and collecting there. It keeps it a basic dry sump in a way.
 
Mihylo33

Mihylo33

ossagp:
Exactly. (As stated before.) Most bleed backs etc are on the pump or very near it rather than upstream, therefore makes it quite simple to trace or clear a line simply by removing the filter if there is one. Some filters contain a valve of sorts known as a bypass and that can keep oil from bleeding back down too. Having it remain up in the lines is a two edged sword: If it stays up in the head where it gets hot, and in the case of early honda xr's even in the supply tube which runs up a stud on the cylinder it ends up baking when the motor is shutoff hot.
anyway, Joni it isn't something to stress about. right now honda crf's are the only bikes i know that have a "one way valve". that one is again, not used for the purpose of holding the oil up stream (the outbound flow) of the pump. it rests in the bottom of the case, consists of a screen and a "reed" that keeps the oil that is scavenged (the downward force from the piston pushes the oil out) from the crank case in the tiny reservoir from drifting back to the crank cases and collecting there. It keeps it a basic dry sump in a way.
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Almost every time I read one of your posts I get an education. Especially when Floyd is involved. :thumb::cheers:
 
JoniX

JoniX

Thank you for the information guys! Sorry I've been slow replying, I've been quite busy the last few weeks. I'm going to dig into the engine tomorrow and have a look at the oil pump, as well as measure the clearances on the journals (probably way out of spec).

And I have still not decided whether I want to drop $900 for a completely new head with valves, or go for a good used one. Used ones seems to be fairly rare around here, and every parts bike that comes up seems to already have sold the head.. seems to be a common problem with these.

Currently I have my eyes on this one, but the journals seems to have slight scratchings so I'm not so sure.
 
JoniX

JoniX

I've measured the journal using plastigage, and it seems to be 0.076 mm play. But I'm unsure if I did it correct, I put two pieces of plastigage, one on top and one on the bottom, and both showed about 0.076 mm on the worst part. Am I supposed to add up those measurements, or go by one of them?

The manual specifies 0.020-0.062 as the normal values, and 0.15 as the service limit. Would that mean it's still useable, or is it a bad idea?

And final question.. Looking at exploded views, I was under the impression the oil pump would be on the left side of the engine, but looking at it there's no cover besides the flywheel. Do I have to split the engine to get to the pump, or is it actually on the right side?

EDIT: turns out I'm too stupid to look at exploded views. It's on the right side.
 
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