84 Honda CR 250 Modifications

[Ando]

I don't know how many times it has been said on here that the CR250RE 1984 water pump cover was a "ONE OF"!!!!!

[smed]

Looks like this bloke may have a similar problem........
http://www.dirtbikeworld.net/forum/showthread.php?p=1552833

I think we know this bloke

[Kenneth S (222)]

Sitting there contemplating this bike, and a logical sequence of steps to take, it occurred to me that I have never have really understood for sure how the ATAC mechanism worked in this bike and why it is linked to the inside of the waterpump. I assumed it had something to do with the centrifugal force created by the spinning of the pump activated the shutter in the exhaust port but I haven't really given it much thought beyond that. You could say I had other things with this bike on my mind. To assess this issue properly though, I think I need to know exactly how the whole ATAC mechanism is supposed to work and what the pump actually does in relation to it. I noticed that one piece has a rectangular key on it which is off center and locates to a part coming down from the exhaust port and that piece could easily be put in back to front, possibly changing the behavior of the whole mechanism. Can someone shed some light on what drives what and how this part of the bike works?

Thanks in advance for any assistance.

Ken

[crs-and-rms]

i will take those measurements for you tomorrow night

[STW996]

Ken, You are correct in the way the ATAC system works but it has no bearing on the water pump, they used it as it was a drive point thats all.

It will have no effect on the running of the pump.

I thought we had spoke about this some time ago re the issue you are having with your 250 and we had the same with one of ours. We replaced the head (after having it faced and still had the same problem of overheating) and now have not had the same problem again.

I assumed it was a slight crack in the head that I could not pick up by eye.

[Kenneth S (222)]

Hi Shane, yes I found some literature on it today. When working correctly, at about 6000 rpm, the mechanism on the inside moves out and activates the closing of the ATAC valve in the exhaust port.

We did talk. I have tried 2 heads on it and it did it with both. You don't have any spare right hand side clutch covers kicking around you want to sell do you. It wouldn't have to be too good to be better than what I have.

[Hardo]

You don't have any spare right hand side clutch covers kicking around you want to sell do you. It wouldn't have to be too good to be better than what I have.

Kenneth, are you sure mate???

Look at this one....
http://www.ebay.com/itm/1984-Honda-CR250-CR250R-Dirt-Bike-Engine-Clutch-Cover-repaired-/121062085071?pt=Motorcycles_Parts_Accessories&hash=item1c2fdcd1cf&vxp=mtr

 

[crs-and-rms]

hi ken have done the mesurements will send tomorrow for you

[holeshot buddy]

wow 7 pages on how to modify a 1984 cr250
thats a lot of mods

[Simo63]

wow 7 pages on how to modify a 1984 cr250
thats a lot of mods

Seven pages and we haven't even got past the waterpump yet ... wait until we get into porting, pipe and carby setup 

[crs-and-rms]

email sent ken hope it came out ok let me know

[STW996]

No need to mod them Rusty you know they are like lighting the way they are!

Ken, Most of the cases I have are worst than yours so I still don't think that is the problem.

If the water impeller moves (rotates) when you turn over the engine then that would pretty much rule it out. They are a simple system.

We have not had to much trouble with the 3 bikes we have (outside of the bike I ride now that had the head problem), if they is no blockage in the lines and you are bleeding it correct (had no issue with this ourselves) than I am at a loss. When you fire it up and remove the cap, the water flow should increase as you free rev it, that would mean it is getting good flow and rules out most things.

Outside of that it can only be head / barrel / cap.

Shane

[GMC]

I’m with STW, I reckon you may have a crack in the head / barrel
I know you swapped the head for another but they could both be duds, stranger things have happened.
Cracks can be hard to see with the eye because they sometimes only open up with heat.

There are too many pages to look back through on this but I thought you said you had checked the water flow? With some clear hoses or something.
The recess in the pump case that is filled in is pretty minor as the outer cover still should have a good open area.
Have you had the motor running at your workshop with the cap off?
As well as watching for flow if the water settles down you can look for bubbles in the water, If there are any bubbles then they could be from combustion gases.
I think there is some testing gear that can check for gases, I think someone already mentioned it
You should talk to some car engine reconditioners about getting the head crack tested, they would deal with this quite a bit whereas motorcycle mechanics would deal with it rarely.
I reckon you need to get it tested properly just so you can at least rule it out.
Compare the cost of getting it tested to the cost of buying more head gaskets.
You can even buy crack testing spray cans from industrial type hardware stores.
I use it on odd jobs.

[holeshot buddy]

listen to shane he knows his honda stuff
geoff you should make some you could retire in 2 years

[Cooch 04]

Was at TM Bills event in Taupo yesterday and got talking to a rider that has said 84 cr250 and has been having exactly the same problem, has had spent lots of money on head gaskets and had numerous mechanics look at the bike but no one has been able to sort it out.He had almost given up and purchased an 85 cr250 to take its place.He had 1 more gasket left so fitted it and left the bolt out that secures top of motor to frame.Rode bike all day and no problems.he seems to think that the frame flex has been the issue all along.Just a thought and may be worrth a try