How to know if head o-rings are bad?

[rablack21]

Heres something you might want to check, the tips of the water pump impeller blades, making sure they are not worn down on the ends.
Sometimes when a pump shaft bearing goes out, it will let the shaft & impeller move in & out & when it does, the impeller will rub on the steel defuser & wear the ends of those blades.
Once the worn out bearing & seals are replaced, the pump is back to were it is suppose to be sitting, except the ends of those blades are sitting to far away from that defuser & the impeller cant flow the coolant like it could when those blades are sitting close, so you end up with less coolant flow afterwards.
Old as all the 250Rs are these days, theres probably quite a few worn out parts we are still using, that are causing some of the hard to figure out problems some are having, but that dont know theres anything is wrong with those parts.


A radiator cap left loose or not on at all, will run a 250R hot quick, so it is important that cap is on & sealing so to hold back some pressure.

I was actually reading where you posted this info on a thread where Jamie was selling a water pump impeller. My water pump bearing is almost brand new, but I didn't pay attention to how the impeller looked last time I had it out. The only actual checking I have done with the water pump as just been squeezing the lower hose together and revving up the engine to see if I can feel the suction/pull in the hose.

[Jerry Hall]

Many of the radiator cap necks in the radiators have damage to the radiator cap sealing surface.  If this sealing surface has a scratch or corrosion pits, the cooling system may not build pressure.  A cooling system needs as much pressure as possible.  

Pressure raises the boiling point of the coolant and helps reduce the size of the steam bubbles as they form on the hot surfaces inside the water jacket.  Increasing the pressure improves the transfer of heat from the hot internal engine surfaces to the coolant, but does not improve the transfer of heat from the coolant to the radiator unless the coolant is boiling inside the radiator.

[udontknowme]

i never believed in them miracle coolant additives. seems like your just covering a problem if you need them

the cap shouldnt allow anything out the overflow hose at 210. if i was doing 1-2nd gear stuff i would have a fan or even 2 of em. its hard to believe the engine would be running well if theres water going in the cylinder. maybe take care of the obvious stuff and see what happens

[rablack21]

That's what has made this issue so difficult to solve. There doesn't seem to be anything wrong with the engine that I can tell. I have divided this issue into 2 possible causes.

1st possible cause - problem with the engine of some sort. But like "udon'tknowme" said, you would think the engine would not run very well if coolant was going into the cylinder. The engine runs fantastic which makes me think this is not the case. I have tried 2 new radiator cap, both seem to be good and tight. the radiator is less than a year old, has very few bent fins, no corrosion, and the radiator cap sealing surface is in mint condition, no burrs or scratches. I did have a little coolant come out of the overflow tube, but I don't run and overflow bottle and I know that if you fill up the radiator all the way it will push a little into the bottle when it heats up. I'm thinking that may this was the extra that ended up spilling out.

2nd possible cause- engine is fine, issue is with radiator not being large enough or not enough airflow through radiator. I am really starting to favor this diagnosis. I am thinking that the testing area in the woods where I have been riding is not allowing enough air flow through the radiator. I am not able to go fast enough to get sufficient airflow through the radiator to keep the bigger bore engine cool enough. It is mainly alot of 1st and 2nd gear riding with alot of clutch, cause there is alot of debris down along the path. And when it does open up, I run it wide open throttle in this area, but run out of room in about 15 seconds, then back to slow, 2nd gear riding or clutch. I am starting to think I am inducing the overheating by these riding conditions. If this is the actual issue then I have two options, ride at faster speeds and not lug around alot and not run WOT throttle for short areas or get a larger radiator to help compensate for some of this.

I got home too late to try to rule one of these issues out. I'm gonna take it for a ride down the road when I get home today and run it in a more open area and keep it moving and see how the temperature reacts. If the temp stays down around normal levels, then I can conclude that the engine is fine, it just needs more airflow through the rad to stay cool.

[Daniel370r]

My  o rings went bad last year I was on a long ride and noticed after I shut it off steam was coming out of the exhaust and my temp was around 220 my inner ring was fried. Another guy I was riding with his started going bad. His would blow a puff of white smoke when he started it. Couldn't smell coolant cause of race fuel and the mix he ran. Didn't notice a loss of power, his inner gasket had a small area that looked black. He ran it that way for a couple rides before it got worse. His would run between 210-220. I would pressure test or pull the head sounds like the same issue. I think if the inner has a small leak it's hard to notice. X2 on the fan we run tight trails somtimes and both bb's heat up fast when your not keeping a fast pace. I would like to put one on mine.

[rablack21]

My  o rings went bad last year I was on a long ride and noticed after I shut it off steam was coming out of the exhaust and my temp was around 220 my inner ring was fried. Another guy I was riding with his started going bad. His would blow a puff of white smoke when he started it. Couldn't smell coolant cause of race fuel and the mix he ran. Didn't notice a loss of power, his inner gasket had a small area that looked black. He ran it that way for a couple rides before it got worse. His would run between 210-220. I would pressure test or pull the head sounds like the same issue. I think if the inner has a small leak it's hard to notice. X2 on the fan we run tight trails somtimes and both bb's heat up fast when your not keeping a fast pace. I would like to put one on mine.

What you and your friend experienced seems very similar to me. I got some new orings coming in tomorrow so I will be checking that for sure as well. Well I don't get though is I thought that might be the issue last year, so I changed the inner ring last year when I was having this issue, but it made no difference. It still ran the same and acted the same. I think I'm gonna the flatness of my head when I take it off as well, and check the inner oring again. I am running a cr250r ignition, and I'm not sure i can run a fan with that setup. Otherwise, I would in a heart beat.

[Daniel370r]

I'm going to look into the fan setup for mine this year. I never heard of a head being warped  on an r but could be possible or maybe a machining defect if it's always done it. The bb motors don't like a slow pace riding I've noticed that I have to keep it in 2 second at a good pace and it stays under 200. I've talked to a couple builders and heard nikasil or running a pump gas dome would help but I haven't tried either one yet. I've done some reading on nikasil and it all sounds good but don't know of anybody that is running it on an r. I'm going to build a 265 stroker and I'm plan on trying it. Lugging or slow pace isn't for a bb with high compression.

[rablack21]

I'm going to look into the fan setup for mine this year. I never heard of a head being warped  on an r but could be possible or maybe a machining defect if it's always done it. The bb motors don't like a slow pace riding I've noticed that I have to keep it in 2 second at a good pace and it stays under 200. I've talked to a couple builders and heard nikasil or running a pump gas dome would help but I haven't tried either one yet. I've done some reading on nikasil and it all sounds good but don't know of anybody that is running it on an r. I'm going to build a 265 stroker and I'm plan on trying it. Lugging or slow pace isn't for a bb with high compression.

I can tell you from experience that running a pump gas dome with have no effect. Mine started out last running with a pump gas dome running 93 before I swapped out the dome and ran race fuel. The heating condition was the same.

[Daniel370r]

Good to know I won't waiste the cash.

[zcarlson12]

I think Tbone had Nikasil on his Duncan cylinder. Maybe he will chime in about the cooling of that for you Daniel370r. I wish I knew more to try and help you Ryan.

[rablack21]

Turns out my head orings are good. Here is a pic. I checked them last night. I also took the R for a ride down the road last night and kept the rpms high. As long as I was moving fast enough to create some air flow, the engine was fine. It never got above 175. I think the main issue was just the slow riding conditions and the limitations of the radiator to cool the bigger bore. Everything is seems to be fine.

[zcarlson12]

Glad you figured it out.

[F-Red]

This is bad!

[udontknowme]

using them walmart orings ?   :highly_amused:

not only is it disintegrated but it appears smashed flat. if its a fairly new oring i would suspect very poor qaulity