Jump to content
Sign in to follow this  

How hot is too hot?

Recommended Posts

I entered my first Vet Expert race in a really gnarly, tight, muddy, sandy course at low elevation in cold weather jetted too lean with a lot of coolant loss and no extra coolant in the pits Yes, I know....recipe for disaster.

So here's how bad it got....

I was running at decent temperatures for the first 1.5 to 2h. The last 1.5 to 2h was largely between 130C and 140C (266F to 284F) and there were short peaks (5min to 10 min) of 150C (300F) and instantaneous flashes to 160C (320F) once or twice.

When I got to check my coolant it took almost a litre to fill the rad ('06 CRF250R.....usually takes about 1.25L to fill from empty) so I was pretty near air cooled for the last 2h it seems

Topped up and rode the poker run the next day at about 100F for 3h. Bike started and ran flawlessly.

So.....did I cook something? Well no doubt I did....just wondering what the most susceptible parts are on the motor ('06CRF250R with Athena 280cc big bore kit).

Rings? Pistons? Valve train? Valve Seats? Cylinder coating? Bearings?

What tends to cook first? How can I test for damage?

Is any part of my motor predisposed to premature failure after an episode like that? What should I watch for.

Thanks for your help.....I will now be sure to have a pit man with gas AND coolant

Share this post


Link to post
Share on other sites

Compression check is one thing to check.

They look odd but MX Bones sells these billet aluminum cooling fins that go inline to the radiator hoses. They really help drop the temps. That and a hi flow water pump or even radiator fans mat be a good idea for you or all of the above. Pretty sure Honda makes a radiator fan kit for the X.

PWR also sells better larger radiators and one model even has a built in oil, coolant heat exchanger.

Definitely change the oil.

Share this post


Link to post
Share on other sites

top end usually takes the toll.. just do tune up.. oil. coolant, check valves, compression check.. ect.. i put oversized radiators on my 450 and possibly a oil cooler as well to deal with extreme heat.. the radiators matched with engine ice brought down the temps a bit but if you go that way i would recommend buying a hi flow water pump to get the most put of it

Share this post


Link to post
Share on other sites

Check your valve clearances. Right intake is the first thing to go on a hot engine. You can buy a cooling fan for the factory radiator, but it is pricy. A oil cooler will also helpa lot.

Share this post


Link to post
Share on other sites

Thanks for the input guys. I really appreciate it.

I will thaw the bike out (back up in the hills where I live it's still winter) and do the top end check.

Would the rings be damaged as well?

Thanks again.

Share this post


Link to post
Share on other sites

The bike ran like a champ on day 2 through a much less demanding poker than the previous day's overheating enduro. On day three, back at home in the shop all compression was lost and the bike would not start.

I did as you advised and checked valve clearances. As predicted, the R intake was closed (all others were in spec). I shimmed down from a 190 to a 165 and got her back to spec and she roared to life with one kick.

So....have I gotten lucky and should I count my blessings and keep riding her hard (NOT overheating of course)?

Or...should I pull the jusg and inspect the piston, rings and cylinder?

The smllest shim honda makes is a 120 and if dropped from a 190 to a 165 in one bad ride. I've heard that once they go, they go faster and faster.

How long can I expect from this bike before more serious (than shimming) headwork is needed?

What should my next move be?

Thanks again.

Share this post


Link to post
Share on other sites

Generally one shim maybe 2 is ok but at that point they start going fast. Check the clearance every 5-10 hours according to a ride meter not calendar time.

If you ride off road, which it sounds like, consider SS intake valves or other steel valves at rebuild time.

Share this post


Link to post
Share on other sites

my water pump seal went and my bike heated up.....valves were in spec but my oil was black and smelt strange........my oil is usually red or pink but not this time........product of heat i guess......but i wonder if my cam chain didnt strech?????????? but thats my story.......care helps

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×