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overheating.looking for advice

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Sep 25, 2009
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#1
I ride a 05 Honda CR85R, I have just finished a complete top and bottom end rebuild. My bike is overheating, is not instant. I race HareScrambles and after approx 2 miles. My radiator boils over and loses antifreeze thru the overflow. Am not fouling plugs, no apparent radiator clogs or damage, water pump appears to be turning properly. Any ideas?

Connie
 
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#2
A lot of things could cause it. Did it get hot before the rebuild?
If not there's a good chance that you have a vacume leak. Possibly through the base gasket, reed valve assembly, carb boot, etc. Could also be head gasket leakage. Pull the radiator cap off when cold & run the motor. Make sure the coolant is flowing and that you are not getting bubbles or exhaust in the coolant
Other common cause would be ignition timing too advanced or jetting too lean
 
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#3
No overheating prior to rebuild.The crank went out sent the piston beating around the cylinder, reason for rebuild. Curious?? can the spark plug run hot. Have always used BR10EG plugs, the shop that sleeved my cylinder sent BR10ES home
 

Patman

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#4
Single radiator bikes in a low airflow situation being ridden hard. I'll guess you might have been close to an overheating situation previously. I'll wonder a bit if the sleeve isn't not helping the bike run a bit hotter than before. Try flushing the cooling system and running straigh DISTILLED water with just a little bit of Redline Water Wetter, the antifreeze could also be hurting your cooling ability if not in the proper ratio. Running tap water is another trouble spot and might have caused som buildup on the metal parts not cleaned by a shop. When we went big vore on my son's CR85 Eric Gorr sent along a Fluidyne radiator to help keep it cool in the heat, never had an issue even in some very tight trails after a long fast run in the open in the middle of July in Texas.
 

_JOE_

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#5
I've heard a steel sleeve doesn't transfer heat as well as a plated aluminum bore.

Have the radiator cap and cooling system pressure tested. If it can't build pressure it will boil over at a lower temp.
 
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#7
mx2stroke said:
No overheating prior to rebuild.The crank went out sent the piston beating around the cylinder, reason for rebuild. Curious?? can the spark plug run hot. Have always used BR10EG plugs, the shop that sleeved my cylinder sent BR10ES home
Were the crank seals replaced? Bad crank seals can be the source of running lean which would cause additional heat & inadequate lubrication.
The spark plug is not suspect. The only difference between the plugs you have is center electrode & ground strap design, they are the same heat range. A better plug would be the BR10EIX, but it will have no influence over combustion chamber temperature.
You can also rule out thermal transfer differences between a plated bore & a steel sleeve bore. The fact that it is boiling over indicates that heat is being transferred from the combustion chamber to the coolant.
You have a problem that was caused at some time between the cause of the crank failure & the rebuild completion. Focus on what happened in that time frame. You could have a cooling system failure, but unless the the radiator is defective there is no point in changing it.
 

Patman

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#8
Let's ask a silly question. Are you SURE it's boiling over and not getting pressurized from a combustion leak? The head & base on this bike are quite picky about sealing.
 
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#9
My first chore is to reseal & replace the gaskets. I have been riding for years however just recently started learning the mechanics. Has anyone had any luck with permanent gaskets? Thanks so much for all the help!!
 
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#10
No experience with permenant head gaskets, but Patman is correct that the CR85 can be challenging when it comes to head gasket sealing. I have had success using Permatex Copper Coat head gasket sealant. Make sure that the mating surfaces are flat by sanding them in a figure 8 motion on a piece of glass with 400 wet/dry sand paper taped to the glass. Make sure that the head stud threads are in good shape, coat them with anti-sieze, and torque the bolts in sequence starting at 25%, then 50%, then 75%, then full load.
 

Patman

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#11
No, no, no silicone sealer! The service manual doesn't call for it for a reason. Use the proper cut gaskets from a quality supplier or OEM, check the surfaces and carefully assemble and torque the fasteners. The only place that goop has a place on that bike is maybe the crappy exhaust spigot seal to help keep it from drooling down the front of the engine. precission machined surfaces should seal properly with the correct gaskets with no band-aids necessary.
 
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#12
Related to Jgrossijr's post; what's the correct (full) torque on the CR80 head? Last time I went with shop manual specs I had blowby issues on the right side of the head gasket (yes, I resurfaced both cylinder and head with fine sandpaper on a mirror and installed a new gasket). I solved problem by tightening the nuts some more and bike runs fine to this day. Are OEM specs a bit conservative in the real world?
 

Patman

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#13
Sounds like your fasteners might be past their limits or your torque wrench needs tested to see if it is within spec.

Sounds like you might also not have perfectly matched surfaces.
 
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#14
Patman said:
No, no, no silicone sealer! The service manual doesn't call for it for a reason. Use the proper cut gaskets from a quality supplier or OEM, check the surfaces and carefully assemble and torque the fasteners. The only place that goop has a place on that bike is maybe the crappy exhaust spigot seal to help keep it from drooling down the front of the engine. precission machined surfaces should seal properly with the correct gaskets with no band-aids necessary.
Who said anything about silicone sealer?
Permatex Copper Spray-A-Gasket Hi-Temp Sealant is an aerosol product formulated as a sealant which helps dissipate heat, prevents gasket burnout and improves heat transfer.
TYPICAL APPLICATIONS
• Cylinder heads gaskets
• Exhaust manifolds gaskets
• Turbo charger flanges
• Carburetor gaskets
This is a popular head gasket sealant that has been used by professional engine builders for 20+ years. It's not "goop"
Here is a link to a technical data sheet.
Permatex Copper Coat
 

Patman

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#15
My bad I read "Permatex Copper" which seems to be a common solution for many less than flat surface owners and didn't register that is was the spray sealant. Still my preference is not to use any extra 'stuff' since extra 'stuff' was not part of the original assembly by the factory and some gaskets come pretreated anyway.