overheating.looking for advice

[mx2stroke]

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

 

[JGrossijr]

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

 

[mx2stroke]

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]

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_]

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.

 

[whenfoxforks-ruled]

Is it the stock bore size? Pressure test the cooling system. The money you saved sleeving, buy the fluidyne radiator.

 

[JGrossijr]

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]

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.

 

[mx2stroke]

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!!

 

[JGrossijr]

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]

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.

 

[bigboss]

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]

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.

 

[JGrossijr]

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]

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.

 

[whenfoxforks-ruled]

I like the spray on the cr80 head also. I had nightmares back in 95, no particular reason, and the spray was all that worked. Lapped the head, and cylinder, change the studs and nuts, the spray worked. No mods other than pipe and silencer. The rider? I remember having periods of Junior burning up clutches, I know it was the rider! But, anything you add extra, is just that, hardly measurable, but extra indeed! Replacing fatigued nuts and studs is a yearly/depends on the use/abuse thing. How sure are you that your torque wrench is calibrated? Do they fatigue also??? As much as I remember rebuilding it, I could hardly figure it was the coolant's fault. I could see the leak inside, the plug was black and gooey, and bubbles in the radiator, no visible leak.

 

[_JOE_]

Are the stud threads supposed to be oiled before torquing?

 

[Patman]

If it's any help Eric Gorr told me NOT to remove the head when we change rings after he built ours because.... this very reason LOL!

 

[JGrossijr]

Related to Jgrossijr's post; what's the correct (full) torque on the CR80 head?...Are OEM specs a bit conservative in the real world?

'95-'07 calls for 20 lbs/ft.
Torque specifications are a means to an end. The real issue is bolt stretch. There is an ideal amount of stretch for maximum clamping force based on fastner material and diameter. Since it is difficult to measure bolt stretch in most applications, torque figures are established that are "somewhat" indicative of bolt stretch. Condition of threads on both the male & female component, condition of flange/washer surface, presence & type of thread lubricant, etc. will effect the amount of torque required to get proper stretch. Add to this the fact that every time a fastner is torqued it looses a percentage of its strength.
Best practice is to assure that new nuts are used each time, the clamping surfaces are clean and free of surface imperfections, bolts or studs with damaged threads are replaced, and anti-sieze is applied to the threads. This will assure consistent clamping results from fastner to fastner.

 

[whenfoxforks-ruled]

Eric is the one that told me also, thanks to Doug Goins from Service/Thomas(now), use the copper spray, circa 1995. We had over 30 races, and 1 moto dnf. Do they still market the red rocket, with out a power valve? I have picked up its an 85 now a days. I will have to ask Ryan where he picked up leaving the head on. I know I have talked to Eric about removing the top end like this(05?), always hated it. BUT, for the cr, sounds like a winner. IF you get it to seal, NEVER take the head off again!

 

[T_Bois]

I've used the Permatex Copper Sealer back in the 70's on my 750 H2 triple. I always had to use it to stop the heads from leaking. I also increased the torque a bit, but back then the type of torque wrench I had was one with a needle and scale.

One thing you can do is take the head and cylinder to a machine shop and have them check the surface with a strait edge, they may be able to check your torque wrench as well.

What are you using to clean the surfaces before you assemble the head / cylinder and are you following the correct torque sequence? I know someone suggested starting at 25% and increasing the torque until you reach the correct amount, but there also a sequence you must follow.

 

[bigboss]

I solved the blowby problem by tightening all four nuts about 90 degrees. I just thought that factory specs should do the trick, especially on an aluminum engine. In their defense I did reuse the old studs, bolts and washers so that may be it. I use my torque wrench a lot so I'm pretty sure that it's at least close to accurate.
I did not check straightness of the head (or cylinder) with a straight edge but doesn't the fine sandpaper on mirror technique work? I've used it on several (2 stroke) bikes in the past without a problem. Is the CR80 engine simply more demanding compared to other 2 strokes? I like the tip on not removing the head if it's not leaking. I never thought of that. On the CR80 the cylinder can be easily removed as a whole right?
Oh, I cleaned the surfaces with carb cleaner as I always have. I sanded both cylinder and head to a very fine, clean surface. Which brand of gaskets do you recommend. I used a K&S set last time. Again, with success in the past. Anyway, thanks for your thoughts guys.

 

[Patman]

If the surface is warped "sanding" it may not resolve the issue depending how much it is imperfect and how imperfect you move the piece on the media. Think for a second if it is even the slightest bit off and you end up rocking it back and forth but you can't feel it doing that you could just as easily make it worse.

An additional 90 degrees on the fasteners is a pretty significant increase, try with some time when you tighten a fastener to a known lower value and then turn an additional 90 and see what you get. If you tightened a lug nut on a car to spec and then cranked it another 90 I bet you would end up snapping it.

I typically only use OEM or Cometic gaskets on my bikes and have never had an issue.

 

[_JOE_]

Check with your Honda dealer. They might have a top end kit. They had one for my bike and it wasn't too pricey.

Patman is right, 90 degrees makes a huge torque difference. The difference between 80 and 150 ft lbs on a car lug nut can be less than a quarter turn.

 

[whenfoxforks-ruled]

Carb cleaner leaves a residue. Hot soapy water and dry. Spray or wipe the steel parts with wd40. Taking the whole top end off is different, especially the first time. Make sure you take the sparkplug out. How do you sand the head, circles or figure eights?