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Diagnosing Headgaskets
Lots of threads for overheating, thermostats, radiator caps, and overflow tanks now that the summer is upon us. Before you go out and buy a bunch of parts that don't need to be replaced, then spend countless hours replacing them, only to find out they didn't correct the condition you're concerned with, your time and money might be better spent learning how the system actually works and diagnosing the problem correctly the first time.

Some members are under the impression that when a headgasket blows, it BLOWS!! That isn't always the case. The problem generally starts long before the gasket finally gives up. It looses integrity and starts bypassing compression from the combustion chamber into the water jacket. Not only are the hot gases forced into the coolant, they also cut into the composition portion of the gasket causing the material to be sheared off. From there, the fiber can end up in any number of places in the water jacket. The head, the waterpump, the thermostat, the radiator, etc.
I recently had to replace mine. The bike would run warm, the cooling fan would run continuosly. However, it took nearly 100 miles of riding before the symptoms would appear. At first, I thought it was bits of sealant I had used. After filling the cooling system, I could go another hundred or so miles, then the overheating would reoccur. It wasn't the sealant.
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Headgaskets are not as difficult to diagnose as most make them out to be. There are "tell tale" signs that can only be caused by a blown headgasket or a headgasket that is failing.

Before testing, verify that your radiator cap and recovery system are in good working order. It is imperative that the radiator cap is working correctly.

Overflow tanks: They are not overflow tanks. They are storage for the coolant "recovery" system. Inspect your radiator cap and you'll see TWO seals. One for the top of the radiator neck, and one for the lower portion. The area in the neck between these two seals is the "operating chamber" that allows the recovery system to work. As the coolant increases in temperature, the pressure increases, because it is a closed system. To allow for expansion, the radiator cap (lower seal) vents coolant to the recovery bottle. As the coolant decreases in temperature, it creates a low pressure area in the radiator and the coolant is then drawn back in to the radiator, past the same seal, thus keeping the cooling system "full" at all times. The seal at the top ensures that the system stays tight. If coolant can leak out, air can leak in. If air can leak in, the coolant will NOT be drawn back into the system.
If your seals are badly worn, or cracked, replace the cap. If the seals appear good, have the cap tested to ensure it is operating correctly.
Inspect the sealing surface of the radiator neck for both seals. Make sure there are no "nicks" or low spots that would affect the operation of the system.
Commonly overlooked is the upper portion of the neck where the radiator cap "locks" into position. This is a double step. Once the cap is snug, you must PUSH DOWN and TURN the cap for proper seal. Unfortunately, some owners lack "finesse" and jamb the cap opening it or securing it, which causes the tangs on the neck to be deformed. This will result in no seal or poor seal and negatively affect the operation of the recovery system.


Remove the faux tank.
Fill the radiator to the proper level. If it's low, there's a reason.
Remove the hose from the radiator neck to the recovery bottle "AT" the recovery bottle.
Place the hose into a funnel/bottle to catch any coolant that may be expelled.
Bring the bike up to operating temperature, watching for coolant discharge at the hose. A small amount of coolant is normal due to heat expansion
After the bike has reached operating temperature, and the cooling fan has cycled (twice), the system temperature AND pressure should now be stabilized.
Since it's cycled the fan twice, this is a good indication that the thermostat is functioning correctly, the water pump is circulating coolant and obviously the cooling fan and thermostatic switch are working as well.
Rev the engine a few times, watching the recovery hose, and see if the cap is still venting coolant due to excess pressure.
Since the pressure due to engine temperature has already been accounted for, there is only one other place the pressure can be coming
#1 07-26-2009, 05:22 PM,
Thanks GL again :-SS
I made it a sticky
The only stupid questions are the one's that are not asked.

#2 07-26-2009, 06:37 PM,

I'm confused as to why it takes these symptoms 100 miles to seems as if the bike should be fully warmed up after 15 minutes of riding, or so.........

Is it because the head expands away from the block as it heats, giving the gasket more room to leak??

I'm not questioning your theory, just trying to understand all this........... Idea
A rainy day off beats a sunny day at work any time..................
#3 08-10-2009, 05:35 AM,
It really depends on the severity of the leak. As I said, the compression is leaked into the cooling jacket which causes the cooling system pressure to rise and the radiator cap to vent. Over a period of time, the cooling system eventually developes a large enough air pocket to cause the engine to overheat.
Aluminum expands at nearly four times the rate of cast iron. When dealing with aluminum engines, the reverse is "generally" true.
As the engine heats up, the head and block expand and the gasket can reseal.
This test simply allows you to see if you have unwanted pressure being built up in the cooling system.
I've tried pressure testers, leakdown testers, and even headgasket test kits with varied results. Mostly inconclusive.
Checking it this way doesn't cost a dime, you don't have to tear anything apart, and it's pretty darn accurate.
#4 08-10-2009, 07:15 AM,
Well, I didn't have to complete the test.

I got everything apart and set up with a bottle on the vent tube. Started the bike, didn't even have to let it get to where the fan kicks on. The bike is smoking out of both sides, smells sweet, and once it warmed up I've got a consistent drip of coolant from the exhast on the right side sitting on the bike, about half way back.

Is it safe for me to assume I've got a blown or badly leaking head gasket?

Man am I bummed. Be back after while. :cry: :cry: :cry:

Sorry, I should have posted this on the other thread. If you guys can move it, please do...thanks
A rainy day off beats a sunny day at work any time..................
#5 08-10-2009, 09:25 AM,
To further this conversation just a bit... I'll be diagnosing why I have a very small leak at #2 cyl after Christmas (looks like may be head gasket). In the event that the root cause is leak at head gasket, and if the head is NOT warped, does the head have to be re-surfaced prior to re-install? If so, what is the surface finish spec? Clymer's doesnt reference this.

Also, with respec to your waterpump post, I was looking up all the parts you listed and can find them all except the following... what are they?... 91333-567-010, 91345-580-000, 11396-371-000, 91305-216-000

Thanks, and Merry Christmas to all.
#6 12-22-2009, 12:57 PM,
I'm not sure what you mean by surface finish spec but I doubt that the head will be warped more that the service specification of 0.004" in which case re-surfacing is not necessary only careful cleaning.

On the part numbers, the first two are the o-rings on the front of the oil pump the third is the waterpump housing gasket and the fourth is the o-ring for the water pump cap.

#7 12-22-2009, 02:26 PM,

That is one nice diagnostic, simple and effective. Thanks for the tip. ^Smile^
#8 12-22-2009, 04:41 PM,
Hello All . If you don't have the wrench time to tell if you have a combustion leak into your cooling system help is here ! Your flaps {friendly local auto parts store} sells a type of test strip that detect elements of combustion in coolant. I would just put 15lbs pressure on the system and see if if holds ? The test strips work and can detect the early flaws . Always more than one way around a problem later joe !
#9 12-22-2009, 08:47 PM,
Ok, if I do have to do the head gaskets, what additional gaskets are required. I'm listing what I see are the most obvious, what else is missing?

Head gaskets x2
Valve cover gaskets x2
Intake O-rings x4
Exhaust rings x4

And possibly while the heads are off . . .
Valve stem seals x8

Are there any Cam seals I should replace?

Also thinking the header to muffler tapper gaskets x2 while the pipes are down.
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#10 06-20-2010, 12:03 PM,
Dont forget the O rings for the oil orifice
The only stupid questions are the one's that are not asked.

#11 06-20-2010, 02:03 PM,
tricky Wrote:Dont forget the O rings for the oil orifice

And the gaskets for the coolant transfer pipes.
#12 06-20-2010, 02:16 PM,
glhonda Wrote:
tricky Wrote:Dont forget the O rings for the oil orifice

And the gaskets for the coolant transfer pipes.

And the moly lube for the threads on the bolts.
The only stupid questions are the one's that are not asked.

#13 06-21-2010, 08:48 AM,
According to Clymer's "Apply moylbdenum disulfide grease to the cylinder head flange bolt threads and to the undersides of the bolt heads". Is that the same grease used on the finger flange inside the rear wheel final drive assembly? I do have that grease, I'm wondering if "anti-seize" would work as well?
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#14 06-26-2010, 12:06 AM,
Yes,use moly 60.
#15 06-26-2010, 05:00 AM,

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