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wayne509

Checking A Pressure Relief Valve

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Just sold a bike (Scorpa SR 125 with the sherco 125 2T motor and radiator etc) and unfortunately the head gasket has apparently blown on the fellas first time out on it.

Surely the pressure relief valve should have let water/pressure out first shouldn't it? It blew a water pipe off then after putting it back on and filling with water it started chucking steam from the exhaust.

I want to help with the bits to fix the bike and wondered if there is an easy way to test the pressure valve before I shell out for another?

Edited by wayne509

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Did he put oil in his fuel ?

I would think the bike was still on the same tank of fuel as when I sold him it. I filled the tank from the same mix of fuel my other lads 125 is running. If anything it would have been running a touch rich. Definitely not the cause.

The bike does have a S3 high compression head on it though .... probably the culprit but would think the pressure relief valve would have shown symptoms before it failed totally

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By the pressure relief valve, are you referring to the radiator cap? If so, most radiator shops can test it.

No not the radiator cap. To fill the radiator there is a cap but it is basically just a bolt. There is a separate pressure relief valve just next to it.

You can see the part here ... part 8

screenshot_zpsc0d80a4b.jpg

Edited by wayne509

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If it has built up enough pressure to pop a hose off and the relief valve didn't relese then I would certainly change the valve to be on the safe side. Presuming the hoses were secure in the 1st place.

The problem you may have is the the new owner doesn't know too much about bikes and the original cause needs to be determined 1st. You need to know if the fan was working and the waterpump is operating properly. Another cause of head gasket failure especially with a high comp head is reving the nuts out of it can pop the inner o ring but I doubt it will be admitted if that was the cause, If so a cheap fix just half an hour and 2 o rings.

I would reccomend the bike is looked at by someone who knows exactly what they are doing otherwise you will end up keep giving them parts untill they accidently fix it.

Good Luck.

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Hi Steve

I believe the new owner is returning to trials after many years and does have experience in fettling bikes. As far as whats wrong with it .... We know the fan is operating properly as we ran it up to temp when he was viewing it. My lad has been riding it twice a week for 6 months with no issues so I am putting it down to co incidence and sod's law. I have advised him to check the waterpump but pretty confident all is ok there as a complete kit was fitted about a month ago. He is going to take the waterpump cover off turn the motor over by hand and check the impeller is turning as it should and there is no damage to it. I am going to get him new water pump seals for the sake of a couple of quid and yes you are right .... never mind checking the old valve I will just get him a new one and obviously new head o rings.

I gave him the standard head too so think he is going to go with fitting that as everyone I have talked to say those high comp heads are more trouble than they are worth.

Hopefully this will sort everything out

Edited by wayne509

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Hi Steve

I believe the new owner is returning to trials after many years and does have experience in fettling bikes. As far as whats wrong with it .... We know the fan is operating properly as we ran it up to temp when he was viewing it. My lad has been riding it twice a week for 6 months with no issues so I am putting it down to co incidence and sod's law. I have advised him to check the waterpump but pretty confident all is ok there as a complete kit was fitted about a month ago. He is going to take the waterpump cover off turn the motor over by hand and check the impeller is turning as it should and there is no damage to it. I am going to get him new water pump seals for the sake of a couple of quid and yes you are right .... never mind checking the old valve I will just get him a new one and obviously new head o rings.

I gave him the standard head too so think he is going to go with fitting that as everyone I have talked to say those high comp heads are more trouble than they are worth.

Hopefully this will sort everything out

I was going to comment, yet your last sentence may sum it up.

I do not know of a pressure test set for this, although one may me devised with adaptation. One thought would be removing the old one for inspection, as it is likely a simple spring loaded ball, and insuring it is not seized. No further info and I am not in the mood to break mine to find out! Ha!

Cheers,

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They do run hot with a high comp head, I'm going to have to fit the uprated water pump to mine when the weather heats up.

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Hi there , I’m having trouble with my sons sherco 125 2003.

it was popping the thermostat out 

put a new one in and now coolant coming out not from the thermostat but from the radiator somewhere . 
how do I check the blow off valve as I suspect the problem lies there 

any help or tips very much appreciated as this bike is slowly draining the life and wallet out of me 🤔🤔

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