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Suspected head gasket. Any other cause yamaha yp125r

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marc1234
L Plate Warrior



Joined: 19 Aug 2018
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PostPosted: 20:43 - 19 Aug 2018    Post subject: Suspected head gasket. Any other cause yamaha yp125r Reply with quote

I'm new to bikes and have someone helping irl.

I bought this bike as a non runner and was told it was a head gasket job.


I changed the head gasket but there is still water and oil mixing and looks like combustion going into the coolant.

Is it likely the head needs to be skimmed or something? is there any other explanation?
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Nobby the Bastard
Harley Gaydar



Joined: 16 Aug 2013
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PostPosted: 21:12 - 19 Aug 2018    Post subject: Reply with quote

Could be the base gasket, which will mean pulling the cylinder off.
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RhynoCZ
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Joined: 09 Mar 2012
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PostPosted: 21:32 - 19 Aug 2018    Post subject: Reply with quote

The head (or other place) might be cracked. Water pump propeller shaft seal?
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marc1234
L Plate Warrior



Joined: 19 Aug 2018
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PostPosted: 21:34 - 20 Aug 2018    Post subject: Reply with quote

RhynoCZ wrote:
The head (or other place) might be cracked. Water pump propeller shaft seal?


I was wondering about that, a friend said he could smell petrol from the radiator filler and I could see faint what seemed to be smoke. is it possible that smoke or something like it could come from the oil?
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Speedy23
Two Stroke Sniffer



Joined: 04 Dec 2017
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PostPosted: 09:52 - 22 Aug 2018    Post subject: Reply with quote

Did you not check the block/head mating surfaces for flatness when you had it apart?
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Teflon-Mike
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Joined: 01 Jun 2010
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PostPosted: 14:16 - 22 Aug 2018    Post subject: Reply with quote

Why was the head-gasket blown to begin with?

This is the impertinent question you should have been asking at the beginning. It's not a moving part, its not a load bearing part, if the engine's any good it aught to last the engine's life-time.....

If the head-gasket 'seal' lets go, it's most usually because the engine has over-heated; and the 'seal' is broken because the metal in the engine expands more where it's hottest and 'warps'.. warpage that doesn't always go back to flat when it cools.

So what would make the engine over-heat... find and fix, because if not.. just replacing the head-gasket wont solve the problem, and it will just do it again.

THEN, you have myriad other issues, during head-gasket replacement, where sloppy mechanics are as likely to make a 'new' problem; like not torquing the head down properly, or doing studs up in sequence, or screwing up the mixture refitting carb or exhaust, on top of pre-existing prob that made it over heat and blow head-gasket to start with.

Back up; start over; check cooling system; radiator; thermostat; coolant; hoses.. check for kinks, check for collapsed hoses, check for engine movement that can cause a pipe to kink as engine moves; check exhaust; check carb, check spark plug; check water-pump, check water pump drive; check head flatness, barrel flatness; start over, from scratch, find and fix original problem to cause failure; put it back together as per book, all variables checked, and eliminated; and do it carefuly and diligently, like following instructions to torque down the head, stage setting the whole flange to one wrench setting, then repeating, all on the flange, and again, to 'final' torque; then checking and setting, following patern after some bed in miles.

Here and now is there's no obvious one-hit fix, we're pigging in the dark, trying to do diagnosis by voodoo, for both original problem that caused HGF and any and all secondary problems that have resulted in 2nd HGF not fixed first time round or made by HG replacement.

Get book; follow instructions; work slowly, systematically, logically and diligently; and you will get there in the end; BUT... diving straight in to fix the obvious, not find root cause and fix it all properly, was your most likely problem, and trying to do same again, will just give you more.
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