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Blown headgasket after 1.5 hour

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Hi guys,

I would like to have your thought on my problem. I bough a cr 125 2005 2 weeks ago in running condition to have a fun bike and a spare in case I get trouble with my crf 2012. I immediately changed the piston, all gasket and bearing for new oem parts. Also installed a vforce 3 and a R304 shorty while I was there. Saw somewhere the powervalve 7mm stopper pin mod and decided to give it a try.

Once everything back in one piece, I went to the track to get some fun. The bike had absolutely no low end power and poor mid, even for a 125! then I read more on the powervalve mod and figured out it's not helping on 125 after 2002, is that right? My gearing was also way off, it doesn't help either. I rode 45 minutes without issue.

Next day, bring back the bike again on the track, still with the stopper pin... 45 minutes later I saw blue smoke coming out of the radiator overflow tube. Shut down the motor as soon as I saw it... There is now fuel in my rad fluid. I checked the spark plug and the tip is brown and the rest black, I don't think I was running lean.

The headgasket is shot, could it be related to the powervalve being stuck wide open because of the pin? Would something like this happens if the head bolt were not properly torqued? Is it safe if I get the head milled, new headgasket and remove the damned pin?.

Thanks!

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I'd remove the pin but I doubt that is your issue. Did you retourque everything after the first few heat cycles to make sure nothing was loose? I'd say either loose head bolts or a warped head is most likely your issue. Take the head off and set it on a flat surface such as a piece of glass. Take a feeler gauge and see if you can get it between the head and glass anywhere. If it isn't to bad a lot of time you can simply sand it flat yourself. If not then it may need machines. Depending on how bad it looks, if that's even your problem, a new head is roughly 75 bucks or so. That may be the ticket to put your mind at ease. Did you run the bike before you replaced the top end? Any signs of coolant leaking or anything?

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Post up a pic. I would like to see it.

If you head has been over heated in the past the aluminum between the squish and the water channels becomes annealed. The aluminum becomes soft and cannot hold back the pressure of the combustion chamber. Take an awl and try to scratch the milled deck of the head. If the aluminum is soft you will be able to tell.

I had this problem with and 00 head I got with one of the project bikes I bought off of Craig's list.

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I'd remove the pin but I doubt that is your issue. Did you retourque everything after the first few heat cycles to make sure nothing was loose? I'd say either loose head bolts or a warped head is most likely your issue. Take the head off and set it on a flat surface such as a piece of glass. Take a feeler gauge and see if you can get it between the head and glass anywhere. If it isn't to bad a lot of time you can simply sand it flat yourself. If not then it may need machines. Depending on how bad it looks, if that's even your problem, a new head is roughly 75 bucks or so. That may be the ticket to put your mind at ease. Did you run the bike before you replaced the top end? Any signs of coolant leaking or anything?

Haaa totally forgot to retorque everything... I feel ashamed now lol. As for the warped head, well it was working fine before the rebuilt so I guess it's not that bad. Either way I will get the head milled before getting it back together. I got a friend who can machine it for free.

I'll try to post pic later today or tomorrow.

Thank you guys!

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Post up a pic. I would like to see it.

If you head has been over heated in the past the aluminum between the squish and the water channels becomes annealed. The aluminum becomes soft and cannot hold back the pressure of the combustion chamber. Take an awl and try to scratch the milled deck of the head. If the aluminum is soft you will be able to tell.

I had this problem with and 00 head I got with one of the project bikes I bought off of Craig's list.

I'll try, thank you for the tips!

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It may have already been warped previously but at this point it's hard to tell. Check it first before having it milled because it may still be flat. Who knows. Watch how much you take off because you can/will change the squish and compression of the engine. If your friend isn't familiar with 2 strokes you could have even worse problems. If its still flat out a new head gasket on and see what she does. Make sure to torque everything to spec and then retourque after a heat cycle or two.

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As for the milling, my friend is a die hard 2 strokes lover and a machiniste, he know what do to the get the same compression and squish as stock. I would like to try it with just a new headgasket but I don't know if I want to take the risk of to eventually have to buy a third gasket and reinstall everytthing. I wanna ride that thing lol

Also, I must admit that the break in was very brief.. I did a few relax laps, let it cool, and then ran the hell out of it for the rest of the day.... As far as I know, doing this can hurt piston ring, but could it also break a head gasket?

Thanks again! I appreciate all your answers.

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As far as your break in I see nothing wrong with that. You don't want to baby it to long. Everybody has a different way of doing it but for the most part take it easily for the first few minutes and then run it. Your problem is either from something previous that you don't know about or just simply not having the nuts torqued down to spec and they worked loose. Hopefully it's the later.

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You were right Curt, 2 of the 5 head bolt were loose, and I can see where the head gasket wasn't sealing properly. Luckily the piston and cylinder are still in good shape.

Now one last question, I already flushed the coolant, but is there something else I should do to clean the radiator and head from the mixted gas?

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