1991 cr125 Head Gasket

Hi Guys,

So basically I am a fool :thumbsup:. I assumed after buying my bike that the guy would have had some coolant in the rad. Big mistake. Because of my own stupidity in not checking it over heated and blew the head gasket (the one closest to the spark plug). Basically I was wondering what I need to check as I plan to replace the gasket but need to know what else could be wrong as a result of it going on me.

Are there any things that I should check as a matter of course and what tips can you give me for making sure there is no further damage as a result of the gasket letting go. I have not had to replace one before so anything you can think of would be helpful. Thanks.

Thanks for any advice given.

piston/cylinder come to mind pretty quickly. a full over heat could have coused some big internal damage.

and you know, them powerbands strech a tne if you over heat your motor. lol

i hop that everything in the end will be fine in your motor and the only thing what would need replacing is the head gasket.

How long/hard did you run it before it died?

It wasnt all that long at all and not very hard as I was just warming it up. I had had a quick 10 minute run out on it and then took a rest. The next time out I had done 2 and a half laps when I heard a high pitched noise from the engine. I am pretty sure it was just whistling due to the hole in the gasket. I pulled over immediately and saw either smoke or steam coming from the top of the engine. I am unsure as to whether there was in fact water there as it may have come out as steam if there was a little left in it. Needless to say I didnt fire it up again but when I was turning the kick start I could see oil and water (i think as I had topped it up a little to see) coming from the join between the head and the cylinder.

So what do I need to do? Remove the top part of the head and scrape the old gasket off and fit the new gasket or is there more to it? Are there any specific things I should check on?

Thanks for the replies.

Edited by rchippex

Well it depends on how hot it got. If you are lucky, then yeah a new gasket (and some coolant :thumbsup:) will be all you need. If you aren't lucky, then you may have messed up your cylinder and/or piston and/or head. I'd pull off the head and look at the piston and cylinder walls. See if they look ok. Pump the piston up and down and see if anything looks wrong. If nothing is obviously bad, throw on a new gasket and see if it seals (make sure you didn't warp the head). 10 minutes is a pretty long ride with no coolant... But maybe there was some down around the cylinder? Have you checked? If there is/was you might be ok. Good thing your gasket blew and made noise and you knew enough to stop riding asap! :thumbsup: Keep us posted.

Well I took the poor girl apart yesterday and had a look at the damage. Luckily it was minimal. The gasket had a decent gap in it confirming what I knew to be the problem. There was still some coolant in the chambers around the cylinder so I think this saved me from some more intense damage.

I checked the cylinder and luckily there were no signs of a worn piston or piston ring. The movement of the piston was fine and there was no scoring or signs if the plating coming free. I think I was very lucky to come away with minor damage. Fitted the new gasket and all seems well now. A lot more compression than before and runs better too.

Thanks to everyone for the replies.

Well sadly things are not as rosy as I had thought. After fitting new gasket and everthing seeming fine I took the bike out for a run and found that the water was still leaking.

Off came the head again and this time I noticed one of the studs was raised by around 1mm. This had caused the gasket to become pushed up around the stud. We tried to sink the stud back down but it would not budge. Upon looking at the underside of the cylinder head we found that one of the bolt holes for the stud to go through had been countersunk to get around the problem of the raised stud. I am guessing the previous owner couldnt be assed to sort the stud out and so created a workaround by countersinking to accomodate the shoulder of the stud that was raised.

So basically what should I do? We cannot get the stud to move and after replacing the gasket we found that we still had a leak from the same place at the front of the cylinder head and as well as that there was a water and air leak from two of the nuts which retain the cylinder head. Is this a sign of the nuts and/or studs being worn?

Literally any ideas are welcome.

Sounds like the cylinder/head may have overheated too much and become warped either when you rode it or previously. Also might be why the guy didn't have a lot of coolant in the bike, it all leaked out. Leaks coming from the nut area would indicate to me that the gasket is not sealing all the way.

I'm not an expert, but I wonder if you could get around this by using a slightly thicker head gasket? Otherwise you may have to take it to someone and have them check for warpage, and then possibly mill the head/cylinder to be flush again...

Are you using a torque wrench to properly tighten down the nuts?

Sadly I dont have a torque wrench but I didnt think it would make all that much difference. I thought about a slightly thicker gasket but wouldnt that change the compression? We did check the cyclinder head for warping with a straight edge and didnt see any signs of it.

I think I am going to take it into to a shop and have them look at it now just so I know for sure that it is right when it is done.

Thanks for the reply.

you can pick up a decent tourque wrench at sears for 24.99,(the old kind that just tells you the tourque, not the clicking ones) and ya, it can make a pretty big difference.

Do they have Sears in England?

lol whoops didn't notice that,theyve got ebay though see ifyou can find a cheap one there.

I've leveled heads with glass and sandpaper. Use 800 and 1000 grit and it'll do just fine.

Obviously a machine shop could do better. Hell, with how easy it is to put a head gasket on a 2 stroke I'd try just replacing the gasket first. If it still leaks then have the head and deck leveled and you'll be fine.

Should be an easy job. Just keep a good eye on it afterwards regardless of which direction you go.

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