I have a bit of a leak happening around my head gaskets. Got the engine second hand off a guy who had 'just done the top end' and he has used a gasket seal on it. First track day out it leaked a bit (pink coolant and pink leak) but since then it seems to have stopped leaking a visible amount.

Is it possible that it leaked first time out then somehow sealed itself though prolonged heat of a track day? Bit perplexed really.

How common are these leaks and what are the main dangers?

Also looking to ditch the stock coolant overflow in favour of an HRC style one. I assume that the radiator doesn't really require a backup coolant supply so the bottle is used more as an overflow and breather?

Instant gasket/sealant should never be used on an NSR250 head. No exceptions. Whoever "recently did the top-end" like that is a muppet!

They probably re-used the circlips too, with that kind of integrity.
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Andy.
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I know! I couldn't believe it when I saw it.

If you have a leak around the gaskets you must stop riding the bike . The pressure from the cylinder will push into the radiator and force out the coolant , you will damage your pistons as your bike will overheat . You will get a false reading on the temp gauge as there will be no coolant for the sensor to read and you think the bike is running cool while it is over heating . Strip the heads and barrels , check both sides to make sure they are perfectly flat on plate glass . If not , rub them down . Use blue marker to highlight any problem areas . Refit and look for bubbles in the radiator while the bike is running , bubbles are bad .
About the sealant , some swear by it while others swear about it . Use some grease on the base gaskets so that they don't stick as much to the casings .

Neal wrote:Strip the heads and barrels , check both sides to make sure they are perfectly flat on plate glass . If not , rub them down . Use blue marker to highlight any problem areas . Refit and look for bubbles in the radiator while the bike is running , bubbles are bad .
About the sealant , some swear by it while others swear about it . Use some grease on the base gaskets so that they don't stick as much to the casings .

Is it necessary to strip the barrels as well, or can the head gaskets alone be done? Or are you also suggesting I take everything off and check (and rebuild) it all while I am there?

I think I will fit a rear head to the front cylinder if I have it in bits. Can anyone tell me if an R rear head will fit on an SE barrel? Will squish be affected?

Cheers

i recently fit a rear to the front on my SE and it runs really well with the few other simple mods i did. Your problem will be finding a rear and dont forget the hose and plug you will also need.

Strip the head off and check it , strip the barrel off and check it , measure the ring gap (max 0.8mm ? ) And decide about changing pistons after that . Sort the leak out first before you damage new pistons bro .

andyo wrote:i recently fit a rear to the front on my SE and it runs really well with the few other simple mods i did. Your problem will be finding a rear and dont forget the hose and plug you will also need.

Was this an SE rear head or an R rear head? I understand there is a difference between the two?

I will check the head is repaired before changing the pistons. Good idea.

I can't remember the exact difference between the two but you can use either one on a stock bike . As allways , check the squish before you start it . You can still use the stock br ecm plug with the rear head swap - i never had a problem with doing it .

Neal wrote:I can't remember the exact difference between the two but you can use either one on a stock bike . As allways , check the squish before you start it . You can still use the stock br ecm plug with the rear head swap - i never had a problem with doing it .

Ok that's cool. Could you point me towards a how-to on measuring squish accurately? There isn't much that I could see in the top end rebuild section on the site. Don't want to get it wrong.

i used an SE head when doing mine and didnt check squish although obviously better if you can.

Everyone has there prefered method , the way I use is make a + sign from the solder . Place it on top of the piston so that the straight part is over the gudgeon pin from edge to edge of the barrel .refit head and gasket , torque head down . Turn kickstart very slowly untill the piston squashes the solder once . Remove head and measure the tips of the solder , 1mm- 1.2mm is ok .