hey all,
ok ive spend $2000 on my MC21 and its now roadworthy and registered but now its got a new problem .
Alright heres the history of this problem:
The bike was running fine when i bought it, so i think ive done the damage myself while we were getting aquainted, anyway i recently noticed it started using coolant which i topped up and replaced the radiator cap and thought id solved the problem,
But now ive noticed the lower cylinder doesnt fire as well; it sort of has to clear its throat alot when i start it and has backfired once and the pressure of the exhaust gas coming out of the silencer is only like one third of that coming out of the upper cylinder pipe
So i went to the Honda shop and the guy said take the pipes off and see if its blocked, i did this and was surprised to find they werent, and in fact you can look straight thru the silencers (normal?) and the chambers sound like they have nothing in them either (explains the loudness of this bike).
What i did notice was that when i turned the engine over without the chambers on the coolant was coming out with each stroke of the cylinder

so, my questions are:
is this most probably the result of blown head gasket or something worse?
how hard is it to get into the engine and fix the problem (any special skills/tools needed?)?
is there danger in using the bike in this condition or leaving it sit in my garage for a month like this?
and it had to be a leak from the heads part of the engine doesnt it? not the crank?

ok thanks!
Tim

sounds like a head gasket. very easy to fix. get it sorted now, do NOT leave it sitting around too long.

Definitely sounds head gasket. Have you had the head off?

Stop turning the engine over!

Remove the drain screw on the lower barrel (little bolt on the forward face) and let the coolant out - dispose of properly!

You may have coolant in the crankcase, as it may have leaked past the rings. This is not good.

Personally, I'd remove the head and the barrel too, so you can check that the crankcase is water free.

When you remove the head from the barrel, have a close look at the gasket, and you'll probably be able to see where the coolant is leaking. Also have a really good look at the barrel, as it is possible (though unlikely) that the barrel is cracked. Haven't left it to freeze with just water in there have you?

When you rebuild, use new gaskets top and bottom, and torque it up correctly.

Let us know how you get on.
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hi,
thanks for the replies,
i opened up the cylinder heads this morning, and sure enough the lower (forward?) cylinder had about 20mL of greeny-grey oily coolant gunk in it, which i assume was screwing up the sparking and ignition.

anyway ive been looking on the net about replacing head gaskets and they say u need to scrape it off with a dedicated stanley knife, which is odd because all that was between my barrel and head was a thin sheet of metal with EXUP on it that came off by itself these are black with white exup on them but in some areas (closer to the inside of the head) the black paint is gone/blistered and there silver metal below is visible, is that a blown head gasket? the actual metal looks like it is still in good shape.

the barrels and heads look crack free and other than the gunk, everything looks to be really good. oh and the pistons are only single ring so i assume they came with the wiseco stickers which are on the wheels.

well im getting new gaskets on saturday, but if u guys could inform me of anything else i should order before then itd be good,

ok thanks a lot,
Tim

oh and the lower cylinder head was on a lot looser than the top head, is it possible it was just too loose , so that the coolant was able to flow through it?
thanks again,
tim

Hi Tim,

Yes that's correct for the top gasket. It's metal and definately needs replacing as it will have been crushed when put on originally, so you need a fresh one. The EXUP is not Yamaha related but means that the lettering should be next to the exhaust port and facing up!
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NSR300R - Why did i ever have a 250...

timnsr250se wrote:oh and the lower cylinder head was on a lot looser than the top head, is it possible it was just too loose , so that the coolant was able to flow through it?
thanks again,
tim

Strewth mate!!
Yes its possible the head was on "too loose". As both heads should be tight as per specified torque settings.Why were they loose? DO NOT just put new head gaskets on as you need new piston kits too.
Throw your single ring pistons in a skip as some t*** has fitted race ones that wont last very long. Although they might last long enough to take all the coating off the bores when they nip up.