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FlyingDutchMan
7th January 2006, 19:27
My bike recently threw a wobbly + threw 1/2 its oil on the road + my rear tyre, and the engine decided to over heat. Found the oil leak was caused by a pinced o-ring seal, so I replaced that, the oil filter and the oil. Took the entire cooling system off the bike. Checked valve clearances while it was off - and they're all within the required limits. Cleaned all coolingbits, and removed a blockage. Rettached it all. Filled with water + noticed it leaked from every single hose connection and o-ring seal. Went out and got some radiator sealant and used a little of that. Flushed out the system and filled with 1/4 gycol and 3/4 water. Reassembled everything else + went for a burn. Worked damn well until I redlined and then cruised at 100km/h. The temp got near the redline and then the bike started running like it was on 3 cylinders. Got most the way back home and pushed it for the last little bit. Got home and checked oil - thats ok. Started it and it ran pretty smoothly - realised that the 3 cylinder running would have been due to vapour lock. Easy fix. Sweet. Checked water level (this is a bitch - the filler cap is underneath the petrol tank - honda can be stupid at times!). There was next to none. Topped it up & idled it, filling it untill all the air bubbles were gone. Except the air ubbles kept coming, but the water level didn't go down (the temp was nowhere near boiling). As far as I tell this must be a blown head gaskett and the combustion gases are escaping into the water. They can't go into the oil as water encircles every cylinder all the way round - oil is externally plumbed to the head and drips down the gear train (on the other side of the water jacket from the cylinders). Would I be correct with the blown head gaskett diagonsis?

Fun-o-fun, now I have get either get a new engine (~$600), or a new head gasket ($~honda rip-off) + hours and hours of work on my behalf. What do you recon is the best option?

Patch
7th January 2006, 20:18
Hi mate,

Generally you will get the oil mixing with the water if the head gasket has perished - creamy substance on radiator cap and/or on oil cap, and sometimes dipstick depending on how bad it is.
The only real way to tell is to compression test each cylinder and go from the test results - normally range between 130 - 150, all cylinders should be within 10% of each other or so.

If test results are ok and everything else is fine, must just be an airlock. Follow the waterflow from the radiator filler point down the system and try to see the highest point the water reaches in the motor - possible airlock point.

On my car and 4x4 they have a bolt or cap that you undo or remove, fill the system with water until it runs out bolt or cap. helps to reduce airlocks, so worth looking for. If their isn't one, idle motor with cap off, squeeze radiator hoses, wait for thermostat to open, squeeze hoses wait for air to stop bubbling.

Hope this helps in some small way.
Cheers.

Mental Trousers
7th January 2006, 20:42
Pull the carbs off, take the plugs out, turn it over a few times. Anything come out the spark plug holes??

thealmightytaco
7th January 2006, 21:34
You can get purely water loss with a head gasket problem, wont necessarily cause oil/water mixing as well, depends on where it's failed. Sounds like a head gasket, high pressure gas bubbling through indeed. And it might last a little while longer but at some point it'll blow it well and truly, fill that cylinder with water and completely screw the entire thing as it tries in vain to compress water.

I'd say just do the head gasket, not sure how major that is for a bike. In a cage it's easier to just do the motor swap cause you've got the carbs and every other bloody thing above them, but they seem to be nicely beside the cylinders on most bikes (I think, prepared for slap down here). But from what little I've seen and played with on bikes, I'd be keen to do the gasket.

FlyingDutchMan
8th January 2006, 19:43
I'm pretty sure its the head gaskett, but I'll do a compression test to make 100% sure. And I think it will be incredibly unlikely that oil will be in the water - have a look the picture below:
http://www.motosoc.org.nz/mystuff/head.gif
Where you see the gears (cam gear train), is the only place that oil travels through the head gaskett (from head to sump).

I drained the water out of the bike before parking it up just to make sure that it wouldn't seep into the cylinder + cause me grief.

EDIT: I should add that Honda wasn't stoopid just once in the design of the bike - to remove the head, the cam shafts need to be removed first as the bolts holding it on are directly underneath them. :crazy: Should I mention they're 12 sided bolts too?

F5 Dave
9th January 2006, 16:24
Well they do seem to do some silly things, but we kept requesting smaller lighter high performance motorcycles & the designers probably threw up their hands & said, oh well, compromise service for features.

Yeah if it’s bubbling, & you are sure you have bleed away any airlock then you are pressurising it some how & the pump is the engine. The comp test won’t show it up. It would have to be such a big leak for you to notice & who is to say one cylinder seals better or worse anyway?
If you did a leak down test & the engine was warm then you’d have a better chance of seeing it. But even then. . .

So head gasket & check if head needs a plain. Might be Pirate gasket available, google & find out. You could buy a new engine, but then what other problems are you buying?

Just thinking if you cooked the engine a comp test would be a good idea to see that the engine is ok. Does it not have a resevoir? & if it gets that hot why didn't you stop & let it cool down?

FlyingDutchMan
9th January 2006, 20:24
Tried to get a cmpression tester today. Most where about $30-40, but did any have a 10mm thread on it? Nope. I'll be trying another place tomorrow, but I'm not too hopeful. On the brightside, I went into Honda today and it looks like the head gaskett will cost about $80. Less than the $300 I was expecting. But I won't buy that until I've got the head off & measured its flatness as well as the flatness of the engine block. Might have to get them skimmed (if possible) to make sure its nice and flat.

Sketchy_Racer
9th January 2006, 23:22
yes they are a pain in the arse... mine blew the head gasket, and you have to but a special long reach tool to get the head bolts off. They are a 8mm Dodecagon bolt. The Gasket cost me 100 bucks but im doing the valve seats as well (just a recut not replacing) but removing the valves ruins the valve stem seals, and with thema at $17.00 each, and there are 16 of the bastards its very expensive. and you can only skim off to the measure of standard specs because of the gear driven cams.

i have a complete manual for this bike, i can send you a link to use if you need it.

Cheers, Glenn

FlyingDutchMan
10th January 2006, 08:43
yes they are a pain in the arse... mine blew the head gasket, and you have to but a special long reach tool to get the head bolts off. They are a 8mm Dodecagon bolt. The Gasket cost me 100 bucks but im doing the valve seats as well (just a recut not replacing) but removing the valves ruins the valve stem seals, and with thema at $17.00 each, and there are 16 of the bastards its very expensive. and you can only skim off to the measure of standard specs because of the gear driven cams.

i have a complete manual for this bike, i can send you a link to use if you need it.

Cheers, Glenn

The 216MB PDF that I put together from JPGs? I have that one if you don't - good images too. This one: http://www.ravemasta.com/~crxorg/CBR250ServiceManual.pdf

Yeah I'm not too worried about doing the valve seats - its only worthwhile if the valves aren't sealing properly... otherwise thats just getting too carried away.

F5 Dave
10th January 2006, 09:19
Vesrah do aftermarket valve seals in packs. They might cover the CBR.