So I've just put last years engine back together to sell the bike. I have stripped, cleaned, and rebuilt the head with fresh valves (second hand but all measure better than the 'old' valves).

Started it up and all running fine, but as it got hot there was a sh*tload of white smoke. Now I used a little grease to hold the exhaust gaskets in and expected a bit of smoke from the build process.

After a while, it was still smoking, I shut it down as it was getting pretty hot standing still.

I've run it a couple of times since, and while the engine is in the normal heat range (from 70 - 85ish), it doesn't smoke. A bit of blue smoke from unburnt fuel as it appears a little rich while stationary, nothing you wouldn't expect. As the temp climbs though the white smoke comes back. I held the bike at 5 grand and watched it go from no smoke to quite a lot as the temp went north of 90 degrees to about 112.

What are the symptoms for leaky stem seals (they didn't leak a year ago when the head came off the engine)? Would it not smoke all the time regardless of temp, particularly on the over run?

Could it still be a bit of grease and crap in the header? (The header is off the engine that blew so probably copped a spray of oil down the pipe on number 3).

If it is leaky seals what can I look for to diagnose where? Will the plug be dirty? Header? Exhaust port?

I am tearing my hair out with this bl00dy thing and never want to see the inside of another 400 in my life.

Also note no smoke on start up, and it does not appear to be pressurising the cooling system, so not a blown or leaky head gasket. No evidence of water in the crank case. Coolant is muddy but nothing I wouldn't expect after it has sat for so long and has a bit of corrosion in it.

So run it again, just at idle this time to watch the radiator (which only has water - and the smoke looked too thick to be 'just' water).

I honestly can't tell if there are bubbles or not, as the fluid movement from the water pump is too quick and disturbs the surface too much.

I let the bike get to over 100 degrees (which resulted in boiling the fluid over) and got no smoke.

I really need to ride it and see what it does to be sure. Not much else I can test at a stand still.

just because it's not pressurising the coolant system dosn't mean that it isn't a blown head gasket.
The head gasket could have blown on an oil passage way, causing oil to leak into the cylinder.

It's possible that it could be valve stem seals, how come you didn't replace them when you had the valves out???


Personally i'd take it out for a good ride and then when you come back if it isn't smoking too badly i'd leave it. Burning a little oil won't hurt, if anything it'll help to lube the engine.


The honda civc type-R burns a tiny bit of oil from factory. Thats why you see alot of them blown up, people don't realise and don't top-up the oil...

That's just it, it shouldn't be valve stem seals, or a head gasket.

The gasket is new and the head/valves etc were all within tolerances.

Hard to take it out for a ride as it's a race bike. I'm still hopeful its just the crap from being rebuilt.

Pulled the motor apart and cylinders 3 and 4 were oily, and the bores very oily. So pretty clear it was leaky seals.

Pulled the valves out and found a very knackered seal in each cylinder, so I went through all the valves checking the seals and replacing any that were dodgy.

Put the engine back together (whole process took 5 hours or so) and started it holding the rpm at about 4500ish once warm, and of course it smoked once it got hot as it needed to burn off all the crap already in the cylinder. Still there seemed to be more than I was expecting. I shut it down as it got to 100 degrees and let it cool.

I came back and went through the process again once it had cooled to 85. A little smoke but not really.

So I left it a good 30-40 minutes and did it again, running it from 70 degrees to 100 degrees holding it at around 4000 rpm (which made it smoke previously) and got no smoke.

Here is hoping it is fixed.

Fingers crossed mate

Mate youve had some tuff luck-lets hope thats sorted it.

Can you reuse a new headgasket that has been tightened down? (Also can you reuse a headgasket that has been on an engine for an unknown amount of time?)
They are £60 to replace according to GF, so I wouldn't want to change one, then have further problems aside from what I have fixed/replaced already, resulting in another £60 headgasket.....

Thanks
From Adrian

BIke is sorted. Took it out to an industrial area and gave it a smashing.

It's a tad rich at the moment so you get a bit of unburnt fuel at gearchanges etc but NO SMOKE.

The engine with the flywheel, lightened crank, rvf pistons and stock 29 head n carbs feels almost as strong as the ported 23 head and flatties. Fack me.

Correct me if I am wrong but.......

As for re-using the headgasket, don't as a general guide. Its not so much the metal itself, as the coating on the metal that forms the seal. The coating is the black sh*t that you have to clean off everything before refitting a new gasket. Yes the metal does form a mechanical seal, but it's the coating that is vital and forms the bond.

Mine had been torqued down, the bike run for maybe 10-15 minutes total, then the head removed. There was no damage to the coating so in my mind was a relatively safe bet to reuse. There are some coatings you can get that you can spray onto gaskets to re-use. But buggered if I can remember what they are. The engineer who built my RS250 years ago used a spray on copper sealer instead of using ANY gasket on the cylinder head or base.