The more I read your first post... ' Jet of steam coming from the valve breather'... The more convinced I am that the crankcase is building up pressure.
We had a 40k miles VW that had a blocked crankcase breather filter, if we removed the oil filler cap after a minute of engine running, lots of gas would explode from the filler opening. We cleaned the crankcase breather filter in petrol and that cured it. The VW sends all the crankcase gasses into the inlet manifold, so that the engine burns them.
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When I ran it last time I unscrewed the engine oil dipstick slowly until off, no pressure felt against the cap & no steam just oil getting chucked out from the turning gears. I'll block the breathers like you mentioned earlier the next time I try running it.
if water/coolant is being emmited as steam from the valve cover breather then you must have water/coolant migrating fom the head gasket somewhere..... is the barrel/cylinder damaged[as it is the only original top end part that is common to the problem on both occasions] on the mating surface or not flat somewhere along its face that mates against the head.
The barrel all looked good before assembly, with no sign of damage to the previous head gasket. Probably have to try another barrel next.
When Petrol burns it creates water... Hydro-carbon... HCO + O2 = H2O + CO2. So maybe some Combustion gasses are getting into the valve chest, either through the valve guides or past the piston rings. The crankcase should be connected to the valve chest via the oil drainage hole.
Does the exhaust also emit steam..
Can you block all the breathers, to see if the crankcase is building up pressure?
Best of luck..
No steam from exhaust, I'll have a go blocking the breathers on the weekend. Thanks
I thought the crankcases were machined larger to accept the 300 aeffe cylinder on a Future 4rt ..
I never noticed but most likely crankcases have been machined for the 300 big bore kit. The S3 barrel & piston were probably added by one of the previous owners as Wiggy's bike would have had Future parts, the rest of the top end I removed is Aeffe.
I haven't checked but most likely minimal as I don't want to risk damaging the replaced top end - which is on loan! Surely it could only be coolant due to the constant uninterrupted flow of steam? before the top end replacement was put on it had been ridden for a 3-4 hours with the same problem & the coolant loss was about 30ml.
Hi, My 2008 Future 4rt 300 (Wiggys old bike) once warmed up starts to release an uninterrupted (even with revs) & continuous jet of steam from the top valve cover breather hose (a drip of water forms approx every 10 seconds from the condensate forming in the hose). First thought it was head gasket so replaced this, no luck, so I then swapped a complete top end from a standard 250 working bike (apart from leaving on the aftermarket S3 barrel & piston which all looked fine) & ran it twice for about 25 minutes (not ridden just on tick-over with a few revs of the throttle) & both times it boiled up within 3 minutes, fan kicks in as normal, engine sounds normal, no steam from bottom crankcase breather or radiator, no white smoke from exhaust, water pump impeller fine & both engine & transmission oils still perfect with no sign of water & oil emulsifying.
With the standard 250 valve head now fitted the only difference with this Future bike to a standard one is a small brass decompression valve (reducers engine brake) fitted to crankcase just below barrel (probably similar to what Honda fitted as standard from 2014 onward).
A long-shot but has anyone had a similar issue or may know the cause? Thanks in advance.
4rt steaming like a kettle
in Montesa
Posted
When I ran it last time I unscrewed the engine oil dipstick slowly until off, no pressure felt against the cap & no steam just oil getting chucked out from the turning gears. I'll block the breathers like you mentioned earlier the next time I try running it.