Hydro Lock?

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PaulGreen
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Hydro Lock?

#1 Post by PaulGreen » Sun Dec 09, 2018 3:08 pm

Hi,

This evening I got my carbs set up properly and fitted to the bike. I put some fresh fuel in with some 2T oil at 40:1 just in case of auto lube probs and kicked it over.
It started 2nd kick but only very, very briefly before locking.
I took the plugs out and everything ran freely again, and it spewed out some fluid from the upper left plug-hole - it looked more 2 stroke than fuel but not certain. I turned it over with no plugs several times then flashed it up again.
Exactly the same thing happened.

The bikes been stood untouched for several years.

I'm coming towards the end of a veeeeerrrrry lengthy rebuild - at least I thought I was

What's the verdict?
Engine out? Again?
Is there some other way of checking things out?

Your, depressingly,
Paul.
There was a lot of fuel/oil

PaulGreen
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Re: Hydro Lock?

#2 Post by PaulGreen » Sun Dec 09, 2018 4:37 pm

A bit if rummaging around on here suggests that maybe a leaky check valve on the oil pump?

Looks like the rear head and barrels will gave yo come off?
If I remember correctly I think I can do this with the engine left on the bike.

Cheers,
Paul.

MK
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Re: Hydro Lock?

#3 Post by MK » Mon Dec 10, 2018 9:50 am

After that description the first thing I'd check is the TDC of all cylinders.
Unscrew the plug on the generator side and mark each TDC with a felt pen.
Opposite cylinders TDC's must match within a few mm's (theory says 100%, but the coupling via the gears imposes up to some 6 deg offset).
If the crank twisted, one cylinder will be waaaaaay off.
Bye
Martin

PaulGreen
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Re: Hydro Lock?

#4 Post by PaulGreen » Mon Dec 10, 2018 10:30 am

Thanks for that, however I dived in this morning and took the upper head and barrels off.
The crankcase is full to the brim of 2 stroke so I guess it's the traditional check valve failure.
I'll drop the barrels back on and do as you suggest, though I wouldn't expect the crank to be twisted - the engine didn't really start up, it just fired

Thanks,
Paul.

MK
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Re: Hydro Lock?

#5 Post by MK » Mon Dec 10, 2018 11:18 am

It doesn't require even one full rotation to twist a crank.
It's enough to pass the affected cylinders TDC once if the combustion chamber is filled with any fluid.

And yes, if it's freshly twisted it'll run poorly afterwards.
Bye
Martin

silverstrom
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Re: Hydro Lock?

#6 Post by silverstrom » Mon Dec 10, 2018 4:25 pm

PaulGreen wrote: Mon Dec 10, 2018 10:30 am I wouldn't expect the crank to be twisted - the engine didn't really start up, it just fired

Thanks,
Paul.

You can bend rods with a hydraulic lock using the kick start lever. Don't underestimate the forces and gearing involved.

This is a lesson for everyone: if your bike has been sitting a while always turn the engine over slowly a few times with the kick start lever. Gently, until you're certain the engine isn't full of oil and gas. Having had check valve problems myself I employ this method often. Better safe than sorry. If the engine is full of liquid and you jump on the kick start lever you could end up with a big headache.

PaulGreen
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Re: Hydro Lock?

#7 Post by PaulGreen » Mon Dec 10, 2018 5:44 pm

I spent an hour on the previous day trying to start it, it turned on the Kickstarter easily. Maybe there wasn't enough oil passed up through the rings at that point?
Anyway, I think I've got away with it, I've drained as much oil as I can out of the crank cases and dropped the barrels back on. I've checked TDC as MK suggested and all seems ok.
For peace of mind I'll drop the bottom head off and check properly tomorrow.
Barrels, piston and heads all seem ok too.

Without splitting the cases it's going to be impossible to get all of the oil out, but I would think that would be ok? Just smokey for the initial start?

I've taken the oil pump and check valves off, soaked them in petrol and gently poked inside with a very thin Allen key to free them off. It's now sat with a head of oil in a drip tray to see if they're still passing. I'll still fit the extra valves though.

Thanks all for the input,
Paul.

silverstrom
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Re: Hydro Lock?

#8 Post by silverstrom » Mon Dec 10, 2018 6:28 pm

I suppose what happens is the oil in the crank well gets forced through the transfer ports and into the cylinder. You can't compress it and you lock up. Glad you were lucky and found no problems.

I've had loads of oil in my engine due to bypassing check valves. Once you get it started and running well it will smoke like it's on fire. Used to take me 100 km of riding to get rid of the oil.

Did you have oil in the upper pipes? And the lower pipes? All good?

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Re: Hydro Lock?

#9 Post by PaulGreen » Tue Dec 11, 2018 7:31 am

This morning I've taken the lower head off and checked TDC on all 4 pistons - all appears ok so far. There was a tiny discrepancy between the height of both upper TDCs and both lower TDCs (if that makes sense?). ie TDC on both uppers was a fraction lower than both TDCs on both lower cylinders, however I'm expecting that to level out when i get all 4 barrels properly torqued down. Something to check out on the rebuild. The TDC on the opposites happened at the same point when I turned the engine over via the generator.

I've dropped the front exhausts and there's no sign of any oil in there.

I left the oil pump, still connected to the tank, but with the oil feed lines disconnected, in a drip tray over night and......
Two of the check valves are passing, only a couple of drops each but obviously over time they all add up.
So i'll get hold of some check valves and put it back together. Hopefully should be straight forward from here!

Paul.

silverstrom
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Re: Hydro Lock?

#10 Post by silverstrom » Tue Dec 11, 2018 5:24 pm

PaulGreen wrote: Tue Dec 11, 2018 7:31 am So i'll get hold of some check valves and put it back together. Hopefully should be straight forward from here!

Paul.
That will solve your problem Paul. Since adding the new valves I haven't had one drop bypass, even after a year sitting in the garage not being used.

I'm now working on sourcing barbed fittings to replace the stock check valves. M6 thread with the barbed end being 3.5 mm o.d and 2.0 mm i.d. On the next build I'd like to use the fittings with the inline valves and eliminate the stock check valves.

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