Liquid cooled motors, discharging some fluid after a refill. Normal?

[Kenneth S (222)]

Thanks guys,
Yes that make a lot of sense, the head gasket is designed to hold combustion pressure in, not cooling system pressure out, so I will gradually increase the pressure as you suggest.

I haven't added here that after I had the same problem with the head BigK sent me, the welded one, I figured that eliminated the head as the problem, so when I had Greg Ball bore my cylinder and skim the top of it, I also had him skim the original head and put the original fittings back in it for me, so I am now using the original.

Yes Monty, I have a good collection now of blown head gaskets and others that were ruined each time I have had to pull the bloody thing apart, well over 10 times this season . I will never need any more of the other gaskets though as I have had to buy sets each time

One other variable which has occurred to me recently. The bike was in such bad shape when I got it, I decided to replace the hoses just so I knew they were OK. I did not buy a set made for the bike, at the time I couldn't find one and I have not since found one. I went to the local Pirtek shop and bought standard radiator hose. One of the reasons I want to run the clear hose test is to make sure that none of the hoses going around bends have closed off the flow.

And yes, it has crossed my mind I'd like to give Mr Hardo a bit of a hurry up

I'll keep you posted.

[evo550]

What bore size are you on ? I don't know alot about Honda oversizes, but generally Honda will do a genuine piston to about .5mm o/s then some aftermarket manufacturers continue up to about 2mm o/s maybe even bigger, those big pistons may require an aftermarket gasket to go with them and not the standard Honda gasket. Had this problem with an oversized fourstroke piston, blew 2 genuine headgaskets until I found out you could get oversized gaskets to suit.

[Kenneth S (222)]

What bore size are you on ? I don't know alot about Honda oversizes, but generally Honda will do a genuine piston to about .5mm o/s then some aftermarket manufacturers continue up to about 2mm o/s maybe even bigger, those big pistons may require an aftermarket gasket to go with them and not the standard Honda gasket. Had this problem with an oversized fourstroke piston, blew 2 genuine headgaskets until I found out you could get oversized gaskets to suit.

That makes sense as well. I'm on 67.44mm and the gasket measures 68.5mm. I did the flow test through the clear tubes and I am getting very good circulation of coolant on both sides. Being the softer clear plastic tubing the pressure in the system was more noticeable as the tubes began to balloon up until the coolant shot out the overflow. I also did the pressure test on the barrel and head intact as described above and there was no leak fully submerged under water until the pressure was high enough to leak through the head gasket.

I am stumped. 

I inspected the top of the barrel closely and even through I sent it away with the head to be skimmed and matched, there still seems to be faint pitting where the gaskets is supposed to seal. I am beginning to think that it wasn't skimmed enough and that could be it.

[GMC]

I also did the pressure test on the barrel and head intact as described above and there was no leak fully submerged under water until the pressure was high enough to leak through the head gasket.

Say What?
The normal running pressure of an engine would be more than your average compressor puts out.
It shouldn’t have leaked at all during your test.

[Kenneth S (222)]

I also did the pressure test on the barrel and head intact as described above and there was no leak fully submerged under water until the pressure was high enough to leak through the head gasket.

Say What?
The normal running pressure of an engine would be more than your average compressor puts out.
It shouldn’t have leaked at all during your test.

Geoff I pressurized the cooling system hoping it would show me a leak in the head or cylinder. I gradually increased the pressure until the head gasket leaked bubbles into the combustion chamber. Backwards so to speak.

[GMC]

I also did the pressure test on the barrel and head intact as described above and there was no leak fully submerged under water until the pressure was high enough to leak through the head gasket.

Say What?
The normal running pressure of an engine would be more than your average compressor puts out.
It shouldn’t have leaked at all during your test.

Geoff I pressurized the cooling system hoping it would show me a leak in the head or cylinder. I gradually increased the pressure until the head gasket leaked bubbles into the combustion chamber. Backwards so to speak.

Well that’s your problem then.
 The head gasket should have held more pressure than what you should have been able to give it.

So…
# Still has warped head or barrel.
# Head not tensioned correctly.
# Head bolts stretching
# Studs in head pulling through head
# Dodgy head gasket

[PEZBerq]

If you tested the cooling system at 6  - 7 bar as mentioned earlier in this thread then that is way more pressure than the normal operating pressure with 1.4 bar radiator cap. What pressure did the gasket start leaking?

[Montynut]

Kenneth indicated that the head gasket leaked into the combustion chamber. The normal pressure differential between the combustion chamber and cooling system is usually very high when the engine is running i.e. Compustion pressure less cooling system pressure which would be many many BAR of pressure.

The only question is that the gasket is designed to seal high pressure in the combustion chamber from getting into the cooling system not the other way round. Kenneth had high pressure in the cooling system. The head gasket may not hold pressure in that direction so to speak nearly as well as it does in its designed 'normal' pressure differential although given the test was at ambient temperature I would have thought that it should have held full air compressor pressure easly as GMC says.

GMC may be onto something regarding the head studs maybe they have been stretched beyound their working tension at some point meaning that they no longer do their job when tensioned up correctly. High temperature fasteners at work for example have a relatively short life of only two tension cycles before they are replaced.

That cylinder does not look like it has been skimmed at all.

[Kenneth S (222)]

If you tested the cooling system at 6  - 7 bar as mentioned earlier in this thread then that is way more pressure than the normal operating pressure with 1.4 bar radiator cap. What pressure did the gasket start leaking?

Its hard to say as I manually let in a little more pressure in stages, at a guess I think it was up around 5-6 Bar before it leaked.

I had the studs at the specified tension but they do look worn. I did notice though when I pulled it down, they did not seem as tight as they did when I put it together. That could be my imagination though.

[GMC]

I see what you guys are saying about the water jacket being meant for low pressure, but that is only as far as the hoses and radiator is concerned.
I stick rubber plugs in exhausts and pump them up to 50 Psi without problems so I don’t see why 2 flat surfaces (head & barrel) bolted firmly together can’t hold at least 100 Psi. The gasket sits firmly between these surfaces and cannot work as a one way valve.

I knew a guy with an old 202 that couldn’t keep the head screwed down tight. It had been cooked a few too many times and the head bolts kept pulling through the block. He had to helicoil all the head bolts in the end. That was a cast iron block but your barrel may have suffered some odd fatigue at some point.

A doctor once over dosed my son when he got milliliters and milligrams mixed up.
Are you sure you have the correct tension for the head bolts.
Do you use a torque wrench?
With so many different figures thrown around it is easy to get confused. Just look at this thread, some of us talk in Bar and others in Psi.

Bolts stretching under load isn’t that uncommon.
I think from memory KLX head bolts suffer from stretching, especially when big bore kits are fitted.

[GMC]

That cylinder does not look like it has been skimmed at all.

Just had another look at that picture and I reckon your could be right.

An easy check is to use some valve grinding paste on a thick sheet of glass.
Work the barrel around in a circular motion. It will change the texture of the surface, if the whole surface changes at once then it should be flat but if it only changes the texture in some spots and not others then it is not flat.

[mick25]

 as gmc said 
But If you dont have any valve grinding paste you could try a sheet of 1000grit or so wet and dry on a sheet off glass draging the barrell  back and forth to find any low points

[Lozza]

Can you post a pic of the gaskets. Said a long time ago the cylinder top sinking over the exhaust port is common. Has the head been machined much? As heads can flex from combustion pressures

[Kenneth S (222)]

I can post a pic of the latest gasket but I don't think it will show much. It was brand new and all I had done is start the bike in the pits at a race meet when the fluid started to come out the overflow, I didn't even get a chance to ride it this time. These gaskets self destruct as you take the head off because the soft waffle type sealing surface around the coolant ports sticks to the surfaces and tears apart when you take the head off.

Geoff maybe you have identified the cause. The more I think about it, the more the evidence is mounting up that supports your worn cylinder thread/tired stretched studs theory. When the cylinder was skimmed, the guy obviously took the studs out. When I received the cylinder back, the studs were loose and I had to adjust the height of them. I remember thinking how sloppy they felt in the thread, with no resistance at all. If you add to that how when I loosened the head nuts the other night that they felt unusually loose compared to how tight I had tightened them, the thread inside the cylinder could be on the way out. So even though I am doing all the right things, the old and tired studs combined with the sloppy loose thread inside the cylinder is not maintaining the tension. Another fact supporting this theory is when I received this bike, I noticed most of the bolts had been over tensioned and I had to replace most of the fasteners so chances are the past owner did not treat the head nuts correctly.

As a next step I will double check how flat the surfaces are first and provided they are flat as I suspect they will be, to eliminate this possibility of tired thread and studs creating the problem, perhaps I should helicoil the cylinder threads and replace all the studs. I have never had to use a helicoil but I am sure it can't be too hard to work out. Any tips on how I should go about it?

Before I do that though and waste more money on what might be a faulty cylinder or head, can someone recommend where I can send the cylinder & head to do a professional pressure test to rule out a mechanical fault with them?

[yamaico]

As a next step I will double check how flat the surfaces are first and provided they are flat as I suspect they will be, to eliminate this possibility of tired thread and studs creating the problem, perhaps I should helicoil the cylinder threads and replace all the studs. I have never had to use a helicoil but I am sure it can't be too hard to work out. Any tips on how I should go about it?

Helicoils are a piece of cake, however it is really important that they are installed exactly perpendicular to the head surface. A whole new set of problems will arise if they are not...