Topic: How did I blow a head gasket!? And I amnsure this ain't water vapor...

[samm_j2]

Pewe,  when you say pistons look ok compression wise does that mean the compression should be higher or compression is ok at 150?

I would imagine valve guides seals sit as they should, I will take a picture,.

I am not running the airbox so the breather from the rocker cover just goes to back of bike. This is the breather this is smoking.

The breather from the back of the case is going to the oil tank.

I am unaware if there was another vent from/to airbox

[PeWe]

The piston dome look OK, compression should be much higher.
150PSI is way too low if your compression tester is OK.
150PSI can be a value on a stock CB750 K0-K6.

Did you reuse the MLS headgasket?
I have reused MLS before which worked, another assembly not with lower compression, only 170ish instead of expected 195-200PSI. New gasket and got 195-197.5 PSI.

[samm_j2]

Pewe thanks,

Ok, got case split and crank out to look at bearings as psi got down to 20 for oil pressure. They look ok? I am not entirely sure what to look for as far as wear except gouges?

[PeWe]

Shells look OK. The greyish surface still cover all of the bearing.
Must feel good to know.

If engine should have been running out of oil preesure, not that nice.

Be careful when assemble not making a mistake. I should use new o-ring between cases at front, 18x3.
Inspect for other things.

Is the cylinder taken off too?
If yes, bores without scratches? If rings have scratched. Ring end gaps another detail.
Valves are closed completely? Bent leaking valves if cam has been mounted wrong?

[bryanj]

Shells look ok but way too much sealant on there, what sort did you use

[PeWe]

Shells look ok but way too much sealant on there, what sort did you use

Yes, way too much sealant.
It might have entered the oil flow up to head, blocked one oil orifice and cam with rockers shot as this case began.

It look like Hondabond. It should be a very thin layer, almost transparent.
Only where cases mate.
There are surfaces that does not mate which is obvious when looking close.
The towers for case bolts around crank need just a little, not into oil flow holes.

[samm_j2]

I used honda bond, does it not go on the edges of the seals?

When I put it back together I won't use as much.

If shells look ok then any other ideas on why I was getting 20psi oil pressure when hot?

And any thoughts on valve breather blowing fumes when warm???

About to take springs off head and check for valve play...

[maxheadflow]

"I also only have 2 orings between the cylinders and head, each side of cam chain tensioner. One of them was smashed into a triangle shape..."

There is you problem on the breather issue.  Those O rings should not have been smashed. With the head gasket you are using they probably shouldn't have been used. 

Only 20 psi at 3000 rpm or idle?

[samm_j2]

Maxheadflow, so when I reassemble should I not use those orings with an MLS head gasket?

And no, 20psi and 5000rpm 30psi at 7000rpm 

[maxheadflow]

Maxheadflow, so when I reassemble should I not use those orings with an MLS head gasket?

And no, 20psi and 5000rpm 30psi at 7000rpm 

Probably not.  While others have used MLS gaskets on Hondas, I've not.  I have used then on other bikes. On them the O ring not used.   

As a general rule, if after assembly and removal, the O ring should not be damaged.  When damaged it is strong indicator that it is being crushed and permanently deformed and that it could be keeping sealing surfaces from sealing. 

Heck if that O ring is on the oil feed passage it could be part of the reason for low oil pressure.

BTW. You may want to check the head and cylinder for flatness.

Can you post a pic on how the O rings were positioned?

[samm_j2]

Maxheadflow, here is a photo or two, not the best. Ill double check flatness...

[maxheadflow]

What's the head gasket look like?  Does it have holes for the O rings?

What thickness head gasket?

[samm_j2]

Maxhead flow,

Yes, gasket has large enough holes for oring.

Also did not notice and valve guide looseness or wear. If I plug the valve guide seal and pull valve stem I get suction which I think means the valve guide seal was doing its job...

I spoke with Ken at cycle x and he wished I would have shipped him the motor before I tore it apart...
Ken also thought 150psi sounded great. But still open as to if it is actually low. He said it depends on cam and I have cx2...

So again I am left here wondering what the hell I did wrong when assembling this. The only thing that seems out of norm are these two orings and the triangular one in particular...

Head gasket is roughly .75mm or .030 inches

[maxheadflow]

Looking at the squish of the O rings, I don't think they were the issue.  I'd be concerned about one that started to squish inward tho. The one might have blocked off the passage to the cams. Typically you really only want to squish O rings about 0.005" to 0.015 inch but the locations where the O rings were placed were large enough to allow them to move someplace. If the groove is small they can hold things a part..

I'm kind of at a loss as to what the issue is. The only wild assed guess that I can figure out would be that the metering orifices in the heads are missing.  This could cause excessive squirting of the cam oilers which would mist into the cam cover causing what looks like smoke and the low oil pressure. You might have seen oil dribbling out of an exhaust rocker cover.

That's all I got. Hopefully Ken can help.

[samm_j2]

Thanks maxheadflow, I appreciate it!

The oil meter jets that go under the cam are there, free and clear. HOWEVER, the orings that go on the other end with a blocked passage are not there!? How important are those little bastards!?

I wonder if that was letting oil....

That would explain low pressure .

The smoke on start up and all the carbon build up in the chambers and on pistons is still puzzling. As is the smoking breather...

On more of a bummer not I checked ring gap, as someone above was curious.

Top ring was .020 on all
Second ring was .031 on all

Which I think is fine. But I snapped the second ring on piston 1 and 2! I was being super gentle!! Grrr...

Now new rings and a hone to the list...

Guess I am starting all over with this one! Haha well almost!

[PeWe]

Too thick o-ring?
I use stock size viton, 11x2.5mm on those 2.  No other o-rings.
Worked fine on various CB750 bores with MLS.

If cylinder is decked, the machined holes are lower and  thinner o-ring might be needed.

[Don R]

 I have an early sandcast head that didn't have the end o ring on the cam towers. I was told it is #85 or older.

[maxheadflow]

Thanks maxheadflow, I appreciate it!

The oil meter jets that go under the cam are there, free and clear. HOWEVER, the orings that go on the other end with a blocked passage are not there!? How important are those little bastards!?

I wonder if that was letting oil....

That would explain low pressure .

The smoke on start up and all the carbon build up in the chambers and on pistons is still puzzling. As is the smoking breather...

On more of a bummer not I checked ring gap, as someone above was curious.

Top ring was .020 on all
Second ring was .031 on all

Which I think is fine. But I snapped the second ring on piston 1 and 2! I was being super gentle!! Grrr...

Now new rings and a hone to the list...

Guess I am starting all over with this one! Haha well almost!

Plugged metering jets would not cause an issue, but bored out ones could. Possibly the wrong ones? I was thinking too much oil is making it through the jets causing the oil orifices in the cam towers to spray not dribble..

Missing O rings on the ends could allow oil to leak out. Might be part of the issue but I really don't know on that one.

Smoke on start up is typically caused by leaky valve seals but if the motor was filling up from a leaky check valve in the pump, it might cause the issue.

The ring gap is of concern.  First off, I'd expect the gaps to be about the same.  Spec on new stock pistons/bore is 0.008 to 0.016" and 0.028 as worn out. I would imagine an 836 kit might have looser tolerances but 0.031 is excessive.

This makes me question your leak test.  If you are using the same hose adapter as the compression tester, are you removing the valve in the end of the adapter when doing a leak test?   From what I see you should have some leakage.

[samm_j2]

I did not grind down the end rings at all. I remember looking at the spec sheet that came with the pistons and everything was ok.

The second ring gap does seem to be too big... honestly they both seem too big. I am trying to the a copy of the paper that cam with the piston. If anyone knows where to find it let me know

[samm_j2]

Max head flow, I used different hoses for compression and leak down test. There was no schrader valve on the leak down test. If this is what you are referring to?

Since everything is appart I am going to get some crank work done. Ken suggesting balancing the crank and alternator. He suggested lightening the alternator instead of lightening the crank. I was only going to do one or the other but not both. If I get crank work can I re use the shell bearings as they seem to be in good shape?

Appreciate everyone's input and help with this 

[PeWe]

Lightened alternator work fine. My K6 has a much lighter one with functional  charging.

[maxheadflow]

Max head flow, I used different hoses for compression and leak down test. There was no schrader valve on the leak down test. If this is what you are referring to?

Yeah, that's what I was referring to..

[Don R]

 My late friend that had a drag bike said to lighten the rotor, he twisted the end off a crank once with a heavy one. His 1124 stroker motor ran no balancer, I put one on a lathe and just used the starter part so I don't need to roller start it. (someday)

[seanbarney41]

Those missing o-rings are the issue.  I have seen lunched cam lobes and bearings from long term running like that.  Cam getting overheated would possibly cause excess oil vapor and/or smoke out the breather.

[ekpent]

 I remember another member who did not have those and had a problem and I think he posted a Hack-a Week or whatever that internet 'mechanics' name is and he left them out of the build he was doing for show. Ooops. Supposedly someone pointed it out online and he corrected it later.