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

[samm_j2]

So looks like I need more help. Bike WAS happy so I decided to drive it around for once.

Recap on history, 78 cb750f. I rebuilt the whole thing and replaced everything in the motor. Put an 836 kit in it with weisco pistons, kibblewhite high rev springs, and have had umm... a few different cams in it, currently cx2. Bike MAYBE has 1000 miles on, rarely sees high sustained rpm. Before I rebuilt the bike it was literally in a box.

Anyways the breather that comes off the valve cover blows out fumes, I have read that everyone thinks that its just water vapor and go ride the bike. So I put 30 miles on it in one run, talking about 45 min averaging 7000 rpm. The breather was still smoking when I got home. I should also note it does not smoke in start up, it only starts smoking when warm. (Another strange note, it gets some some out the exhaust when first starting up but goes away when warm... )

To finish everything off I now have oil between the cylinders and the head... did I blow a head gasket!? How does this happen? I did not think that I had high compression as the f head has a larger combustion chamber.

I will try to attach a vid.

https://photos.app.goo.gl/azyxUwg2T4gNvY8DA

As always, thanks!

[samm_j2]

I just did a compression test, 150psi across the board. Alsondid a leak down test, 100% across the board...

Maybe I don't have a blown head gasket!? I would imagine a blow head gasket would cause these scores to have lowered. Also makes me wonder about the smoke on start up? Would a leak down test show worn valve guides and valve guid seals? I did have cycle x do a valve job and replace the valve guides when I rebuilt the motor...

The oil between head and cylinders still has me wonder... maybe it was just residual oil from when I started the motor without the valve cover on, had to make sure inwas getting oil to top end!

But seriously, what is with the fumes from valve cover hose? AND exhaust smoke when cold???

Thanks

[samm_j2]

Here is what made me think I blew the head gasket?

[TwoTired]

Curious what oil is in the bike and what oil consumption you are experiencing.

When you did the leak down test did you listen for air escaping into crankcase, intake or exhaust?

Cheers,

[samm_j2]

Two tired,

Oil consumption is minimum, meaning inhave not noticed any...
I was running partial synthetic but today I switched back to straight dino oil.

I listened during leak down and herd not a peep!

 

[bryanj]

Oil in that area could be from the studs holding the cam towers down, the holes they go into are supposed to be blind holes but if a po has used bolts instead the hole can be broken open and oil will get down the threads and leak out. Also possible is one of the rubber pucks has slipped or you did not seal them to head. Finaly it is possible to fit the rocker gasket backwards as it looks identical but isnt and that will leak. Unfortunately all these fixes mean engine out unless you have a frame kit installed.

As to smoke from breather cant answer that one but hope whoever bored it understood Honda piston clearances, smoke on start up is valve seals/guides and the F2 is notorious for wearing out guides, hope they were checked and sized properly

[Old Moe Toe]

The 78F has 4 studs that are open to the outside world. To beat this problem there are 4 acorn nuts that go ontop of those studs. You need to put the acorn nuts on the correct studs or oil leaks out. That is one reason those heads can leak oil. There can be other reasons.
If like Bryan said you put the rocker cover gasket on the wrong way around, you can fit another one leaving the engine in the frame. I know this for a fact as I have done it.

[PeWe]

Compression tested with throttles fully open?
150PSI is low for  10.25:1 piston. 175-190PSI range to be expected.
Pistons for K head used in F2 head with larger chambers?

Check the spark plug cavities and see if there are oil leaking inside. This can be the rubber pucks under the cam holders that do not seal.
Cam holder studs have usually a hole going thru also visible where plugs are, the roof. If not sealed small leak.

MLS gasket or fiber?
MLS has rivets that can be squeezed between head and cylinder block and make head not mating correctly. I had to hammer them flat and drill small dents where the rivets mate with head and cylinder.

Fiber gasket must be tightened again 24 hours later. If gasket has compressed much, nuts moves 1/4 or so when retighten, wait another 24 hours and retighten head again by backing nut 1/4 turn, tighten it to correct torque.

I have reused 836 MLS, my  72mm MLS not, it was flattened around bores despite not much use.

Knock pins between head and cylinder must always be checked so they do not bottom out. I always measure with caliper.

Practical test with head not tightened, no nuts without gasket will show clearance, also good for piston/head clearance rotating crank.
If cam has higher lift a test with valves for 1 cylinder will show OK clearance too without gasket.
Carefullly rotate crank, no plugs in head.
A hot high duration cam need valve to valve check too. Head on bench, cam mounted with 1 cyl valves with weaker springs. At low lifts valves are close. Min 1mm.
DP315 cam on a K head with 34/28mm valves are close, 1mm.

This to complete an eventual fix if you must open.

[newday777]

Here is what made me think I blew the head gasket?

This is typically from weeping rubber disc pucks under the cam towers. Did you use Honda pucks or aftermarket? Any sealant on them?
And yes as Per said, thickness of the gasket to the dowel height is critical.

The steam or 'smoke' in the video tube wouldn't be normally seen on a stock bike as that tube goes in the stock air filter(which your bike doesn't have?), it is recycled through the air intake normally.

[TwoTired]

Two tired,

Oil consumption is minimum, meaning inhave not noticed any...
I was running partial synthetic but today I switched back to straight dino oil.

I read a thread some time back about some synthetic blend oil brands that evaporated quickly.  To the point where oil level got critically low and damaged the engine from oil starvation between oil change intervals.  The machines involved had crankcase recirculation so the breather outlet wasn’t observed.  Neither was the exhaust tinted with oil smoke.  But, the oil level went down noticeably in 1000 miles. 

It will be interesting if your oil change effects the crankcase outlet vapor.

Cheers,

[PeWe]

Two tired,

Oil consumption is minimum, meaning inhave not noticed any...
I was running partial synthetic but today I switched back to straight dino oil.

I read a thread some time back about some synthetic blend oil brands that evaporated quickly.  To the point where oil level got critically low and damaged the engine from oil starvation between oil change intervals.  The machines involved had crankcase recirculation so the breather outlet wasn’t observed.  Neither was the exhaust tinted with oil smoke.  But, the oil level went down noticeably in 1000 miles. 

It will be interesting if your oil change effects the crankcase outlet vapor.

Cheers,

I have seen oil consumption with carbonized chambers and pistons without smoking.

Not when twisting hard nor following  throttle  reduction to close followed by open throtttle a little.
Bore/piston vs guide with seal leak.
No heavy oil burn smell either.
Oil, part of the combustion.

[samm_j2]

Ok, cycle x did the boar and valves. I would assume they checked everything. I know the F models wear out valve guides but I can't imagine they would be worn after only 1000 miles?? How long does it take for them to wear?

I also had the f drain hold modification done or whatever, where they press the brass sleeve in. This is done on the studs that normally have the acorns right? Does this modification mean I no longer need the acorn nuts?

I had thw leaking cam tower pucks and studs, it showed up on the upper fins. I went in and honda bond the pucks AND took the front 4 cam town studs and put a sealant on the front 4 (exhaust side) cam studs. I have not had the same leak symptoms, upper head fins.

So what you guys are telling me is that oil this low CAN be from the pucks and studs?

There is no oil in the spark plug area.

The gasket is a MLS.

If the rocker gasket was on incorrectly wouldn't I have oil on the top of the head? There is no oil in the head (maybe a tad on the bottom fin) just oil on the jugs.

[PeWe]

Clean the oil off and see if more will come after a ride.
I have got oil when assemble the cam with rockers flowing over looking as oil leak later on.
Spray degreeser around the head and cylinder and rinse with warm water. If lucky no more oil.

Breather cover on valve cover has its o-ring and 3 M6 tightened?
I have got oil flushing over there and spread by the wind around when riding due to missed o-ring or front M6 not tightenef .
Tacho cable into valve cover another leaker that can flow oil around. Some of the M6 for valve cover has threaded hole going thru the head.

Possible that oil pass the gaslet and down the screw. Yamiya x- screw sets have sealer on them. I have not sealed mine

The low compression need another test with full throttle.

[samm_j2]

Just got some degreaser, that was my thought also. Gonna clear and gonfor a ride.

Again, I thought that compression would be lower on a f with larger combustion chambers.

Throttle was wide open when compression test was performed. What could the cause of the low compression be if leak down is solid? I used 2 different compression test gauges to make sure.

Thanks.

[samm_j2]

Cleaned throughly and just went on a short (less than 20 min) but very aggressive high rpm run on the freeway and some curves around town. I think the head gasketnis fine as the area of concern is bone dry.

But it still smokes from the dawn breather and smoke on start up....

[L5wolvesf]

Oil consumption is minimum, meaning inhave not noticed any...
I was running partial synthetic but today I switched back to straight dino oil.

I can't speak specifically to Honda motorcycle engines but the typical break in period usually requires conventional oils (not synthetic) to properly break in the motor.

[PeWe]

Pistons for K heads will make lower compression with an F2 head with its larger chambers.

I think a CR 12.5:1 piston for K will be OK with an F2 head to get CR 10 something.

Piston kits for the larger F2 chambers are usually specified for F(2) 1978. Dynoman and CycleX have those numbers.

If you have photos of your pistons when making the build, the domes and height over the piston wrist pin will tell.
Photo with CR12.5:1 piston at TDC for K heads. The dome is rather visible over the cylinder gasket area.

[samm_j2]

Ok well... I have decided to take the whole damn thing apart...
When I was riding around this afternoon my oil pressure dropped to about 20-30psi which is probably too low right? PeWe you got me thinking about them crank bearing when I smoke the cam... so I am taking everything apart.

I got pictures of the pistons and if the are the right ones then why was my compression low at 150psi? There is also a lot of carbon build up especially for only 1000-2000 miles.

The valve guides were new and installed by cycle x, anything to look for to see if the f head has worn them already?

I only have 2 dowel pins between the cylinders and heads, are there sulpose to be more??? (Edit: ken told me to leave the tall rubbers out. When I reassemble should I put back in?)The outer portion of cylinders 1 and 4. 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...

I have not yet split the case, what am I looking for in the main bearings as far as wear? There is some side to side play in the rods but no up and down that I can see/feel...

There is also what I guess would be piston slap in the sleeves? Should I re hone and re ring??

[maxheadflow]

Were the heads ported?

Did the valve spring kit require machining of the vlave spring seats?

I assume when you say 100% leak you really mean 0% leak.

Leaking or loose valve guides may not show up on the leak / compression test.

[samm_j2]

Head was not ported, I may end up doing that now that its off...

Springs did not require machining when installed.

Correct 0% leak. It was keeping 100/100psi

Is there a way to tell if the guides are worn?? I removed a few springs and wiggled valve stem and got no play what so ever...

Thanks

[Don R]

The 78F has 4 studs that are open to the outside world. To beat this problem there are 4 acorn nuts that go ontop of those studs. You need to put the acorn nuts on the correct studs or oil leaks out. That is one reason those heads can leak oil. There can be other reasons.
If like Bryan said you put the rocker cover gasket on the wrong way around, you can fit another one leaving the engine in the frame. I know this for a fact as I have done it.

 And the acorn nuts go on copper head nut washers. They probably should be new ones.

[maxheadflow]

Head was not ported, I may end up doing that now that its off...

Springs did not require machining when installed.

Correct 0% leak. It was keeping 100/100psi

Is there a way to tell if the guides are worn?? I removed a few springs and wiggled valve stem and got no play what so ever...

Thanks

Your issue does appear to be some kind of pressure issue.  I'm not sure what.  It's likes something is blowing back into the crankcase. While my first thought would be cylinder leakage my second would be a casting hole from the exhaust back into the crankcase. Cracked head?  Don't know.  0 leakage and consistent cylinder pressures  seems to indicate that things are good as far as leakage is concerned. While loose valve guides and leaky seals can be result in oil in chambers and startup smoke, they (imo) should not cause excessive breather flow.

You can wiggle the valve face end in the guide to check for looseness. It's best done with everything clean.  Is it possible that the valve collars are hitting the seals?  Honda seals are usually pretty robust but I know little about the aftermarket stuff.

What is of wonder to me is the cylinder.  I'm not sure about the ring in the cylinder you show.  Most of the cylinder looks like it has 30000 miles on it while the ring looks like what I'd expect for 2000 to 3000.   Does the cylinder have a fresh bore?

[samm_j2]

I will clean the head and check the valves tomorrow morning.
The cylinders did have a fresh boar and hone hone done by cycle x. After I get the case split and check the main bearings I plan to call ken in the morning and see what he thinks.

Thanks max head flow

[samm_j2]

Another piece of info, the smoke that came from the breather hose, when I pulled a tippet cover off smoke also came from this area. I have no idea what this means but maybe someone  will help help me figure this out.

Thanks

[PeWe]

Pistons look OK compression wise.
It look like burned oil inside? Even if carbs are jetted very rich not that thick carbon?

MLS does not need the oil return o-rings. I have  added the 2 o-rings for oil to head in my builds.
Valve guide seals sits as they should?
The breathers are OK? From valve cover to air via a long tube, the rear at engine case to oil tank.
Is it another ventilation that originally goes to airbox on that model?