Topic: Sudden white smoke from cam cover breather and exhaust

[Tracksnblades1]

Is it a Hientz ketchup commercial by Carly Simons…….?

Has it been determined whether it’s running on all four….?

[TwoTired]

Are you using a synthetic oil?

Some years back I read about some synthetics that had a low vapor point, causing loss of oil between oil changes on a more modern Honda.  With a 5000 or more oil change interval, the loss was enough to cause oil starvation and seriously screwed up the motor still under warranty. Honda wouldn’t pay for the repairs, even though it was Honda synthetic oil that was used, because the owner’s manual states not to run the motor on low oil.  Anyway I mention this because the modern bikes don’t vent crankcase vapors to atmosphere.  Oil vapors are routed to combustion chamber, so any oil vaporization would never be seen.  All my bikes also route crankcase vapor to intake as well.  So, even though I was using Honda’s synthetic,  didn’t notice vapor either.  I did notice oil level dropped between oil changes on my CB 550, though.  Had to add at least a quart between oil changes, and it was low again at oil change time (1000-1500 miles).

So, I’m thinking maybe your vapor is actually from the oil itself?  Maybe?  Just  a thought.  But, if you are using a non-synthetic oil blend, then … never mind.

[Jonm99]

Are you using a synthetic oil?

Some years back I read about some synthetics that had a low vapor point, causing loss of oil between oil changes on a more modern Honda.  With a 5000 or more oil change interval, the loss was enough to cause oil starvation and seriously screwed up the motor still under warranty. Honda wouldn’t pay for the repairs, even though it was Honda synthetic oil that was used, because the owner’s manual states not to run the motor on low oil.  Anyway I mention this because the modern bikes don’t vent crankcase vapors to atmosphere.  Oil vapors are routed to combustion chamber, so any oil vaporization would never be seen.  All my bikes also route crankcase vapor to intake as well.  So, even though I was using Honda’s synthetic,  didn’t notice vapor either.  I did notice oil level dropped between oil changes on my CB 550, though.  Had to add at least a quart between oil changes, and it was low again at oil change time (1000-1500 miles).

So, I’m thinking maybe your vapor is actually from the oil itself?  Maybe?  Just  a thought.  But, if you are using a non-synthetic oil blend, then … never mind.

TBH, I don't know what oil was in there when I got it back from the shop, but either way, there is very little mileage on it since. Anyway, I've now swapped out the oil for a blend, hopefully that will help, although still seeing smoke in the meantime. I'll take it for another run this weekend (weather permitting) now that we've have dialed in the carbs and valves, to see if it improves. Will update here ASAP.

[scottly]

Alternatively, can it be a blown valve stem seal?

Bad valve stem seals cause oil smoke in the exhaust, not vapor out of the breather. The early 750s didn't even have seals on the exhaust side, and my K1 has always puffed a bit of oil smoke from time to time.

[scottly]

The K7's actually have an individual bowl vent for each carb in the form of a very small hole in the carb body while the K8's have a crossover tube connecting the four bowl vents into a common vent at the #2 carb. It took me a minute to realize this when I first encountered a set of K7 carbs since I am more familiar with the K8's. 

You are correct Wilbur, they are very, very small holes! The drill bit in the pics is .0135"(a .017" bit went in a little way, but was tight, and I didn't force it).

[Jonm99]

Update:

I was (finally) able to get that leak down test done. Results are as follows:

1=18
2=6
3=12
4=10

One seems to be the culprit (that is also the oily plug), although the other cylinders aren't (apparently) in great shape either. Can someone please explain how I can derive what exactly the issue is from this test? I read in this thread rings or guides... am I supposed to know now if it's the rings or if it's the guides? Or did I read it wrong and the conclusion from the test is "rings or guides", and that's as far as we are going to know without pulling the engine? Can it not be a hole in the piston or a damaged cylinder wall?

Basically, I am trying to figure out what parts to order (in advance) while minimizing the time the engine is apart and I am waiting on parts to arrive. Is there a shopping list that I will need for sure (beyond a seal and gasket kit)?

Thanks!
J

[Don R]

 Are you sure the valves were closed? Also, was the piston at the top, middle or bottom of the bore? Sometimes piston position may tell you something.
 If you have a leaky intake or exhaust valve you can usually hear the leakage in the pipes or carbs. If it's rings or guides leaking you may hear it in the crankcase. 

[Jonm99]

Pistons were at TDC during the test (one at a time of course) and the leak was from the cam cover breather. No leak as far as I can tell from anywhere else...

[Tracksnblades1]

Pistons were at TDC during the test (one at a time of course) and the leak was from the cam cover breather. No leak as far as I can tell from anywhere else...

Sometimes to verify, a couple drops of oil will lower the leak down rate if the compression rings are at fault….

[scottly]

Update:

I was (finally) able to get that leak down test done. Results are as follows:

1=18
2=6
3=12
4=10

 I supposed to know now if it's the rings or if it's the guides? Or did I read it wrong and the conclusion from the test is "rings or guides", and that's as far as we are going to know without pulling the engine? Can it not be a hole in the piston or a damaged cylinder wall?

If it was a serious problem like a hole in the piston, a damaged cylinder wall, or a bad valve, the #1 cylinder wouldn't have 140 lbs compression.

[Jonm99]

Update:

I was (finally) able to get that leak down test done. Results are as follows:

1=18
2=6
3=12
4=10

 I supposed to know now if it's the rings or if it's the guides? Or did I read it wrong and the conclusion from the test is "rings or guides", and that's as far as we are going to know without pulling the engine? Can it not be a hole in the piston or a damaged cylinder wall?

If it was a serious problem like a hole in the piston, a damaged cylinder wall, or a bad valve, the #1 cylinder wouldn't have 140 lbs compression.

That's a good point... I'll assume rings for now. Aside from a set of rings, seals, and gaskets, anything else I should be ordering and replacing while I have the engine apart?

[Jonm99]

***update***

So finally got around to pulling the engine. So far I see a couple of problems:

1. cylinder #1 sleeve seems to be at an offset to the cylinder block which basically creates a sharp edge against the rubber puck.
2. cylinder #3 has a mark in the same area but the mechanic that is working on it seems to think that it is from a non leveled head (no offset between sleeve and block).
3. Cam chain roller is on its last leg and needs to be changed (although not related to the issue at hand).
4. While I'm in there, I will replace the rings and engine seals. Anything else I should be considering for replacement?

For #1 - mechanic suggests to lightly sand down the sharp edge with a dremel - and assumes that the puck will spread to fill the gap. This is concerning as it will permanently damage the head itself. On the other hand, there is no one in my neck of the woods that could remove the sleeve and put it back in aligned (assuming that is at possible), so the only other option if this doesn't work is to replace the head anyway.
For #2 - he suggests to shave an ever so little off the top of the head to ensure that it is completely level. No idea if this is common practice or a disaster waiting to happen...

Pics attached, appreciate your feedback as usual :-)

[madmtnmotors]

Those rubber “barrel” seals are secondary defence against oil weepage that were added to later models and weren’t even used on early engines. Smoothing the sharp edges from this misalignment would not be a problem. Based on the burned out section on the gasket your combustion is leaking past the steel ring in the gasket from the cylinder side. I’m guessing the burned side of the gasket was facing up towards the head? This would lead me to suspect either a faulty gasket (cheap chinese gasket?) or there is a dip or divot in the surface of the head at that location. After cleaning the head surface use a straight edge to check for a low spot at that point. If there is a low spot the gasket may not seal well at that spot allowing combustion gasses to escape and start burning through the gasket. Resurfacing the head can correct this as your mechanic suggested as long as they don’t have to cut too much and as long as there has not been much material removed from the head by previos head surfacings.

[scottly]

First thing I would do is measure the thickness of the "fire ring" in the gasket at various positions around all four cylinders, especially at the front versus the rear, to see if the areas near the blown out sections of 1&3 are less compressed than the other side. I would also fit the head onto the cylinder without the gasket to see how close it comes to the cylinder before bottoming out on the hollow alignment pins.   

[HondaMan]

That 'misaligned' rubber seal hole in the stud's passageway is quite common in the engines made after 1975. I have seen it many, many times. What happened was:the cylinder's iron liner crept and rotated somewhat during operation, probably because of some debris left in the bored cylinders before the iron liners were installed (in other words, a small assembly mistake made a long, long time ago). So long as the rubber seal still fits into the hole, it won't cause any future issues. However, when the cylinder rotated it also cross-torqued the head gasket's metal ring in that area, which slightly damaged the high-pressure seal there. That's why the metal ring in the head gasket is now disintegrated or distorted, and when it finally broke far enough to let combustion pressure reach that offset drain hole, it then pressurized the crankcase, causing the white smoke.

So, what to do?
#1: if you just hone and re-ring the pistons, it will not last long and it will not have the high-RPM power it once had. The bores are no long a true round shape (this is normal) and introducing new, round rings will cause compression leakage. The 100% way to "fix" this is to rebore with the next oversize pistons (CrusinImage makes nice kits for the K7, I have used them many times). This would be the 0.5mm oversize set in this case.

#2: Before reassembling in ANY case, have the head milled flat, as it is not where the gasket leaked (at the least!). This usually means to have it flat-ground 0.0005"-0.010". Also the cylinders, and have them milled flat -0.010". This is sometimes referred to as "head flattening" and "cylinder deck milling". The reason: the head and cylinder are now warped where the gases escaped, so it's not flat and won't seal, period. Also: all new head gaskets today are 0.010" thicker than the one you just removed: it was made from asbestos, and that's outlawed now, so the head gaskets have grown in thickness from their original 0.8mm thickness to now 1.00mmm thick. This difference MUST be milled off the cylinder deck, or it WILL leak oil after reassembly, from those 2 oil ports at the center rear of the cylinders. PM me your mailing address and I will also send you 2 new O-rings to use in those holes at reassembly to prevent his problem, no charge.

[Jonm99]

Thanks guys!

@Hondaman - I just had the head milled and unfortunately it looks like they shaved off more than they were supposed to (this would be too "easy" if they did what they said they would do...) and the result is I've lost the "seating" around the oil galleries. Long story short, the only solution I can think of is to have them remill around the relevant oil galleries to recreate the seats. Will this work (assuming we still have a minimal height for the cylinder head)? If so, any chance you would know what the depth and diameter of these seats are (I've attached a pic of the milled head and another of what it should look like - off the web). I think the red and blue arrows have different depths... Also, it would be helpful to know what the original height of the cylinder head is - that will help me figure out how much was actually shaved off.

As for the shaving of the cylinder block - it looks to me like the pistons are already very (very) close to the top - maybe a previous owner already did this? Don't think I can shave anymore off...

Regarding the seals, thank you so much for your kind offer! Are these non standard? I am going to need a new top end set of seals and gaskets anyway, so wouldn't want to bother you with that if it is normally included in such a set.

[HondaMan]

This picture of the head looks OK: the head side doesn't have the recesses for the O-rings - just the cylinders have that recess. The second picture in your post above is of the cylinders, not the head.

Yep, these O-rings are not 'standard' per the usual gasket set: the OEM version of these O-rings were 2.4x11mm. The ones I'll send you are 2.6x10.9mm, a standard Parker size, but thicker. The extra thickness makes up for modern head gaskets being thicker than in the last century. Without this, it WILL leak oil from those 2 oil ports at the back of the cylinders, reliably so. You'll see posts about that in these forums, often.

On the top of the cylinders you can measure the depth of the recess where these O-rings sit to see if someone has milled the deck before. When Honda made them they were 1.0mm (0.040") deep, give or take 0.1mm (0.004"). If they were milled before, it will be 0.75mm (0.030") deep. I have had to mill them twice before when someone wrecked their cylinder block after it had been previously milled (they gouged the top with something), in which case you can just use the regular O-rings of 2.4mm thickness without leaks.

[Jonm99]

Oh, that's a relief! My mistake on the images not being of the same part... sorry about that. Nevertheless, when I look at the image of my cylinder head before it was milled (attached), it looks like there is a recess for the 2 o-rings in question. Is that just from wear, and not supposed to be recessed anyway?

Will DM you for those o-rings... really appreciate that.

Thanks

[madmtnmotors]

This picture of the head looks OK: the head side doesn't have the recesses for the O-rings - just the cylinders have that recess. The second picture in your post above is of the cylinders, not the head.

Oh, that's a relief! My mistake on the images not being of the same part... sorry about that. Nevertheless, when I look at the image of my cylinder head before it was milled (attached), it looks like there is a recess for the 2 o-rings in question. Is that just from wear, and not supposed to be recessed anyway?

Will DM you for those o-rings... really appreciate that.

Thanks

The third picture is indeed a picture of the original head and it looks like small recesses at the head stud locations on the exhaust side but I guessing that is an optical illusion since there would be no need for any oring recess on the exhaust side since the oil feeds are on the intake side. A measurement of the overall thickness of the head may indicate how much was milled away.

You are going to want to measure all of the dowels to make sure none of them end up too long now that mill work is done.

[Jonm99]

A measurement of the overall thickness of the head may indicate how much was milled away.

You are going to want to measure all of the dowels to make sure none of them end up too long now that mill work is done.

Do you by any chance know what the original measurement / height of the head is? And what the minimum height allowed would be after milling?

Regarding the dowels, am I supposed to shorten them accordingly?

[madmtnmotors]

Do you by any chance know what the original measurement / height of the head is? And what the minimum height allowed would be after milling?

I'll bet Hondaman knows!

Regarding the dowels, am I supposed to shorten them accordingly?

Just check them first to be sure. You could dry assemble the head and cylinders with all the dowels without the gasket to make sure none of them keep the head and cylinders from fully mating. Me, I just measure the overall length of the dowels compared to the sum of the bores they reside in.

EZPZ 

[HondaMan]

Those 8 short dowels will be OK after the milling: they were 1mm short to begin with. Just make sure they don't stick up more than 0.8mm above the cylinder's deck surface, which you can do with even cheap calipers. I've only experienced an issue with them once, in a VERY modified cylinder set from a 750K3 that was milled more than 1.5mm. All those little dowels had to be shortened, but the guy had a lathe so it wasn't hard. The rubber seals got squished extra, too, but they worked OK with no changes because the ID of those 8 holes is quite big. This wasn't in a bike's engine, but a midget racer car - he cut off the transmission to use just the engine! I guessed his final compression ratio to be in the 14:1 range, but wasn't allowed to try to verify it - racing secrets, ya know.
Cool stuff, it was...

[Tracksnblades1]

Kenny shows cylinder head thickness at 2.842 on his web site under tid bits….🤔

[newday777]

Kenny shows cylinder head thickness at 2.842 on his web site under tid bits….🤔

🤔🤔🤔
Is that inches or mm that Kenny is stating?🤔

[Tracksnblades1]

He’s from Hazelhurst Wisconsin USA. Where are you from ?

Perhaps you can answer your own question simply by doing the inch to metric conversions and reading in context what was published….🙄

Perhaps if you start your metric conversions with the 0.015 cylinder head expansion it will become crystal…

Would not 0.015mm = 0.00059055118 inch…. compared to 0.015 inch = .381mm.  Crystal now…?

Have a great Day..

🙄🙄🙄

I have a couple spare cylinder heads but I think they’ll measure a bit more than 2.842mm thick (0.111 inch) .
 What do you think?

I can double check if you prefer…..

🙄