Topic: K7 mystery oil smoke #4 cylinder

[flybackwards]

I completely rebuilt my K7 motor last year - And yes, it worked fine and still does except... After a few hundred miles I decided it was pretty much broken in and took a 45 minute freeway trip. Everything was fine and it seemed to run well. I got home parked in the garage and thought all was good. Then - next startup I got some oil smoke from the #4 cylinder exhaust and thought crap! After a few minutes it went away the bike ran just fine during the ride. This now happens each time I start it. A moderate amount of oil smoke for three maybe four minutes and then its gone and only the one cylinder. Seems sure that oil is leaking into the cylinder after run and then burning off. Seems to need a cool cycle it to happen. Does not happen on a warm start. What does the hive mind think for a possible cause? Before I start taking things apart! Thanks.

[denward17]

Have you looked at the spark plug for that cylinder yet?

[Tracksnblades1]

Did you recondition the valve guides during your rebuild..?

[grcamna2]

Did you recondition the valve guides during your rebuild..?

This.

[newday777]

"I completely rebuilt my K7 motor last year -"
As above a very possible cause could be worn valve guides.

Tell us what you did in the rebuild. There are several possible causes and you've left out full valuable information on getting a good diagnosis.
Did you hone cylinders and put in new rings? What were the ring end gaps(did you measure at 3 spots in the stroke of the cylinders?)
Did you have it bored bigger with bigger pistons and rings? Again what were the ring end gaps and piston clearance bores in each cylinder?
What work to the head did you do or have done?

[flybackwards]

Deliberately left it vague thinking there might be some thoughts. The pistons / block were a match bored assembly from CycleX - I did not make measurements on their work - they have a good reputation for this kind of thing. The head was completely rebuilt by Terry at Wolfeworkx using all Kibblewhite parts - guides, seals, valves, springs. All the valve seats were refaced and the head cleaned. My prime suspect at this point is the head gasket which was one of the CycleX dual layer steel items - claims not to need retorquing. A good warm highway run followed by oil getting into the cylinder says maybe the gasket did not seal and likely it did need to be retorqued. Thats where I am going first.

[BenelliSEI]

While you’re there check to see if any valve seals popped up or split? If the head gasket is leaking enough to let oil into a cylinder, it should be coming out the sides as well?

[HondaMan]

If you take the head off again, contact me for some special O-rings for the oil ports between head & cylinder, to prevent future leaks there.

[flybackwards]

Thanks everyone - I won't be getting to this until spring - I am liking the valve stem seal idea for the first look...

[PeWe]

- High oil level inside valve cover before the smoking start?

It was one thread a few years ago  where it smoked oil after start due to high oil level inside valve cover.
I think the engine had heavy duty cylinder studs that are thicker, head gasket with small oil return holes.
Maybe it was a K1 with no oil seals on ex guides.

I do not recall if only new head gasket got the oil return holes drilled or if head oil return holes were drilled too. The holes for studs can be tight not much space left for oil return when using hd studs.
MLS gaskets can be reused if not used much. Just tighten the nuts a little bit more than last time.

If using MLS head gasket, some have small holes, even smaller than the earlier cylinders.

It flow easier with warm oil.

Both my CB750 have HD studs and drilled holes in head. At least 9.0mm drill thru all + 9.5mm thru the 2 oil feed holes (2 inner studs carb side, each side of cam chain tunnel)

[scottly]

Have you looked at the spark plug for that cylinder yet?

[PeWe]

Have you looked at the spark plug for that cylinder yet?

Maybe not oil, floading carb causing smoke?

[Deltarider]

Is it your habit to always use the sidestand? If so, try to use the mainstand for a wile and - who knows - maybe the issue disappears.

[robvangulik]

#4 is on the high side....

[Deltarider]

#4 is on the high side....

I know. For some reason the 4 cyl. Hondas I have seen with just one pipe smoking, it was always #4. I have no explanation for this and my observation is ofcourse of no scientific significance, but I have often wondered why.

[flybackwards]

That is all very interesting - I have big studs and an MLS gasket - no mods or drilling done. Maybe I'll put a block under the side stand so its more level at rest and see.

[PeWe]

Good if the smoke can be identified.
Black too rich fuel or grey bluish oil burn.

More oil consumption things when at it
Modified engine with hotter cam:
I had a huge oil consumption that did not smoke a few years ago.
At least not when I had stopped with bike when oil level was max 5 mm up on stick. Very soon out of oil.

I had followed how it disappeared during only 150km from 10mm under max to almost nothing on dipstick.

Called my wife with instructions where in the garage she could grab oil, road description on  google map where I waited, ca 60km from home.

Refilled and drove home. I instructed her to watch for smoke when driving behind.
 I did a few WOT on 2-4 gears. No smoke visible despite heavy throttle offs-on at high rpm.

High lifting cam and guides not sunken enough. K valves have a huge valve keeper groove that can/will enter the guide seal and massage the seal to leak more. Inlet will work as an oil pump and suck oil rather quick.

My earlier heads had either F2 inlet valves or 5mm stemmed valves with not that high/long keeper groove.
Around 12mm free lenght on those valves.

This was a 392 head that might be different. Not made for K valves to start with.... Guides with depth might need extra attention.

Head fixed after guides sunken even deeper.
That head got DP315 cam that does not have much lift, only 0.368" minus 0.12" lash.
Most focus on valve to valve clearance due to the duration.
My cam instructions to the port guy that was nice to fix it for free.

So there is a good reason for CycleX iron guides for higher liting cams.
Maybe when lift is more than 0.360 lift with stock guides. Important to measure the distance from seal to valve groove before mounting the springs.
Shims under springs will make distance shorter.

Or put the stock guides on a lathe to cut the stopper groove deeper plus cut and reshape the guide where it sticks out in the port.

Ca: 9.4 mm not good when measured cam lift was 9.98mm at 0 lash, subtract lash of 0.10mm and ca 0.05mm more of the rocker play.

Lift 9.8 mm WILL push the groove into the seal.
The first time higher consumption when using the throttle more frequent. After a few thousands km seals are sloppy and oil just disappear.
Good with frame kit to fix it during the weekend. Cleaning the pistons from carbon, use another head while the oil pump head is fixed in the shop.

A good distance seal vs groove is real cam lift + 0.5mm.
Found on this forum in older post.
10.5mm a good number