Topic: 1978 motor rebuild, white smoke at idle, SOLVED??

[Dolomite]

Quick back story, motor completely rebuilt and bored over ~430 miles ago. After a ride the other day, noticed white smoke intermittently while stopped/ idle. Disappears when throttled up and riding. I'm thinking it's time to have the valves rechecked but wanted to see if anyone had any better insight. Oh, also its only coming from the right pipe, so cylinders 3 & 4. Thanks!

[kerryb]

I was led to believe that white smoke comes from water or moisture, like the leaking head gasket on my water-cooled goldwing.  Blue is from oil, and black is from excess carbon or rich mixture.
So is there some way you pipes have water in them, maybe from condensation.  Does the smoke go away after enough time/heat to dry it out?  Is the bike going through heat/cold cycles to build up condensation inside?  Is the bike sitting out in the rain while you are at work?

[bryanj]

It is possible to get white smoke from oil if it is all burning in the cylinder, had it myself many years ago on a 650 triumph converted to 750 with a Morgo conv. New rings cured it

[Dolomite]

Kerry- bike is always covered when not in use but the smoke doesn't go away, and it has an oil smell to it

Bryan- do you think the rings could have went after just 400 miles?

[pjlogue]

I would run a compression check.  If you find a low cylinder, put a little oil in the cylinder and recheck.  If compression is better you know the rings aren't sealing well.  No change in compression then it's likely the valves.

I would try putting some more miles on the engine before pulling things. 450 mi isn't a lot of miles for breaking in new rebuilds.  You may find the smoking goes away and compression inproves in another 400-500 mi.

-P.

[Dolomite]

Thanks PJ, I suppose I'm just a little precautionary as I don't want to ruin an engine I just invested nearly 2k in. My mechanic who rebuilt the motor is going to get me an estimate today to check the valves, and if it's not too bad I may just have him do it for the peace of mind.

Would you guys say it's safe to continue riding?

[ekpent]

 Check and see what your spark plugs look like and see if one is a way different color then the rest to get more data. I don't think its going to blow up riding it some more.

[Dolomite]

Great thought EK, I'll check that later today.

[bryanj]

Were the oil rings one piece or three piece and are you sure the compression rings were in the correct grooves and the right way up.
Also if it was rebored was the clearance correct, there are a lot of machinists bore too big

[Dolomite]

Bryan- I can't recall what style the rings were and my mechanic was the one who had it bored at a machine shop and installed everything so I'd have to check with him, and I'm not certain he'll remember that from building an engine almost 9 months ago. I know the smoke only started recently and was not existent before.

[Bodi]

Agree on no panic. It does sound like oil is burning in the cylinder(s), that's usually rings or intake valve guides but could be head gasket. Oil is pretty cheap though, and unless plugs foul you're still riding until you decide to get into the engine.
A compression test now is a good idea, and a blowdown test to maybe locate the leak if it has poor compression. You can check how much is venting from the crankcase (disconnect the top vent hose from wherever it goes and stick it out where you can see what blows out) - a lot of oily fumes from a hot engine indicates rings leaking. Some blowby is normal, but it should be minimal.

[pjlogue]

Thanks PJ, I suppose I'm just a little precautionary as I don't want to ruin an engine I just invested nearly 2k in. My mechanic who rebuilt the motor is going to get me an estimate today to check the valves, and if it's not too bad I may just have him do it for the peace of mind.

Would you guys say it's safe to continue riding?

I would hope your mechanic would not charge you for looking at the engine he rebuilt for $2K less than 500 miles ago!

Unless the mechanic did a catastrophic Oops in rebuilding, the only way I can see for it to be burning oil would be the rings not seating in the one cylinder or a failure of a valve seal.  (valve seal unlikely if installed correctly)  Overfilled oil would be another cause of smoking but that would be in all exhausts.  Could be a head gasket leak but they tend to be pissing oil outside the engine, not into a cylinder. 

Compression check would be the 1st thing to do on a list of checks.

-P.

[Dolomite]

Bodi- I have the crank vent going direct to atmosphere with a filter on the end. Some small white smoke when warming up has been typical from there.

PJ- the 2k included 1000 in parts and he is a friend so if he needed to charge some working time as this is his livelihood I have no qualms with that (his rate is already 75hr so considerably lower than most. I do tend to keep my oil quite topped off. I used the cyclex no leak mls gaskets so I'm skeptical of those failing causing a headgasket leak.

[scottly]

If you paid someone $1000 to do the work, and something isn't right, he should fix it.

[754]

2 things here,
 If he put the motor together, he should have ballpark idea what it takes to check the valves. And he should at least look at it for you.
 If boring and or honing  are done wrong, it will use oil.. if a head and cylinder are not resurfaced to correct surface finish the gasket can fail.,
 It sounds like rings, if it comes apart , get someone else to check cylinder clearance and hone pattern.

[PeWe]

My CB750 K2 had a K1 head without ex guide seals. It smoked when riding according to people behind.
Replaced it with a later refurbished head with oil seals on all guides, no more smoke.

The old gasket was OK, no leaks that way.

If you are lucky, seal only.
Or 3-piece oil rings not correctly seated. If expander overlaps, no good.

EDIT:
Maybe strange to check, oil level inside valve cover direct after a ride? Seen thru the tappet hole.

[Phoenix]

I rebored to fit cruzinimage 836 kit.  To get it done I went to the "#! engine shop in Indy".  I wanted it bored at 10 over per HM.  He wanted to do it at 20.  He would not do it my way.  Went to another shop and told him my story and wrote out what I wanted.  He said fine.  Put it back together and it smoked.  Took it apart and measured it.  It was 20 over.  Had to sleeve it and start over.  You are your own advacate.  Read up on what you need.  Don't necessarily trust some guy.  Make sure he's worked on bikes like yours.  Get Hondamans book.  You'll pay for it in no time.  If your bike doesn't work, it's up to this guy to prove he didn't do it.  Good luck.

[754]

I think you mean 1 thou over and 2thou over . Machinists that know what to do, and WONT LISTEN have ruined a lot of engine parts.. if someone took it there for you they won't pay for your parts .
 The worst part about 836, it's a lot of boring , if they screwed up a 836, get it bored to 850 or what ever that size us.. regular bore job at that point.

[Nurse Julie]

Don't you mean 1 thou of an inch piston / bore clearance 🤔 That is the usual for Cruzinimage pistons any more than that it will smoke like a chimney.

[PeWe]

1 thou of an inch piston / bore clearance = 0.025mm?

My old 836 cylinder had  NOS RC836 (cast), clearance up to 0.2mm without smoking!

Cruzinimage psitons need extra tight bores compared with other pistons? Different alloy?

[Nurse Julie]

1 thou of an inch piston / bore clearance = 0.025mm?

My old 836 cylinder had  NOS RC836 (cast), clearance up to 0.2mm without smoking!

Cruzinimage psitons need extra tight bores compared with other pistons? Different alloy?

Yes, rebore for Cruzinimage pistons is done to piston / bore clearance of 1.0 thou " as different alloy mix than Honda OEM pistons. OEM Honda pistons need less clearance than Cruzinimage at 0.8 of a thou". Are the RC836 pistons made by Honda?

[PeWe]

1 thou of an inch piston / bore clearance = 0.025mm?

My old 836 cylinder had  NOS RC836 (cast), clearance up to 0.2mm without smoking!

Cruzinimage psitons need extra tight bores compared with other pistons? Different alloy?

Yes, rebore for Cruzinimage pistons is done to piston / bore clearance of 1.0 thou " as different alloy mix than Honda OEM pistons. OEM Honda pistons need less clearance than Cruzinimage at 0.8 of a thou". Are the RC836 pistons made by Honda?

The old RC836 made in Japan by the manufacturers Russ Collins used for the early sets with one oil control ring. The groove same as the later forged so so could use oil 3- ring.

I have a cylinder for 61.5mm Cruzinimage K7 pistons. Maybe clearance is around 0.025- 0.03 mm something.
My K2 runs 61.0mm cruzinimage pistons in old only honed bores around 0.04mm clearance. No smoking. 

Maybe at cold start giving it really rich mix of fuel if not started for a while .
That look to bring a little oil out too. No problem after 30 sec.

Mm is easier to use. Honda CBs are mm bikes, not imperial

This is good to know. Really tight fit for these pistons. I noticed that the rings are really hard when assemble the cylinder. Cracked some nails.

My forged JE 71 25mm pistons must have over 0.06mm (0.0025") piston/bore clearance.

[Dolomite]

Update: finally got time to do some checks. Number 4 plug was oily wet. Changed all oil, 20w50 VR1 high zinc (only took 3q oddly?), new filter and changed to denso 24exs-u plugs. Still getting the white smoke at idle. I did notice once the bike was nice and warm idle oil pressure drops to around 20psi. I'm going to pickup a set of feelers to check valve clearances (this damn pandemic #$%* is making it difficult to go get stuff done). But if all that checks out I'm at a loss. Is it possible the number 4 ring didn't seat right? But then it would get worse at high rpm, not better right?

[scottly]

Do a spit-sizzle test. Is #4 exhaust pipe as hot as the other three after running a short time, like 30-40 seconds?

[bryanj]

Starting to sound more like a valve guide or stem seal or maybe bored too loose on that cylinder