Author Topic: CB350F still smoking after 2 rebuilds... Ideas anyone? NEED HELP. (Read 25089 times)

Bluegreen · « **Reply #50 on:** September 15, 2012, 05:12:30 PM »

Maybe a silly question. Are your rings in the right way up?

My friend rebuilt a motor a couple of years ago and he did that. Pulled it apart, put the rings in the right way and presto, problem gone.

ekpent · « **Reply #51 on:** September 15, 2012, 05:14:48 PM »

I would as someone suggested at least pull the plugs and post up a pic so for kicks we can get a little better idea of whats happening in each individual cylinder.4-1 exhaust pipes are hard to identify one or two bad cylinders unless the head pipes are running cooler. If oil is getting by big time the plugs should show signs. Any oil gathering at the back of the pipe?

camelman · « **Reply #52 on:** September 15, 2012, 07:03:11 PM »

I'm on board with ekpent. Oil and excess fuel will both show signs on the plugs.

craywm · « **Reply #53 on:** September 15, 2012, 07:43:43 PM »

It kind of looks like burnt oil but it could also be condensation mixed with excess carbon. Its hard to tell really. Ill snap a pic. Also, i didnt see the plug pic request. Ill snap one for you all and post it tomorrow. I tried leaning out my mixture and it seemed to help a little bit. Yes my rings are on correctly and spaced correctly. Im going to swap the mixture screws with the old ones. Maype the new ones werent made right? Ill for sure post a pic tomorrow of the plugs and of the tailpipe area. I hope all is well in there! But we have yet to see. The smoke is more grey. Not as blue as oil. The engine is not over heating either. Any other info i should get for you all?

craywm · « **Reply #54 on:** September 16, 2012, 08:35:07 AM »

Can anyone tell me if this is possible. What if too much material has been removed from my head causing the head nuts the top out on the top end studs which wouldnt allow the crushing of the head gasket as needed?. When i retorqued my head bolts, i noticed on the ones with a capped head, if i tried to turn them they would turn and spring back to the way they were before like they were topping out. This was at 15.5 ft-ibs with spec at 14.5 ft-ibs. Only increased it to get a tighter seal. Figured 1 ft-ib would seal it up but not damage anything. If this was the case, id need uncapped head nuts or add a spacer nut washer to each stud. Which is better?

speedy gonzalais · « **Reply #55 on:** September 16, 2012, 09:55:47 AM »

if there's too much fuel the plugs will be black but dry, if its oil they will be black and wet as you havnt run the engine much, what u said about the bolts springing back, did you blow the oil out of the threads before putting the bolts in? also did u buy new bolts or use the old ones? I would think that you would have external leaking as well as internal if the head wasn't tight enough.

camelman · « **Reply #56 on:** September 16, 2012, 03:08:11 PM »

I've had that issue with the nuts springing back after being torqued down. I tried using thicker washers to see if the nut was just bottoming out, but the thicker washers made no difference. Make sure you apply oil, grease or locktite to the threads before you torque the bolts, and that's all you can do.

The reason the nut is twisting and then returning is because the cylinder stud is twisting. If you've torqued to the upper torque spec, then you'll have plenty of clamping force on that bolt. I think each one of those nuts exerts around 5000 pounds of force, so you really don't need to worry about not getting that last foot pound of torque. I did not experience any issues with the nut springback that I dealt with.

Torquing your head bolts down really won't have an impact on oil burning if the bolts are already torqued close to spec. Oil leakage at the head gasket will go to the outside of the engine and manifest itself as leakage coming from between the jugs and the head. If you really are burning oil in your engine, then it is coming from the rings or the valves. Not from a leaking head gasket.

Can you post pics of your plugs? Or, as "andre andre ariba" said, let us know if the plugs are wet and oily or dry and sooty.

Camelman

craywm · « **Reply #57 on:** September 16, 2012, 03:38:46 PM »

all the plugs were wet! and crusty! tell me if these pics are good enough

craywm · « **Reply #58 on:** September 16, 2012, 03:43:20 PM »

heres 2 and 4

craywm · « **Reply #59 on:** September 16, 2012, 03:44:33 PM »

craywm · « **Reply #60 on:** September 16, 2012, 03:45:46 PM »

4, sorry all these pics were too large for 1 post

camelman · « **Reply #61 on:** September 16, 2012, 06:38:00 PM »

Wet with fuel. If the exhaust smoke is white and immediately goes away, then you're dealing with excess fuel. Fluffy black smoke is excess fuel too, just better burnt. Blue lingering smoke, which can look whitish, is oil.

A worn out battery can create poor combustion too.

FYI, I meant neversieze, not loctite.

craywm · « **Reply #62 on:** September 16, 2012, 06:59:22 PM »

The smoke definently lingers. I can look behind me as i ride and see it! Its wet and the wet substance smdoesnt. Smell remotely like oil. Ill pull the exhaust and have a look at that end. In the meanwhile im ordering a bk performance head gasket. Anyone opposeed?

MCRider · « **Reply #63 on:** September 16, 2012, 07:19:27 PM »

Quote from: craywm on September 16, 2012, 06:59:22 PM

The smoke definently lingers. I can look behind me as i ride and see it! Its wet and the wet substance smdoesnt. Smell remotely like oil. Ill pull the exhaust and have a look at that end. In the meanwhile im ordering a bk performance head gasket. Anyone opposeed?

I didn't get to ride mine today. Got it started and it still smokes. Am intrigued about the idea of how much jetting contributes to this.

In the meantime i've got some pesky oil leaks to solve before riding.

jason41987 · « **Reply #64 on:** September 16, 2012, 09:35:41 PM »

if you cant get your CB350F to quit smoking, did you consider getting it the patch, or the gum to help it quit?

camelman · « **Reply #65 on:** September 16, 2012, 10:14:29 PM »

I don't think it is your head gasket, but that's up to you if you want to order one. Do you have a local bike shop you can take it to? Any senior service tech should be able to figure out what's going on. They'll likely check it out for you for free too.

craywm · « **Reply #66 on:** September 17, 2012, 03:59:03 AM »

Whats the patch? Or the gum?

jason41987 · « **Reply #67 on:** September 17, 2012, 04:31:14 AM »

well aside from my joke earlier.. my guess would be one of two things, my first guess would be burning oil, second would be the fuel mixture too rich...

how many miles on your bike? ive been reading how the SOHC/4 engine cylinders wear in an elliptical shape... if theres a bit of mileage on it, new rings may not be enough and you might need to bore it out a bit... this comes to mind when you mention all youve done so far and still getting smoke... im not sure if the 350s have the issue or not, but throwing it out there

after all youve done with your carb i dont think it would be that to be honest, it seems youve completely rebuild that too

craywm · « **Reply #68 on:** September 17, 2012, 04:36:44 AM »

I know it may not be my head gasket but im pretty sure its not the carbs. I replaced the mixture screws with the old ones and even resynced. No change. I also burnt almost a quart of oil off( no oil leaks). So i think its in the engine. If its valves or rings ill have to replace the head gasket anyway so i wanted to get one!

jason41987 · « **Reply #69 on:** September 17, 2012, 05:11:52 AM »

well if you didnt do it before, you could have your heads re-bored and made parallel at a local machine shop and that could very well be the problem from what i gather about these engines

craywm · « **Reply #70 on:** September 17, 2012, 05:46:40 AM »

yeah thats what i was planning on doing. truing up the head surface. ive heard that the cylinder block is manytimes not the problem as it has a much harder time warping. plus the jugs are made from alot stronger steel keeping their shape. i was only going to true the head block instead of both.

Im ruling out valves as well. i checked them all and they were good plus i replaced the intake seals. forget about the exhaust valve for now as clearly from the look of the plugs, the smoke is being produced in the cylinders not in the exhaust. the plugs were WET. only one was slightly dry and looked like a rich mixture but still not normal. they were all gunked up. i was surprised they hadnt fouled yet. and there was BLACK oil around the bottom of the threads which didnt smell like gasoline at all. it was def. oil. when i pull of the head it will be prettty clear how the oil is getting into the cylinders if its going through the head gasket. there will be oil all over both sides of the head gasket.

I think this is possible without external leaks because of how the head is warped. on the previous rebuild, the head gasket was covered both sides with oil without any external leaks. i must just be very lucky. if i dont see any oil on the head gasket, it has to be the rings or a crack. so then i will get some new rings, rehone the cylinders, and throw it all back together (after a deep clean of course).

itd be really nice to get ahold of a compression adapter that wont tear up my plug threads.. would it be different? if the headgasket was blown would that cause it to be higher or lower? considering the amount of oil in the cylinders?

craywm · « **Reply #71 on:** October 11, 2012, 08:49:18 AM »

hey all,

was able to break down the engine. just for anyone who is having any similar problems.

The NEW head gasket was blown near the center camchain area and on one of the oil return passages. i have some pics but am unable to upload at this time. i ordered a new head gasket and had only the head surface machined. i am also going to use yamabond (very sparingly) around some of the oil passages and definently around the camchain shaft. Ive heard of people doing this with a very thin coat. ill upload a few pics of the head gasket and head as i took it apart. theres some good shots of how the head gasket broke. since it was new, it had a very clear story to tell. before i broke down the engine again. i had inserted 1 qt of oil and it had burnt through that below the dip stick. fingers crossed that this rebuild will be the final! then i can get to riding it!

HondaMan · « **Reply #72 on:** October 11, 2012, 08:18:34 PM »

Quote from: craywm on September 15, 2012, 02:46:00 PM

I replaced the fuel mixture screw and springs with new ones (still have the old ones) think thats what could be happening from a new mixture screw? The bike was warm at that point in the video. I had just gotten back from a ride! But still comes to life quickly

If the new screws were from Keyster, swap back to the OEM ones, for sure. I've had almost 75% wrong parts like those in Keyster carb kits for all of these SOHC4 bikes. Only [some] of their gaskets actually fit right.

krusty · « **Reply #73 on:** October 11, 2012, 11:25:48 PM »

I checked back through this thread, I may have missed it, but has the following been done? A compression and leak down test? I have seen with 4/1 exhaust systems where there is a problem with only one cylinder burning the oil. At least a compression test will give a comparison between all cylinders.

KRMK3 · « **Reply #74 on:** October 12, 2012, 03:17:45 PM »

Just a thought but did you check the ring end gaps in the bores to see whether they were within spec before re-assembly ? From the video it seems to be burning oil and it looks to me like it is a piston/bore/ring problem and not valves/guides. A rich fuel mixture wouldn't show itself with blueish exhaust smoke. Is the oil pump scavenging properly, if not that may be the problem.
Good luck with it.

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Author Topic: CB350F still smoking after 2 rebuilds... Ideas anyone? NEED HELP. (Read 25089 times)