Author Topic: CB350F still smoking after 2 rebuilds... Ideas anyone? NEED HELP. (Read 25028 times)

craywm · « **on:** September 11, 2012, 05:16:09 AM »

Okay all,

so i just finished rebuilding the top end on my 350 for the second time. the reason for rebuild 1 was Gas in the oil, reason for rebuild 2 was blown head gasket (and a ton of oil burning). so i replaced the rings, cleaned everything up, replaced base gasket, head gasket, and stem seals (exhaust has so seals as this was a early honda design), and also lightly honed cylinders to help the rings seat. I ordered an athena gasket kit (ive heard they manufacture good gasket replacements).

So i finished putting it together yesterday and i was getting alot of white smoke, like a smoke screen while revving. i was hoping that there was just unburnt oil left in the exhaust from the prev rebuild. mind that this was after a complete rebuild with gasket replacements. so i let it run for about 30 min. there was a light change in the smoke but on revving there was still a fair amount. checked oil (perfect) and let it run longer. after 30 minutes i took her out to see if i could burn it out of the exhaust. no such luck. it seemed to get a little bit better but not by much. i also just rebuilt the carbs so she ran great though i didnt push her hard. the whole short ride she was blowing smoke out the exhaust..

so im at a loss.. is there anything ive missed here? i really dont want to do another rebuild. I KNOW my rings are all the right way.. and i replaced all the gaskets. it runs fine just smoke like crazy.. i ordered an adapter for my compression tester but it did not fit correctly so i decided not to use it.. but its pretty clear whats happening. i only honned each cylinder for about 45 seconds on medium speed to remove glaze. you dont think that this could cause too much oil to stay in the cylinders do you? i really dont want to have to rebuild and buy a new head gasket.. everything is torqued properly.. i also replaced all my oil seals as well.. i just dont understand. honda designed it not to leak with all new seals.. why would it still spring a leak.... PLEASE HELP!

Mo · « **Reply #1 on:** September 11, 2012, 05:25:09 AM »

What was the status of the bike before the rebuild? You could try to pour about 1 cup of kerosene in with the oil. The kerosene will wash out a lot of the carbon deposits inside the engine (it would smoke for a little and then clear up).

Have you tried changing the oil again?

craywm · « **Reply #2 on:** September 11, 2012, 05:32:42 AM »

the original state was gasoline in the oil (bad rings) so i rebuilt to replace rings which were very gummed up. oil is fresh valvoline 10w-40 motorcycle oil. I cleaned the valves and pistons and honned the cylinders so there should be very very little deposits left. the only place i could imagine a deposit would be in the exhaust from the prev blown head gasket (oil was in EVERY cylinder). the only thing that i did not do for this rebuild was have the surfaces trued by a machine shop. though i did run a stone over them and they look great. before rebuild there were NO oil leaks.

craywm · « **Reply #3 on:** September 11, 2012, 05:47:50 AM »

i should probably mention its a 74 cb350F1

craywm · « **Reply #4 on:** September 11, 2012, 06:16:57 AM »

i just noticed that i torqued down my head bolts in the wrong order.. would this cause a head failure like this? i just mirrored the torque pattern accross the head..

2wheels · « **Reply #5 on:** September 11, 2012, 09:31:42 AM »

Oil should be 20W 50, or so I think anyway.

But I feel your pain, really. Did you take the valves out of the head? And check the clearance between valve stem and valve guide (I just wiggle the valves once the springs are off)

Also, I wonder if gasoline in the oil has got to be rings?

By the way, I am having the same problem with a Honda ATC 3 wheeler. Smokes like crazy even after a mini rebuild, honed, new valve stem seal?? To my very inexperienced eyes it looked good inside.

speedy gonzalais · « **Reply #6 on:** September 11, 2012, 12:10:44 PM »

Any smoke/ breathing from the crank case ? you can get the engine upto running temp remove the exhausts and inspect the valve stems for oil deposits, you can usually see if its seeping through the guides, personally i always get the head skimmed especially after a gasket failure, i always leak test the valves and guides and the pistons/ rings too, theres nothing worse than rebuilding an engine only to have to strip it again afterwards its very thrustraiting

also a quick look at each plug can tell you a lot.

MCRider · « **Reply #7 on:** September 11, 2012, 12:24:06 PM »

This isn't to your point, but I'll say it for those that may care: gas in the oil is not an automatic indicator there is something wrong with the engine. It can occur anytime the petcock is left on for a time like overnight or longer. It simply vaporizes out of the carbs and condenses on the cylinder walls. No new set of rings in the world will keep it from washing down the cyl walls.

The oil should be changed of course, but not necessarily the rings. Oh yeah, turn the petcock off any time its going to sit for more than an hour.

Modern bikes have vacuum operated petcocks that turns themselves off whenever the engine is turned off.

Can't help you with the smoking.

lrutt · « **Reply #8 on:** September 11, 2012, 12:36:32 PM »

When you say a light hone? did you get a GOOD cross hatch. That is key. And if it's smoking like you say, don't baby it. Take it out anf flog the crap out of it. That could very well bed the rings in. It worked on a Triumph I did. Smoked like hell for 15 minutes or so and should not have so I run the crap out of it. within 15 minutes it was smoke free and has been a gem every since.

MCRider · « **Reply #9 on:** September 11, 2012, 12:42:03 PM »

Quote from: lrutt on September 11, 2012, 12:36:32 PM

When you say a light hone? did you get a GOOD cross hatch. That is key. And if it's smoking like you say, don't baby it. Take it out anf flog the crap out of it. That could very well bed the rings in. It worked on a Triumph I did. Smoked like hell for 15 minutes or so and should not have so I run the crap out of it. within 15 minutes it was smoke free and has been a gem every since.

That's good to know. I stopped an oil leak on my project by retorquing the head nuts. Dodged a bullet.

If the smoking (mine smokes too) can be cured by running the crap out of it, well, I can do that!

dave500 · « **Reply #10 on:** September 11, 2012, 01:14:55 PM »

did you check the ring gaps?have a closer look at the guides again.

craywm · « **Reply #11 on:** September 11, 2012, 01:19:13 PM »

guides are good. gaps are good. i think it must be a blown head gasket again.. odd though since its brand new.. thats what i get for not truing the head though.. im going to try to retorque and run the thing to hell but not sure how much good it will do. ill try it though!

dave500 · « **Reply #12 on:** September 11, 2012, 01:37:20 PM »

have you taken it for a decent long ride yet?dont thrash it just yet though.

craywm · « **Reply #13 on:** September 11, 2012, 01:46:21 PM »

uhhmm a 10 min ride and thats all. smoked the whole way

kslrr · « **Reply #14 on:** September 11, 2012, 03:25:55 PM »

You don't run-in an engine buy flogging it. You run the risk of cracking a ring. To seat the rings, don't take it any higher than 7k to 8k rpm for the first 1000 miles. Change the oil. Then you can start shifting at higher rpms.

Now, what I just said above is based on run-in advice for newer, modern bikes. If this dosen't apply to a 30 yo with new rings, please someone correct me.

camelman · « **Reply #15 on:** September 11, 2012, 03:47:59 PM »

That doesn't sound line oil burning to me. White smoke after warming up the engine and exhaust sounds like a rich, or poorly mixed, fuel mixture. I'm actually going through the same in my 350f right now. I have new guides, valves, bores, pistons and rings along with new gaskets throughout. For some reason my exhaust isn't blowing black when it is rich, but it sure is rich. I'll be rebuilding my idle screw assemblies and possibly replacing jets and o-rings. I'll revisit the float heights too. I imagine your issue is similar, so you might want to revisit those carbs. FYI, the idle screw assemblies are usually screwed up by a PO by this point in the life of the bike.

Camelman

dave500 · « **Reply #16 on:** September 11, 2012, 04:20:54 PM »

dont take it over 5000 for the first couple hundred miles,dont let it idle and do lug the engine slightly with accelleration for short three gear shift burst.,,i think you might just still be burning off assembly oil?your only breaking in the rings not the entire engine.

MCRider · « **Reply #17 on:** September 11, 2012, 04:49:36 PM »

Engine break in procedures can rapidly devolve to an oil thread. Google it and you'll see, every possible routine is reccomended.

Some initial hard running seems to be the ticket for seating rings on a newly honed cylinder.

If its already smoking like a chimney, why not.

speedy gonzalais · « **Reply #18 on:** September 11, 2012, 11:55:28 PM »

I would take the advice on taking it for a long ride, I recently done a top end rebuild on one of them high performance 150cc pitbike engines that are based on the c90 engine, new valves, guides, piston and rings, the thing smoked like Hell for the first hour of riding then suddenly cleared up.

craywm · « **Reply #19 on:** September 12, 2012, 04:00:22 AM »

Okay ill give it a go!

lrutt · « **Reply #20 on:** September 12, 2012, 04:21:25 AM »

Quote from: MCRider on September 11, 2012, 04:49:36 PM

Engine break in procedures can rapidly devolve to an oil thread. Google it and you'll see, every possible routine is reccomended.

Some initial hard running seems to be the ticket for seating rings on a newly honed cylinder.

If its already smoking like a chimney, why not.

Of the dozens of engines I've gone through, I've always followed the normal break in procedures. Not hard but not soft. No sustained speeds, varying things, thoroughly warmed up then shut down, repeat. This Triumph did not respond at all so as a last resort, took it out and really blasted through the gears for several minutes. Cleared it right up. That's all I can say from my experience.

craywm · « **Reply #21 on:** September 12, 2012, 04:43:12 AM »

Looks like i got something new to try! I can def ride the crap outa it! If it still doesnt stop ill retorque and try again. If that doesnt stop it.. Its back to the head to true it and istall a new head gasket! I hope this is just rings seating.. Ive never had new rings act this way before. But i gues it could always be the head gasket too. I dont seem to be hearing any valve noise, and id imagine if the head gasket was blown less oil would get up to those valves and id hear something. So that supports the theory of ridding it to hell. I heard lots of valve noise with my first head gasket failure. Ill keep tryibg. At what point is it "bad" for the engine to be burning oil?

craywm · « **Reply #22 on:** September 12, 2012, 05:07:57 AM »

btw while revving this thing smokes like the bat mobile... lol not a chimney! but while it idles it hardly smokes at all. i bet its those rings trying to seat on my cross hatches. i heard a terrible noise while honning but still only did it for 30-45 seconds. it didnt seem like it was bad for the cylinders. i cant imagine these rings will take much more to break in

thanks for everyones help and confirmed stories of success after break in! feels good to know i may have not messed it up, and that my ol' Betsy will be ready for riding atleast for the next couple months. Thanks!!

killersoundz · « **Reply #23 on:** September 12, 2012, 08:28:16 AM »

break it in see if it goes away. took mine 100 miles of break in with new rings before all the smoke went away. if it doesn't, my money is on valve guides

craywm · « **Reply #24 on:** September 12, 2012, 09:33:29 AM »

I checked the guides.. They were good! And it didnt smoke like this before i rebuilt it! So it cant be the guides. It has to be either the new rings breaking in or the new head gasket blew. When i rev it the smoke increases alot.. That supports the ring theory since more oil will be burnt if the pistons are cycling faster. If it was a head gasket blow itd act the same but i have to assume the top end would have oiling issues. Ill give it 50 miles

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Author Topic: CB350F still smoking after 2 rebuilds... Ideas anyone? NEED HELP. (Read 25028 times)