Author Topic: Oil leaking from cb350f exhaust (Read 2520 times)

Nick0 · « **on:** April 12, 2014, 05:45:21 pm »

So I have just rebuilt my cb350f top end, new rings, honed all cylinders, new gaskets, lapped all valves, new valve seals. Compression readings are 140, 135, 125, 140. Plugs are black and sooty. Black oil is dripping from the exhaust pipe (new Mac 4-1) where the header connects to the muffler And it's smoking. What is this a symptom of ?

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calj737 · « **Reply #1 on:** April 12, 2014, 06:31:14 pm »

It's likely to be the internal finish of the exhaust pipe being burnt away. Condensation accumulated, hot exhaust hit it, and the surface of the coating colors the moisture. Seeks lowest point first (drains down header and hits collector) and then drips through your collector seal, or is condensation sweating through.

Simple physics. If it truly is oil, you've got a problem with the valve train work you did. I'd suspect a problem in the #3 cylinder as you indicated it had the lowest compression. Bad guide or seat on that valve? If it's not being burned away during combustion, it's leaking during the exhaust stroke and exiting through the header.

calj737 · « **Reply #2 on:** April 12, 2014, 06:52:23 pm »

Something else: if you've just completed all that engine work and are getting a 10% low cylinder! you need to triple check your valve adjustments on that cylinder. Possibly, it's slightly out and creating a low comp. number.

Else, I think you're heading for removing that head to troubleshoot a valve-side leak. Maybe the lapping was perfect? Maybe you got a guide or seal in jiggered? Either way, if you've got oil down there, you've got a problem in the head you need to resolve.

Nick0 · « **Reply #3 on:** April 12, 2014, 06:56:19 pm »

I have not yet adjusted tappets, could that solve it?

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Nick0 · « **Reply #4 on:** April 12, 2014, 07:04:47 pm »

Re-torque ?

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Nick0 · « **Reply #5 on:** April 12, 2014, 07:22:16 pm »

Quote from: calj737 on April 12, 2014, 06:52:23 pm

Something else: if you've just completed all that engine work and are getting a 10% low cylinder! you need to triple check your valve adjustments on that cylinder. Possibly, it's slightly out and creating a low comp. number.

Else, I think you're heading for removing that head to troubleshoot a valve-side leak. Maybe the lapping was perfect? Maybe you got a guide or seal in jiggered? Either way, if you've got oil down there, you've got a problem in the head you need to resolve.

I didn't replace the guides, just seals. Thanks for the info

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flybox1 · « **Reply #6 on:** April 12, 2014, 07:25:54 pm »

Quote from: Nick0 on April 12, 2014, 06:56:19 pm

I have not yet adjusted tappets, could that solve it?

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did you adjust them after your rebuild?

Nick0 · « **Reply #7 on:** April 12, 2014, 07:30:21 pm »

Long story I adjusted them with the cam 90 degrees out, idiot mistake (accidently alined the cam sprocket marks vertically as apposed to horizontally) and I haven't re-adjusted them since then

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calj737 · « **Reply #8 on:** April 13, 2014, 04:51:09 am »

I wouldn't think a re-torque is in order yet. But definitely double check the valve adjustments. It would be good medicine to re-torque after a couple of hundred miles or a couple of hours of full running.

Nick0 · « **Reply #9 on:** April 13, 2014, 09:54:06 am »

Quote from: calj737 on April 13, 2014, 04:51:09 am

I wouldn't think a re-torque is in order yet. But definitely double check the valve adjustments. It would be good medicine to re-torque after a couple of hundred miles or a couple of hours of full running.

thanks for replying, I'll try to adjust the tappet clearances this afternoon

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skidooextreme · « **Reply #10 on:** April 13, 2014, 10:00:43 am »

I had the similar situation but mine was a lot of moisture ...black liquid

Nick0 · « **Reply #11 on:** April 13, 2014, 10:04:15 am »

Quote from: skidooextreme on April 13, 2014, 10:00:43 am

I had the similar situation but mine was a lot of moisture ...black liquid

did yours smoke ?

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Nick0 · « **Reply #12 on:** April 13, 2014, 11:15:30 am »

I'm also getting smoke out of the crankcase breather tube

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2strokeTrush · « **Reply #13 on:** April 13, 2014, 11:18:51 am »

In my (Little) experience very fine cloudy smoke can be attributed to the new exhausts internal coating being burned away, This would also make sense because MAC's tend to be a little thinner walled system. But if the smoke is blue and heavy ( doesn't dissipate quickly) its Oil. Like mentioned, somehow oil is leaking out the header on the stroke, down the hot pipe and leaking or being burned off. Funny if it is though since you just finished a adjustment, but that could be off to. Perhaps a exhaust valve is not seating correctly?

Just some food for thought.

Nick0 · « **Reply #14 on:** April 13, 2014, 11:33:24 am »

Smoke is thick and white when I rev it, never blue. I guess this is a good sign maybe I'm just overreacting. Once I get my rear wheel spacers sorted out I'll take it for a long ride and try to burn off all the coating and any moisture in the engine

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calj737 · « **Reply #15 on:** April 13, 2014, 11:39:09 am »

Did you get anywhere with the valve adjustmens? After a good ride, check your plugs and double check your valves. Some preventative investigation to protect all the work you've just done.

2strokeTrush · « **Reply #16 on:** April 13, 2014, 04:22:07 pm »

Quote from: Nick0 on April 13, 2014, 11:33:24 am

Smoke is thick and white when I rev it, never blue. I guess this is a good sign maybe I'm just overreacting. Once I get my rear wheel spacers sorted out I'll take it for a long ride and try to burn off all the coating and any moisture in the engine

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Did you find One ? I could get One for you no problem

Nick0 · « **Reply #17 on:** April 13, 2014, 04:40:07 pm »

Quote from: 2strokeTRush on April 13, 2014, 04:22:07 pm

Quote from: Nick0 on April 13, 2014, 11:33:24 am
Smoke is thick and white when I rev it, never blue. I guess this is a good sign maybe I'm just overreacting. Once I get my rear wheel spacers sorted out I'll take it for a long ride and try to burn off all the coating and any moisture in the engine

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Did you find One ? I could get One for you no problem

http://forums.sohc4.net/index.php?topic=135866 you have this part?

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2strokeTrush · « **Reply #18 on:** April 13, 2014, 08:26:28 pm »

I live near a vintage salvage yard, I can guarantee they could dig one up for you.

Nick0 · « **Reply #19 on:** April 13, 2014, 08:52:40 pm »

Quote from: calj737 on April 13, 2014, 11:39:09 am

Did you get anywhere with the valve adjustmens? After a good ride, check your plugs and double check your valves. Some preventative investigation to protect all the work you've just done.

didn't get a chance to adjust my valves today

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Nick0 · « **Reply #20 on:** April 13, 2014, 09:11:05 pm »

Quote from: 2strokeTRush on April 13, 2014, 08:26:28 pm

I live near a vintage salvage yard, I can guarantee they could dig one up for you.

yea could you check for me, thanks

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Nick0 · « **Reply #21 on:** April 15, 2014, 07:14:22 pm »

I took the muffler off the bike yesterday to sort off a rearset clearance problem and the black "oil" does appear to be only the coating on the inside of the pipe, whew.

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Author Topic: Oil leaking from cb350f exhaust (Read 2520 times)