Author Topic: ***NEED HELP WITH OIL LEAK!!!!****  (Read 1936 times)

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Offline pelicanwheel

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***NEED HELP WITH OIL LEAK!!!!****
« on: January 21, 2010, 12:54:59 PM »
Hi  everyone -
I have a 1976 CB750 K6 that has a fresh rebuild.  The engine is stock,and extremely clean - as new.  I have an oil leak somewhere on the front of the engine that is significant.  I'm having trouble isolating the source.  When the engine is running, oil seem to be coming from somewhere near the number three muffler clamp (on the right side pair of mufflers).  It is hard to see where the leak is coming from because the oil is so clean, as well as the engine.  It look like the source is somewhere at the head gasket union (yikes!).  To make matters worse, the front valve adjustment caps on the valve cover are leaking (these are after market plugs, and I can sort that issue out later) but it takes a few minutes before they leak.  When the caps do leak, it interferes with isolating the main leak, as oil drips everywhere.

The main leak looked like it was coming from behind the clamp, so I took the two mufflers off on that side of the bike.  Here is what I find:

The spark plug boots in 2 and 3 are clean and dry

The spark plug wells in 2 and 3 are clean and dry

if you took the front wheel and forks off the bike and looked at the front of the engine, unfettered, here is what you see:

The top landing of the head is dry (until the caps start to leak)

The 3" wide fin below the top landing - and  in between the 2 and 3 exhaust ports - is dry on top and bottom

The 3/4" wide fin below that is dry

The 3" wide landing below that is dry on top and bottom

The 3/4" fin below that is dry

The next two 2 1/2" wide fins have oil on them.

The new head gasket is a color that I can tell discoloration from being wet.  It is an even color everywhere, so I dont think its leaking.  And at the rate of leaking, compression would be low if it was the head, and I have very good compression.


When I look back into the space behind these fins (between the mufflers), there are manufactured holes that I cant really see whats going on in there.

Can any one point me in the right direction?  I dont want to take the engine out prematurely, or worse, start to take it apart when I didn't need to.

Thanks much


Offline pelicanwheel

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Re: ***NEED HELP WITH OIL LEAK!!!!****
« Reply #1 on: January 21, 2010, 12:57:16 PM »
Also...the oil accumulate on the number 3 pipe and drips off near the center of the pipe near the foot peg.  After a while, a little oil runs down number four.

The leak is coming from the center, NOT the ends, as is common with a bad head gasket.

Offline pelicanwheel

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Re: ***NEED HELP WITH OIL LEAK!!!!****
« Reply #2 on: January 21, 2010, 01:00:40 PM »
one more thing.  The rate of loss is about a drip per second while the engine is idling and it starts within 30 seconds of running the bike.

The valve capss takes about a minute or so before they leak, so I have about 30 seconds to find the main leak.

Offline bucky katt

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Re: ***NEED HELP WITH OIL LEAK!!!!****
« Reply #3 on: January 21, 2010, 04:56:30 PM »
there are "pucks" under the cam towers and that is usually where the leak youre describing comes from 99% of the time. when you pull the motor to re-torque the head, check to be sure you have the pucks there and if so, that theyre fitted properly
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Offline Duke McDukiedook

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Re: ***NEED HELP WITH OIL LEAK!!!!****
« Reply #4 on: January 21, 2010, 05:17:01 PM »
+1, this seems to be a common problem.
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Offline MCRider

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Re: ***NEED HELP WITH OIL LEAK!!!!****
« Reply #5 on: January 21, 2010, 05:32:46 PM »
besides the pucks, there is another more insidious potential point of leakage. The outboard, forward studs that hold down the cam bearing caps are screwed into holes that are open to the atmosphere, at the midpoint of the cylinder fins, if the stud wasn't there. If that stud had ever been removed, as they sometimes are in a rebuild, whatever replaces them may leak through those threaded holes and drip into the cylinder head fins at about the mid-point, half way up from the head gasket and halfway down from the cam cover gasket.

I had removed my studs and from many cam swaps had stripped these holes out, used 1/4-20s for a while, then helicoils to repair the threads. They leaked like sieves. Never could seal them up. But probably didn't try hard enough. Early on I should have replaced the studs using an industrial quality thread sealer.

If you clean the head thouroughly, then poof some talcom powder in there, with the bike on the centerstand running, you should be able to see the leaks with a CSI style flashlight (or any light really, CSI is cool). If from those threaded holes, you'll actually see the oil drip from those holes. You'd think that smashing the cam tower down on the head it would be enough. But its not, the hot oil will wick its way under the towers, hence the pucks, and if they are OK, the stud holes are leaking.
« Last Edit: January 21, 2010, 05:34:37 PM by MCRider »
Ride Safe:
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1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline pelicanwheel

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Re: ***NEED HELP WITH OIL LEAK!!!!****
« Reply #6 on: January 22, 2010, 08:09:29 AM »
Thanks guys...I did a search of the posts here and came across both those issues as being the potential culprits. 

So out goes the engine...

Stay tuned!

Offline pelicanwheel

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Re: ***NEED HELP WITH OIL LEAK!!!!****
« Reply #7 on: January 22, 2010, 03:26:55 PM »
Ok...got the engine out.  I dont know how I could have omitted one of the pucks...but there it was (or not was)..one was missing!!!!!


That's the good news towards isolating the problem.  The bad news is that it is the puck on the 1 and 2 cylinders - cam tower.  Its the puck closet to the center.

My leak seem to be coming from the other tower near number 3.  I could imagine that the oil could seep all the way over and appear to be coming from 3, but I can't see how since the bike leans to the left when idling on the kick stand.  I would think gravity would prevent it from going "uphill" towards the number 3 exhaust port where the lead is near.

Any thoughts?

Also, is it the four studs for the tower that is where it can also leak?  If so, how do I correct this?  Remove them and seal or something? thanks.

Pelican

Offline MCRider

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Re: ***NEED HELP WITH OIL LEAK!!!!****
« Reply #8 on: January 24, 2010, 10:52:59 AM »
Ok...got the engine out.  I dont know how I could have omitted one of the pucks...but there it was (or not was)..one was missing!!!!!


That's the good news towards isolating the problem.  The bad news is that it is the puck on the 1 and 2 cylinders - cam tower.  Its the puck closet to the center.

My leak seem to be coming from the other tower near number 3.  I could imagine that the oil could seep all the way over and appear to be coming from 3, but I can't see how since the bike leans to the left when idling on the kick stand.  I would think gravity would prevent it from going "uphill" towards the number 3 exhaust port where the lead is near.

Any thoughts?

Also, is it the four studs for the tower that is where it can also leak?  If so, how do I correct this?  Remove them and seal or something? thanks.

Pelican
Yes its the studs whose holes are open to the open air in the fins. If the studs have never been removed, they shouldn't be the problem. You can look in between the fins on the head and see the bottom of the holes. Once mine began leaking I never got them fixed. I was going to try some kind of thread sealer but have never looked into it.
Ride Safe:
Ron
1988 NT650 HawkGT;  1978 CB400 Hawk;  1975 CB750F -Free Bird; 1968 CB77 Super Hawk -Ticker;  Phaedrus 1972 CB750K2- Build Thread
"Sometimes the light's all shining on me, other times I can barely see, lately it appears to me, what a long, strange trip its been."

Offline pelicanwheel

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Re: ***NEED HELP WITH OIL LEAK!!!!****
« Reply #9 on: January 27, 2010, 11:42:32 AM »
It was a bad cam tower puck along with the valve cover gasket being upside down.  Corrected both and now I'm leak free.

Thanks everyone