Author Topic: head gasket leak (Read 5595 times)

longshanks · « **on:** July 18, 2011, 05:08:45 PM »

I just noticed before I took it for a ride today that the head gasket is slightly leaking oil and there are small oil deposits on the cylinder fins. The bike has 23k on it and I'm not sure if its ever been replaced. Is this a common problem? I've seen it on many other cb750's.

Bike is a K6

Skunk Stripe · « **Reply #1 on:** July 18, 2011, 05:16:15 PM »

Well age can be a factor but it could also be that the head bolts need to be re-torqued. Mine is doing this, not bad yet but still, I should re-torque. My reason for holding back is if I snap an old head bolt, thats it for my riding as I just dont have the time to fix something like that quickly. So I will either wait till fall or till it gets worse.

OldSchool_IsCool · « **Reply #2 on:** July 18, 2011, 05:16:24 PM »

Common problem. Temp fix is to jam rolled up paper towel between the fins, replace when saturated. Perm fix is to pull the engine and replace gaskets.

Gordon · « **Reply #3 on:** July 18, 2011, 05:52:59 PM »

Re-torquing head bolts on the 750 requires pulling the engine, so IMO if you're going that far you might as well just replace all the top end gaskets. How bad would it suck if you pulled the engine, re-torqued the head, reinstalled it and it still leaked?

longshanks · « **Reply #4 on:** July 18, 2011, 07:51:31 PM »

I'm pretty sure its the gasket as I looked at it again and it looks like pieces of it flaked off. Time to overbore???

Skoti · « **Reply #5 on:** July 20, 2011, 05:13:23 AM »

Try this:-

CB750F1 head gasket repair
« on: May 21, 2010, 02:20:00 am »QuoteModifyRemoveSpent loads of cash doing up the bike over the winter and first time out discovered the head gasket leaking oil at the front outer head studs where they go through 'O' rings.

Rather than spending more cash I tried a botch up and after 700 miles it's still holding .

Here's what I used:-

http://picasaweb.google.co.uk/lh/photo/SM_BwkFUCP7kGETbr6pYwg?feat=directlink

Cleaned away all traces of oil, grease and caked on grime with brake cleaner and cotton buds until absolutely spotless all the way around the front outer stud boss.

Applied this P U sealant/adhesive purchased from local motor factors and left to set for 24 hours.

http://www.u-pol.com/product-cat/162/tiger-seal%E2%84%A2-pu-adhesive-and-sealant.htm

I ran a bead of sealant from under the exhaust rose at the front to half way along the gasket edge at the side. I used a piece of small plastic tube fixed onto the nozzle of the tube to get access right into the gasket edge.

http://picasaweb.google.co.uk/lh/photo/OjtPCJf8sGatBcJSMvO_5Q?feat=directlink

http://picasaweb.google.co.uk/lh/photo/MzemzVl7rdTPVeV3s-OJrQ?feat=directlink

Hope this might help others

Skunk Stripe · « **Reply #6 on:** July 20, 2011, 05:29:26 AM »

Maybe it is just me but I would not do that. It says to be permanent and I would not like that to be a permanent fix.

nayto550 · « **Reply #7 on:** July 20, 2011, 05:40:17 AM »

I would probably just let it leak until I had a chance to repair it properly. Most air-cooled engines are extremely forgiving when it comes to leaky head gaskets. I once rode my 550 for about 3 months on a leaking head gasket with no ill effects except a dirty engine.

Skoti · « **Reply #8 on:** July 20, 2011, 07:01:43 AM »

I think that it's probably not the cylinder head gasket that's causing the oil leak but the rubber 'o' rings that are inserted into the cylinder head gasket around the front outer cylinder head/ cylinder barrel studs.
It's said that the rubber 'o' rings shrink with old age and loose sealing effect.

Those 'o' rings seal the oil returning from the valve gear and camshaft area in the cylinder head, the oil then gravity feeds back down to the engine sump via waisted front outer cylinder head/ cylinder barrel studs.

I'm not suggesting this is a proper fix but it saves the time and expense of removing the engine from the frame and renewing the cylinder head gasket and 'o' rings.

When I originally posted this fix I'd done 700 miles without any further oil leakage, I've now done over 2,500 miles and all is still well.

Incidentally my CB750F1 had done 23k when the oil leak developed as well.

Skunk Stripe · « **Reply #9 on:** July 20, 2011, 07:53:50 AM »

My thought was when the time does come where you have to do the work, how hard is that bond going to be to break and then how hard will it be to get off the fins.

MCRider · « **Reply #10 on:** July 20, 2011, 08:53:24 AM »

Some have alluded to this, but I'll state it outright. The leak is from oil returning to the sump under gravity. Yes it is fairly common. If it were from the pressure feed side, you'd know it. It would squirt out like you cut an artery. And it has nothing to do with what the head cheeze is really there for, to seal the combustion chambers.

So its not a mortal wound, you can run like that nearly indefinitely, the biggest determinate is how dirty do you want to get. IF it starts blowing back on your pant leg, and you've got someplace nice to go, that may be the last straw. And you may have to add more between changes. And it gets on the garage floor.

The cotton rope in the fin trick, similar to the paper towel, can go a long way to "kicking the can down the road".

Skoti · « **Reply #11 on:** July 20, 2011, 12:24:49 PM »

Quote from: Skunk Stripe on July 20, 2011, 07:53:50 AM

My thought was when the time does come where you have to do the work, how hard is that bond going to be to break and then how hard will it be to get off the fins.

The stuff I used is the same as "Sikaflex" so should come back off if cut with a sharp blade. But terrible stuff to clean off your skin!

Skunk Stripe · « **Reply #12 on:** July 20, 2011, 01:12:31 PM »

Ah ok. It looked like a hard epoxy style material. Must not have read enough.

Elniniomuchachos · « **Reply #13 on:** December 04, 2011, 08:38:00 PM »

+1000 on the sealant. I just changed the head-gasket on my 77' 550 engine and the damn thing started leaking worse than it did before. (I think the head may be warped some) I added some Permatex gasket maker in between the fins where the gasket is and no leaks now

. That means clean jeans and boots

... for now. We'll see how this holds up, but I'm hoping it's a while before I have to dive back into this thing. I've had the top end off on this bike more times than I want to admit... Now the only little leak I need to take care of is coming from the oil pump.

Anyways... Thanks for posting your idea!

CoachDoc · « **Reply #14 on:** December 04, 2011, 10:16:20 PM »

I've got a very small leak on my 550 on the right side. I'm going to live with it as long as it doesn't get any worse. When I first got the bike going after many years of dormancy, there was a considerable leak on the left side in the vicinity of the shifter and oil pump. This leak quickly went away entirely. I'm suspecting one of the seals plumped up after reaquainting itself with hot circulating oil after being dry for so many years. To be safe I have all the pertinent seals on hand if the leak returns.

Elniniomuchachos · « **Reply #15 on:** December 04, 2011, 10:29:52 PM »

Quote from: CoachDoc on December 04, 2011, 10:16:20 PM

I've got a very small leak on my 550 on the right side. I'm going to live with it as long as it doesn't get any worse. When I first got the bike going after many years of dormancy, there was a considerable leak on the left side in the vicinity of the shifter and oil pump. This leak quickly went away entirely. I'm suspecting one of the seals plumped up after reaquainting itself with hot circulating oil after being dry for so many years. To be safe I have all the pertinent seals on hand if the leak returns.

My leak was the, come to a stop and a huge cloud of smoke from oil being burned off the exhaust erupted, type. Also it resulted in two pairs of jeans being ruined and my left foot boot being shiny. SO I'm glad it's fixed. haha

camelman · « **Reply #16 on:** December 04, 2011, 11:20:40 PM »

I ruined a pair of jeans riding with the same type of leak on my 350F. It didn't look very bad, but was enough to put a sheen of oil on the rear tire. If I rode on the highway for more than 30 minutes, then I was guaranteed a little slippage in the turns when I exited the highway... at least until I scrubbed the oil sheen off the tire. I had a 6 hour ride to the mountains like that once too and almost ran out of oil because of that "small" leak. It might not look like much, but that little dribble can become an issue.

Keep an eye on your oil level and fix it this winter.

Camelman

Elniniomuchachos · « **Reply #17 on:** December 04, 2011, 11:57:27 PM »

Quote from: camelman on December 04, 2011, 11:20:40 PM

I ruined a pair of jeans riding with the same type of leak on my 350F. It didn't look very bad, but was enough to put a sheen of oil on the rear tire. If I rode on the highway for more than 30 minutes, then I was guaranteed a little slippage in the turns when I exited the highway... at least until I scrubbed the oil sheen off the tire. I had a 6 hour ride to the mountains like that once too and almost ran out of oil because of that "small" leak. It might not look like much, but that little dribble can become an issue.

Keep an eye on your oil level and fix it this winter.

Camelman

Indeed. That oil leak I had was ridiculous... The whole left side of my bike is pretty much coated in oil. I'm going to have to take the 4-4 off and degrease them, along with the frame and rear rim/hub. Oil leaks aren't fun

aperry · « **Reply #18 on:** September 12, 2012, 04:00:58 AM »

Hi guys,

I'm reviving this thread to see how the Tiger Seal and Permatex is working out (after 9 months or so)? Anyone else tried this kind of solution?

I have what I would imagine is a fairly common leak in my 750K3 head gasket area (mostly left side). At high speeds the wind spatters some oil from the fins onto the sprocket cover area. A few drops on my pants too. I haven't tried the rolled paper towel trick yet, but I will give that a try first.

In the meantime I'm interested to know how the sealer is working out for those who have tried it. I know this isn't considered a permanent fix, but I'm not looking forward to a top-end rebuild, and this seems like a more permanent fix compared to the paper towel method. The results described in this thread seemed encouraging.

Thanks!
Aaron

Skoti · « **Reply #19 on:** September 12, 2012, 06:52:59 AM »

Hi Aaron,

I've done over 4,000 miles on my CB750F1 since the tiger seal repair was done and it's still holding out fine.

Kind regards

Skoti.

aperry · « **Reply #20 on:** September 12, 2012, 07:14:05 AM »

Excellent, that's great to hear. I'll look around for some of that stuff. When I looked it up online yesterday, I couldn't see anywhere that it was rated for high temps. But it looks like your experience with it demonstrates that it handles high heat plus oil just fine.

Thanks!!
Aaron

Tugboat · « **Reply #21 on:** September 13, 2012, 12:21:01 PM »

Shove a piece of rope between the fins as an Oil Tampon. Seriously.

aperry · « **Reply #22 on:** September 13, 2012, 12:45:37 PM »

Quote from: Tugboat on September 13, 2012, 12:21:01 PM

Shove a piece of rope between the fins as an Oil Tampon. Seriously.

I did that with the rolled paper towel this morning and put about 30 miles on it. Seems to work well. No oil on the engine (yet), but I haven't looked at the paper towel yet to see how saturated it may be. I'll probably go with this for a while and see how it does before going with a sealant.

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Author Topic: head gasket leak (Read 5595 times)