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Oil Seepage, Head Gaskets, and 7k+ RPM

NickE

Member
Joined
May 4, 2021
Total Posts
12
Total likes
1
Location
Detroit, MI -- USA
Recently re-built from the ground up my CB350K4, every part that could come apart from another part was removed from that part. At the time my engine guy mentioned that he'd seen CB350K4 motors with half the mileage (mine was at 22k) and twice the wear, particularly the oil pump and bottom end was as tight as he's seen. I replaced every gasket, oil seal, and even found a NOS Rubber Ball for the bottom end. Every O-ring was replaced with either oem or brand new proper sized modern o-ring. The cam was re-worked by MegaCycle and the bike pulls hard over 7k. It's a joy to ride now and I've had a blast breaking it in and riding it for the last 1500mi.

I have one issue. I have 64mm stock bores, new rings and no overbore. Good compression. The headgasket used in the rebuild was an "OEM" it had silicone "fire rings" around the oil galleries in the back of the head.

Everything was completely dry up top for 600mi after the re-build, I had just started shifting up around redline, 9k. I had to get somewhere quick one night and jumped on the freeway and held 70mph (17/36) or 6800rpm ish for 20min or so. The next morning before work I noticed that the gap at the head gasket looked damp, and after a few more trips at 70mph and up that the head gasket is seeping, likely at the galleries. I'm considering a bypass and bearing system for the cam, but honestly that's a ton of investment for a daily CB350.

I talked to a tech rep at Cometic, they can't get 64mm fire rings.. I am thinking of just biting the bullet on a nice new valve/guide/spring system, but I don't expect to spin 12k anytime soon. Overboring the cylinders and putting in new pistons and rings to match just so I can get a top quality headgasket is absurd.

What is the best way to eliminate my issue, I was thinking that a better headgasket would help, but if the best in the business at custom headgaskets can't help me what are my other options?

I want to be able to ride my bike for long distances at decent rpm, for long trips (>1hr) spinning 6k shouldn't be an issue, and 7k for 45min shouldn't burn anything up. Obviously pushing the motor at 8500 for any length of time isn't healthy, but I'd like to commute in Detroit without seeping oil.

Nick
 
In my experience, more with 450s than 350s in the last few decades, using a new dry head gasket isn't always enough regardless of brand. I used a dry Cometic head gasket on my 450 initially but around 600 miles or so it began to seep oil in the front along the cam chain tunnel. By coincidence I had to pull the bike apart for a frame repair and while the engine was out I replaced the head gasket with another Cometic and used a thin smear of silicone sealer in those areas and it is oil tight now. For yours, I'd suggest a thin smear of sealer (of your choice, many don't like silicone sealer but the reputation is bad only by those who seriously overdo it and it gets into oil passages) around the sealing areas at the rear studs where the oil flow goes to the top end on both sides of the gasket. Not right up to the studs, more like at least 1/4" to 3/8" away from the edge of the gasket where it encircles the stud as a second barrier of sealer. I've done it many, many times over the years and it's been totally safe as long as you don't overdo it. My 450 has over 2600 miles on it now, during many of which it was thrashed while riding in the mountains or at the drag strip and all is well.
 
You didn't mention your top nuts torque and if you retorqued after the rebuild? And your retorque process.
Edit: and if you checked the cylinder & head mating surfaces for flatness?
 
Copper head gasket with some spray Copper Coat on it.

I oil the studs/nuts and torque to 16 ft/pounds. I use the Copper Coat on all the top end gaskets.

DSC03543.jpg

DSC03544.jpg

Not sure if this supplier is still in business but there are others. You can reuse the copper gasket by cleaning and annealing it.

Edit to add .... copper gaskets allow the engine to run cooler, I know you are looking at the oil gallery leakage and copper gaskets need some sealer around the knock pins.
 
I don't know that you have to spend nearly the cost of a full gasket set on the head gasket. I always try to buy Vesrah gaskets if available

https://www.dimecitycycles.com/gasket-set-cb350g44-cb350k1-k444-cl350k1-k5-complete.html

Thanks. I've seen Vesrah recommended a lot.

I guess my thought was I've had so much better luck with genuine Honda parts. Coupled with the fact I don't have any upper leaks (just everywhere else, lol) and see all these various techniques to keep that from happening with aftermarket. But I also wonder if many issues just aren't surface prep or assembly? Maybe I've just lucked out in this regard.
 
Thanks. I've seen Vesrah recommended a lot.

I guess my thought was I've had so much better luck with genuine Honda parts. Coupled with the fact I don't have any upper leaks (just everywhere else, lol) and see all these various techniques to keep that from happening with aftermarket. But I also wonder if many issues just aren't surface prep or assembly? Maybe I've just lucked out in this regard.

After all these years and who knows, really, how many times these engines have been apart and reassembled by God knows who and how, it's no surprise to me that some of them leak regardless. I've used plenty of aftermarket gaskets and while OEM gaskets would be preferable, they're just not as available now and frankly you'd be hard pressed to be sure what you see in an eBay ad would truly be NOS too. I've used Vesrah and NE brand, both from 4into1, and other than head gasket seepage cured with a little sealer all the other gaskets in the sets I've bought have been fine.
 
I have a 1976 CJ360. It recently developed an oil leak from the upper part of the engine. My initial guess was a leaking head gasket. I followed advice on VHT and cleaned the engine and then dusted with talcum powder to help locate the source. It appears to be right side of the engine on the back side. What’s odd is that oil accumulates on one or two fins ABOVE the head gasket (also on fins below). I have not yet pulled the tank to get a better look. But does anyone know if a leaking head gasket could cause oil to accumulate on the on fins above the head gasket during a ride (nothing extreme — 20 minutes at speeds up to 40 MPH and revs up to 6,000)?
Thanks for any insight that can be offered.
 
Have you checked to see if it may be coming from one of the tappet inspection covers?
 
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