Topic: Dreaded CB350F Head Gasket Oil Leak

[danfr]

I just had the factory (Parker) make me a batch of 50 of the O-rings on the oil pickup funnel (16.5x2.00mm), a critical one that no one offers today. I'll be posting those in the For Sale section and on my website in the upcoming "Baby Fours" section.

Hondaman, do you still have these O-rings on the oil pickup funnel? and what part exactly is the 'oil pickup funnel'?

I just picked up an older gasket kit made in Japan so fingers crossed it'll be quality and seal up. I plan on going opening up my top end to take care of my leaky head. My plan is to use Permatex Copper Spray A Gasket on the head gasket and use Permatex Form-a-Gasket to reinforce the O-rings where the head and cylinders meet.

of course, I'm open to suggestions and insight!

Cheers

Dan

[danfr]

Ok, so I resurfaced my head (I work at a engine machine shop so it's free and couldn't hurt), I used a harder ball hone to deglaze the cylinders (I noticed my last rebuild had an oil leak because the chrome rings were not seating), I used hondabond on the o-ring jets and I used copper spray a gasket on the head gasket. I finished the rebuild and worked out a couple other non related bugs and took the bike out yesterday. The bike smoked a bit initially (assembly oil i'm thinking) but afterwards, I have seen no oil leak externally and no signs of an internal oil leak.

hope this helps anyone out there.....

cheers

[hoodellyhoo]

Glad to hear of your success. Please keep us posted as you put on more miles.

[HondaMan]

Ok, so I resurfaced my head (I work at a engine machine shop so it's free and couldn't hurt), I used a harder ball hone to deglaze the cylinders (I noticed my last rebuild had an oil leak because the chrome rings were not seating), I used hondabond on the o-ring jets and I used copper spray a gasket on the head gasket. I finished the rebuild and worked out a couple other non related bugs and took the bike out yesterday. The bike smoked a bit initially (assembly oil i'm thinking) but afterwards, I have seen no oil leak externally and no signs of an internal oil leak.

hope this helps anyone out there.....

cheers

Cool! I have to bookmark this for my upcoming 350F rebuild (poor thing...).

[danfr]

Here's a couple shots


The head resurfacer in action. well, when I was done.



I used a courser grade flex hone to help the crome rings seat. Previously I have used a finer flex hone (probably for standard moly rings) and the rings did not seat at all.

I used made in Japan gasket kit that I picked up at a swap meet in April. The kit was dusty and looked pretty dated but the O-rings for the jets were taller (and dark blue in colour).

Still no leaks so far, but I have a little bit of smoke coming out the exhaust still. after talking with my more experienced coworkers, it is likely from the heavy amount of assembly lube I used on the rings and bore.

anyhoo, feel free to ask any questions or if anyone need some photos. happy to be out there riding again!


Cheers

[craywm]

danfr:

I am currently on the rebuild from hell on my 1974 CB350F.

Long story short, I rebuilt initially to fix a rather large leak down of gasoline to the oil. I replaced the rings with a light hone. I got crazy smoke for a while and decided to rebuild again. came up with a really oily head gasket. rebuilt it 3 more times and now im on my 4th (snapped a cylinder stud on my last head retighten to fix oil burning. Replacing all seals again, had the cylinders/head honed and resurfaced last time. I am going to use 3bond around my head oil passages. I am spraying the head gasket. Shes a 1974 CB350F with around 35k and shes going to run again.

Anything I should watch out for in particular with my engine rebuild? I want this to be the last one. I had my head resurfaced be fore the last rebuild but only ran it for probably an hour before I decided to rebuild again because of my nice smoke screen I was giving off. My cylinders are within wear limit so im using STD size rings.

[craywm]

PS attached is a pic of my '74 with the same exhaust original paint. The lower handlebars help my back. still have the original handlebars and original mirrors with turn signals. came with clear and clean title too 35k. I like its original condition and clean nature. Wish I could find that original exhaust!

[danfr]

Anything I should watch out for in particular with my engine rebuild? I want this to be the last one. I had my head resurfaced be fore the last rebuild but only ran it for probably an hour before I decided to rebuild again because of my nice smoke screen I was giving off. My cylinders are within wear limit so im using STD size rings.

Hey Craaywm,

There's a few things I looked for...

O-rings! (the O-rings around the pump between the head and cylinders) It sounds like these are the biggest trouble for people. My first rebuild, I used an Athena gasket kit and the second time through, I used an older made in Japan kit that had no labels. I wish I took photos of the difference! The Athena O-rings were shorter in length and never created a good seal. Actually, hardly they hardly sealed if at all. If you can, source a good pair of O-rings.

Piston Rings: The piston rings you are using are very likely a chrome style. Chrome rings have a harder time seating so be sure that your deglazed pistons were honed with a coarse flex hone. With my first rebuild, the rings did not seat as the flex hone was too fine.

Guides: Check to make sure your guides are not worn, replace the seals, and if you can check that your valves seal with a vacuum test.

I used Copper Spray a Gasket on the head gasket as extra insurance. This is my first time using it, but I have heard others using it with success, so I though it was worth a shot.

As you can see on one of my previous posts, I also used Hondabond around the O-rings. Not too sure if it helped, but it couldn't hurt!

This is all stuff that has worked for me. I'm sure others have their own process with good results. Hope it helps. You have a great looking bike!

Cheers

Dan

[craywm]

Hey danfr. Exactly what I was going to do. not sure what the rings im using are. Here is another one like them.

http://www.ebay.com/itm/HONDA-CB350F-PISTON-RINGS-4-SETS-STD-SIZE-13011-333-005-/121117272128?pt=Motorcycles_Parts_Accessories&hash=item1c3326e840

Im also using a really generic Gasktet set. I too had hard time with the Athena kit. I put threebond around the oil passages before as well and its difficult to remove. That's how I determined the oil was from unseated rings. I had a machine shop put on the hone. Hope it will work, Ill snap a pic of them later. I also have pic of the head and head gasket after a major amount of oil was taking into the cylinders. I thought this was from the oil passages but its actually from the rings. Last thing I would have checked because it was the first thing I was trying to fix..

Thanks!

[danfr]

Yup, those are the same chrome rings I used.

Where I work, we always ask what rings the customer is planning on using as it determines the final finish of your cylinders and speaking from experience, it does make a difference. Maybe give the machine shop a call and ask them; I know I would. It would be a shame to have to go through all of this again.

Best of luck!

[craywm]

Danfr,

I may be using the same gasket set as you too. My oil passage seals are a dark blue as well. Ive attached a few pics of this.

What type of hone is required for chrome rings? Im putting up a pic of my cylinders honed on here to see if you can tell if they are fine. I cant contact the machine ship until Monday now.. unfortunately.

Are those the same type of exhaust gasket yours came with? these are like paper and copper wire?

[danfr]

Yup, looks to be the same kit. My gasket kit had a yellow cardboard backing to it and the same style gaskets.

Can't really tell you by the photos. Use your nails and feel for roughness. If you're buttoning it together this weekend, just make sure you don't kill it with kindness. Those rings need to be seated so you want that engine loaded up when you break it in. I try to go 2 up and search for hills after a rebuild. There are lots of different theories for break in, but this has worked for me so I'm gonna stick with it.

Cheers

[craywm]

Okay Thanks, how coarse should this feel with my nail? Minor nudges or like hanging up my nail? Also, did yours smoke while it was breaking in (seating of chrome rings)?

I used the same rings on my prior rebuild but used a crappy hone that was coarse. They were unable to seat properly and they looked terrible on the seating surface when I looked at them today. Im also replacing a cylinder stud so I am cleaning everything up and noticed the rings. I usually ride right between 2500 rpm and 5-6000 to break in. Through the  back roads.

Also, Do you know what your cylinders bores measured? or did you not mic them?

I read a great article that said too high rpm will glaze over the cylinders but too low rpm may cause the rings to never properly seat. I like a healthy mixture of hills and midrange rpm with a few WOT in second gear pulls.

May just be better for me to wait it out and just make sure everything's ready over the weekend and contact my mechanic on Monday.

P.S. - yep that's the same kit as mine. So hopefully we come up with the same results!

[craywm]

Danfr+All,

Im not sure if this is normal but all of my cylinder studs are slightly bent one way. I wasn't planning on replacing these as they have worked fine in the past. is this a normal thing?

[danfr]

You should feel a roughness, almost gritty feeling.

I did not mic my bores, so I couldn't tell you.

I believe the studs all had a slight lean towards the front of the bike. Not too sure if it matters, but I make sure that the ring gaps are never front and centre so that any oil will avoid draining out. and yes, I was burning oil for a little while. I'm a little neurotic so I go crazy on assembly oil.

cheers

[craywm]

yeah it feels slightly gritty, might now be coarse enough. Do you use thread lock on your cylinder studs? also what do you mean about the ring gaps? don't keep them front and center?

Thanks

[danfr]

No, I do not use threadlocker. I actually use a little bit of oil on the threading. Prior to reassembly, I also chase every nut and bolt that needs to torqued with a tap and die. I like a consistent amount of torque and any rust, foreign material or whatever could throw that off.

After you turn off your engine, any residual oil will follow gravity down and since the 350F engine has a slight lean forward, the oil in the cylinders will run forward to the front. I like to make sure that when I install my rings, that there is no gap at the front so that residual oil is contained and ready for the next time you startup the bike. It's an odd habit of mine. Could be worth nothing but it definitely cannot hurt.

Cheers

[craywm]

Thanks for all the info Danfr. That makes total sense with the oil. I like that tap idea too. My head is in great shape minus the stripped threads for the head cover. someone a while back overtorqued the head cover screws  and stripped the threading out of the head on a few. theres still enough thread there to get some of them to tighten to 8 Ib-ft which is still capable of sealing and everything. eventually this puppy will need a new head but I havnt been able to find a good used one. Thanks for all the input!

[craywm]

was able to call the mechanic, hone is good for chrome so im going to continue with my rebuild. I will update.

[craywm]

Danf/ all,

Here are some pics of a cylinder of mine after being honed at the machine shop. the rings cut where the ring gap was a mark into the cylinder wall. They were able to hone off most of it and I cant feel it with my nail and barely can with the tip of my finger. will this prevent my rings from seating properly? I have a few other small lines on other cylinders too.

Should I get the machine shop to hone off the rest of this or will my chrome rings take care of whats left of the cuts?

[craywm]

hello all,

Here are a few more pics of my progress:

Head cylinders and head cover. cleaned up ready to go


Half of studs in. next half to go:


Block after installing the cylinder studs. You can see how a jimmy rigged the carbs so I didn't have to take them out. now sure if it was worth it yet.


valves with a minor cleaning. exhaust valves are still very dirty from burning oil. Do these look okay?