'84 Nighthawk S Cam Oil Baffle Cover/Plate

[capt42104]

Hello all!

I want to provide some interesting information I recently discovered on my project Nighthawk S.  I am currently doing what I term a "soft restoration" on a low milage (3150mi) 1984 Honda Nighthawk S (CB700SC) which has included rebuilding or servicing the forks, brake calipers, clutch and brake master cylinders, brake and clutch lines, lubricants, tires, brake pads, steering stem, battery, spark plugs, carb rebuild and O-ring replacements, etc. With that am now replacing a slightly seeping cylinder head cover gasket. Since these valves are hyd it is not common to remove the cover for much of anything but rebuild or leak mitigation, so many of us have not really poked around under the cover. Anyways, once the cover was off I noticed some interesting engineering in what Honda calls "oil baffles" on the cam covers. I noticed that one had what looked like deformed rubber gasket material so I removed it to find the gasket material had in fact failed. The I removed the remaining 3 and that all had rubber deterioration. These little cups are filled with oil from the pump then provide oil to the cam lobes. With these covers all not sealed I could see an issues right away with possible oil starvation to the lobes. Thankfully the cams look good and have no visible scoring. I hope.

With this, I went on a journey to procure 4 new baffle covers. After some research my looking at various OEM suppliers (RockymountainATV, Partzilla, CMS, Ebay, etc.) I could see there have been several revisions as the '84 part number has been superseded 4 times(12221-MJ0-005,015,025, then finally 12221-MCN-721 by '86 and the mid 90s revival of the DOCH 750. So far I have received an order from CMS and all were labeled 12221-MJ0-025. One of the new plates has a tiny weep hole, like the 4 original plates, and the other three are clearly not drilled. I can see you need a bleed hole to ride the oil supply of air, but it appears Honda decided this design was not needed after all. It should be noted that only Rockymountain listed the last revision for purchase.
I am waiting on orders from 2 other suppliers, one was the 3rd rev and the other is the last rev.

The pic of the uncovered baffles shows the difference from the one with and without the bleed hole. Notice the cup is full (hole) and the other is not (revised cover with no hole). At cold starting RPM the oil bleed oil bypassed quite a bit of oil by the way.

Any thoughts on which version would be better? I may not have a choice as I don't know what the other 2 orders hold for me. Hopefully, I can get 4 of the same type.

[Gene]

 I have a 85 CB 650cc NH. I'm wondering if my bike could possibly have the same problem?

Good luck on the restoration, I started on mine 14 months ago. it had 13,500 on it, and other than the usual things, I had to rebuild the carbs. I'm thinking you might have to do the same. If you end up having running problems, (mine was mostly just off of idle) it might be because Honda intentionally leaned the carbs out to comply with federal laws.

If you want, you can go to https://carbjetkits.com/ to see how easy it is to select new jets. If you go this route, be aware that their kit does not include gaskets.

Good luck and keep us informed of your progress.

[Bob H]

... One of the new plates has a tiny weep hole, like the 4 original plates, and the other three are clearly not drilled. I can see you need a bleed hole to ride the oil supply of air, but it appears Honda decided this design was not needed after all.

...The pic of the uncovered baffles shows the difference from the one with and without the bleed hole. Notice the cup is full (hole) and the other is not (revised cover with no hole).

Any thoughts on which version would be better?

Disclaimer - I am completely ignorant on these covers, and if they should have a hole or not.
But it would seem that the amount of oil to the cams would not be affected by that issue.

Isn't all the magic happening below that cover? Like the oil supply line to the region?
That is such a low mile bike, under 4,000 and mine had about 40,000 when I changed my valve cover gasket earlier this year.

Mine is a 1993 (late model 750) and does not appear to have those small holes. Honestly I paid no attention to them but they are part of the photos I took. I was amazed how good my cams look at 40,000 virtually no wear, all surfaces polished, no scoring anywhere. ADV rider has threads of KTM's eating cams below 10,000 as a common occurrence on some of the twins.



The main thing I paid attention to was how EXPENSIVE the 8 cork seal things are that hold the valve cover on.
I went OEM to make sure the "crush" tension on the 8 cover things was correct and not China junk.
Even so, it was a bit iffy tightening down. I did criss-cross pattern and just kept snugging up a bit at a time until it seemed like it got tight and hit home.

I used a very thin coating of Hondabond on both sides of the new valve cover gasket rather than just the recommended area at the half-moons because whatever was "recommended" has resulted in all of these eventually leaking for everyone. I figure that cover will never need to be removed again, and it does not leak now.

[capt42104]

I have a 85 CB 650cc NH. I'm wondering if my bike could possibly have the same problem?

Good luck on the restoration, I started on mine 14 months ago. it had 13,500 on it, and other than the usual things, I had to rebuild the carbs. I'm thinking you might have to do the same. If you end up having running problems, (mine was mostly just off of idle) it might be because Honda intentionally leaned the carbs out to comply with federal laws.

If you want, you can go to https://carbjetkits.com/ to see how easy it is to select new jets. If you go this route, be aware that their kit does not include gaskets.

Good luck and keep us informed of your progress.

Thanks for the info! Yeah I am also deep into correcting a previous carb rebuild attempt and use 6sigfma out of AZ for all my carb jet kits. A previous rebuilder blasted the jets with something and ruined them. Luckily these are not hard to replace. I did notice 6sigma richens up the inner two cylinders on their stage 1 kit.

[capt42104]

... One of the new plates has a tiny weep hole, like the 4 original plates, and the other three are clearly not drilled. I can see you need a bleed hole to ride the oil supply of air, but it appears Honda decided this design was not needed after all.

...The pic of the uncovered baffles shows the difference from the one with and without the bleed hole. Notice the cup is full (hole) and the other is not (revised cover with no hole).

Any thoughts on which version would be better?

Disclaimer - I am completely ignorant on these covers, and if they should have a hole or not.
But it would seem that the amount of oil to the cams would not be affected by that issue.

Isn't all the magic happening below that cover? Like the oil supply line to the region?
That is such a low mile bike, under 4,000 and mine had about 40,000 when I changed my valve cover gasket earlier this year.

Mine is a 1993 (late model 750) and does not appear to have those small holes. Honestly I paid no attention to them but they are part of the photos I took. I was amazed how good my cams look at 40,000 virtually no wear, all surfaces polished, no scoring anywhere. ADV rider has threads of KTM's eating cams below 10,000 as a common occurrence on some of the twins.



The main thing I paid attention to was how EXPENSIVE the 8 cork seal things are that hold the valve cover on.
I went OEM to make sure the "crush" tension on the 8 cover things was correct and not China junk.
Even so, it was a bit iffy tightening down. I did criss-cross pattern and just kept snugging up a bit at a time until it seemed like it got tight and hit home.

I used a very thin coating of Hondabond on both sides of the new valve cover gasket rather than just the recommended area at the half-moons because whatever was "recommended" has resulted in all of these eventually leaking for everyone. I figure that cover will never need to be removed again, and it does not leak now.

Honestly I was hoping I would not have to dive into the cyl cover, but after an initial test ride I noticed a classic oil weep from the one of the half-moons. Since I already sourced a gasket and the stupid expensive sealing washers, I jumped into it. What caught me eye immediately was the blown out rubber seal on one of the plates.

I just received the latest version of the plates from partzilla (12221-MCN-721) and they are solid, no holes. Those are going in now.

Thanks for the info and picture as well! Really helpful.

[Bob H]

... What caught me eye immediately was the blown out rubber seal on one of the plates.

OK, I see why you are messing with them. My bike has 10 times the miles and did not have that issue.

... I did notice 6sigma richens up the inner two cylinders on their stage 1 kit.

That is the first I have ever heard of different jetting for inner cylinders.
Not saying it's wrong, just never heard of it and I tend to have my ear to the railroad tracks on Honda Nighthawks. Maybe someone else can comment. I can only guess that it is an attempt to avoid heat to inner cylinders but honestly never heard of that being a problem either.

I followed Pete's lead and got jets from carbjetkits.com their options are for consistent equal jets across the 4 carbs. When I got my OEM gasket set for carbs from Partzilla they were labeled for 700s and I learned that the bikes share the same carbs after fairly extensive review of carbs on 700s and the late model 750.

When I think of synchronizing the carbs, I can't imaging why I would want the inner 2 jetted differently.
My California bike was jetted very lean. The increased jet size allowed for a more smooth power band up to redline, where before it was kind of hesitant to climb above 6,000 rpm

[capt42104]

I am real happy with the 6sigma kit, but did recently acquire a DynaJet kit that I will install this winter. The 6sigma solved the idle and low/mid throttle response concerns I had, but I still have a little flat spot a few thousand RPMS before and to redline. The DynaJet kit comes with new slide needles instead of just throwing washers under the OEM ones, which is preferable in my book. It is noteworthy my 700 is a 49 state bike in completely stock form with 3200miles on it.

RE the inner cylinder jetting, I recall this was a common practice in the early 80s with guys that amateur raced their air-cooled 4cyl bikes. We lived in the Central Cali and it was and still is 100+ most of the summer months. I do recall doing larger mains in the middle when I jetted my Suzuki GS750ES, but not my Kawi GPz750 and Gpz 550. I can say the sync was not affected at all on my 700 as I checked it every time I take the carbs out between the OEM and 6sigma jet setup. I will update when I do the DynaJet kit.