Topic: 1978 750F Head Assembly Questions

[asphalt900]

Hello All! A Couple Questions concerning the 1978 750f
1. Looked high and low for the Cylinder Stud Grommet in diagrams/for sale, cannot find mention of it anywhere. This is the "cone" shaped rubber grommet found on the 3rd and 6th forward cylinder studs. Didn't come in the gasket kit and does not show-up in any schematic I've seen. Any Clues? Also seems this is a revision to replace the additional 4 High O-rings 12115-300-000 and dowels found on earlier cb750's. Cylinder is manufactured for placement of the additional dowels/orings, Aftermarket Head Gasket also allows this addition. Would this be "extra" insurance against leakage?
2. Read a couple topics regarding the "beveled" High-0-rings, 12115-300-000, found in the Aftermarket Gasket Kits. Are these prone to leak? And last, seems based off some other topics the 6 sealing discs are too thin. Included a photo of what I have, are these "thin" ones? Thank-You for Your time!! Clay

[asphalt900]

More Photos. Thanks, Clay

[dlhoulton]

I just rebuilt a 77 cb750F and used the same gasket kit. In your second post, the first picture. That "cone" shaped rubber grommet is just an "O" ring that should be in your kit. It gets "cone" shaped or formed due to the shape of the area it gets pressed into when the cylinder head get bolted to cylinder. Look at the underside of the matching part and you well see it is "cone/beveled" shaped. Those four metal "Special knock pins" and "Cylinder stud bolt packing's" went from 8 to 4 on later year models. I don't know if it's wrong but when my 78 and 77 cb750 were rebuilt they both had 8 and I just went ahead and put the 8 back in.
As for the six pucks I'm not sure if those are too thin. I followed "Hondaman's" as well several others advice and applied a very small amount of a "gasket type" compound/sealer around edge of those pucks to insure they stayed in place and gave a little bit of assurance.
Hope that makes some kind of since.

[asphalt900]

Thanks dlhoulton! That makes Perfect sense NOW, Thank-You! Just bought some "Original" Bolt Packing O-rings on ebay. Referring to one of Hondamans posts that he had an issue with sealing using the supplied Packing Seals out of the Althena Kit. Just trying to cover all bases. DON'T want to have to pull the engine again!!! Clay 

[madmtnmotors]

In your second post, the first picture. That "cone" shaped rubber grommet is just an "O" ring

Correct

just an "O" ring that should be in your kit.

Incorrect.
These are fat little O-rings that are no longer made for the CB750F. Good news is, Honda still uses them in other engines. The original CB750 part number is: 91301-410-000 and is item #6 on this parts fiche:
http://www.servicehondapsn.com/fiche_section_detail.asp?section=2451943&category=Motorcycles&make=Honda&year=1978&fveh=131108


The identical 5.5x3mm o-ring from http://www.boats.net/ is: 11-91353-921-310

Also, be aware that the "abandoned" oil return studs (the ones that get the aforementioned fat little O-rings) use acorn nuts and copper washers up top, in place of the standard head nut and steel washer.

[flybox1]

Do yourself a huge favor, and check out brandEn's leak free top end thread.
Lots of good info there.....

[asphalt900]

Thank-You for the GREAT info Gents!!! I purchase a few items from the O-Ring Store and they normally have the "odd" sizes but don't have the 5.5x3M in any selection. Thank-You madmtnmotors for supplying the correct size! I'll use your advise and purchase the correct Honda part# item as stated. Flybox1, how do I find the article by brandEn? I'm trying to make sense of where the pressurized oil is delivered and where it is dumped back into the crankcase and where it can be lost outside the engine, I'm getting close. Does the "Only Camshaft oiling source" come up, and around,the 2 inner intake side studs? I'm a Kawasaki fella and this arrangement is the same but the cams are feed on the outer-ends. The Honda studs Must be Super close to the milled hole in the galley!!
Just for info. This engine ran fine but misted the Left leg with oil at speed. Not being familiar with the internals I thought, as with the Kaws, a bad seal to the upper-end. So if they oil from the rear what would cause a mystery leak between 1 and 2 cylinders towards the front? The pucks seemed tight before removal and oil free underneath. Thanks, Clay 

[koendd]

there you go

http://forums.sohc4.net/index.php?topic=107040.0

[dlhoulton]

madmtnmotors,  thanks for the correction. I do now remember not being able to find those "O" rings and buy cross referencing first by number then buy description found them available through Honda Marine. The 5.5x3mm "O" rings are still used in Honda marine engines. I went to the same link you provided to get them. Sorry for the wrong info I provided.

[madmtnmotors]

thanks for the correction.

Happy to help. I spent many hours scouring the forum(s), service manuals, parts fische's, and any other source I could find trying to wrap my head around the oil path in these later F motors. Once I had it figured out, I still wanted to put the acorn head nuts on the wrong studs.

I did notice in brandEn's thread referenced above that he did not use the acorn nuts (and copper washers) on the abandoned oil return studs. It may not make a difference, this would have been done to prevent oil from weeping past the threads and might not be absolutely necessary...

[flybox1]

I made sure to use acorn nuts and copper crush washers on these studs.  Please dont forget this step. 

Clay...I have an extra set of those 5.5 x 3mm stud o-rings, or you can order them from boats.net .  PM me if you are interested.  They wont work on HD studs, BTW, only on the OEM studs.

the Google Custom Search bar up there in the left corner of the forum page is a great place to search key words 

http://forums.sohc4.net/index.php?topic=107040.0

[asphalt900]

Thanks to EVERBODY for Helping me along!!!! Think I got it for the most part, figured out. Every machine has it's Achilles-heel of some sort. ONLY thru living with them for a while can one sort thru and find the True Answers. Used to think the CBX was a nightmare but it's much easier the longer you live with it. Will be back, I'm sure, to ask the experts! Thanks Again!! Clay

[Red Good]

Anyone have a link to where the acorn nuts and copper washers go . 5-8 spots in a 78 F motor ? I have several and none came to me assembled .

[madmtnmotors]

Anyone have a link to where the acorn nuts and copper washers go . 5-8 spots in a 78 F motor ? I have several and none came to me assembled .

You want to make sure you have the right barrels to begin with. In the picture below you can see the underside of the barrels have four oil returns closed up. This is where the fat little o-rings go at the base of the stud on the outboard side of the inboard cylinders (#2 and #3):



It is these same locations where the acorn head nuts and copper washers will go up top as shown here at position 5,6,7, and 8:



And you want to be sure you have the right head. The F2 heads only have four oil returns:



The F0/F1 (75/76) heads and barrels are the same as the K7/K8 with eight oil returns and do not require the large o-rings at the base nor the acorn nuts/copper washers.

EZPZ 

[bryanj]

Position of the acorn nuts is shown in the F2/3 genuine Honda manual, cant get to mine at moment