SOHC.co.uk Forums > CB750
1978 CB 750 F2 - Oil pouring from above head gasket
stoutgoose:
First start since rebuild and within a a couple of minutes running oil starts dribbling from the head above the gasket line from between cylinders 2 and 3. A small pool had formed within a few seconds.
Scanning the forum, I found a old post below that mentions using the domed nuts and copper washers on studs 5-8. During the rebuild I put in ARP studs and the nuts that came with them which were for the F2 yet didn't have domed ones. Also, I don't recall any of the washers being copper. Irritatingly, there was no mention in the manual about either copper washers or the import of the domed nuts.
My question is this; how can so much oil come from this area, and has anyone else experienced this? I'll be removing the engine to rectify this but am worried it may be something else as well.
Old thread:
"hya there serge, to help you understand, look at your f3 head, there are only four oil return holes...
Each "pair" of valves share one hole, whereas on the k series heads,there is a return oil hole next to EVERY valve.....
Be VERY VERY carefull that you do TWO THINGS RIGHT. Down at the crankcases BEFORE you put the barrels on, make sure you have installed the four tiny "o" rings on the studs that do not have the knock pins, I believe from memory these are labelled 5,6,7and 8 in the tightening sequence, but NOT IN EVERY MANUAL!! ( I have two manuals that show different tightening sequences!)
The purpose of these "O" rings on the studs is two-fold, the stop oil rising up the way AND believe it or not (BUT ITS ABSOLUTELY TRUE!!) they stop water and weather from entering down the way so to speak, this can be proved by looking at your cylinder head in a moment!
IF, you take a screwdriver or other probing device (but not your personal tool so to speak) and poke it down "those" (5,6,7and8) stud HOLes ON YOUR CYLINDER HEAD, AND LOOK through the fins, "OH MY GOD" YOU MAY WELL EXCLAIM, "why can i see my screwdriver?"
You will then be in the enviable position of being in the f2/3 "know" This is because "those" holes are not fully enclosed like in the k series, and should you forget OR neglect to replace those copper washers and domed nuts with new copper washers OR put the domed nuts on the wrong studs, you WILL get oil pissing out between the fins when the motor is started.........MORE THAN ONE person has experienced this! ( including me!) and I now have a mission to stop other people from the pain this causes!!
If ever you get the chance to see UNDERNEATH the barrells of a k and an f2/3 side by side, DO IT!
If ever you get the chance to see a k series AND f2/3 series head side by side DO IT!
Only close inspection reveals the differences and its well worth the looking and then the knowing!
kindest of regards,
kaceyf2"
MrDavo:
Sorry to hear that, there’s nothing more disheartening than getting an engine back in and everything fastened up, only to realise that it’s going to have to come out again. That’s when I go and get drunk instead.
I’m not familiar with the F2 head, but I assume they still have the large rubber bungs under the cam holders. My CB750 leaked badly from there, but I had to change them anyway when it ate it’s crankshaft. The originals had turned to stone with age and didn’t seal anymore.
K2-K6:
Below is a copy from official workshop manual for your engine.
[ Guests cannot view attachments ]
Shows location of special capped nuts and sealing washers to prevent oil leaks.
For sealing they mean the copper type. If you're unfamiliar with copper annealing, just heat to red on a gas ring and quench in water to soften the material and they'll seal properly.
Hope it helps your rebuild.
Spitfire:
This could have caught me out, I bought an F2 as a project and did not realise the difference as I had only ever worked on K engines, luckily I spotted it on this or the US site.
Cheers
Dennis
Bryanj:
Not trying to be silly but it is possible to fit the rocker gasket wrong and it leaks
Navigation
[0] Message Index
[#] Next page
Go to full version