Topic: 1978 CB 750 F2 - Oil pouring from top of head.

[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"

[Nurse Julie]

Why don't you post this same question over here on the UK forum as well, you may get some help or advice.

[HondaMan]

There's another thing that causes your leak....the O-rings that fit into the head gasket around the 2 oil passages at the back of the cylinders, between cylinders 2-3, are too thin. They came to you that way in the gasket kits, because the gasket kit vendors will neither listen, nor care, that their head gaskets are 0.2mm thicker than the OEM version. So, these 2 O-rings MUST be 0.2mm thicker, or else the cylinder deck must be milled 0.020", to make it seal again. I send these out for donations to these forums, unless you are in UK: if so, then find a Parker O-ring dealer and get #01-111 O-rings, 2.62 x 10.77 metric size.

Oh - and you will need a new head gasket, sorry to say...

[scottly]

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.

Do you mean the leak is above the head gasket, and below the valve cover gasket? If so, another likely cause is the rubber "pucks" that fit under the cam towers. Some aftermarket pucks are too thin, and don't seal properly.

[stoutgoose]

Are these the tubular/flat walled o rings that fit around the four dowels?

I used a CycleX MLS gasket and their gasket/rubbers set. Ken at CX said it was not necessary to use the rubbers with the MLS, however I did as a 'just in case'. I had the head skimmed .006" and the block decked by .006", and added a thicker base gasket to compensate. I also ground the dowels to compensate for the decking and skimming. The MLS gasket is .040" thick and was much the same thickness as the original Honda gasket that came off the engine.

I didn't use any form of Copper seal on the gasket; it went on dry. Is the MLS gasket an issue?

There's another thing that causes your leak....the O-rings that fit into the head gasket around the 2 oil passages at the back of the cylinders, between cylinders 2-3, are too thin. They came to you that way in the gasket kits, because the gasket kit vendors will neither listen, nor care, that their head gaskets are 0.2mm thicker than the OEM version. So, these 2 O-rings MUST be 0.2mm thicker, or else the cylinder deck must be milled 0.020", to make it seal again. I send these out for donations to these forums, unless you are in UK: if so, then find a Parker O-ring dealer and get #01-111 O-rings, 2.62 x 10.77 metric size.

Oh - and you will need a new head gasket, sorry to say...

[stoutgoose]

I will check these again, however I used new pucks and properly sealed them in with Hondabond, so they shouldn't be the culprit I hope?

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.

Do you mean the leak is above the head gasket, and below the valve cover gasket? If so, another likely cause is the rubber "pucks" that fit under the cam towers. Some aftermarket pucks are too thin, and don't seal properly.

[HondaMan]

No, these are the 2 O-rings that seal the main oil passages between the cylinders and head. They are the 2 in the center back of the cylinders, by the cam chain tensioner. The issue is: the OEM Honda head gasket was thinner than today's head gaskets by about 0.2mm (0.030"-0.032"): today all head gaskets are 0.040" (1mm) thick. The difference can be made up in 2 ways: you can either deck the cylinders by 0.020" (0.05mm) or increase the thickness of these 2 O-rings: I often deck the cylinders by 0.010" anyway, and still use these O-rings.

In UK you can find these O-rings from a Parker O-ring dealer: they are Parker #01-111 all over the world.

Are these the tubular/flat walled o rings that fit around the four dowels?

I used a CycleX MLS gasket and their gasket/rubbers set. Ken at CX said it was not necessary to use the rubbers with the MLS, however I did as a 'just in case'. I had the head skimmed .006" and the block decked by .006", and added a thicker base gasket to compensate. I also ground the dowels to compensate for the decking and skimming. The MLS gasket is .040" thick and was much the same thickness as the original Honda gasket that came off the engine.

I didn't use any form of Copper seal on the gasket; it went on dry. Is the MLS gasket an issue?

There's another thing that causes your leak....the O-rings that fit into the head gasket around the 2 oil passages at the back of the cylinders, between cylinders 2-3, are too thin. They came to you that way in the gasket kits, because the gasket kit vendors will neither listen, nor care, that their head gaskets are 0.2mm thicker than the OEM version. So, these 2 O-rings MUST be 0.2mm thicker, or else the cylinder deck must be milled 0.020", to make it seal again. I send these out for donations to these forums, unless you are in UK: if so, then find a Parker O-ring dealer and get #01-111 O-rings, 2.62 x 10.77 metric size.

Oh - and you will need a new head gasket, sorry to say...

[madmtnmotors]

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:


"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!"

Did you make sure these four fat little O-rings were in place at the base of the cylinders prior to assembly? These are odd little o-rings are 5.5mm I.D. and 3mm thick and separate the crankcase from the atmosphere on the F2/F3 models. These are even more important than the copper washers and acorn head nuts (which should also be used IMHO).

One other caveat is the cam tower bolts vs the cam bearing bolts. There are two bolts in the middle of each cam tower that hold down the cam tower and also capture the middle of the rocker pivot pin. Then there is one bolt at each cam bearing that is paired with the cam bearing stud. So you have two cam bearing bolts and two cam tower bolts for each cam tower. The problem is that the tower bolts are 63mm long and the bearing bolts are only 58mm long (almost a 1/4" shorter). The problem arises if you get these bolts mixed up because the longer (63mm) tower bolt will "punch through" the casting at the 58mm bearing bolt location if these bolts are mixed up. The bearing bolt hole will not accommodate the 63mm bolt. The casting at the bottom of the bearing bolt hole is very thin and does not take a great deal of effort to "bust through" if the longer tower bolt is used at the bearing bolt location. This issue is exacerbated by the fact that the oil feed for the cam bearing passes through the bore in the tower of this bearing bolt.

So the bearing bolts have high pressure oil behind them, and if the bottom of the bearing bolt bores have been compromised, these will leak PROFUSELY. I still have jeans with oil stains from my experience trying to track down this very issue I have described.

Hopefully you will be able to resolve your issue without too much grief.

[stoutgoose]

Update to close the thread. I removed the engine and stripped the valve gear to take a look at the studs. I located the copper sealing washers which weren't in the correct place (my manual made no mention of sealing washers and cap nuts). I removed the Kibblewhite nuts on studs 5-8, annealed the sealing washers and put them on studs 5-8 along with the correct cap nuts, and reassembled the bike.

Problem solved. The engine is now leak-free. It is rather surprising just how much oil can find its way down a stud thread and under a standard steel washer.

I'm now off to burn my 'Honda' manual and the Haynes version, and locate a real one. Many thanks for all your replies.