Topic: 1978 head gasket

[jmac851]

I am rebuilding a 1978 cb750 and find that the standard head gasket that is found in all of the complete sets has the 2 lower outside stud holes are just large enough for the collars to pass through. The manual says to install an o-ring on this collar. Do I install the o-ring on top of the gasket or under the gasket? Do I cut the hole larger to be the same size as the 2 inner rear drains?

[flybox1]

do not cut the gasket.
the only o rings are the ones on the (2) oil drain passage studs. 

see this thread before you do any more.
http://forums.sohc4.net/index.php?topic=107040.0

[jmac851]

On page 36 of the Honda service manual, it shows a picture of the 4 O-rings that are to be installed on the top of the cylinder before installing the head for a 1978 engine. What's the story.

[flybox1]

fig 3-37 only shows two o-rings

[flybox1]

http://images.cmsnl.com/img/partslists/honda-cb750k8-four-usa-cylinder_bigma000044e03_db19.gif

only two (#7) in this one, as well.

[jmac851]

Figure 3-37 on page 36 shows 4. 2 are on the intake side and 2 are on the exhaust side. The intake side ones are the oil feed lines from the pump and the two on the exhaust side seem to do nothing. Those studs have no oil near them.

[madmtnmotors]

We really need pictures of what you're looking at. The later models used 2 o-rings and 8 "barrel" shaped rubber seals in conjunction with eight dowels, plus the two locating dowels on the front corners for a total of ten dowels, eight "barrel" seals, and two o-rings. The two locating dowels at the front corners do not get o-rings. Early models did not use the eight dowels nor barrel seals and many omit them without ill effect. These would be located at the eight oil return studs (4 if we're talkin "F" model), and the 2 o-rings are used at the two oil feeds at the center rear.

Try Branden's "leak-free top end" thread...

[jmac851]

My bad.  I was looking at the picture and I didn't read the text.

[madmtnmotors]

Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0

He uses an "F" model but the "K" is similar.

[pdeg]

This is topical ... I was going to ask the same question.

I too have an F2... and I only have 4 of those dowels and  "barrel shaped" O rings...  NOT counting the 2 longer ones for locating the head.

I presume that these go into the oil return studs.  Looking at the head.. I only see 4 return holes .. 1 for each of the sets of valves.

This gives me 2 questions.

1. That leaves 4 "shouldered"  stud holes in the barrels empty ?

2. More importantly .. will these fit under the Cycle X  MLS head gasket... You say NOT to enlarge the gasket.
    The leak free thread guide says he left them out all together.

Many tx

Picture below

[flybox1]

Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0

He uses an "F" model but the "K" is similar.

Agreed.
I put his thread link up in my first thread, too.    Its too valuable.
The ONLY o-rings not to be left out here are the two oil passage o-rings on the intake side, on either side of the cam chain tunnel. they have a small recess.
In pdegs picture above, they are on either side of the while cam chain roller. 

[pdeg]

Yep..

The 2 on the intake side near the cam chain tunnel are the oil feed up the studs from the gallery on the block
behind the barrels to the valve gear.  They have just  o-rings in the recess..

At this stage, regarding oil return .. will fit the dowels and probably the barrel shaped O-rings into the oil
return studs, under the MLS  They may not seal, and they are the old ones..  but I cant see any harm..

Just another query ... Are there any washers under the bolts that hold the head down.  There are washers
on the nuts... but I do not recall any on the bolts.

**************** Take that back ..

Just fitted the head....... if you leave the dowels in .. they are proud of the barrels about 2 thou.
..  As the gasket does not have the holes large enough to let the come up just the little bit.  That
would mean the head would not seat....

So I have left them all out !!!!

Peter



Tx guys
Peter