Topic: Three top-end questions

[AbbyRider]

I'm at the start of doing a top-end rebuild, and after opening things up a bit I've got a few questions:

1. In the first photo, you can see that there are a few chunks missing out of the head cover, in the area under the breather cover. Will this affect anything? Looks like maybe the cam chain whipped around in there or something? I did find bits of metal in my oil pan, so I'm assuming that's where they came from.

2. In the second photo, I'm showing something that's always bugged me. It's extremely difficult to get my plugs out because of the bolt that sticks down close to it. I think it's a flange bolt. Is this bolt the right length? Is it supposed to stick down that far? Bottom 1/2" of the threads aren't doing anything anyways, and it drives me nuts.

3. This one bothers me the most. Third photo shows some sort of patch that the PO used on the cylinder head. This would be the depression closest to cylinders 3 and 4. Looks like some sort of plastic material was epoxied in. I have no idea what might have happened there, but is this a section of the cylinder head that would be stressed at all?

Bike is 1978 CB750F. Thanks in advance for your sage advice and/or guidance.

[bryanj]

(1) They are all like that---HONEST

(2) Wrong bolt fitted, its too long (parts book will tell you correct size

(3) there is a bulletin somewhere about a screw that can fall out and punches a hole in the casting, as long as it dont leak carry on using it

[AbbyRider]

Awesome. Thanks. Not sure why all the bolts are too long on this engine. PO must have swapped out ALL of the flange bolts for longer ones for some reason. Unless it was a cruel, practical joke at the Honda factory.

[ekpent]

Might not be a bad idea to verify that the too long bolts are still metric and that the PO did not change them out to an american thread before replacing. Hard to out guess them sometimes.  The gray patch has the same color as JB Weld.

[754]

If you need any 78 f motors, i have a few for sale, 4 hours from you.. Also there is a frame in town with reggie if someone wants to put one together..

[754]

 The parts in the breather look like they are cast that way, and just poked thru, to eliminate machining.
 your #3 pic, nothing touches in that depression, so chance of damage in there is remote. I would be leery of the PO's work if they had used any type of sealant or filler there. Cam tower must sit flat or undue wear/binding can occur. the round pucks in there can leak if they harden, replacement with fresh ones is better than using a layer of sealant

[MCRider]

Might not be a bad idea to verify that the too long bolts are still metric and that the PO did not change them out to an american thread before replacing. Hard to out guess them sometimes.  The gray patch has the same color as JB Weld.

That's a good point. So we know the engine has been invaded. In that spot, and 3 others like it, there shouldn't be a bolt at all, but a stud; 6/58. The stud would be threaded into the head, so the bottom end of the stud may just be visible in that open part of the hole in your picture. The bearing cap goes on and a nut is threaded onto the stud. So the bearing caps are held on by a stud and nut affair on the front (exhaust side) and a bolt only on the back (intake side).

Often people will remove these studs to clean and/or blast the head. They may just replace them with bolts to shortcut the reassembly. This can be a bad thing. If you rely on the strength of the threads in the head to get the torque you need on the bearing caps, something may fail. By using the stud, you just thread it in to a soft bottom and stop. Then you thread the nut on top and that takes the torque.

Also, in removing the studs, its not uncommon that they pull the threads out of the head. rather than helicoiling the hole, which is difficult in that area, they can run a 1/4-28 American SAE bolt in there. Its pretty close to a 6mm diameter and fine thread.

Did you have a curious oil leak out of the middle fins of the head?

[Pecantree]

#1 Good to know about the valve cover. Same issue on mine, thought for sure I'd have to buy a new one.
Thanks Bryanj!
I'm curious what you find under the sealer

[AbbyRider]

In that spot, and 3 others like it, there shouldn't be a bolt at all, but a stud; 6/58. The stud would be threaded into the head, so the bottom end of the stud may just be visible in that open part of the hole in your picture. The bearing cap goes on and a nut is threaded onto the stud. So the bearing caps are held on by a stud and nut affair on the front (exhaust side) and a bolt only on the back (intake side).

MCRider: In looking at my engine and referring to the parts diagram, I'm fairly sure that the bolt that's sticking down and in the way of the plugs is #90054-300-000 - which is called up as a 6x58 Flange Bolt. Goes through the camshaft holder and down into the cylinder head. I measured the bolts - they're 6x58. Am I missing something?

Did you have a curious oil leak out of the middle fins of the head?

Ah, yes. Actually, I've got oil leaking all over the place. The pucks were quite hard, and will get replaced. PO had replaced all gaskets but hadn't cleaned off previous to his work. So I have a feeling that shoddy workmanship has led to much oil getting displaced down the front of my engine, down the back of my engine, and all along the downtubes of my frame.

[AbbyRider]

If you need any 78 f motors, i have a few for sale, 4 hours from you.. Also there is a frame in town with reggie if someone wants to put one together..

Thanks for the offer! If all goes well with the work I'm doing, I'm probably going to sell this bike in Spring and look for another project. And Kelowna's only 3 hours for me - 2-1/2 if I'm feeling lucky.

[AbbyRider]

The parts in the breather look like they are cast that way, and just poked thru, to eliminate machining.

This is both a relief and a worry - means that the metal chunks in my oil pan came from somewhere else.

[MCRider]

In that spot, and 3 others like it, there shouldn't be a bolt at all, but a stud; 6/58. The stud would be threaded into the head, so the bottom end of the stud may just be visible in that open part of the hole in your picture. The bearing cap goes on and a nut is threaded onto the stud. So the bearing caps are held on by a stud and nut affair on the front (exhaust side) and a bolt only on the back (intake side).

MCRider: In looking at my engine and referring to the parts diagram, I'm fairly sure that the bolt that's sticking down and in the way of the plugs is #90054-300-000 - which is called up as a 6x58 Flange Bolt. Goes through the camshaft holder and down into the cylinder head. I measured the bolts - they're 6x58. Am I missing something?

Did you have a curious oil leak out of the middle fins of the head?

Ah, yes. Actually, I've got oil leaking all over the place. The pucks were quite hard, and will get replaced. PO had replaced all gaskets but hadn't cleaned off previous to his work. So I have a feeling that shoddy workmanship has led to much oil getting displaced down the front of my engine, down the back of my engine, and all along the downtubes of my frame.

I'm guessing that you are looking at the page for the "camshaft and holder"? Bolt #4 is indeed the bolt you need and its 6x58. Those bolts hold down the cambearing cap and they go in the intake side. On the Motogrid fish, the quantity is not listed as they are no longer available, but if it was it would say (4).  If you'll notice paired with each bolt is the 6mm nut that goes on the exhaust side. The stud that they (4) go on is not on this page.

You have to go to the "cylinder head" page of the parts book. It is #13, a 6x58 stud part number 90055-300-000. Do you see it? They are no longer available either. A real curve ball.  So the bolts only go in the intake side. The stud and nut affair goes in the exhaust side. If you are having mysterious oil leaks for sure suspect the pucks. But also, once the seal of the factory stud-in-head is broken, you have the very real (I know) chance of oil wicking down the threads of a bolt in the exhaust side, dripping into the fins at the bottom of the hole in your picture, in the plug cavity and exiting the fins at midpoint. At a stop the oil will drip and drain forward as the engine is tilted, at speed it will blow out and back all over creation.

My suggestion is to try and get those OEM studs again, clean the holes mercilessly, with a QTip and acetone or whatever, and reinstall the studs using a locktite type thread sealer. Tighten them into the head only far enough that you have enough sticking out to put the nut w/flat washer on top of the bearing cap. You may need to dry fit them to be sure of install depth. Let the sealer dry hard before putting the nut on and torquing it.

Don't worry, it will still leak.   

[MCRider]

I notice that the nuts on my K2 are to be used with flat washers. On the Fish for your 78F, the nut is a flanged variety, (quan 4    ). So you don't need the flat washer, disregard that and replace it with a flanged nut. Flanged is more elegant.

Still available: 94050-06000 (94050 is Honda code for a flanged nut-06000 means 6mm.)

[AbbyRider]

Ahhh... I see it now. So the hunt for studs begins. (that's what SHE said)

[MCRider]

Ahhh... I see it now. So the hunt for studs begins. (that's what SHE said)

I was thinking about the lengths of the studs being the same as the bolts. When you think of it, the bolt is measured from under the flanged head to its threaded end. The stud is end to end. So the bolt is actually longer by the thickness of the head, causing it to thread deeper into that threaded hole than the stud and nut affair, even though they are considered the same length. And so, hit your spark plug wrench.

[AbbyRider]

MCRider - exactly! That's why when PO used the 58mm long bolts he didn't account for that extra length. Should have used 50mm if he wanted to use lazy-ass bolts. Oh well - I needed to get in there anyways, so it's an easy fix by using the proper studs and flanged nuts. There are a few online parts stores that carry them. $2.05 a piece for the studs, which isn't bad. In fact, I just ordered them.

[MRieck]

Ahhh... I see it now. So the hunt for studs begins. (that's what SHE said)

Have 5 or 6 dozen of those studs

[Pecantree]

Don't worry, it will still leak.   

This scares me
In kind of an Aw Jeez kind of way!

[MCRider]

Don't worry, it will still leak.   

This scares me
In kind of an Aw Jeez kind of way!

Well that's the cynical side of me coming out. Done properly, it should be tight as a drum.    I just buttoned mine up, so we must hope.

I've built many that didn't leak, but its been a long time.

[AbbyRider]

Have 5 or 6 dozen of those studs

Can I buy 4 from you? Would be much appreciated. Can PM you if you prefer.

Dwayne