Topic: I'm stumped

[tofan]

I have a 1978 750F which the engine #CB750E-3152880. The new OEM dynamo gasket (part #11397-300-306) doesn't align and I found out the location of the dowel pin doesn't match the parts diagram.

In the attached parts diagram I highlighted the screw where the dowel pin is aligned with on my bike. In the gasket image in red I circled where the dowel pin is supposed to go and the hole circled in blue is where the dowel pin is located on the bike.   

What am I missing here?

[Ozzybud]

Looks like for some reason someone has moved the locating pin down!
In the picture of the case it looks like the remainder of the old pin was ground off or buggered up.
Open up the gasket and roll with it.
Pic of a Honda gasket below. Pin should be at 9:00

[tofan]

Looks like for some reason someone has moved the locating pin down!
In the picture of the case it looks like the remainder of the old pin was ground off or buggered up.
Open up the gasket and roll with it.
Pic of a Honda gasket below. Pin should be at 9:00

No other hole is big enough to fit the dowel pin. Even if I did move it up the gasket doesn't align with all the screw holes. I wish I saved the old gasket to show the difference. I'm starting to think the crankcase is not the right one, but I can't find a match.

[tofan]

Looks like for some reason someone has moved the locating pin down!
In the picture of the case it looks like the remainder of the old pin was ground off or buggered up.
Open up the gasket and roll with it.
Pic of a Honda gasket below. Pin should be at 9:00

Sorry! I just reread your post. Maybe they did grind it off. I'll take a closer look. But still... the gasket doesn't align with all the holes.

[pekingduck]

Very curious situation. 

Is the dowel pin hole in the case cover at 8 o'clock or 9 o'clock?
If you start to thread a screw into the 9 o'clock position, do the threads start immediately, or a little bit inward?

[HondaMan]

Maybe...flip the gasket over?
That should 'rotate' the big hole upward one screw position.

I've had [those green] gaskets before that lacked being punched to fit the dowel(s), but it's been a while since that was happening to me. There was enough material on those to punch the right size hole, but the accuracy was tricky to do right.

[Vintageguy]

I just completed the replacement of my coil(s) cover on my 1978 750F, which is 201 bikes earlier than yours. My dowel pins were located at roughly 7:00 and 2:00 if looking at the cover from the outside. Don't know if that is factory or not, but worked for me. Looks like the one you highlighted in yellow is correct for the lower one. Don't know where you got your gasket, but some of these aftermarket ones are poor quality in the accuracy department.

[Ozzybud]

Looking at pictures on Ebay of used parts it looks like your location @ 7:00 is correct! Also one @ 2:00

Modify gasket in 2 places and you will be good to go.

[HondaMan]

I'm curious about something here: is the engine's serial number oriented ACROSS the engine, or LATERALLY with it (i.e., parallel to the drive chain)?
At the end of 750 production there was a sudden, and largely undocumented, change done to the engine cases, and their only witness (that I've seen) is that the serial number got turned 90 degrees from the usual position. There is precious little info available about the cases with that change, although I have seen 8 of them myself. I don't remember having any gasket-hole troubles like this, though, on reassembly?

[craz1]

Or just make your own gasket, easily done.

[scottly]

Even if I did move it up the gasket doesn't align with all the screw holes.

Have you tried flipping the gasket yet??

[Ozzybud]

I'm curious about something here: is the engine's serial number oriented ACROSS the engine, or LATERALLY with it (i.e., parallel to the drive chain)?
At the end of 750 production there was a sudden, and largely undocumented, change done to the engine cases, and their only witness (that I've seen) is that the serial number got turned 90 degrees from the usual position. There is precious little info available about the cases with that change, although I have seen 8 of them myself. I don't remember having any gasket-hole troubles like this, though, on reassembly?

[Ozzybud]

I'm curious about something here: is the engine's serial number oriented ACROSS the engine, or LATERALLY with it (i.e., parallel to the drive chain)?
At the end of 750 production there was a sudden, and largely undocumented, change done to the engine cases, and their only witness (that I've seen) is that the serial number got turned 90 degrees from the usual position. There is precious little info available about the cases with that change, although I have seen 8 of them myself. I don't remember having any gasket-hole troubles like this, though, on reassembly?

Interesting history about the engine stamp area.
1st is a picture of my F1 and there is not enough real estate to rotate 90⁰
2nd is a pic of his bikes engine stamp. Clearly somewhere else.

[Ozzybud]

6 of the 8 1978 F2's on BAT exhibit a missing engine stamp pad in the area it is on all preceding years of the 750 SOHC engines.

[Medyo Bastos]

Flip your gasket over


Sent from my iPhone using Tapatalk

[scottly]

The serial number pad orientation has nothing to do with the OP's problem; the 750 alternator covers and their gaskets were all interchangeable as far as fit.

[scottly]

No other hole is big enough to fit the dowel pin.

You may have to open up 1 hole, once you figure out which way the gasket goes. A .45ACP case can be used as a gasket punch in a pinch.

[Ozzybud]

I was just posting that HondaMans observation is correct and the casting changed. I was not saying it had anything to do with the gasket.
Just some interesting facts

[tofan]

I'm curious about something here: is the engine's serial number oriented ACROSS the engine, or LATERALLY with it (i.e., parallel to the drive chain)?
At the end of 750 production there was a sudden, and largely undocumented, change done to the engine cases, and their only witness (that I've seen) is that the serial number got turned 90 degrees from the usual position. There is precious little info available about the cases with that change, although I have seen 8 of them myself. I don't remember having any gasket-hole troubles like this, though, on reassembly?

It's parallel with the drive chain.

[tofan]

Even if I did move it up the gasket doesn't align with all the screw holes.

Have you tried flipping the gasket yet??

Not yet. Haven't had time. I'll update once I get a chance.

[tofan]

Very curious situation. 

Is the dowel pin hole in the case cover at 8 o'clock or 9 o'clock?
If you start to thread a screw into the 9 o'clock position, do the threads start immediately, or a little bit inward?

8 o'clock. I will test the thread hopefully tomorrow.

[tofan]

I just completed the replacement of my coil(s) cover on my 1978 750F, which is 201 bikes earlier than yours. My dowel pins were located at roughly 7:00 and 2:00 if looking at the cover from the outside. Don't know if that is factory or not, but worked for me. Looks like the one you highlighted in yellow is correct for the lower one. Don't know where you got your gasket, but some of these aftermarket ones are poor quality in the accuracy department.

You have 2 dowel pins? Is that normal?

Got mine from eBay and supposed to be OEM.

[CycleRanger]

Fascinating. I didn't know the late F's had different case castings.
I wonder why Honda would make new molds at the very end of the run.

This late F cover appears to have the dowel in the lower hole as well.
https://www.cmsnl.com/products/cover-dynamo_11631410010/

[tofan]

Fascinating. I didn't know the late F's had different case castings.
I wonder why Honda would make new molds at the very end of the run.

This late F cover appears to have the dowel in the lower hole as well.
https://www.cmsnl.com/products/cover-dynamo_11631410010/

I don't a have a period copy of the 78F parts fiche but I'll bet it shows a different gasket number (likely unavailable either way) after a certain engine number.

That's what mine looks like

[tofan]

This is interesting. I did a little more digging online and came across these two gaskets that seem to have the dowel hole in the position I need. They come up as part numbers 11397-300-040 and -303. Looked both of them up on partzilla and seems to also match what I need but unavailable. CMSL has them too.

And I just looked through the parts list available in the technical documents library and it shows it as -040