Topic: 1977 750F - Oil Filter Bolt Question!

[senyah750]

Hi Everyone,

I hope all is well! I ran into a bit of a conundrum last night while changing the oil on my '77 750F and hoping someone will know the answer...

After scouring different schematics of various 750 models, I believe I have been running a K model oil filter bolt instead of the longer F model version. I am thinking this because there is an oil filter 'boss' attached directly to the crankcase which I was unable to find in any of the F model schematics. I was able to find the filter boss on a '79 750 K model, however. (Reference links below):

     '77 750F2: https://www.cmsnl.com/honda-cb750f2-750-super-sport-1977-usa_model491/partslist/E++12.html

     '79 750K: https://www.cmsnl.com/cb750k-750-four-k-1979-z-usa_model496/partslist/E++12.html#row15422425010
        Filter Boss: Part #14 (15422-425-010)

Could the PO have possibly added this to make up the difference of the shorter K model screw? Since the F models have a cooling sandwich plate they require a longer oil filter bolt, so that is my only guess..

I have since purchased the longer oil filter bolt for the F model as well as the oil filter collar which I was also missing, but am wondering if the oil filter 'boss' needs to stay connected to the crankcase even with the longer bolt? I'm thinking no, but wanted to be absolutely sure. I have read some other posts about oil not being properly directed through the oil filter and want to make sure I have the correct parts!

Thanks in advance for any help!!
-Steve       

[fxef79]

Stay tuned... I have a K engine that seems to have the F oil filter arrangement... including that finned "spacer" and the longer bolt.  But I found it was missing that "collar" you describe.

That "collar" seems pretty darn difficult to find, and no one has been able to give me dimensions of it for me to replicate it, otherwise.

Therefore, given the oil filter case itself is supposedly the same on the K and F engines, I just obtained one of the shorter K bolts, and this weekend I'll be removing the finned "spacer" and assembling this "K-style".

I had a very similar question about what I think you're describing... the "boss" on the engine case.  See here:
http://forums.sohc4.net/index.php/topic,181323.0.html
and here:
http://forums.sohc4.net/index.php/topic,181318.0.html

When I do this, I'll take pictures and share and at least then you can compare what it looks like in "real life" to your engine... the parts drawings often leave something to be desired when it comes to really what this stuff looks like.

[senyah750]

Awesome! I appreciate that!!

[HondaMan]

That's an interesting adaptation boss to the "F" engine, haven't seen one like that before (!).
The original arrangement was a longer oil filter bolt that went thru both the filter cover and the 'cooler' plate. In the later versions of the F3 there was a boss made up instead, which held the oil cooler plate to the engine when removing the filter cover. But, it frequently unscrewed itself along with the filter bolt, leaving you with the filter still trapped inside the filter cover and no convenient way to separate the adapter from the bolt. But, this whole thing was a 'band-aid' that came along because of an infamous mistake in translation of the Honda manuals in 1974, which suddenly switched the oil requirement from 20w50 above 50 degrees F to an inaccurately-translated statement that the owner should use 10w40 oil. This was wrong, and this weight oil is FAR too light for use in the F2/3, which is the hottest-running version of these SOHC4 engines.

So, when the dust settled, most of us (who knew the whole story) simply removed the 'cooler plate' and installed the shorter bolt with just the filter cover and filter. The 'cooler plate' was modified 3 times to try to make it work: it doesn't cool the oil any better, but they tried...

It looks like the adapter boss in yours might be the boss that was supplied with the Lockhart or Hooker oil coolers. Those coolers DO work: they came with an adapter plate where your cooler plate is, which has 2 hoses fittings on the top side to go up to a small cooler that gets mounted up under the steering tree. The Lockhart version mounted to the horn bracket and you mount the horn atop that bracket with longer 6mm bolts: the Hooker version has a bracket that mounts to the horn bracket to make the cooler sit more centered (the Lockhart one sits a little off-kilter to the right).  These parts were all made in USA, and the adapter plate was quite well done, with a boss that tended to stay in place better than the Honda versions did.

[fxef79]

Stoked the Hondaman weighed in. Dude, I’m saving up to buy your book!

Senyah750,
I’m sitting here now doing the change Hondaman just described... removing the cooler, using the shorter bolt.

Here are the measurements I got for you:
Bolt lengths are from the end of the threads to the shoulder that will ride on the outside of the filter case:
Short Bolt: 79.4 mm
Long bolt: 107.8 mm
Pics:






The “boss” on my engine is not an ad on item, it’s part of the cases. On the top side of it it measures 12 mm tall. It’s 29 mm in diameter.

Pics




Just for fun (because I’m getting rid of it) I put the “cooler“ on so you can see how it’s base essentially comes out flush with the top of that “boss“.  That is where the “collar” I don’t have should end up. In the last pic note there should be an o-ring installed - it’s the same as the one on the oil filter case itself.

Pic:





a few shots showing how much of the “short” bolt threads extend beyond the base of the oil filter case itself.  Used a small straight edge in one to give better perspective.








Finally, showing the spring, washer, filter, and how much the filter stand proud of the mating surface of the oil filter case.





For the observant, note I recognize that is not the original washer. PO, or prior PO, clearly discarded it stuck to an old filter, as I understand it’s quite common. Found this one in my miscellaneous washer collection. Can’t imagine tolerances on it are terribly important.

[Medyo Bastos]

Those are off a dohc


Sent from my iPhone using Tapatalk

[fxef79]

Senyah750 - Looking at your case compared to mine, I don't see how the long bolt is going to screw into the case.  It seems the threaded socket is a lot larger.  Note how much thinner the walls of it are compared to mine.  Or, put a different way, note the I.D. of your separate threaded "boss" mates to the hollow bolt... whereas the O.D. of it is certainly larger.  I don't see how the long bolt is going to work... it's the same diameter and threads as the short bolt.

[senyah750]

Holy cow! Thanks for the info HondaMan! I, too, have your book on my shortlist!

It looks like the adapter boss in yours might be the boss that was supplied with the Lockhart or Hooker oil coolers. Those coolers DO work: they came with an adapter plate where your cooler plate is, which has 2 hoses fittings on the top side to go up to a small cooler that gets mounted up under the steering tree. The Lockhart version mounted to the horn bracket and you mount the horn atop that bracket with longer 6mm bolts: the Hooker version has a bracket that mounts to the horn bracket to make the cooler sit more centered (the Lockhart one sits a little off-kilter to the right).  These parts were all made in USA, and the adapter plate was quite well done, with a boss that tended to stay in place better than the Honda versions did.

That's interesting for sure. The bike doesn't currently have an oil cooler. Maybe the PO put the original cooling plate back on? It does make me wonder what happened there if you haven't seen a boss like that on an F2 engine. Ever since the top-end was rebuilt about 3 years ago, I've been running a 20w-50. Again, I think I picked that tip up from you from another forum a long while back --- So thank you!!

Looking at your case compared to mine, I don't see how the long bolt is going to screw into the case.  It seems the threaded socket is a lot larger.  Note how much thinner the walls of it are compared to mine.  Or, put a different way, note the I.D. of your separate threaded "boss" mates to the hollow bolt... whereas the O.D. of it is certainly larger.  I don't see how the long bolt is going to work... it's the same diameter and threads as the short bolt.

Good call.. I just got some time to go back out and take some pics (attached). You are absolutely correct about the diameters and that the longer bolt isn't going to make any difference now that I realize how far out this boss sticks out from the crank case.

Looks like I'm going to have to leave the boss as-is. Do you guys think this setup will have any adverse effects with oil flowing to the filter? Could that boss possibly (hopefully) act as the oil filter "collar" which would be needed with a longer bolt?

I may be a bit paranoid but I wouldn't want to cause any harm (she's all I got!). I have a few longer (150+ miles) rides planned and want to make sure she's being properly lubricated and everything.

Again, I really appreciate everyone's time and help with this!

[fxef79]

OK, so here's my thoughts, based on my extensive experience of seeing these oil coolers on all of 2 engines... mine and yours. 

This ebay listing is the only place I've ever found a photo of the cooler AND the "collar" to get an idea of relative size. 

https://www.ebay.com/itm/HONDA-CB-750-K-FOUR-1969-76-OIL-COOLER-HEAT-SINK-PLATE-SPACER-DRAG-CHOPPER-RACE-/402136700432

Note in the photos how the collar appears to be flush with the outer surface of the "fins"?  However, note in our pictures how when the oil cooler is placed on the engine, the engine's built-on "boss" sticks slightly into the cooler?  That would indicate to me that when that collar is placed in there, it would therefore stand slightly above the surface of the cooler internal fins... and the rubber ring on the oil filter would likely seat on that collar, thus pressing the filter slightly into the case, and compressing the spring a bit.

Now, look at your additional "boss" that gets screwed into the engine case... it seems it also stands a bit above the surface of the cooler internal fins... and so I think it fulfils that same function as the collar that you don't have.  In your case, with the additional threaded boss and the short bolt, you don't need the collar.  But with my engine that has the smaller inside diameter threads on the engine case, I wouldn't be able to use your threaded boss... I have to use either the long bolt, with the oil cooler, AND the collar (which I don't have)... or I have to remove the cooler, and just use the short bolt (which is what I've decided to do - at least until I get some reliable dimensions on that collar and can reproduce one, or locate one for less than the price of unobtanium from Germany.

[senyah750]

Note in the photos how the collar appears to be flush with the outer surface of the "fins"?  However, note in our pictures how when the oil cooler is placed on the engine, the engine's built-on "boss" sticks slightly into the cooler?  That would indicate to me that when that collar is placed in there, it would therefore stand slightly above the surface of the cooler internal fins... and the rubber ring on the oil filter would likely seat on that collar, thus pressing the filter slightly into the case, and compressing the spring a bit.

Nice find! That is the first picture I have seen as well with the collar shown with the cooler.. That definitely helps visualize everything.

Now, look at your additional "boss" that gets screwed into the engine case... it seems it also stands a bit above the surface of the cooler internal fins... and so I think it fulfils that same function as the collar that you don't have.  In your case, with the additional threaded boss and the short bolt, you don't need the collar.

Thanks for the reassurance.. I haven't ran into any issues with this setup, but always good to have other opinions! I will put back together the way I've always had it.

But with my engine that has the smaller inside diameter threads on the engine case, I wouldn't be able to use your threaded boss... I have to use either the long bolt, with the oil cooler, AND the collar (which I don't have)... or I have to remove the cooler, and just use the short bolt (which is what I've decided to do - at least until I get some reliable dimensions on that collar and can reproduce one, or locate one for less than the price of unobtanium from Germany.

Seemingly from the other posts its okay to not run that cooler, so all should be fine on your engine with the shorter bolt. If I come across any dimensions of that collar, I'll be sure to share. And yes, they are crazy expensive and I can only find them on the CMSNL website..

Again, I appreciate your help! Hope you have a great riding season!

[HondaMan]

Stoked the Hondaman weighed in. Dude, I’m saving up to buy your book!

Senyah750,
I’m sitting here now doing the change Hondaman just described... removing the cooler, using the shorter bolt.

Here are the measurements I got for you:
Bolt lengths are from the end of the threads to the shoulder that will ride on the outside of the filter case:
Short Bolt: 79.4 mm
Long bolt: 107.8 mm
Pics:



Just for fun (because I’m getting rid of it) I put the “cooler“ on so you can see how it’s base essentially comes out flush with the top of that “boss“.  That is where the “collar” I don’t have should end up. In the last pic note there should be an o-ring installed - it’s the same as the one on the oil filter case itself.

Pic:

Those 2 pix look like the F3 oil 'cooler' plate setup. The boss on the engine is also normal. The longer oil bolt should be longer than the sort one by the thickness of the oil cooler plate. I have seen 3 different lengths: one that came to me one day was leaking oil badly at the filter, and it turned out that the filter bolt was a non-Honda bolt, apparently for some other bike: it was 5mm longer than the one for the F2/3 and would not pull up tightly. I just removed the 'cooler' and installed a regular bolt (because I didn't have the F2/3 long one that day) and sent him on down the road with the cooler and his extra-extra-long bolt in a plastic bag in his backpack.

Lots of those filter washers get thrown away accidentally! It doesn't seem to do much damage to the filter to run without it, but sometimes the spring can chunk out little bits from the filter's seal. The filter catches them, though.