Topic: Thinking of Buying a 1978 CB750F... Chain Adjustment Question

[Graydude]

Be happy to help as so many on this site did for me.  Let me know.

[Imago]

I just got an email from my seller who checked the serial numbers:

engine: CB750E-3152471
frame: CB750F-2252456

Hmmm - one of the last SOHC engines made I guess... thoughts on parts availability or other woes I may encounter?

[Graydude]

The only issues you'll have will be if you need rings, pistons and valves.  Everything else internally will be the same as the K motor.  If your pistons are shot you will need to decide between going with a big bore kit ($$$) or switching over to K motor, non-domed pistons and rings.  I got mine from Z1 enterprises for $200.  You will still probably need to bore .5 MM over but you can cross that bridge when youi come to it.  Hopefully your valves will be servicable but I would recommend new valve guides and seals.  You won't know where you stand until you run it.

[Imago]

The only issues you'll have will be if you need rings, pistons and valves.  Everything else internally will be the same as the K motor.  If your pistons are shot you will need to decide between going with a big bore kit ($$$) or switching over to K motor, non-domed pistons and rings.  I got mine from Z1 enterprises for $200.  You will still probably need to bore .5 MM over but you can cross that bridge when youi come to it.  Hopefully your valves will be servicable but I would recommend new valve guides and seals.  You won't know where you stand until you run it.

Yup, I'm heading up in my truck tomorrow morning with my gas can, a battery and my booster cables. With any luck the bike won't need much of anything, but I'm the eternal optomist!

[Terry in Australia]

I just got an email from my seller who checked the serial numbers:

engine: CB750E-3152471
frame: CB750F-2252456

Hmmm - one of the last SOHC engines made I guess... thoughts on parts availability or other woes I may encounter?

Ah, so you've got a 1978 F3 engine in a 1977 F2 frame mate. Well chances are the engine was replaced because the old one crapped out, so hopefully the new engine will still be good. Ride it before you do anything. Cheers, terry.

[Imago]

I just got an email from my seller who checked the serial numbers:

engine: CB750E-3152471
frame: CB750F-2252456

Hmmm - one of the last SOHC engines made I guess... thoughts on parts availability or other woes I may encounter?

Ah, so you've got a 1978 F3 engine in a 1977 F2 frame mate. Well chances are the engine was replaced because the old one crapped out, so hopefully the new engine will still be good. Ride it before you do anything. Cheers, terry.

Beg to differ. My research shows the F3 (May 1977 to May 1978) frame starts at 2200001 and engine at 31000001. Wouldn't that mean that frame CB750F-2252456 and engine CB750E-3152471 are both F3 and likely original?

[2wheels]

Great news, I think you will like the bike.
I'd like to ask a favor though.
Can you take some close up pictures of the luggage rack attachment?
I would like to put one on my bike have am having trouble visualizing what I need.

[Graydude]

Beg to differ. My research shows the F3 (May 1977 to May 1978) frame starts at 2200001 and engine at 31000001. Wouldn't that mean that frame CB750F-2252456 and engine CB750E-3152471 are both F3 and likely original?

I'll bet a 12 pack they are both orginal and mated.  It really does not matter which year any way as you have the last series engine and that's that.

[Terry in Australia]

I just got an email from my seller who checked the serial numbers:

engine: CB750E-3152471
frame: CB750F-2252456

Hmmm - one of the last SOHC engines made I guess... thoughts on parts availability or other woes I may encounter?

Ah, so you've got a 1978 F3 engine in a 1977 F2 frame mate. Well chances are the engine was replaced because the old one crapped out, so hopefully the new engine will still be good. Ride it before you do anything. Cheers, terry.

Beg to differ. My research shows the F3 (May 1977 to May 1978) frame starts at 2200001 and engine at 31000001. Wouldn't that mean that frame CB750F-2252456 and engine CB750E-3152471 are both F3 and likely original?

Page 1 of my Factory Honda manual states that the 1977 F2 frame numbers start with 2100001 and the 1978 F3 frame numbers start with 3100002. It doesn't mention months though, so you might be right. It is unusual that your engine and frame numbers are so far apart though, hence my suggestion that you've got a later engine in your frame. Cheers, Terry.

[Imago]

Got it home! Pictures tomorrow....

It started up pretty well, firing on all 4 cylinders. A few initial observations:

a) it has a weepy head gasket, some oil on the fin next to the exhaust clamp on cylinder 1 which dripped onto the header, smoking a bit when we first got it fired up... Is it possible it will tighten up? Or am I being too optomistic?
b) nice and quiet... and smooth. Looks to me like a MAC exhaust system.
c) all lights work but the signals light but don't flash... a new flasher is in order?
d) smoked a bit, smartened up a great deal as it warmed up, but that may have been the old gas before my fresh gas got through... time will tell.
e) wouldn't idle too well without a lot of choke. A good carb cleaning is on the agenda to ensure the idle passages are clear.
f) he threw in a motorcycle battery/maintenance charger and a nearly full jug of fork oil... he had replaced the seals not too long ago.
g) might need brake pads and front caliper attention... it took a few seconds to loosen as we rolled it towards my truck.
h) the SHOEI helmet is my size, but the Bristol chaps and jacket are not... like new though.
i) the Vetter III is nice and has lowers, but he never installed it as he couldn't find the proper mount. Anyone have a proper mount to trade for a Kawasaki mount?
j) one of my Lester rims will fit on the back, but my front is for a 6 bolt set up. Anyone want to trade my 6 bolt Lester for a 5 bolt? Alternatively I've been told a certain year GL100 front end will bolt right in, is stronger and lighter but I'm not exactly sure which year I need. Would be simpler just to trade rims. The original comstar wheels are perfect on this bike, and actually not as ugly as I thought they'd be. Hmmmmmmmm.
   
All in all a definite keeper.

I'll post some photos tomorrow, particularly of the luggage rack for the fellow who is trying to fit his. I can see why he is perplexed, it is a bit complex.

When will it be spring?

[Terry in Australia]

I'm betting that it's not a head gasket, but rather, the rubber pucks under the cam towers allowing oil to drip out between your exhaust flanges mate, that's the most common leak on old CB750's that have been sitting for awhile.

Your pilot jets are most likely blocked, (most common reason for poor idling in PD carbs) they're pressed in, but you can (carefully) grip them with vise-grips etc and twist them out, then use a fine wire (guitar strings are useful) to poke out the gunk and spray carb cleaner through all the circuits, and it'll idle again. Cheers, Terry.

[Retro Rocket]

Geeze Terry, you are getting slack mate, when ever i see you have posted in an "F" thread i usually find, throngs of abuse followed closely by superlatives like, #$%*, mongrel, or red headed step child..!!!   you ok.?, what's up mate.....

[Imago]

I'm betting that it's not a head gasket, but rather, the rubber pucks under the cam towers allowing oil to drip out between your exhaust flanges mate, that's the most common leak on old CB750's that have been sitting for awhile.

Your pilot jets are most likely blocked, (most common reason for poor idling in PD carbs) they're pressed in, but you can (carefully) grip them with vise-grips etc and twist them out, then use a fine wire (guitar strings are useful) to poke out the gunk and spray carb cleaner through all the circuits, and it'll idle again. Cheers, Terry.

Thanks... if it's the pucks, will they start doing their job again or are they toast?

[Retro Rocket]

I'm betting that it's not a head gasket, but rather, the rubber pucks under the cam towers allowing oil to drip out between your exhaust flanges mate, that's the most common leak on old CB750's that have been sitting for awhile.

Your pilot jets are most likely blocked, (most common reason for poor idling in PD carbs) they're pressed in, but you can (carefully) grip them with vise-grips etc and twist them out, then use a fine wire (guitar strings are useful) to poke out the gunk and spray carb cleaner through all the circuits, and it'll idle again. Cheers, Terry.

Thanks... if it's the pucks, will they start doing their job again or are they toast?

If you are going to take the time to go in and have a look then replacing them would be the right thing to do....

[754]

 The wheels are ugly... you are just feeling the effect of "newBikestruck"

 one morning you will wake up look at them and wonder why you let em in the yard..

 I got an alloy rim 6bolt GL wire wheel with discs.. they are 6 bolt, might be right diameter, but I think they are THICKER than F rotors..

[Grnrngr]

Nice score, especially after letting it sit for a month. It would have been gone within days around here, probably for his asking price since it has "the goodies". Get it running good, throw a little seal restore stuff in the oil, and rebuild your spare motor while you ride this one til it's finished.

[754]

 I have seen a couple Late 78 K with different cases, must be the last batch... serial boss is turned 90 degrees and closer to middle.. a buddy of mine got a lower end, when I saw it I thought it was a DOHC..
 is there any F's that were made with thise cases ??

[Terry in Australia]

Thanks... if it's the pucks, will they start doing their job again or are they toast?

No mate, sadly they're toast. Still, they're much easier to replace than the head gasket. Just make sure you glue them in with a little Threebond. Cheers, Terry.

Geeze Terry, you are getting slack mate, when ever i see you have posted in an "F" thread i usually find, throngs of abuse followed closely by superlatives like, #$%*, mongrel, or red headed step child..!!!   you ok.?, what's up mate.....

Ha ha, no, I've got a soft spot for the F2's Mick, it's those fugly F1's (or F0's as people are calling them now, not that they ever did "back in the day") I can't abide. A good F2 (or F3) is a thing of beauty, if it's in good condition, of course.

I have seen a couple Late 78 K with different cases, must be the last batch... serial boss is turned 90 degrees and closer to middle.. a buddy of mine got a lower end, when I saw it I thought it was a DOHC..
 is there any F's that were made with thise cases ??

Yeah Frank, I've got a set of F3 cases with the serial number block moved 90 degrees like that, i don't think it was that uncommon.

[Imago]

Here's some pics of it in the truck at it's new home this morning.. -2 Celcius but supposed to go above freezing today.

I took some extras of the luggage rack for the fellow who inquired about it... if there's anything particular you'd like to see, give me a shout.

[Imago]

A couple more...

[Imago]

And finally...

[754]

 nEED 2 MORE MOTORS.. i GOT A PAIR.. WANNA MAKE ROOM FOR EARLIER STUFF...

[ekpent]

I got a luggage rack when I bought a 76 F1 and they are different than normal.They are made to swivel or turn up and towards the back after removing a couple of bolts so the rear tail cowl can clear it to open the seat.Does not seem to be a very large number of them still out there.

[Imago]

Yup, in pics 96 & 97 you can see the wing nuts and carriage bolts that come off to allow the rack to swing back so the seat can fully open.

[Stev-o]

You sure that is a Mac exhaust? Doesnt appear to be...